Tag Archives: gene drives

The latest and greatest in gene drives (for flies)

This is a CRISPR (clustered regularly interspaced short palindromic repeats) story where the researchers are working on flies. If successful, this has much wider implications. From an April 10, 2019 news item on phys.org,

New CRISPR-based gene drives and broader active genetics technologies are revolutionizing the way scientists engineer the transfer of specific traits from one generation to another.

Scientists at the University of California San Diego have now developed a new version of a gene drive that opens the door to the spread of specific, favorable subtle genetic variants, also known as “alleles,” throughout a population.

The new “allelic drive,” described April 9 [2019] in Nature Communications, is equipped with a guide RNA (gRNA) that directs the CRISPR system to cut undesired variants of a gene and replace it with a preferred version of the gene. The new drive extends scientists’ ability to modify populations of organisms with precision editing. Using word processing as an analogy, CRISPR-based gene drives allow scientists to edit sentences of genetic information, while the new allelic drive offers letter-by-letter editing.

An April 9, 2019 University of California at San Diego (UCSD) news release (also on EurekAlert) by Mario Aguilera, which originated the news item, delves into this technique’s potential uses while further explaining the work


In one example of its potential applications, specific genes in agricultural pests that have become resistant to insecticides could be replaced by original natural genetic variants conferring sensitivity to insecticides using allelic drives that selectively swap the identities of a single protein residue (amino acid).

In addition to agricultural applications, disease-carrying insects could be a target for allelic drives.

“If we incorporate such a normalizing gRNA on a gene-drive element, for example, one designed to immunize mosquitoes against malaria, the resulting allelic gene drive will spread through a population. When this dual action drive encounters an insecticide-resistant allele, it will cut and repair it using the wild-type susceptible allele,” said Ethan Bier, the new paper’s senior author. “The result being that nearly all emerging progeny will be sensitive to insecticides as well as refractory to malaria transmission.”

“Forcing these species to return to their natural sensitive state using allelic drives would help break a downward cycle of ever-increasing and environmentally damaging pesticide over-use,” said Annabel Guichard, the paper’s first author.

The researchers describe two versions of the allelic drive, including “copy-cutting,” in which researchers use the CRISPR system to selectively cut the undesired version of a gene, and a more broadly applicable version referred to as “copy-grafting” that promotes transmission of a favored allele next to the site that is selectively protected from gRNA cleavage.

“An unexpected finding from this study is that mistakes created by such allelic drives do not get transmitted to the next generation,” said Guichard. “These mutations instead produce an unusual form of lethality referred to as ‘lethal mosaicism.’ This process helps make allelic drives more efficient by immediately eliminating unwanted mutations created by CRISPR-based drives.”

Although demonstrated in fruit flies, the new technology also has potential for broad application in insects, mammals and plants. According to the researchers, several variations of the allelic drive technology could be developed with combinations of favorable traits in crops that, for example, thrive in poor soil and arid environments to help feed the ever-growing world population.

Beyond environmental applications, allelic drives should enable next-generation engineering of animal models to study human disease as well as answer important questions in basic science. As a member of the Tata Institute for Genetics and Society (TIGS), Bier says allelic drives could be used to aid in environmental conservation efforts to protect vulnerable endemic species or stop the spread of invasive species.

Gene drives and active genetics systems are now being developed for use in mammals. The scientists say allelic drives could accelerate new laboratory strains of animal models of human disease that aid in the development of new cures.

Here’s a link to and a citation for the paper,

Efficient allelic-drive in Drosophila by Annabel Guichard, Tisha Haque, Marketta Bobik, Xiang-Ru S. Xu, Carissa Klanseck, Raja Babu Singh Kushwah, Mateus Berni, Bhagyashree Kaduskar, Valentino M. Gantz & Ethan Bier. Nature Communicationsvolume 10, Article number: 1640 (2019) DOI: https://doi.org/10.1038/s41467-019-09694-w Published 09 April 2019

This paper is open access.

For anyone new to gene drives, I have a February 8, 2018 posting that highlights a report from the UK on the latest in genetic engineering, which provides a definition for [synthetic] gene drives, and if you scroll down about 75% of the way, you’ll also find excerpts from an article for The Atlantic by Ed Yong on gene drives as proposed for a project in New Zealand.

