Welcome to The Scientist Speaks, a new podcast produced by The Scientist’s Creative Services Team. Our podcast is by scientists and for scientists. Once a month, we will bring you the stories behind news-worthy molecular biology research.
Mosquito-borne diseases afflict a large portion of the world. In this month’s episode, we consider genetic methods to eradicate diseases such as Zika fever, Dengue fever, and malaria. We spoke with Omar Akbari, professor of Cell and Developmental Biology at the University of California, San Diego, to learn more.
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CRISPR-Accelerated Gene Drives Pump the BrakesDesigners of gene drive systems roll out prototypes that show how safety components can “come standard”By Julianna LeMieux, PhD - July 1, 2019
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Humans wiped out mosquitoes (in one small lab test)If we could eliminate a species, should we? BY SUSAN MILIUS
For the first time, humans have built a set of pushy, destructive genes that infiltrated small populations of mosquitoes and drove them to extinction.
But before dancing sleeveless in the streets, let’s be clear. This extermination occurred in a lab in mosquito populations with less of the crazy genetic diversity that an extinction scheme would face in the wild. The new gene drive, constructed to speed the spread of a damaging genetic tweak to virtually all offspring, is a long way from practical use. Yet this test and other news from 2018 feed one of humankind’s most persistent dreams: wiping mosquitoes off the face of the Earth.
For the lab-based annihilation, medical geneticist Andrea Crisanti and colleagues at Imperial College London focused on one of the main malaria-spreading mosquitoes, Anopheles gambiae. The mosquitoes thrive in much of sub-Saharan Africa, where more than 400,000 people a year die from malaria, about 90 percent of the global total of malaria deaths.
To crash the lab population, the researchers put together genes for a molecular copy-and-paste tool called a CRISPR/Cas9 gene drive. The gene drive, which in this case targeted a mosquito gene called doublesex, is a pushy cheat. It copies itself into any normal doublesexgene it encounters, so that all eggs and sperm will carry the gene drive into the next generations. Female progeny with two altered doublesex genes develop more like males and, to people’s delight, can’t bite or reproduce.
In the test, researchers set up two enclosures, each mixing 150 males carrying the saboteur genes into a group of 450 normal mosquitoes, males and females. Extinction occurred in eight generations in one of the enclosures and in 12 in the other (SN: 10/27/18, p. 6).
This is the first time that a gene drive has forced a mosquito population to breed itself down to zero, says Omar Akbari of the University of California, San Diego, who has worked on other gene drives. However, he warns, “I believe resistance will be an issue in larger, diverse populations.” More variety in mosquito genes means more chances of some genetic quirk arising that counters the attacking gene drive.
But what if a gene drive could monkey-wrench a wild population, or maybe a whole species, all the way to extinction? Should people release such a thing? To make sense of this question, we humans will have to stop talking about “mosquitoes” as if they’re all alike. The more than 3,000 species vary considerably in what they bite and what ecosystem chores they do.
The big, iridescent adults of Toxorhynchites rutilus, for instance, can’t even drink blood. And snowmelt mosquitoes (Ochlerotatus communis) are pollinators of the blunt-leaved orchid(Platanthera obtusata), ecologist Ryo Okubo of the University of Washington in Seattle said at the 2018 meeting of the Society for Integrative and Comparative Biology.
Estimating what difference it would make ecologically if a whole mosquito species disappeared has stirred up plenty of speculation but not much data. “I got pretty fed up with the hand-waving,” says insect ecologist Tilly Collins of Imperial College London. So she and colleagues dug through existing literature to see what eats An. gambiae and whether other mosquitoes would flourish should their competitor vanish.So far, extermination of this particular mosquito doesn’t look like an ecological catastrophe, Collins says. Prey information is far from perfect, but diets suggest that other kinds of mosquitoes could compensate for the loss. The species doesn’t seem to be any great prize anyway. “As adults, they are small, not juicy, and hard to catch,” she says. The little larvae, built like aquatic caterpillars with bulging “shoulders” just behind their heads, live mostly in small, temporary spots of water.
The closest the researchers came to finding a predator that might depend heavily on this particular mosquito was the little East African jumping spider Evarcha culicivora. It catches An. gambiae for about a third of its diet and likes the females fattened with a human blood meal. Yet even this connoisseur “will readily consume” an alternative mosquito species, the researchers noted in July in Medical and Veterinary Entomology.
Collins also thinks about the alternatives to using genetically engineered pests as pest controls. Her personal hunch is that saddling mosquitoes with gene drives to take down their own species is “likely to have fewer ecological risks than broad-spectrum use of pesticides that also kill other species and the beneficial insects.”
Gene drives aren’t the only choice for weaponizing live mosquitoes against their own kind. To pick just one example, a test this year using drones to spread radiation-sterilized male mosquitoes in Brazil improved the chances that the old radiation approach will be turned against an Aedes mosquito that can spread Zika, yellow fever and chikungunya.
Old ideas, oddly enough, may turn out to be an advantage for antimosquito technologies in this era of white-hot genetic innovation. Coaxing the various kinds of gene drives to work is hard enough, but getting citizens to sign off on their use may be even harder.
14 NOVEMBER 2018As a global community, we are facing life-threatening challenges that undermine our future, from catastrophic loss of biodiversity to acute public health threats.
Malaria cases are on the rise again after decades of progress, and fragile ecosystems are undergoing intensifying rates of extinctions. These challenges require new and complementary tools if we are to achieve the Sustainable Development Goals and the Aichi Targets[i].
As the Convention on Biological Diversity (CBD) meets for the 14th Conference of the Parties (COP14) in Egypt in November, decision-makers from countries around the world will have an opportunity to reaffirm the importance of enabling research to support responsible innovation and evidence-based decision-making.
Closing the door on research by creating arbitrary barriers, high uncertainty, and open-ended delays will significantly limit our ability to provide answers to the questions policy-makers, regulators and the public are asking. The moratorium suggested at CBD on field releases would prevent the full evaluation of the potential uses of gene drive. Instead, the feasibility and modalities of any field evaluation should be assessed on a case-by-case basis.
Much of the progress we have made in the past century in improving the livelihoods and wellbeing of communities around the world is the result of increased knowledge acquired through scientific research. Science has not brought solutions to all our problems, but improved understanding and evidence have been key to progress. Innovations in vaccines, for example, have saved millions of lives: the 74% percent reduction in childhood deaths from measles over the past decade is a demonstration of the life-changing power of scientific research [ii].
Gene drive is a well-established field of research. First observed in the 1920s in mice and Drosophila, gene drive is a naturally occurring phenomenon that has been the subject of investigation for many years. Recent advances in gene editing tools have allowed notable progress in the two years since gene drive was first discussed at CBD, helping deliver increased knowledge and greater understanding of the possible applications of gene drive, while shedding further light on its risks, limitations, and potential.
While these advances are important, there is still much more to be achieved before any gene drive organisms could be considered for regulatory evaluation. Key institutions, such as the African Union, have called for continued work in this field, emphasising the value of the opportunity and the need for informed case-by-case assessment of this technology by national authorities [iii].
Scientists, alongside regulatory experts, funders and sponsors of the research, are working together to ensure research is carried out safely and responsibly, by building on previous experiences, using published policy and information, and putting in place monitoring and containment systems to prevent accidental releases [iv] [v]. Ongoing discussions are also taking place to determine suitable conditions for field evaluations.
Member States can enable the Convention on Biological Diversity to be a platform for knowledge and experience sharing. We should not decide against the use of a tool before potential costs and benefits can be fully evaluated. We urge governments to ensure the decisions taken at the Convention on Biological Diversity’s next meeting do not amount to a moratorium on gene drive research, but instead offer a balanced and constructive way forward for Parties to learn and monitor this field of research.
CLICK HERE TO DOWNLOAD THE LETTER.Signed :Prof. Austin Burt
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Imperial College London
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University of Sciences, Techniques and Technologies of Bamako,
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University of Cambridge,
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Johns Hopkins University
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Principal Investigator, Target Malaria Burkina Faso
Dr. John Godwin
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Prof. Nora J. Besansky
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Imperial College London,
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Australian Institute of Tropical Health and Medicine
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SUBMIT[i] Bellard et al., (2016) “Alien species as a driver of recent extinctions” Biology letters vol. 12,2.
Spatz et al., (2017) “Globally threatened vertebrates on islands with invasive species”. Science Advances,
Vol. 3, no. 10
WHO (2017) World Malaria Report
WHO (2015) Global Technical Strategy for Malaria 2016–2030
[ii] WHO http://www.who.int/immunization/diseases/measles/global_coordination/en/index4.html
[iii] See for e.g., the African Union High Level Expert Panel report (2018) Gene Drives for Malaria Control and Elimination in Africa and the WHO Vector Control Advisory Committee (VCAG) Report of the fifth meeting of VCAG and Report of the eighth meeting of VCAG (2018)
[iv] See for example:
Extinction on demand. The promise and peril of gene drives. A new genetic-engineering technology should be used with care. The Economist. PDF HERE.
Gene drives promise great gains and great dangers. Don’t ban, don’t rush. The Economist. PDF HERE.
Forcing The Farm How Gene Drive Organisms Could Entrench Industrial Agriculture and Threaten Food Sovereignty. ETC Group. PDF HERE
HERE'S THE PLAN TO END MALARIA WITH CRISPR-EDITED MOSQUITOES
Study: Gene Drive Wipes Out Lab Mosquitoes
In lab tests, this gene drive wiped out a population of mosquitoeshttps://www.sciencenews.org/article/lab-tests-gene-drive-wiped-out-population-mosquitoes
Mosquitoes Genetically Modified To Crash Species That Spreads Malaria
"Driving" Mosquitoes to Their Demise
TAKING THE BITE OUT OF PATHOGENS: HOW RESEARCHERS AT UC SAN DIEGO ARE DIVORCING MOSQUITOS FROM MALARIA AND OTHER INFECTIOUS DISEASES
LIAM HUBER AND MAYA GOPALAKRISHNAN | ONLINE REPORTERS | SALTMAN QUARTERLY 17-18
At UC San Diego, Dr. Omar Akbari pioneers a new method to combat some of the world’s deadliest contagions. (Source)
Picture the deadliest animal in the world. What comes to mind? Fearsome teeth, bulging muscles, and lethal venom? Great white sharks, Bengal tigers, and black mambas? In reality, the deadliest animal in the world has none of these features, is smaller than a fly and causes the deaths of more than one million people every year. Mosquitos, and the pathogens they spread, are far more insidious threats to humankind than the creatures that attract most of the public’s attention.
Junru Liu, a third-year undergraduate at UC San Diego, has the joined the war on these grim reapers. Earlier this year, Liu responded to an intriguing post on Port Triton. By the middle of winter quarter, she was working in Dr. Omar Akbari’s laboratory, and became a part of an international network that is pioneering the use of genetic drive to combat infectious diseases like malaria, West Nile, and Zika.
Globally, these pandemics are still a scourge on humankind. According to Akbari, deaths caused by mosquitoes are often underreported, artificially suppressing the mortality rate of these diseases. To control mosquitos, vulnerable communities often drain wetlands or employ pesticides, but both of these practices carry a considerable environmental toll. Moreover, as Liu points out, traditional means of combating infectious disease usually run up against microevolution: vectors accumulate resistance, making disease-fighting strategies less effective. Consider the rise of antibiotic-resistant bacteria in industrialized countries, for example, and imagine the calamity if a similar outcome was replicated in mosquito-borne illnesses in the developing world.