Effective safety strategies for CRISPR (clustered regularly interspaced short palindromic repeats) gene drive experiments

It’s very peculiar being able to understand each word individually in clustered regularly interspaced short palindromic repeats (CRISPR) but not being able to puzzle out much meaning other than the widely known ‘it’s a gene editor’.

Regardless, CRISPR is a powerful gene editing tool and that can lead to trouble. Even before CRISPR, we’ve had some genetic accidents. Perhaps the best known is the ‘killer bee’ or Africanized bee (from its Wikepedia entry),

The Africanized bee, also known as the Africanised honey bee, and known colloquially as “killer bee”, is a hybrid of the western honey bee species (Apis mellifera), produced originally by cross-breeding [emphasis mine] of the East African lowland honey bee (A. m. scutellata) with various European honey bees such as the Italian honey bee A. m. ligustica and the Iberian honey bee A. m. iberiensis.

The Africanized honey bee was first introduced to Brazil in 1956 in an effort to increase honey production, but 26 swarms escaped quarantine in 1957 [emphasis mine]. Since then, the hybrid has spread throughout South America and arrived in North America in 1985. Hives were found in South Texas of the United States in 1990.

Africanized bees are typically much more defensive than other varieties of honey bee, and react to disturbances faster than European honey bees. They can chase a person a quarter of a mile (400 m); they have killed some 1,000 humans, with victims receiving ten times more stings than from European honey bees. They have also killed horses and other animals.

Getting back to how powerful CRISPR is, a group of scientists has developed a set of strategies for safeguarding gene drive experiments (from a January 22, 2019 eLife press release also on EurekAlert),

Researchers have demonstrated for the first time how two molecular strategies can safeguard CRISPR gene drive experiments in the lab, according to a study published today in eLife.

Their findings, first reported on bioRxiv, suggest that scientists can effectively use synthetic target sites and split drives to conduct gene drive research, without the worry of causing an accidental spread throughout a natural population.

Gene drives, such as those trialled in malaria mosquitoes, are genetic packages designed to spread among populations. They do this via a process called ‘drive conversion’, where the Cas9 enzyme and a molecule called guide RNA (gRNA) cut at a certain site in the genome. The drive is then copied in when the DNA break is repaired.

“CRISPR-based gene drives have sparked both enthusiasm and deep concerns due to their potential for genetically altering entire species,” explains first author Jackson Champer, Postdoctoral Fellow in the Department of Biological Statistics and Computational Biology at Cornell University, New York. “This raises the question about our ability to prevent the unintended spread of such drives from the laboratory into the natural world.

“Current strategies for avoiding accidental spread involve physically confining drive-containing organisms. However, it is uncertain whether this sufficiently reduces the likelihood of any accidental escape into the wild, given the possibility of human error.”

Two molecular safeguarding strategies have recently been proposed that go beyond simply confining research organisms. The first is synthetic target site drive, which homes into engineered genomic sites that are absent in wild organisms. The second is split drive, where the drive construct lacks a type of enzyme called the endonuclease and relies instead on one engineered into a distant site.

“The nature of these strategies means that they should prevent an efficient spread outside of their respective laboratory lines,” Champer adds. “We wanted to see if they both had a similar performance to standard homing drives, and if they would therefore be suitable substitutes in early gene-drive research.”

To do this, the team designed and tested three synthetic target site drives in the fruit fly Drosophila melanogaster. Each drive targeted an enhanced green fluorescent protein (EGFP) gene introduced at one of three different sites in the genome. For split drives, they designed a drive construct that targeted the X-linked gene yellow and lacked Cas9.

Their analyses revealed that CRISPR gene drives with synthetic target sites such as EGFP show similar behaviour to standard drives, and can therefore be used for most testing in place of these drives. The split drives demonstrated similar performance, and also allow for natural sequences to be targeted in situations where the use of synthetic targets is difficult. These include population-suppression drives that require the targeting of naturally occurring genes

“Based on our findings, we suggest these safeguarding strategies should be adopted consistently in the development and testing of future gene drives,” says senior author Philipp Messer, Assistant Professor in the Department of Biological Statistics and Computational Biology at Cornell University. “This will be important for large-scale cage experiments aimed at improving our understanding of the expected population dynamics of candidate drives. Ultimately, this understanding will be crucial for discussing the feasibility and risks of releasing successful drives into the wild, for example to reduce malaria and other vector-borne diseases.”