Clearly, a new approach was wanting. Dr. Akbari entered the field of vector control as an undergraduate at the University of Nevada in Reno. Interning as a public servant in vector control, Akbari became more aware about deficiencies in the current methods for controlling mosquitos. Gradually, his interest turned to a new technology that promised to be less expensive, more sustainable and more self-scaling: genetic drive, a principle based on the revolutionary gene editing tool CRISPR/Cas9.
Genetic drive works, in Liu’s words, by replacing a wild-type trait with a trait that has been specifically tailored by researchers. The Akbari Lab focuses on eliminating the gene in mosquitoes that allows them to transmit pathogens and replacing it with a gene that makes the mosquito body inhospitable to infectious agents. According to traditional Mendelian genetics, once this gene has been introduced into a breeding population, it could be expected to either spread or evaporate, depending on how it influences the reproductive fitness of the mosquito. But genetic drive goes one step further, Akbari explains.
Without genetic drive, there is only a fifty-percent chance that the target gene will be passed onto offspring. Genetic drive, however, cuts and pastes the target gene into the chromosomes from both parents, rather than just one. As a result, it is almost certain that all offspring will inherit the gene.
There are two ways to apply this to vector control, says Akbari. The first is to target recessive genes that lower female viability, reducing the mosquito population as a whole. The second is to increase the frequency of a gene that makes mosquitoes unable to carry or spread the pathogen. This option, while less tempting than the first for anyone scratching a bite, would avert the ecological consequences of extinguishing an entire species. At the same time, it provides the hope that impoverished regions may be liberated from, say, the parasite that causes malaria, or other deadly vectors.
The day that this could happen is still some time away, Akbari and Liu say. Liu is still tinkering with Drosophila fruit flies, which are a good model for their vector relatives. Meanwhile, others in the Akbari lab are sequencing the genotypes of different mosquito species, finding microRNA target sites for CRISPR/Cas9 to intervene, splicing out the culprit gene that hands the reins of the global mosquito population to lethal diseases. At the moment, Akbari’s personal goal is to develop a cassette to eradicate Zika, while others contribute to gene drives for malaria and dengue virus. Not far in the future, Liu envisions eggs of genetically modified mosquitoes that are grown in a lab at UC San Diego and delivered to developing regions around the world. There, those mosquitoes and their offspring will be unable to spread the pathogens that cause deadly diseases, hastening the demise of those diseases. The network of laboratories working toward sustainable and long-term vector control, Akbari believes, reflects the global scale of the issue, and the impact that a solution like genetic drive could have.
Before that promise is realized, Akbari foresees two hurdles to his research: one technical and another ethical. At this point, genetic drive is not as robust as desired, and would likely breakdown and become less efficient over an evolutionary scale. An even greater challenge, Akbari says, is getting the public, stakeholders, and governments on board with the wide-scale release of genetically modified mosquitoes. Genetic drive cannot be confined to one region, he points out, so the engineered genes could potentially spread across the entire planet. Copious testing would be required to monitor the effects of genetic drive on the global ecosystem. Moreover, Akbari believes that listening to concerns and educating the public with data and logic is a vital piece of the puzzle.
For now, Liu herself is more focused on the technical problems at hand. Until the day that millions of people can afford to be less afraid of an ominous buzz or an itchy bite, she and other members of the Akbari Lab will remain hard at work developing life-saving technologies on a grand scale and pushing the possibilities of the life sciences. Liu has considered pursuing a PhD with the Akbari Lab once she finishes her undergraduate career: after all, it isn’t often that a college student gets a chance to help work on techniques that could improve the health and safety of countless people worldwide.
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Gene Editing for Good How CRISPR Could Transform Global Development
By Bill Gates
Today, more people are living healthy, productive lives than ever before. This good news may come as a surprise, but there is plenty of evidence for it. Since the early 1990s, global child mortality has been cut in half. There have been massive reductions in cases of tuberculosis, malaria, and HIV/AIDS. The incidence of polio has decreased by 99 percent, bringing the world to the verge of eradicating a major infectious disease, a feat humanity has accomplished only once before, with smallpox. The proportion of the world’s population in extreme poverty, defined by the World Bank as living on less than $1.90 per day, has fallen from 35 percent to about 11 percent.
Continued progress is not inevitable, however, and a great deal of unnecessary suffering and inequity remains. By the end of this year, five million children under the age of five will have died—mostly in poor countries and mostly from preventable causes. Hundreds of millions of other children will continue to suffer needlessly from diseases and malnutrition that can cause lifelong cognitive and physical disabilities. And more than 750 million people—mostly rural farm families in sub-Saharan Africa and South Asia—still live in extreme poverty, according to World Bank estimates. The women and girls among them, in particular, are denied economic opportunity.
Some of the remaining suffering can be eased by continuing to fund the development assistance programs and multilateral partnerships that are known to work. These efforts can help sustain progress, especially as the world gets better at using data to help guide the allocation of resources. But ultimately, eliminating the most persistent diseases and causes of poverty will require scientific discovery and technological innovations.
That includes CRISPR and other technologies for targeted gene editing. Over the next decade, gene editing could help humanity overcome some of the biggest and most persistent challenges in global health and development. The technology is making it much easier for scientists to discover better diagnostics, treatments, and other tools to fight diseases that still kill and disable millions of people every year, primarily the poor. It is also accelerating research that could help end extreme poverty by enabling millions of farmers in the developing world to grow crops and raise livestock that are more productive, more nutritious, and hardier. New technologies are often met with skepticism. But if the world is to continue the remarkable progress of the past few decades, it is vital that scientists, subject to safety and ethics guidelines, be encouraged to continue taking advantage of such promising tools as CRISPR.
FEEDING THE WORLD
Earlier this year, I traveled to Scotland, where I met with some extraordinary scientists associated with the Centre for Tropical Livestock Genetics and Health at the University of Edinburgh. I learned about advanced genomic research to help farmers in Africa breed more productive chickens and cows. As the scientists explained, the breeds of dairy cows that can survive in hot, tropical environments tend to produce far less milk than do Holsteins—which fare poorly in hot places but are extremely productive in more moderate climates, thanks in part to naturally occurring mutations that breeders have selected for generations. The scientists in Scotland are collaborating with counterparts in Ethiopia, Kenya, Nigeria, Tanzania, and the United States. They are studying ways to edit the genes of tropical breeds of cattle to give them the same favorable genetic traits that make Holsteins so productive, potentially boosting the tropical breeds’ milk and protein production by as much as 50 percent. Conversely, scientists are also considering editing the genes of Holsteins to produce a sub-breed with a short, sleek coat of hair, which would allow the cattle to tolerate heat.
This sort of research is vital, because a cow or a few chickens, goats, or sheep can make a big difference in the lives of the world’s poorest people, three-quarters of whom get their food and income by farming small plots of land. Farmers with livestock can sell eggs or milk to pay for day-to-day expenses. Chickens, in particular, tend to be raised by women, who are more likely than men to use the proceeds to buy household necessities. Livestock help farmers’ families get the nutrition they need, setting children up for healthy growth and success in school.
Similarly, improving the productivity of crops is fundamental to ending extreme poverty. Sixty percent of people in sub-Saharan Africa earn their living by working the land. But given the region’s generally low agricultural productivity—yields of basic cereals are five times higher in North America—Africa remains a net importer of food. This gap between supply and demand will only grow as the number of mouths to feed increases. Africa’s population is expected to more than double by 2050, reaching 2.5 billion, and its food production will need to match that growth to feed everyone on the continent. The challenge will become even more difficult as climate change threatens the livelihoods of smallholder farmers in Africa and South Asia.
Gene editing to make crops more abundant and resilient could be a lifesaver on a massive scale. The technology is already beginning to show results, attracting public and private investment, and for good reason. Scientists are developing crops with traits that enhance their growth, reduce the need for fertilizers and pesticides, boost their nutritional value, and make the plants hardier during droughts and hot spells. Already, many crops that have been improved by gene editing are being developed and tested in the field, including mushrooms with longer shelf lives, potatoes low in acrylamide (a potential carcinogen), and soybeans that produce healthier oil.
Improving the productivity of crops is fundamental to ending extreme poverty.
For a decade, the Bill & Melinda Gates Foundation has been backing research into the use of gene editing in agriculture. In one of the first projects we funded, scientists from the University of Oxford are developing improved varieties of rice, including one called C4 rice. Using gene editing and other tools, the Oxford scientists were able to rearrange the cellular structures in rice plant leaves, making C4 rice a remarkable 20 percent more efficient at photosynthesis, the process by which plants convert sunlight into food. The result is a crop that not only produces higher yields but also needs less water. That’s good for food security, farmers’ livelihoods, and the environment, and it will also help smallholder farmers adapt to climate change.
Such alterations of the genomes of plants and even animals are not new. Humans have been doing this for thousands of years through selective breeding. Scientists began recombining DNA molecules in the early 1970s, and today, genetic engineering is widely used in agriculture and in medicine, the latter to mass-produce human insulin, hormones, vaccines, and many drugs. Gene editing is different in that it does not produce transgenic plants or animals—meaning it does not involve combining DNA from different organisms. With CRISPR, enzymes are used to target and delete a section of DNA or alter it in other ways that result in favorable or useful traits. Most important, it makes the discovery and development of innovations much faster and more precise.
PAULO WHITAKER / REUTERS Genetically modified mosquitos, Brazil,
In global health, one of the most promising near-term uses of gene editing involves research on malaria. Although insecticide-treated bed nets and more effective drugs have cut malaria deaths dramatically in recent decades, the parasitic disease still takes a terrible toll. Every year, about 200 million cases of malaria are recorded, and some 450,000 people die from it, about 70 percent of them children under five. Children who survive often suffer lasting mental and physical impairments. In adults, the high fever, chills, and anemia caused by malaria can keep people from working and trap families in a cycle of illness and poverty. Beyond the human suffering, the economic costs are staggering. In sub-Saharan Africa, which is home to 90 percent of all malaria cases, the direct and indirect costs associated with the disease add up to an estimated 1.3 percent of GDP—a significant drag on countries working to lift themselves out of poverty.
With sufficient funding and smart interventions using existing approaches, malaria is largely preventable and treatable—but not completely. Current tools for prevention, such as spraying for insects and their larvae, have only a temporary effect. The standard treatment for malaria today—medicine derived from artemisinin, a compound isolated from an herb used in traditional Chinese medicine—may relieve symptoms, but it may also leave behind in the human body a form of the malaria parasite that can still be spread by mosquitoes. To make matters worse, the malaria parasite has begun to develop resistance to drugs, and mosquitoes are developing resistance to insecticides.