Here’s a link to and a citation for the paper,

Molecular safeguarding of CRISPR gene drive experiments by Jackson Champer, Joan Chung, Yoo Lim Lee, Chen Liu, Emily Yang, Zhaoxin Wen, Andrew G Clark, Philipp W Messer. DOI: 10.7554/eLife.41439 Short Report Jan 22, 2019

This paper is open access. For anyone who doesn’t mind reading an earlier version of a paper you can find it at bioRxiv, at https://www.biorxiv.org/content/early/2018/09/08/411876.

elife, which i’ve mentioned here here before in a February 8, 2018 posting is a (from their About eLife webpage)

… non-profit organisation inspired by research funders and led by scientists. Our mission is to help scientists accelerate discovery by operating a platform for research communication that encourages and recognises the most responsible behaviours in science.

A transatlantic report highlighting the risks and opportunities associated with synthetic biology and bioengineering

I love e-Life, the open access journal where its editors noted that a submitted synthetic biology and bioengineering report was replete with US and UK experts (along with a European or two) but no expert input from other parts of the world. In response the authors added ‘transatlantic’ to the title. It was a good decision since it was too late to add any new experts if the authors planned to have their paper published in the foreseeable future.

I’ve commented many times here when panels of experts include only Canadian, US, UK, and, sometimes, European or Commonwealth (Australia/New Zealand) experts that we need to broaden our perspectives and now I can add: or at least acknowledge (e.g. transatlantic) that the perspectives taken are reflective of a rather narrow range of countries.

Now getting to the report, here’s more from a November 21, 2017 University of Cambridge press release,

Human genome editing, 3D-printed replacement organs and artificial photosynthesis – the field of bioengineering offers great promise for tackling the major challenges that face our society. But as a new article out today highlights, these developments provide both opportunities and risks in the short and long term.

Rapid developments in the field of synthetic biology and its associated tools and methods, including more widely available gene editing techniques, have substantially increased our capabilities for bioengineering – the application of principles and techniques from engineering to biological systems, often with the goal of addressing ‘real-world’ problems.

In a feature article published in the open access journal eLife, an international team of experts led by Dr Bonnie Wintle and Dr Christian R. Boehm from the Centre for the Study of Existential Risk at the University of Cambridge, capture perspectives of industry, innovators, scholars, and the security community in the UK and US on what they view as the major emerging issues in the field.

Dr Wintle says: “The growth of the bio-based economy offers the promise of addressing global environmental and societal challenges, but as our paper shows, it can also present new kinds of challenges and risks. The sector needs to proceed with caution to ensure we can reap the benefits safely and securely.”

The report is intended as a summary and launching point for policy makers across a range of sectors to further explore those issues that may be relevant to them.

Among the issues highlighted by the report as being most relevant over the next five years are:

Artificial photosynthesis and carbon capture for producing biofuels

If technical hurdles can be overcome, such developments might contribute to the future adoption of carbon capture systems, and provide sustainable sources of commodity chemicals and fuel.

Enhanced photosynthesis for agricultural productivity

Synthetic biology may hold the key to increasing yields on currently farmed land – and hence helping address food security – by enhancing photosynthesis and reducing pre-harvest losses, as well as reducing post-harvest and post-consumer waste.

Synthetic gene drives

Gene drives promote the inheritance of preferred genetic traits throughout a species, for example to prevent malaria-transmitting mosquitoes from breeding. However, this technology raises questions about whether it may alter ecosystems [emphasis mine], potentially even creating niches where a new disease-carrying species or new disease organism may take hold.

Human genome editing

Genome engineering technologies such as CRISPR/Cas9 offer the possibility to improve human lifespans and health. However, their implementation poses major ethical dilemmas. It is feasible that individuals or states with the financial and technological means may elect to provide strategic advantages to future generations.

Defence agency research in biological engineering

The areas of synthetic biology in which some defence agencies invest raise the risk of ‘dual-use’. For example, one programme intends to use insects to disseminate engineered plant viruses that confer traits to the target plants they feed on, with the aim of protecting crops from potential plant pathogens – but such technologies could plausibly also be used by others to harm targets.

In the next five to ten years, the authors identified areas of interest including:

Regenerative medicine: 3D printing body parts and tissue engineering

While this technology will undoubtedly ease suffering caused by traumatic injuries and a myriad of illnesses, reversing the decay associated with age is still fraught with ethical, social and economic concerns. Healthcare systems would rapidly become overburdened by the cost of replenishing body parts of citizens as they age and could lead new socioeconomic classes, as only those who can pay for such care themselves can extend their healthy years.

Microbiome-based therapies

The human microbiome is implicated in a large number of human disorders, from Parkinson’s to colon cancer, as well as metabolic conditions such as obesity and type 2 diabetes. Synthetic biology approaches could greatly accelerate the development of more effective microbiota-based therapeutics. However, there is a risk that DNA from genetically engineered microbes may spread to other microbiota in the human microbiome or into the wider environment.

Intersection of information security and bio-automation

Advancements in automation technology combined with faster and more reliable engineering techniques have resulted in the emergence of robotic ‘cloud labs’ where digital information is transformed into DNA then expressed in some target organisms. This opens the possibility of new kinds of information security threats, which could include tampering with digital DNA sequences leading to the production of harmful organisms, and sabotaging vaccine and drug production through attacks on critical DNA sequence databases or equipment.

Over the longer term, issues identified include:

New makers disrupt pharmaceutical markets

Community bio-labs and entrepreneurial startups are customizing and sharing methods and tools for biological experiments and engineering. Combined with open business models and open source technologies, this could herald opportunities for manufacturing therapies tailored to regional diseases that multinational pharmaceutical companies might not find profitable. But this raises concerns around the potential disruption of existing manufacturing markets and raw material supply chains as well as fears about inadequate regulation, less rigorous product quality control and misuse.

Platform technologies to address emerging disease pandemics

Emerging infectious diseases—such as recent Ebola and Zika virus disease outbreaks—and potential biological weapons attacks require scalable, flexible diagnosis and treatment. New technologies could enable the rapid identification and development of vaccine candidates, and plant-based antibody production systems.

Shifting ownership models in biotechnology

The rise of off-patent, generic tools and the lowering of technical barriers for engineering biology has the potential to help those in low-resource settings, benefit from developing a sustainable bioeconomy based on local needs and priorities, particularly where new advances are made open for others to build on.

Dr Jenny Molloy comments: “One theme that emerged repeatedly was that of inequality of access to the technology and its benefits. The rise of open source, off-patent tools could enable widespread sharing of knowledge within the biological engineering field and increase access to benefits for those in developing countries.”

Professor Johnathan Napier from Rothamsted Research adds: “The challenges embodied in the Sustainable Development Goals will require all manner of ideas and innovations to deliver significant outcomes. In agriculture, we are on the cusp of new paradigms for how and what we grow, and where. Demonstrating the fairness and usefulness of such approaches is crucial to ensure public acceptance and also to delivering impact in a meaningful way.”

Dr Christian R. Boehm concludes: “As these technologies emerge and develop, we must ensure public trust and acceptance. People may be willing to accept some of the benefits, such as the shift in ownership away from big business and towards more open science, and the ability to address problems that disproportionately affect the developing world, such as food security and disease. But proceeding without the appropriate safety precautions and societal consensus—whatever the public health benefits—could damage the field for many years to come.”

The research was made possible by the Centre for the Study of Existential Risk, the Synthetic Biology Strategic Research Initiative (both at the University of Cambridge), and the Future of Humanity Institute (University of Oxford). It was based on a workshop co-funded by the Templeton World Charity Foundation and the European Research Council under the European Union’s Horizon 2020 research and innovation programme.