Efforts against malaria must continue to make use of existing tools, but moving toward eradication will require scientific and technological advances in multiple areas. For instance, sophisticated geospatial surveillance systems, combined with computational modeling and simulation, will make it possible to tailor antimalarial efforts to unique local conditions. Gene editing can play a big role, too. There are more than 3,500 known mosquito species worldwide, but just a handful of them are any good at transmitting malaria parasites between people. Only female mosquitoes can spread malaria, and so researchers have used CRISPR to successfully create gene drives—making inheritable edits to their genes—that cause females to become sterile or skew them toward producing mostly male offspring. Scientists are also exploring other ways to use CRISPR to inhibit mosquitoes’ ability to transmit malaria—for example, by introducing genes that could eliminate the parasites as they pass through a mosquito’s gut on their way to its salivary glands, the main path through which infections are transmitted to humans. In comparable ways, the tool also holds promise for fighting other diseases carried by mosquitoes, such as dengue fever and the Zika virus.
It will be several years, however, before any genetically edited mosquitoes are released into the wild for field trials. Although many questions about safety and efficacy will have to be answered first, there is reason to be optimistic that creating gene drives in malaria-spreading mosquitoes will not do much, if any, harm to the environment. That’s because the edits would target only the few species that tend to transmit the disease. And although natural selection will eventually produce mosquitoes that are resistant to any gene drives released into the wild, part of the value of CRISPR is that it expedites the development of new approaches—meaning that scientists can stay one step ahead.
THE PATH FORWARD
Like other new and potentially powerful technologies, gene editing raises legitimate questions and understandable concerns about possible risks and misuse. How, then, should the technology be regulated? Rules developed decades ago for other forms of genetic engineering do not necessarily fit. Noting that gene-edited organisms are not transgenic, the U.S. Department of Agriculture has reasonably concluded that genetically edited plants are like plants with naturally occurring mutations and thus are not subject to special regulations and raise no special safety concerns.
The benefits of emerging technologies should not be reserved only for people in developed countries.
Gene editing in animals or even humans raises more complicated questions of safety and ethics. In 2014, the World Health Organization issued guidelines for testing genetically modified mosquitoes, including standards for efficacy, biosafety, bioethics, and public participation. In 2016, the National Academy of Sciences built on the WHO’s guidelines with recommendations for responsible conduct in gene-drive research on animals. (The Gates Foundation co-funded this work with the National Institutes of Health, the Foundation for the National Institutes of Health, and the Defense Advanced Research Projects Agency.) These recommendations emphasized the need for thorough research in the lab, including interim evaluations at set points, before scientists move to field trials. They also urged scientists to assess any ecological risks and to actively involve the public, especially in the communities and countries directly affected by the research. Wherever gene-editing research takes place, it should involve all the key stakeholders—scientists, civil society, government leaders, and local communities—from wherever it is likely to be deployed.
Part of the challenge in regulating gene editing is that the rules and practices in different countries may differ widely. A more harmonized policy environment would prove more efficient, and it would probably also raise overall standards. International organizations, especially of scientists, could help establish global norms. Meanwhile, funders of gene-editing research must ensure that it is conducted in compliance with standards such as those advanced by the WHO and the National Academy of Sciences, no matter where the research takes place.
When it comes to gene-editing research on malaria, the Gates Foundation has joined with others to help universities and other institutions in the regions affected by the disease to conduct risk assessments and advise regional bodies on experiments and future field tests. The goal is to empower affected countries and communities to take the lead in the research, evaluate its costs and benefits, and make informed decisions about whether and when to apply the resulting technology.
Finally, it’s important to recognize the costs and risks of failing to explore the use of new tools such as CRISPR for global health and development. The benefits of emerging technologies should not be reserved only for people in developed countries. Nor should decisions about whether to take advantage of them. Used responsibly, gene editing holds the potential to save millions of lives and empower millions of people to lift themselves out of poverty. It would be a tragedy to pass up the opportunity.
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GENE DRIVES AND THE POTENTIAL BENEFITS OF CRISPR TECHNOLOGY
APRIL 9, 2018
BY MATTHEW EDGINGTON
Marshall and Akbari review a range of different proposed gene drive systems and discuss ways in which CRISPR may be useful in engineering them in a recent issue of ACS Chemical Biology.
In the years since translocations were first suggested as a genetics-based method for the control of insect populations, a number of different gene drive strategies have been proposed. To date, progress toward fully functioning versions of each of these systems has been extremely varied. As such, the rapid advancement of CRISPR gene editing technology has given hope that the development of a wide range of gene drive systems should be simplified and accelerated.
A SELFISH GENE (BLUE) SPREADING THROUGH A MOSQUITO POPULATION
This review is organised according to the expected behaviour of the systems discussed. In particular, the authors discuss threshold-dependent drives (translocations and engineered underdominance), threshold-independent drives (Medea, homing-based systems and driving Y chromosomes) and temporally self-limiting drives (killer-rescue and daisy drives). For each system discussed, the authors outline key details including the drive mechanism, predicted dynamics following release into a wild population and current progress toward engineering them.
For the non-CRISPR-based systems discussed here (i.e. translocations, engineered underdominance, Medeaand killer-rescue), a number of ways in which CRISPR technology could accelerate gene drive development are proposed. Specifically, the authors note that CRISPR should provide a new means of engineering lethal toxins and also that CRISPR has already been used to generate site-specific chromosomal translocations.
THE TOXIN-ANTIDOTE – BASED DRIVE SYSTEM KNOWN AS MEDEA. EMBRYOS WITHOUT MEDEA WILL DIE BECAUSE OF MATERNALLY DEPOSITED ‘TOXINS’.
While discussing threshold-independent drive systems, the authors point out the need to develop remediation measures in case such a system were to produce unintended/undesirable consequences. As such, for Medeathey discuss the possibility of releasing a second generation element that should spread at the expense of both the original version and the wild-type allele. For homing-based systems a range of different remediation strategies are discussed, namely ERACR, CHACR and an immunizing reversal drive. As these are summarized in the review, we do not outline their workings here.
AN EXAMPLE OF AN ENGINEERED UNDERDOMINANCE SYSTEM
Finally, the authors discuss the recently proposed (and not yet developed or extensively modelled) daisy quorum drive system. Briefly, this would use either a daisy-chain or daisyfield drive system to produce an underdominance effect in a target population. Thus, daisy quorum is proposed as a method for generating threshold-dependence using a temporally self-limiting drive system.
This paper provides a good review of a range of different gene drive strategies, some challenges encountered in engineering them and opportunities whereby CRISPR technology could help simplify/accelerate the development of these systems.
John M. Marshall and Omar S. Akbari (2018) Can CRISPR-Based Gene Drive Be Confined in the Wild? A Question for Molecular and Population Biology. ACS Chem. Biol. 13. 424-430 https://pubs.acs.org/doi/abs/10.1021/acschembio.7b00923
PNAS: Welcome to Science Sessions. I’m Paul Gabrielsen.
The Aedes aegypti mosquito carries malaria, dengue fever, yellow fever, chikungunya, and Zika. But there may be a way to eliminate this and other harmful invasive species, through an application of gene editing called a gene drive. A gene drive encodes both a gene edit and the ability to copy that edit so that the next generation is guaranteed to inherit it and the edit rapidly spreads through the population.
Kevin Esvelt of the Massachusetts Institute of Technology proposed that the CRISPR/Cas9 gene editing system, first announced in 2013, could be the engine behind a gene drive. Soon after the proposal, however, Esvelt and others expressed concerns about the effect of such a self-propagating gene drive on ecosystems.
In a recent PNAS paper, Omar Akbari of the University of California, San Diego and colleagues presented what could be a safer form of a gene drive. They developed a method of encoding only part of a gene editing system into the Aedes mosquito. Akbari’s results could lead to a gene drive that achieves the goal of controlling harmful species but carries less risk for unintended and uncontrolled effects on native populations of those same species.
Esvelt begins by telling the story of his gene drive proposal. He was among the first to experiment with the CRISPR/Cas9 system, but almost left the field as CRISPR’s popularity skyrocketed. One morning, his outlook changed.
Esvelt: I was walking to work through the Emerald Necklace in Boston, and there was actually a turtle in the water that day, which was a rare spotting. And I was just wondering, are we ever going to edit any of these organisms? In the wild, I mean. And I concluded, well probably not just because whenever we make a change it's for our benefit not that of the organism, and so natural selection tends to wipe the floor with them. So then I wondered, but wait, what would happen if you encoded the CRISPR system that you used to make a genome edit adjacent to the change you're going to make? Then when it mated with a wild organism, the offspring would inherit your change and the instructions for making it, and it would then edit the original version from the other parent to have your new edit. And then, that would ensure inheritance by the next generation and the next and the next and the next.
PNAS: Esvelt’s musings led to the gene drive proposal. Others had proposed similar systems, going back even to the 1940s. But now with CRISPR, the idea of a gene drive could become reality.
Esvelt: So the first day was pretty much total excitement and elation at all these possibilities because this could be the key to eradicating malaria, schistosomiasis, all sorts of other diseases. The second day all of my doubts kicked in, thinking about - isn't this going to cause problems if it keeps on spreading, as presumably it would? How are we going to ensure that it's safe? You can't really test it in the field safely because it
would probably just take off, so how do you run a field trial? Is an isolated island enough? What if it gets off?
PNAS: In 2017, Esvelt and colleagues wrote that gene drives could spread remarkably quickly through an invasive animal population, but carry a significant risk of spreading to native populations as well. That risk warrants extreme caution in field trials and more research into safer forms of the technology.
This is where Akbari comes in. In the CRISPR system, the protein Cas9 acts as the scissors, cutting DNA at a location specified by a strand of guide RNA. Akbari and his colleagues encoded the gene for the Cas9 protein into the Aedes mosquito genome.
Akbari: Without the presence of the guide RNA, the Cas9 essentially doesn't cut. So, it's off. To turn it on, one would need to either inject the guide RNA into the organism or genetically cross the Cas9-expressing strain to other strains that express guide RNAs.
PNAS: Akbari and colleagues have already employed the Cas9 embedded in the mosquitos’ genome to manipulate eye and body color, among other edits. If employed in a gene drive, Akbari’s partially-encoded system would be called a split gene drive.
Akbari: So the split drive approach, it's a self-limiting approach. So, it essentially can't spread on its own; you would need to continually supply the Cas9 into the population. So, this type of drive is safe in that it can't spread on its own. The split gene drive approach is a good approach for studying and engineering and designing them in the laboratory and understanding how effective they spread in the presence of Cas9. It could be used in the field as a self-limiting-type approach and I think it would work, but again it would also require significant effort in terms of inundating the population with these gene drive-containing organisms and given that property, it makes it less attractive than a full drive that could actually spread itself.
PNAS: Esvelt says that although Akbari’s work can be viewed in the context of a gene drive, it also fulfills one of the basic promises of CRISPR: to accelerate fundamental research.
Esvelt: So the main impact of this paper, which is very well done, is to create tools that will make genome engineering in these mosquitoes fantastically easier.
PNAS: Esvelt’s vision of the way forward for invasive and harmful species control is to give communities and regions the tools they need for small-scale ecological engineering.
Esvelt: For almost all potential applications we need to focus on building local drive systems, that is, constructs that will alter a wild population, but only locally. That is, they cannot spread indefinitely. Just because it is hard to see how you're going to get more than 100 countries to agree, even on something like getting rid of these invasive mosquitoes that spread dengue and chikungunya and Zika and yellow fever.
Thank you for listening. Find more Science Sessions podcasts at pnas.org/multimedia.
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Link to Article by Mario C. Aguilera
Enter Omar Akbari’s insect zoo and it’s immediately clear that you’ve entered a different world. It’s not that you’ve passed through several layers of containment that keep the bugs securely locked away… nor the fact that the temperature has just escalated 20 degrees… nor that the room is kept at 60 percent humidity—just the way mosquitoes like it.
Rather, what becomes immediately apparent is Akbari’s unmistakable affinity for the pests and an ability of knowing just about everything there is to know about them.
Having just arrived on the UC San Diego campus as a faculty member in the Division of Biological Sciences, Akbari comes armed with a unique skill set aimed squarely at disease-carrying insects and the potential to revolutionize how we fight them. Just as canine experts can unmistakably identify this Lhasa Apso and that Shih Tzu, and how to breed each, Akbari’s mosquito expertise affords him uncanny perspectives on how to stop mosquitoes from spreading disease.
New UC San Diego molecular biologist Omar Akbari stands in his laboratory among hundreds of mosquito cages.
With a quick glance inside one of the stacked cages in his lab, Akbari deftly identifies a mosquito’s species… its sex… mating habits…. feeding regimen… and what a mosquito is doing at any given moment. To the casual observer, it might appear as a bunch of bugs sitting idly around a cage. But through Akbari’s lens, this scenario is much more. Years of getting to know these blood-lusting creatures tells
Akbari that these males are passionately waiting for the opportune moment a female is ready to mate, a situation accelerated when Akbari kick starts the mating ritual with a quick blast of air to get things stirred up.
He can carefully describe the process through which a mosquito pierces human skin and extracts blood, and with it the potential of transmitting pathogens. And he explains all of this while a hungry mosquito is feeding off of his blood.
For the love of mosquitosOmar Akbari’s story doesn’t trace the typical narrative of an emerging biologist. No early attraction to science. No stories of youthful adventures as a backyard wilderness explorer. Shockingly, not even a bug-collecting kit.
His story starts in the placid town of Idaho Springs, Colorado. Set in the mountains an hour’s drive from Denver, Akbari grew up the proud son of the owner of the town’s only movie theater. His passion for science began to blossom in high school but didn’t shift gears until he attended the University of Nevada, Reno, where he took a job in a lab that exposed him to the wonders of science.
“I started reading scientific papers and quickly began to love science,” said Akbari, who speaks in deceptively hushed tones but gradually ensnares his audience with the confidence that they are listening to someone who has clearly found his passion and purpose in life. “The ability to explore questions was really interesting to me. The idea that you could actually solve real-world problems became what I’m most interested in—the ability to save lives.”
During his four summers in Reno earning combined bachelor’s and master’s degrees, he found a job that taught him all there is to know about eradicating pathogen-carrying bugs, known as “vector control.” He recalls the thrill of going into the field and bringing back mosquitoes to test for West Nile virus and other pathogens.
“I learned how mosquitoes are controlled but I also learned about the cost and environmental impact, which was shocking and ridiculous,” said Akbari, who also obtained his Ph.D. at Nevada-Reno. “Having first-hand exposure to vector control and seeing the chemicals, oils and insecticides that were in use—I found that to be a major problem. I feel like that motivated me to try and invent a solution.”
During his next stop at a postdoctoral position at the prestigious California Institute of Technology, Akbari’s relationship with mosquitoes deepened. His seven-year stay in Caltech Professor Bruce Hay’s lab provided an unusual level of expertise, along with a lasting bond with the insects.
“Omar is one of the most talented, hardworking and imaginative young people I have seen,” said Hay. “He and UC San Diego are going to do great things together.”
“I was at work all the time and basically lived with the mosquitoes,” he said. “I learned how to rear them. But I also learned from them. If you look at the number of mosquitoes we have in our lab today, you’ll see that we’ve optimized the process of raising them for research. No other lab has this many different strains. (My lab) has become really good at it, and it’s because I lived with them and worked with them so closely.”
Know thy enemy Globally, more than three billion people are at risk of infection from malaria, which causes some 450,000 deaths per year and takes a child’s life every two minutes. For Akbari, these statistics are of interest personally as well as professionally. With two kids of his own at home, he openly wonders about how he would feel if one of his own was bitten by a mosquito and became infected.
Even with a clear affinity for mosquitoes, Akbari is quick to point out that they are perhaps the most dangerous animals in the world. His specialty is the species Aedes aegypti, also known as the “yellow fever mosquito,” which can also spread Zika, dengue and chikungunya—diseases with no effective vaccines.
Akbari and the nine members of his lab are on a mission to invent genetics tools and technologies that control the spread of disease and prevent pathogen transmission. They look to devise ways of driving laboratory-engineered genes—which disrupt normal pathogen inheritance pathways—into wild mosquito populations. Of late, Akbari is excited about prospects of a new weapon. He’s attempting to create genetically sterile mosquito males, which mate with wild females and pass the genes to their offspring. The eggs hatch and die as larvae.
“You are releasing males that mate and produce no viable offspring,” said Akbari. “Over time that suppresses specific populations. This has been shown to significantly reduce specific insect populations.”
The concept has been proven in fruit flies and Akbari is giddy at the prospects of trying the method in mosquitoes that carry pathogens.
“(Akbari) is always full of so many ideas and I think many of us in his lab are amazed at how he comes up with them,” said Anna Buchman, a researcher who has known Akbari for more than 10 years and worked in his lab for the past three. “For example, we are working on Zika-resistant mosquitoes. Omar just gets ideas and says, ‘Let’s just try this.’ A lot of those types of projects actually start to become big things but started in a minor direction.”
With such non-traditional approaches to solving mosquito disease transmission, Akbari will be working alongside researchers in the campus’ new Tata Institute for Genetics and Society in using UC San Diego-developed genetics technologies to eradicate malaria in India, as well as agricultural and health-related applications. As with the entire Tata Institute team, Akbari is committed to developing genetics tools for broad public benefit, and only introducing such advancements under safe and ethical constraints.
Akbari also comes to campus as the leader of a $15 million Defense Advanced Research Projects Agency (DARPA) project to investigate ways to genetically influence inheritance, or “gene drive,” to spread desired genes in wild populations and suppress harmful organisms. Other UC San Diego researchers are part of this Safe Genes research team investigating ways to combat disease-carrying mosquitoes in California.
“For his generation, working in vector biology and insect molecular biology, he’s one of the best and brightest,” said UC Irvine’s Anthony James, Donald Bren Professor of Microbiology and Molecular Genetics and a renowned mosquito scientist. “I’m really happy that there’s somebody of his caliber working on the Aedes aegypti species because they are a big deal. I view him as one of the two or three people worldwide who are doing excellent work on that species.”
‘One success can change the world’Getting to know the “mosquito man” is getting to know someone who clearly values a deep work ethic, but also collegiality and family life.
Deflecting the “I” of his work into the collective “we” is a noticeable aspect of his ethos to highlight his team’s unified efforts.
“The work that we’re doing in the lab and the ideas (Akbari) has are the future of genetic modification,” said Buchman. “I think we are going to see him really contribute in a very significant way to this field. As his career develops he is going to be a person that’s known.”
You’ll see Akbari playing pickup basketball on campus with the same skill and subtle ferocity seen in his research. His lab members will tell you that he no longer spends all day and night with his precious mosquitoes—although he still pours more time and passion into his work than most. These days he promptly gets home to spend ample time with his 6- and 2-year-old daughters and doing the things that dads do (yes, including singing Frozen songs together).
“Many of the projects we work on bridge the borderline of impossible,” said Akbari. “We tend to have far more failures than successes. Constant failure can be very difficult and frustrating to deal with, but I always remind myself that given the scope of our projects, even one success can change the world.”
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Can gene drives end mosquito-borne disease?
Infectious Disease News, February 2018When Omar S. Akbari, PhD, moved his lab of genetically modified mosquitoes from the University of California, Riverside, to the University of California, San Diego, he took only eggs, collecting some from each strain and sealing them in containers for the 90-mile trip south.
“Just the eggs. Not the adults — that’s how they’d escape, if something were to happen,” Akbari, a biologist and assistant professor at UC-San Diego, told Infectious Disease News.
Omar S. Akbari, PhD, biologist and assistant professor at the University of California, San Diego, said the world will have to decide if it wants to use gene drives. “I hope that we do,” he said.Akbari’s lab contains 260 cages filled with 130 strains of genetically modified mosquitoes plus additional cages for more experiments. The lab is designed to keep mosquitoes inside. Four doors separate the insectary from the outside world. Even if a mosquito were to escape from its cage, an air blower triggered by the innermost door should keep it from getting out of the room. For good measure, there are mosquito traps positioned from the insectary to the hallway outside the main lab.
Even if they did somehow escape, Akbari said many of his mosquitoes could not survive in the wild. Some could not even survive in the lab. Using a technology that allows scientists to make desirable edits in an organism’s genetic material, his lab has engineered what he called “interesting mutants.” These included mosquitoes with three eyes, three mouth parts, no wings, notched wings, eyes that were white instead of black and tiny eyes that presumably rendered the insects blind. This was not mad science, Akbari said, because each of the experiments had an applied reason for driving certain genes into a population. For instance, a system that produced striking yellow mosquitoes could be used to optically sort the insects and release only males into the wild.
The experiments were conducted using CRISPR-Cas9, a gene-editing mechanism that scientists can use to drive a self-destructive gene — like one that produces offspring that cannot survive — through a population of insects. In just a short time, CRISPR-Cas9 has made a world without mosquito-borne disease seem more possible.
“I think it’s fair to say it surprised a lot of people with how well it works,” Anthony A. James, PhD, professor of microbiology and molecular genetics in the School of Medicine and professor of molecular biology and biochemistry in the Ayala School of Biological Sciences at UC-Irvine, said in an interview.
Infectious Disease News spoke with several experts about the promise of using gene drive technology, including CRISPR-Cas9, as a tool for mosquito control and its potential to eradicate mosquito-borne diseases.
‘We need better tools’Mosquitoes kill millions of people worldwide each year. According to WHO, malaria infected at least 216 million people worldwide in 2016, killing 445,000, most of them children in Africa. The Zika virus epidemic has caused thousands of cases of microcephaly in infants, mainly in Brazil, which also experienced a large yellow fever outbreak last year that prompted mass vaccination campaigns and raised fears that the disease would spread to the country’s largest cities. About half the world’s population now lives in an area at risk for dengue, which can develop into a serious and sometimes fatal disease. The first indigenous outbreak of chikungunya in the Americas began in 2013, sickening millions of people, according to the Pan American Health Organization.
Efforts to control these diseases have historically focused on using pesticides to rapidly reduce populations of mosquitoes, like the aerial spraying that took place around Miami in 2016 to kill Aedes aegyptimosquitoes that carry Zika. Officials urge people to protect themselves by using insect repellent, covering exposed skin, fixing broken window screens and removing standing water in their yards.
For decades, scientists have been trying to develop better ways to combat mosquito-borne diseases. Previous methods seem primitive compared with gene drives, whose promise has grown since the introduction of CRISPR-Cas9, which has made the process more efficient and straightforward.
“Years of using insecticides and pesticides have shown us that it’s not sustainable,” said James, who began exploring genetic solutions to mosquito-borne diseases in 1986. “We don’t want to continue to put tons of potentially toxic chemicals for off-target organisms into the field. If we have something that’s better and cleaner and highly specific to the target organism, why not use it? We need better tools that are better targeted. Even though this is a new technology that hasn’t been in the field yet, it’s got to be better than pesticides.”