Here’s a link to and a citation for the paper,

A transatlantic perspective on 20 emerging issues in biological engineering by Bonnie C Wintle, Christian R Boehm, Catherine Rhodes, Jennifer C Molloy, Piers Millett, Laura Adam, Rainer Breitling, Rob Carlson, Rocco Casagrande, Malcolm Dando, Robert Doubleday, Eric Drexler, Brett Edwards, Tom Ellis, Nicholas G Evans, Richard Hammond, Jim Haseloff, Linda Kahl, Todd Kuiken, Benjamin R Lichman, Colette A Matthewman, Johnathan A Napier, Seán S ÓhÉigeartaigh, Nicola J Patron, Edward Perello, Philip Shapira, Joyce Tait, Eriko Takano, William J Sutherland. eLife; 14 Nov 2017; DOI: 10.7554/eLife.30247

This paper is open access and the editors have included their notes to the authors and the authors’ response.

You may have noticed that I highlighted a portion of the text concerning synthetic gene drives. Coincidentally I ran across a November 16, 2017 article by Ed Yong for The Atlantic where the topic is discussed within the context of a project in New Zealand, ‘Predator Free 2050’ (Note: A link has been removed),

Until the 13th century, the only land mammals in New Zealand were bats. In this furless world, local birds evolved a docile temperament. Many of them, like the iconic kiwi and the giant kakapo parrot, lost their powers of flight. Gentle and grounded, they were easy prey for the rats, dogs, cats, stoats, weasels, and possums that were later introduced by humans. Between them, these predators devour more than 26 million chicks and eggs every year. They have already driven a quarter of the nation’s unique birds to extinction.

Many species now persist only in offshore islands where rats and their ilk have been successfully eradicated, or in small mainland sites like Zealandia where they are encircled by predator-proof fences. The songs in those sanctuaries are echoes of the New Zealand that was.

But perhaps, they also represent the New Zealand that could be.

In recent years, many of the country’s conservationists and residents have rallied behind Predator-Free 2050, an extraordinarily ambitious plan to save the country’s birds by eradicating its invasive predators. Native birds of prey will be unharmed, but Predator-Free 2050’s research strategy, which is released today, spells doom for rats, possums, and stoats (a large weasel). They are to die, every last one of them. No country, anywhere in the world, has managed such a task in an area that big. The largest island ever cleared of rats, Australia’s Macquarie Island, is just 50 square miles in size. New Zealand is 2,000 times bigger. But, the country has committed to fulfilling its ecological moonshot within three decades.

In 2014, Kevin Esvelt, a biologist at MIT, drew a Venn diagram that troubles him to this day. In it, he and his colleagues laid out several possible uses for gene drives—a nascent technology for spreading designer genes through groups of wild animals. Typically, a given gene has a 50-50 chance of being passed to the next generation. But gene drives turn that coin toss into a guarantee, allowing traits to zoom through populations in just a few generations. There are a few natural examples, but with CRISPR, scientists can deliberately engineer such drives.

Suppose you have a population of rats, roughly half of which are brown, and the other half white. Now, imagine there is a gene that affects each rat’s color. It comes in two forms, one leading to brown fur, and the other leading to white fur. A male with two brown copies mates with a female with two white copies, and all their offspring inherit one of each. Those offspring breed themselves, and the brown and white genes continue cascading through the generations in a 50-50 split. This is the usual story of inheritance. But you can subvert it with CRISPR, by programming the brown gene to cut its counterpart and replace it with another copy of itself. Now, the rats’ children are all brown-furred, as are their grandchildren, and soon the whole population is brown.

Forget fur. The same technique could spread an antimalarial gene through a mosquito population, or drought-resistance through crop plants. The applications are vast, but so are the risks. In theory, gene drives spread so quickly and relentlessly that they could rewrite an entire wild population, and once released, they would be hard to contain. If the concept of modifying the genes of organisms is already distasteful to some, gene drives magnify that distaste across national, continental, and perhaps even global scales.

These excerpts don’t do justice to this thought-provoking article. If you have time, I recommend reading it in its entirety  as it provides some insight into gene drives and, with some imagination on the reader’s part, the potential for the other technologies discussed in the report.

One last comment, I notice that Eric Drexler is cited as on the report’s authors. He’s familiar to me as K. Eric Drexler, the author of the book that popularized nanotechnology in the US and other countries, Engines of Creation (1986) .