After years of research without results, gene drive technology has progressed rapidly in the last several years since the introduction of CRISPR-Cas9. The system is seen as being critical to the future of mosquito control and the eradication of mosquito-borne diseases, but no gene drive has ever been approved for use in the wild, and the technology represents just one of many new areas of exploration.
“There is no silver bullet,” Marcelo Jacobs-Lorena, PhD, professor of molecular microbiology and immunology in the John Hopkins Bloomberg School of Public Health, said in an interview. “If a gene drive is approved and implemented, I don’t think it can, by itself, eliminate a disease. We have to combine all the resources we have. That’s the only way we will conquer malaria or any other disease.”
CRISPR is a helpful acronym for clustered regularly interspaced short palindromic repeats, and Cas9 stands for CRISPR-associated protein 9. Using CRISPR technology, scientists can modify genomic sequences by cutting and editing targeted sections of DNA. CRISPR-Cas9 is not the first gene drive technology to be tested by experts, but it has produced the most encouraging results.
“I personally don’t believe that any other gene drive mechanism will work,” Jacobs-Lorena said.
Key findingsScientists are exploring other methods for mosquito control, including interventions that do not necessarily require a gene drive to implement.
Marcelo Jacobs-LorenaRecently, the EPA approved the use of a strain of Wolbachia for mosquito control. Passed to females during mating, the bacterium ensures that offspring do not survive. It works in both A. aegypti and A. albopictus mosquitoes, which transmit Zika, dengue, chikungunya and yellow fever. But Wolbachia is not effective against the many species of Anopheles mosquitoes that carry the Plasmodiummalaria-causing parasite.
Results from two studies conducted at the Johns Hopkins Malaria Research Institute and published in Science last year raised the possibility of using other genetic methods to control malaria. In one, researchers altered the gene activity of several strains of A. stephensi mosquitoes to boost their immunity to the P. falciparumparasite. They found the process also altered the insects’ mating preferences so that genetically modified males preferred unmodified wild females and wild males preferred genetically modified females. This helped spread the genetic modification to successive generations of mosquitoes — an unexpected finding. It took only five generations, or around 10 to 12 weeks, for the modification to dominate the population. The mosquitoes have maintained a high level of resistance to the parasite for more than 7 years.
“Our discovery is very important because it’s proof that spreading the gene doesn’t have to be based on a genetic mechanism. It could be something that changes the behavior of the insect,” George Dimopoulos, PhD, professor of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, told Infectious Disease News.
In another chance finding, Jacobs-Lorena and colleagues discovered a new strain of the Serratia bacterium engineered to kill the malaria parasite. The bacterium spreads efficiently, making it different from other mosquito-infecting bacteria. The strain, which was unexpectedly found in the insects’ ovaries, is transmitted easily from males to females during mating, then from females to 100% of their progeny, allowing it to move rapidly through mosquito populations.
Bringing all of this together, a study published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) in 2015 showed for the first time how gene drives can be used to spread antimalarial genes into a vector population. The study was the result of a collaboration between James, who had published findings on malaria-resistant genes in 2012, and two researchers from UC-San Diego, Ethan Bier, PhD, and Valentino Gantz, PhD, whose 2015 study in Science demonstrated that CRISPR-Cas9 could be used to spread gene mutations in fruit flies. Together, they adapted the technology quickly as a gene drive in mosquitoes.
In another milestone study published in PNAS in November 2017, Akbari and colleagues showed how they engineered Cas9 strains to be easily expressed through generations of A. aegypti mosquitoes in a set of experiments that produced the “mutants” in his lab. This is only one-half of what is called a split-gene drive. Akbari and colleagues are working on the other half, which involves crossing Cas9 strains with guide RNA that recognize DNA sequences and measuring the rates of inheritance.
Using CRISPR gene-editing technology in mosquitoes is just one application that is being studied by scientists. Numerous breakthroughs in other areas have occurred over the course of just a few years. Last year, researchers from Harvard showed they could use CRISPR-Cas systems to encode a short movie into the DNA of bacteria, a method that could be used to store data within living cells. The quick succession of these results has made researchers optimistic about the technology’s future applications.
“The day before the discovery of antibiotics, the mildest infectious disease was life-threatening. After that, they at least became treatable. There are these major jumps that occur in science and medicine that have a profound effect,” James said. “It’s some scientist somewhere doing something that no one pays attention to and it turns out it’s a big deal, like the CRISPR biology.”
Regulatory barriersWhen the first gene drive is introduced in the wild — perhaps not for another 5 to 10 years, according to Dimopoulos — it is unlikely to happen in the U.S., where James said getting the appropriate regulatory bodies on the same page is too much of an obstacle.
“You have to be in a country that has an integrated regulatory system where all interested parties have a vote and it’s really straightforward. The United States is still so fragmented,” he said. “The USDA, FDA, EPA, CDC — there’s no single body that has a member of each one of those [agencies] that can work together.”
George DimopoulosStill, James said a framework is in place for how to introduce a gene drive system in the wild. Under a four-phase trial plan devised by a working group at WHO, researchers would have to demonstrate that a gene drive is safe and effective. The next two phases would involve studies using large outdoor cages or the release of mosquitoes restricted to a certain geographic area or ecosystem, then an epidemiologic study showing that the drive has an impact on a disease. If all the criteria are met, a fourth phase would involve making it part of a standard disease control program.
James anticipates that the first mosquito gene drive in the wild will involve a small number of releases in a confined area. Researchers will monitor the insects over several seasons to determine the impact. But because no country has adopted guidelines that would specifically permit the release of a gene drive organism, he said it is too early to speculate where the first one might occur.
“There are efforts to bring regulatory structures up to speed. And we’re happy with that,” James said. “We work in public health. We’re trying to save people from these diseases. We don’t want to be known for doing something catastrophically stupid. That kind of defeats the whole purpose.”
Ethical questionsThere are other barriers to using gene drives in the wild, including ethical questions about changing an animal’s biology.
The ethics of gene drives may be a matter of debate, but experts do not foresee them having serious ecological consequences, such as a drive jumping to another species or making mosquitoes a more competent vector for another pathogen — two concerns that have been raised. “This is science fiction,” Dimopoulos said.
Still, to make gene drives a reality, Akbari said it would be important to demonstrate control over a system before a gene drive is released in the environment, to show that it can be reversed in case of any unintended consequences. According to him, this is easily done by designing another gene drive that can target the initial sequences. His lab was one of several in the University of California system that received $15 million in gene drive-related funding from the Defense Advanced Research Projects Agency (DARPA), an agency in the U.S. Department of Defense that invests in breakthrough technologies. Akbari said one of the stipulations of the DARPA funding is that the researchers explore how a gene drive can be reversed.
“This is definitely something that DARPA is interested in, mainly because if the gene drives got into the wrong hands and someone were to try to drive something as some kind of weapon, then how would you counter that weapon?” Akbari said. “We need countermeasures. Having countermeasures is definitely a high priority.”
Experts theorize that a gene drive could be used to make a species of mosquito extinct. Some see little reason not to eradicate a species like A. aegypti, an invasive insect in the Western Hemisphere that has evolved to become a human pest. But is it ethical? According to Sahotra Sarkar, PhD, professor of philosophy and integrative biology at the University of Texas, there may indeed be legitimate reasons to drive a species to extinction but not without first having a public discussion and developing policy guidelines.
“Until that happens, it would be unwise to recommend gene drives to drive any species to extinction,” Sarkar said.
According to Akbari, the science around gene drives is moving so fast that ethical questions about their use are likely going to be harder to address than scientific questions.
Source: Steve Zylius/UCI
Anthony A. James, PhD, professor and microbiologist at the University of California, Irvine, and colleagues showed for the first time how gene drives can be used to spread antimalarial genes into a vector population.“We will reach a point where there is a drive system that can spread and can block the vector competence of malaria or dengue and we’ll have to decide whether or not to use it. I hope that we do,” he said.
Experts also said that engaging and educating the public will be a significant hurdle to eventually using gene drives in the wild — maybe the biggest one. There already have been examples of this, including a plan to release genetically modified mosquitoes in the Florida Keys that was initially voted down by residents but ultimately approved. Outdoor caged trials of the same mosquitoes, manufactured by the British company Oxitec, began in India last year.
Dimopoulos said one of the concerns is that the public will blame the release of a gene drive in the wild for an unrelated disease outbreak.
“We have to face that there is a huge resistance in the world for anything genetically modified. That is the biggest barrier,” Jacobs-Lorena said. “The advantage we have with mosquitoes is that the ultimate aim is to save lives.”
‘Scientists vs. evolution’Whether using gene drives will achieve the ultimate goal of eradicating a mosquito-borne disease is unclear, but some experts are betting on the technology. UC-San Diego is building a new 2,000-square-foot insectary that is 10 times the size of the one in Akbari’s current lab. When it is finished later this year, Akbari will share the insectary with Bier.
The goal of a gene drive is to block a pathogen long enough that it is no longer carried by mosquitoes, humans or any other animals, Akbari said. After that, the question is whether nature will cooperate.
“I do think that evolution probably will find a way,” he said. “But given that we can engineer gene drives pretty fast, it would be an arms race: scientists vs. evolution.”
Dimopoulos said there is chance that something better than CRISPR-Cas9 will be discovered and make it even easier to alter the genes of mosquitoes on a large scale.
“It reminds me a little bit of when they sequenced the human genome,” he said. “If you would have told anyone 3 years earlier that they were going to [do that], no one would have believed you. People would have been laughing. Then, all of a sudden, there it was.” – by Gerard Gallagher
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Caroline Seydel | Genetic Literacy Project |
January 29, 2018Gene drives hold great promise for thwarting mosquito-borne diseases. The concept is tantalizing: Just pop your desired gene into some mosquitoes -- maybe it’s a gene that stops them from biting humans, or one that fends off Zika virus infection -- and then rig it so that all of the larvae inherit the gene, every time. And with that, your gene spreads effortlessly throughout the wild population, reducing the danger of mosquito-borne diseases.
But nature is complex, and the idea of a universally inherited gene unleashed in the wild, with no way to call it back, gives many people pause. Scientists and activists agree the technology needs to be carefully designed and rigorously evaluated for possible risks before insects bearing gene drives are released into the wild. To keep the self-propelled genes under control, researchers are pursuing various strategies for containing the spread of these modified organisms.
One way to do this is to make the gene drive dependent on a second gene, which is inherited normally. The power of the gene drive then fades as the number of bugs carrying the helper gene dwindles in the population. The more genes you want to stitch in, however, the higher the technical hurdle. Even with CRISPR gene editing tools, it’s still daunting to splice foreign genes stably into the mosquito genome.
A newly created strain of Aedes aegyptimosquito, the pest that carries Zika, dengue and yellow fever, lowers that hurdle significantly. Created by entomologist Omar Akbari and his team, then at UC Riverside, the mosquitos make their own Cas9, the DNA-cutting component of the CRISPR gene editing system. With the bugs doing half the work, it becomes much easier to insert or remove genes.
Normally, scientists editing genes with CRISPR must inject into the cell both the Cas9 protein and a guide RNA that dictates where the Cas9 should cut. “You can co-inject the Cas9 and the guide RNA, and it will go in, but the efficiency of that is low compared to having Cas9 that’s being dumped maternally into the egg,” said Akbari, who spoke to the GLP from his new lab at UC San Diego. To show how well it works, the team created double and triple mutant mosquitoes with a single guide RNA injection, something that’s never been done before in these mosquitoes.
Mosquitoes that make their own molecular scissors will make it easier to construct a split-gene drive, which Akbari hopes could eventually be deployed for environmentally friendly mosquito control. “One of the beauties of this system is that it’s species-specific,” Akbari said. “You’re not targeting all insects, or all mosquitoes. You’re targeting just one at a time, and then you can assess to see what happens.” Chemical insecticides, by contrast, kill good and bad insects indiscriminately, and once spraying stops, the bugs return. “It’s a horrible approach, and it probably has consequences on the environment,” Akbari said.
Gene drives, on the other hand, only target the organism they’re designed for. Like all animals, mosquitoes have two copies of each chromosome. Only one of each chromosome gets passed down from each parent, meaning that if a gene is engineered into one chromosome, the offspring has only a 50/50 chance of inheriting that gene. In a gene drive, the desired piece of DNA is patched into one chromosome, but then tricks the cell into copying it into the other chromosome. At that point, because it’s present on both chromosomes, it’s guaranteed to be passed down to the next generation. But it could never be passed to a different species of insect, nor harm a predator that eats the mosquito.
“It looks good on paper, but the practicalities are pretty challenging,” said Luke Alphey, of the Pirbright Institute in the UK, in an interview. He is also working toward split-gene drives in Aedes aegypti, sometimes called a “daisy-chain” drive, containing three or more linked elements. In these multi-part systems, the parts that enable the copying and pasting are broken up into different locations in the chromosome. Gene A can copy itself as long as Gene B is present; Gene B can only copy itself in the presence of Gene C. Gene C can’t copy itself at all; call it the “driving license.” Ordinary selection pressures ensure that gene C, because it confers no evolutionary benefit, will eventually drop out of the population. The first element will spread rapidly at first, while the driving element is common, but it too will fade away. “So that means it isn’t going to spread around the world because as soon as it starts to spread into an adjacent population, it doesn’t have it’s ‘licensing factor’ with it at a high enough concentration,” Alphey said,
While they might not spread around the world, the engineered insects could certainly cross national boundaries, so multinational cooperation is critical for developing responsible guidelines. Accordingly, parties to the UN Convention on Biological Diversity have been studying the potential impact of gene drives on biodiversity. At their December 2016 meeting, they considered, and ultimately rejected, a moratorium on any gene drive research.
Some advocacy groups, unhappy with this decision, have tried to raise suspicion that scientists who oppose the moratorium are inappropriately organizing to influence the process. Edward Hammond of Prickly Research obtained emails detailing the effort to recruit scientists to the Online Forum for Synthetic Biology, where participants discuss concerns about synthetic biology, including gene drives. The correspondence shows that the Gates Foundation, which also funds gene drive research via Target Malaria, paid a PR firm to reach out to scientists who have expert knowledge of gene drive, and encourage them to participate in the online forum and argue against a moratorium.
Whether this organizing was inappropriate is debatable. Robert Friedman, of the J. Craig Venter Institute in La Jolla, California, said gene drive scientists simply wanted to achieve the same level of coordination as activist groups, who presented a letter at the 2016 meeting signed by representatives of 160 organizations, urging a halt to any gene drive research. “The gene drive research community hadn’t really participated in these meetings before,” Friedman said in an interview with the GLP. “I think they felt pretty out-gunned.” Friedman is a member of the UN Ad Hoc Technical Expert Group (AHTEG) on Synthetic Biology, which uses the opinions and concerns raised in the online forum to craft recommendations for biosafety protocols. He points out that in the online forum, when technical questions arise, it’s important to have people who works directly in the field available to answer them. “It helps to have scientists participating in what’s supposed to be an expert group,” he said.
Once the technical challenges are overcome, if some type of self-limiting gene drive system could be successfully created, how exactly could it be deployed to fight mosquito-borne diseases? “There’s a lot of applications, actually,” Akbari said. Mutants could be made that resist pathogenic viruses, for instance, or that can’t detect human odors, meaning they don’t bite us. Because the Cas9-expressing strains make it much easier to create mutants, Akbari said, “this really opens up the door to studying gene function in this organism in a major way.”
Work is already underway to understand the mosquitoes’ ability to smell humans. Matthew DeGennaro leads the Laboratory of Tropical Genetics at Florida International University, where he spends his days making mutant mosquitoes. “In my lab, our bread and butter is knocking out genes and then seeing what they do,” DeGennaro told the GLP. He’s identified a gene that allows the mosquitoes to seek out people by their scent, and by studying the network of gene interactions in play, he hopes to develop new ways to hide humans from mosquitoes. The new Cas9-expressing strains will make this process a whole lot more efficient. The more genes from Aedes aegypti whose functions are known, the more strategies can be constructed to stop them from spreading disease. Maybe that’s engineering the mosquitoes to be “blind” to human odors, or maybe it’s designing new insect repellents that target particular biochemical pathways for long-lasting protection. “Whatever you can dream of, and we know something about, eventually you’ll get there,” DeGennaro said.
What some dream of, however, is engineering these mosquitoes to simply die off. This isn’t as horrific as it sounds, and in fact, it’s already being done. The British company Oxitec created male mosquitoes genetically altered to require a supplement. When the modified males are released into the population, they mate with the wild females, creating doomed progeny that die off before reaching adulthood. In Piracicaba, Brazil, where these mosquitoes have been in use since 2015, the Aedes aegypti population has declined markedly, and cases of dengue dropped by half.
If this sounds drastic, keep in mind there are over 3,500 species of mosquito in the world, so killing off one may not make much impact. Plus, it’s still an improvement over insecticides, which kill indiscriminately. “It’s important to have as many tools as possible to deal with mosquitoes,” DeGennaro said. “We only have so many insecticides that are somewhat safe, and there’s resistance developing to them. Genetically modified insects may be something that we really need.”
Caroline Seydel is a freelance science writer. Find her online at carolineseydel.com or on Twitter @CarolineSeydel.
Maciej Maselko has made wild sex deadly — for genetically modified organisms. A synthetic biologist at the University of Minnesota in Minneapolis—St Paul, Maselko and his colleagues have used gene-editing tools to create genetically modified yeasts that cannot breed successfully with their wild counterparts. In so doing, they say they have engineered synthetic species.
“We want something that’s going to be identical to the original in every way, except it’s just genetically incompatible,” says Maselko, who is due to present his work on 16 January at the annual Plant and Animal Genome Conference in San Diego, California. The research was co-led by Michael Smanski, a biochemist at the University of Minnesota.
The technology could be used to keep genetically modified plants from spreading genes to unmodified crops and weeds, thereby containing laboratory organisms, the researchers hope. It might even help combat pests and invasive species, by replacing wild organisms with modified counterparts. Other scientists say that the approach is promising, but warn that it could be stymied by technical hurdles, such as the ability of modified organisms to survive and compete in the wild. “This is an ingenious system and, if successful, could have many applications,” says evolutionary biologist Fred Gould of the North Carolina State University in Raleigh.
Maselko and Smanski used the CRISPR–Cas9 gene-editing tool not to edit target genes, but to alter their expression. The team guided the Cas9 enzyme to over-activate genes so that their protein products accrued to toxic levels. When they first tested the approach in brewer’s yeast (Saccharomyces cerevisiae), they raised the levels of a protein called actin to the extent that the cells containing it exploded.
To prevent genetically modified yeast cells from mating successfully with other strains, the team engineered two modifications to the yeast cells: one, analogous to a ‘poison’, produced a version of Cas9 that, in concert with other factors, recognized and over-activated the actin gene. The second modification, the ‘antidote’, was a mutation that stopped Cas9 from overexpressing actin.
A yeast strain that contained both poison and antidote produced healthy offspring when mated with a strain carrying the antidote. But when the modified strain was crossed with a different lab strain lacking the antidote, almost all of their offspring popped like balloons, Maselko and Smanski’s team reported in Nature Communications1 in October.
Live cell imaging time lapse of brewer's yeast (Saccharomyces cerevisiae) cells in a compatible (left) and incompatible (right) mating.Credit: Maselko et al., Nature Communications 8:883 (2017).
This week, Maselko is due to discuss the team’s progress towards engineering a synthetic species of fruit fly, using a developmental gene called wingless as a poison. Work will soon commence in plants, mosquitoes, nematodes and zebrafish, says Maselko, who, with Smanski, has applied to patent the approach.
A counter to invasion
A synthetic species could also be used to outcompete and control undesirable species that spread disease or harm ecosystems. In another contribution to the conference, Maselko’s colleague Siba Das, also at the University of Minnesota, is presenting a mathematical model showing how synthetic speciation could combat invasive carp, which has ravaged rivers and lakes in Minnesota and other central US states, by replacing the invasive species.
However, the genetic modifications that stop interbreeding — the poison and antidote — could carry a steep evolutionary fitness cost, says Omar Akbari, a molecular biologist at the University of California, San Diego. The Cas9 enzyme doesn’t always recognize its intended gene and could crank up the activity of other genes. Such ‘off-target effects’ could sap the health of modified organisms. Any impact affecting the organisms' potential wellbeing, Akbari adds, should be easy to detect in lab experiments in fruit flies. “I’m not sure if this is going to generate a fit-enough strain to compete in the wild,” Akbari says.
Gould agrees that it will be difficult to engineer reproductive barriers without incurring evolutionary costs. Scientists could potentially overcome this obstacle by releasing large numbers of modified organisms to increase the odds that a synthetic species will overtake wild organisms. Still, Gould — who is working on other genetic approaches to combating pests — is enthusiastic to see another technology. “I would never want to put all my eggs in one basket,” he says.
RIVERSIDE, Calif. — In a warm and very humid room, behind a series of sealed doors, Omar Akbari keeps a zoo of mosquito mutants. He’s got mosquitoes with three eyes, mosquitoes with malformed mouthparts, mosquitoes with forked wings, mosquitoes with eerie white eyes, and mosquitoes that are bright yellow instead of black.
Akbari loves them unabashedly; he feeds them fish flakes, mouse blood, and sugar water and calls some of them “beautiful.” But they’re not pets: Akbari’s lab here at the University of California, Riverside, is at the leading edge of a revolutionary technology — gene drive — that could one day deploy mosquito mutants to rid the world of scourges like malaria, dengue, and Zika.
The technology is moving faster than anyone dreamed. Just three years ago, the idea of disabling or destroying entire populations of disease-causing mosquitoes using gene drives seemed a distant theoretical possibility. But advances in gene-editing have shoved the field into overdrive. And that vision is now very much in reach.
Gene drives are genetic systems that break the natural Mendelian rules of inheritance. Normally, offspring have a a 50 percent chance of inheriting any given gene from a parent. Using genetic engineering, scientists can greatly increase the odds a specific gene will be passed on. That lets them rapidly push a particular gene — say one that makes mosquitoes sterile or unable to carry the malaria parasite — through a population. And that, in turn, could — at least in theory — halt the spread of certain diseases, like malaria.
“I really think it’s solvable,” said Akbari, a molecular biologist who is in the process of moving his lab to the University of California, San Diego. “It’s not cancer. It’s not Alzheimer’s. It’s literally a mosquito biting you. We can stop that.”
Gene drive gives scientists power to hijack evolution But with that promise comes great risk. Full gene drives can spread unchecked through a population — potentially altering entire species and vast ecosystems.
That’s why the military’s Defense Advanced Research Projects Agency is spending $65 million to understand not only how gene editing technologies and gene drives work — but also how to control, counter, or reverse them. “These are very new technologies and they have a lot of unknowns associated with them,” said Safe Genes program manager Renee Wegrzyn. “The idea of having safety features built in from the start seems like a good approach.”
A normal mosquito (left) and one that has been genetically modified for yellow coloring using CRISPR.DOM SMITH/STATHere are some of the ways scientists are trying to make safer, more efficient gene drives:
Make a ton of mutantsA gene drive will only work against disease if it targets the right gene. One way to find those genes: make a lot of mutants.
Akbari recently created a new transgenic line of dengue and Zika-carrying Aedes aegypti mosquitoes that express the Cas9 enzyme in all of their offspring. While it may seem obscure to non-scientists, the achievement has mosquito researchers buzzing because it means they no longer need to laboriously inject the gene-editing enzyme into each mosquito egg they want to edit.
In a remote West African village, a revolutionary genetic experiment is on its way — if residents agree to it Those injections are physically tricky to do under the microscope; fragile eggs often explode when injected with too much fluid. And the injections don’t always succeed.
The new transgenic line means scientists can edit genes in mosquitoes far more efficiently — perhaps injecting just 10 eggs with guide RNA instead of 500 to generate a mutation. It works so well, Akbari found he could create double and triple mutations with a single injection. Now, he’s freely sharing the mosquitoes, shipping them to other researchers in hopes of speeding up work on gene drives and mosquito genetics.
“Everyone wants them,” he said.
Ensure it takes two to tango
Akbari doesn’t want to create a full-on gene drive that could push new genes through a mosquito population with unstoppable momentum. Like many in this emerging field, he thinks it’s too risky.
“These are very new technologies and they have a lot of unknowns associated with them. The idea of having safety features built in from the start seems like a good approach.”
RENEE WEGRZYN, SAFE GENES PROGRAM MANAGER
Instead, he’s developing a “split gene drive” that requires two parts — a gene editor like the CRISPR-Cas9 system partnered with specific guide RNA that tells the editor where to cut.
Akbari’s gene drive will only work when mosquitoes encoded with the Cas9 enzyme are bred with mosquitoes encoded with guide RNA. To keep the engineered gene moving through a population, new waves of Cas9 mosquitoes must be released and start breeding. If new critters aren’t released, “it just kind of self-eliminates,” Akbari said.
Fight the resistanceOne of the biggest barriers to gene drives is natural resistance. Animals that aren’t susceptible to the gene drive — perhaps because of natural variations in their own genomes — might thrive and take over an ecosystem after a gene drive is introduced.
“It’s a race. Evolution is going to be a problem,” Akbari said. “With what we see, it seems that’s going to happen quickly.”
One way to predict these problems is to use math — to model populations and genetic changes. Akbari and John Marshall, a modeler from the University of California, Berkeley who is part of Akbari’s DARPA-funded team, recently proposed “multiplexing” or creating a gene drive that edits the same gene in multiple places. That makes it harder for any given mosquito to resist the changes the scientists are trying to impose. Think multiple drug cocktail, but with CRISPR.
NEWSLETTERSSign up for our Morning Rounds newsletterScientists are also trying to create gene drives in multiple species beyond mosquitoes — including fruit flies, nematodes, and baker’s yeast — to get a better grasp on how the engineered genes move through large populations.
Get inside a mosquito’s brainGene drives might not work as well for all varieties of mosquitoes. For example, what happens among species that mate only in swarms?
In general, little is known about the behavior of wild mosquitoes, which tend to be feistier than their laboratory brethren. To fill this gap, Craig Montell, a a fly neuroscientist at the UC Santa Barbara, plans to study sex drive, circadian rhythms, and feeding strategies in mosquitoes.
“We can’t yet even imagine the questions to ask,” Montell said. “We really are just scratching the surface of trying to understand the behavior of these animals.”
Create sex-crazed (but sterile) mosquitoesA number of labs are working to create reverse gene drives to deploy if the gene drives they release go awry. But what if those reverse gene drives fail? Montell is working on other backups.
One idea: create sterile males with high sex drives that will rush to breed with the genetically altered mosquitoes, slowing the spread of the gene drive.
Another: engineer mosquitoes that can be programmed to self-destruct when some external factor, say temperature, hits a certain threshold. This mechanism would ensure that the gene drive mosquitoes die out come summer — and then scientists could release another batch later, if needed.
Biologists: Let’s sic ‘gene drive’ on Zika-carrying mosquitoes
A mosquito embryo is infected with CRISPR-Cas9.DOM SMITH/STATTest, test, and test some moreExcited as they are about gene drives, the scientists don’t plan to release any into the wild — at least not yet. (That’s why Akbari’s lab is secured behind multiple sealed doors. His team boils all water before discarding it, to kill off any stray eggs. They even autoclave their trash.) His DARPA contract specifically forbids the release of gene drives.
Instead, Akbari’s team plans to test gene drives in the lab in progressively larger and more ecologically realistic enclosures.
Win over the humansEven if the safety issues surrounding gene drives are resolved, there’s still one big hurdle: humans.
Team member Cinnamon Bloss, an associate professor at the UC San Diego School of Medicine, studies the ethical implications of emerging technologies. And she recognizes that the public is frightened and wary.
“Scientists tend to think if people just understood the technology, they’d accept it,” she said. “I don’t think that’s the case.”
Malaria kills a half-million Africans a year. Gene-edited mosquitoes might stop it The issue is complicated, said Bloss, because it’s not feasible to get informed consent from all human residents when a technology affects large regions or even entire continents. Bloss, who has conducted much of her work on human genetics technologies, said she’s struggling to find any precedent that brings up the many ethical issues raised by gene drives.
Other teams are grappling with similar issues: In West Africa, a group called Target Malaria — funded with $70 million from the Gates Foundation — is educating residents and building support for a possible future release, years down the road, of gene drive mosquitoes.
The careful thought going into the team’s work is praised by Massachusetts Institute of Technology’s Kevin Esvelt, a leading gene drive researcher and watchdog who also receives funding from DARPA’s Safe Genes project. Esvelt urges researchers to conduct work on gene drives openly and safely — and to involve the public in every step of the process.
The work, he said, is too important to let a slip up in a lab — something he calls “bioerror” — derail the entire field.
“There is an overwhelming moral imperative to do something about malaria,” Esvelt said in a recent phone interview. “In the time we have been talking, probably six to eight children have died.”
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Since it first appeared in Northern California in 2008, the spotted-wing drosophila, a type of fruit fly native to Asia, has become the bane of the state’s cherry farms because of the razor-edged “ovipositor” on its tail.
Rather than lay eggs in rotting berries, as domestic flies do, the invasive species punches holes in fruit that’s still ripening, spoiling it. The costs to U.S. agriculture: about $700 million a year.
California’s cherry growers think they may have a way to get rid of the flies cheaply. To do it, they are counting on a technology developed by geneticists: a “gene drive” that can spread DNA alterations among wild flies, potentially killing them off.
Gene-drive technology is among the most widely debated—and feared—inventions of modern biology. Opponents call it a genetic “atom bomb” and want it banned. Others see the possibility of unprecedented public health interventions, like eradicating the mosquitoes that spread malaria.
Now, for the first time, commercial uses are on the table. With funding from the California Cherry Board, scientists at the University of California, Riverside, have installed a gene drive in the invasive pest, the first time the technology has been established in a commercially important species.
The larva of a fruit fly glows red. The fluorescent marking signals that it has inherited a “gene drive,” or selfish genetic element, from its mother.
COURTESY OF OMAR AKBARI
In addition to that effort, which remains confined to the laboratory, two spinout companies from the University of California, San Diego, are also pursuing commercial use of gene drives. One, Agragene, also intends to alter plants and insects. Its sister company, Synbal, wants to harness the technology as a speedy way of engineering lab mice and possibly pet dogs.
“It’s about having genes under precise control in whatever organism you are modifying,” says David Webb, acting CEO of both UCSD spinout companies, neither of which has raised capital.
A gene drive works via a so-called selfish gene that is able to replicate itself and get inherited by most of an animal’s offspring rather than just half, as is usual. The effect is called “super-Mendelian” inheritance.
The problem is that modifying wild animals raises complex ethical and regulatory issues. Some scientists worry that gene drives could run amok—say, if laboratory animals escape and spread changes in the wild. The Broad Institute of MIT and Harvard has even added gene drives to a list of uses of gene-editing technology it doesn't think companies should pursue.
What’s more, any use of such a powerful technology is going to be highly regulated. Such obstacles explain why most gene-drive funding has come from either philanthropies or the military. The Gates Foundation has committed more than $75 million to engineer self-destructing malaria mosquitoes, which it thinks may be needed to wipe out that disease in Africa. This year the U.S. military research agency DARPA began spending a similar amount to develop antidotes to gene drives, should they be used as a weapon.
The California Cherry Board, which represents growers, just wants to get rid of the flies. When the pests arrived a decade ago, the orchards started spraying insecticides called pyrethroids, with trade names like Delegate and Warrior.
COURTESY OF OMAR AKBARI“This is basically the strongest chemical that there is,” says Nick Matteis, an executive with the growers’ organization. The sprays kills the flies and pretty much every other insect, too, including bees. “If you didn’t have to spray, that is a huge deal,” he says.
To the cherry growers, a gene drive looks like a precision tool that could eliminate one species among thousands. In 2013, the organization started funding development of the technology, spending about $100,000 a year, or about a third of its research budget, to have Riverside professor Omar Akbari install a gene drive in that fly’s genome.
“It’s a lot of money from their perspective, but from our end, it’s only enough to pay a salary and a few experiments,” says Akbari, an expert on insect genetics and one of the participants in the DARPA program.
Even so, by July Akbari had success with the gene drive. His technology, called Medea after the Greek sorceress who murdered her children, spread to 100 percent of flies in experiments in laboratory cages, he says.
The next step it to determine what genetic cargo to attach to the selfish gene. Female flies survive the winter because their bodies make cryoprotectants. Adding a gene to block those chemicals could cause the flies to freeze. Another possibility is genetically altering the bugs’ ovipositor so that they change their behavior.
“If you got rid of that knife or dull it, instead of stabbing ripening cherries, they would lay their egg in rotting fruit, like regular flies,” says Akbari. “The flies would still exist, but they would no longer be crop pests.”
People fear that gene drives will be unstoppable once released. In fact, scientists have a wide variety of tricks to keep them under control. In Akbari’s case, his Medea system requires a large number of insects for the chain reaction to begin—at least thousands. That means a few flies hitching a ride somewhere else in a box of cherries would be unlikely to spread the drive accidentally.
The California Cherry Board says it’s now ready to finance larger-scale laboratory studies. To pay for them, and eventually seek approval to deploy a gene drive, the farmers’ group is planning to raise funds from other fruit growers to finance a “public-benefit corporation.” The company would have, as part of its charter, a requirement to keep its technical plans and finances out in the open.
“We’ll create an entity that is basically in the trust business,” says Tom Turpen, a consultant who is advising the farmers in their formation of the new company. Otherwise, he says, opponents of GMOs would likely instigate a paralyzing public debate.
Matteis, the Cherry Board executive, says he's hopeful the public will support the plan. "Any insect considered remotely beneficial to the environment, you would have a much harder time," he says. "But this insect is a recent arrival. There would be less concern about disrupting the circle of life."
"TO GET TO work in the morning, Omar Akbari has to pass through a minimum of six sealed doors, including an air-locked vestibule. The UC Riverside entomologist studies the world’s deadliest creature: the Aedes aegyptimosquito, whose bite transmits diseases that kill millions each year. But that’s not the reason for all the extra security. Akbari isn’t just studying mosquitoes—he’s re-engineering them with self-destruct switches. And that’s not something you want accidentally escaping into the world.
The technology Akbari is designing is something called a gene drive. Think of it as a way to supercharge evolution, forcing a genetic modification to spread through an entire population in just a few generations. Scientists see it as a powerful tool that could finally vanquish diseases like malaria, dengue, and Zika. But US defense agencies see something else: a national security issue.
Last year, former director of national intelligence James Clapper added gene editing to a list of threats posed by “weapons of mass destruction and proliferation.” In July, the US Defense Advanced Research Projects Agency awarded $65 million in four-year contracts to seven teams of scientists, including Akbari, to study gene-editing technologies. The commitment officially made Darpa the world’s largest government funder of gene drive research. Most of that money is going toward designing safer systems and developing tools to counter rogue gene drives that might get into the environment either by accident, or with malicious intent.
That danger may be more real than scientists first thought. Four years ago, when Harvard biologist Kevin Esvelt first suggested the idea of building gene drives with the newly discovered Crispr gene editing system, he was thinking about extinction. Specifically, preventing endangered wildlife from disappearing by spreading a fertility-reducing gene through the invasive animals competing with them for resources. Conservation biologists took the idea and ran with it; they're now considering gene drives to save native birds in Hawaii, New Zealand, and the Farallones. But now, Esvelt is saying they should slow down.
That's based on the results of a new mathematical model he and his colleagues published on Thursdayon the bioRxiv preprint server.Taking into account things like how often Crispr screws up and the likelihood of protective mutations arising, their work shows how gene drives could be ruthlessly aggressive. Just a few engineered organisms could irrevocably alter an ecosystem. While Esvelt doesn't view the technology as inherently threatening, he is now preachingthat it deserves a bold new caution in how it's applied.
"The primary risk posed by gene drive technology is social," he says. "Unethical closed-door research, unwarranted fears, or unauthorized releases of gene drives will damage public trust in science and governance." He still thinks gene drives have potential to save threatened species and battle public health threats. But researchers will have to invent safer forms of the technology first. That's where the Darpa money comes in. Until very recently, gene drives have been largely theoretical—safe ones even more so. But with the new funds, scientists like Esvelt and Akbari are starting to put together the pieces to test them in real life. That starts with bugs that have a gene editor baked into their DNA from the moment of conception. In a paper published Tuesday in the Proceedings of the National Academy of Sciences, Akbari did that for the first time in Aedes aegypti, creating mosquitoes encoded with the bacterial Cas9 enzyme.
These mosquitoes were born with white eyes instead of black ones, after Crispr/Cas9 cut out genes associated with eye pigment.
MICHELLE BUI/UC RIVERSIDECas9 is the DNA-chopping half of the Crispr gene editing system. So Akbari’s team just had to inject the other half—a bit of guide RNA—into the embryos, for Cas9 to automatically execute its patented snipping action. When they deleted a cuticle pigment gene, the mosquitoes turned from black to yellow. How about a wing development gene? Welcome to the world, flightless blood sucker. Good luck crawling your way to a human meal.
These modifications were just for show. But the skeeters with built-in Cas9 will be an important tool as we learn how to best disrupt mosquito populations. Scientists estimate they’ve only probed about 5 percent of the Aedes aegpyti genome. Which means no one knows what the vast majority of mosquito genes actually do. Now they’ll be able to more easily screen knockouts gene by gene. Maybe they’ll find one that makes the mosquito mouth a hospitable home for malaria. Or one that turns off their taste for human blood. The goal is to disrupt the animal—and the ecosystems they’re a part of—as little as possible while still eradicating disease. If you’re going to play God, the idea goes, use a light hand.
In addition to advancing a new way to study mosquito physiology, these strains represent an important building block for efficient gene drives. Normally, the technology would require expressing both Cas9 and the guide RNA together in the same location. But that could make the drive system invasive and uncontrollable. One way to control them is to keep the components separated in the genome. And that’s what Akbari is working on: a less virulent version called a split-gene drive.
His team has already started the process by breeding these Cas9 strains with mosquitoes encoded with guide RNAs. “The only way to keep the drive spreading is to continuously release Cas9 into the population,” Akbari says. “That makes it confinable to a laboratory setting or self-limiting in the wild as the drive will depend on the presence of Cas9 which gets inherited in a Mendelain fashion.
Another way to do that is a “daisy drive,” which is what Esvelt is developing in nematodes on the DoD’s dime. It works by equipping the worms with a self-exhausting supply of genetic fuel. By splitting into three or more parts and then daisy-chaining them together, the desired modification disperses quickly right when you introduce it, but fizzles out after a while. The result is temporary, controlled gene editing of a local species. That’s the idea anyway. Other Darpa-backed groups are working on having a backstop should systems like these go awry, or worse, be released as part of a biological attack.
Teams at the Broad Institute and Harvard Medical school are screening and compiling a suite of chemical off-switches to block gene editors like Crispr/Cas9 and Talens. At UC Berkeley, Jennifer Doudna’s group is hoping to find anti-Crispr proteins to inhibit unwanted gene-editing activity, which would help design resistance-proof gene drives. While the military’s involvement has some in the public concerned about weaponized, Crispr-ized superskeeters, Esvelt sees defense department support as the only way to advance gene drive technologies safely, at least for the time being.
The Darpa program explicitly prevents the release of gene-drive organisms and requires participants to work under stringent biosafety conditions—hence Akbari’s six-door entrance and exit routine. Perhaps one day he’ll have the molecular tools to come and go without concern. But for now, they’re still the safest thing between his gene-drives and the world outside."
UCR RESEARCHERS ARE GENERATING GENETICALLY ENGINEERED INSECTS TO HELP PREVENT THE SPREAD OF INFECTIOUS DISEASES. PDF
Read full article here. pdf
Dr. Akbari quotes:
“I found both of [the studies] exciting in different ways,” molecular biologist Omar Akbari of the University of California, Riverside, says. “I really hope to see these technologies tested in the field.”
CRISPR-based methods do involve putting more complicated molecular machinery into cells, Akbari says, but they could also prove more reliable than the new approach, which relies on complex mating dynamics. “I think gene drive is probably a more powerful technology that’s portable across species,” he says.
ucr_today__ucr_uc_davis_center_to_fight_vector-borne_diseases.pdfUCR, UC Davis Center to Fight Vector-Borne Diseases Center is Powered by $8 Million CDC Grant. pdf
WE ALL DREAM TO SPLICE THE GENES
The CRISPR//Cas9 gene editing tool has quickly earned a reputation as a revolutionary technology, and its merits support the clout. This year has, in fact, seen so many CRISPR-related breakthroughs that it’s worthwhile to take a step back and take in all of the many accomplishments.
1. This week, circulating reports about the successful application of gene-editing human embryos in the US were confirmed by a research paper published in Nature. The researchers “corrected” one-cell embryo DNA to remove the MYBPC3 gene — known to cause hypertrophic cardiomyopathy (HCM), a heart disease that affects 1 in 500 people.
2. This year, scientists successfully used gene editing to completely extract HIV from a living organism, with repeated success across three different animal models. In addition to the complete removal of the virus DNA, the team also prevented the progress of acute latent infection.
3. Semi-synthetic organisms were developed by breeding E.coli bacteria with an anomalous six-letter genetic code, instead of the normal four-base sequence. Additional gene editing was implemented to ensure that the new DNA molecules were not identified as an invasive presence.
4. The CRISPR method successfully targeted the “command center” of cancer — called the hybrid fusion — which leads to abnormal tumor growths. A “cut-and-paste” method allowed the creation of a cancer-annihilating gene that shrinks tumors in mice carrying human prostate and liver cancer cells.
5. Scientists also slowed the growth of cancerous cells, by targeting Tudor-SN, a key protein in cell division. It’s expected that this technique could also slow the growth of fast-growing cells.
6. Gene editing techniques have also made superbugs kill themselves. By adding antibiotic resistant gene sequences into bacteriophage viruses, self-destructive mechanisms are triggered which protect bacteria.
7. Gene editing may even make mosquito-born diseases an extinct phenomenon. By hacking fertility genes, scientists have gained the ability to limit the spread of mosquitoes — a success they credit to CRISPR’s ability to make multiple genetic code changes simultaneously.
8. Using CRISPR, researchers have edited out Huntington’s disease from mice, pushing the symptomatic progression of the condition into reverse. Experts expect this promising technique to be applied to humans in the near future.
9. Outside of the medical field, CRISPR might also provide a more abundant and sustainable biofuel. By connecting several gene-editing tools, scientists engineered algae that produce twice the biofuel material as wild (or “natural”) counterparts.
10. Very recently, the first-ever “molecular recorder” was developed — a gene editing process that encodes a film directly into DNA code — and with this ability, scientists embedded information into an E.coli genome.
11. Last but not least, and on the macro-scale, the US Defense Advanced Research Projects Agency (DARPA) invested $65 million in a project called “safe genes,”designed to improve the accuracy and safety of CRISPR editing techniques. In addition to serving the public interest of avoiding accidental or intentional (cue ominous music) misuse, the seven research teams will remove engineered genes from environments to return them to baseline “natural” levels.
UC Riverside-led Team Wins $14.9 Million to Battle Disease-carrying Mosquitoes
"DARPA award is the largest ever for a UCR researcher"
DARPA funds UCSD gene drive research against mosquito-borne diseases
Building the Safe Genes Toolkit
Small Pest, Big Battle
UC San Diego Researchers Join $14.9 Million Fight Against Disease-transmitting Mosquitoes
Defense department pours $65 million into making CRISPR safer
How will we keep controversial gene drive technology in check?http://www.sciencemag.org/news/2017/07/how-will-we-keep-controversial-gene-drive-technology-check
DARPA Awards $65M to Improve Gene-Editing Safety, Accuracy
Zika, dengue, yellow fever: UC Riverside researcher gets $14.9 million to thwart disease-carrying mosquitoes
UC Davis Joins DARPA-funded “Safe Genes” Program
UC San Diego researchers selected for DARPA project against mosquito-borne diseaseshttps:
UC Zika research aims to ‘collapse’ mosquito populations
Importantly these guidelines may be adopted in the future to help provide information to stakeholders regarding regulatory oversight of articles, including substances, for use in or on mosquitoes (e.g. genetically modified mosquitoes or perhaps even gene drives).
Click here for a pdf of the document.
"Examples of New Animal Drugs (regulated by FDA)