Featured Gene Drives: How to Genetically Modify an Ecosystem

  1. Ygggdrasil

    Ygggdrasil 1,530
    Science Advisor

    Genes normally have a 50-50 chance of being passed from parent to offspring, but scientists may have figured out a way to create gene drives that show up in offspring with a much higher frequency:
    (http://blogs.scientificamerican.com...spr-could-revolutionize-ecosystem-management/)

    This idea had been discussed for a while (it was first proposed by Austin Burt in 2003), but new gene editing methods developed in the past few years seem to make this idea much closer to reality.

    What is most exciting – and concerning – about gene drive technology is that when introduced into wild populations, organisms containing gene drives would breed with the population and could spreading the modified genes throughout the population even if the modifications decrease the reproductive fitness of the organism. The researchers imagine this technology could have a number of applications, for example, modifying mosquito populations to prevent the spread of malaria, modifying agricultural pests and weeds to deal with pesticide and herbicide resistance, and modifying invasive species to limit their ecological damage. A recent paper in the journal eLife discusses how such gene drives could be engineered and their potential applications.

    However, with such far reaching consequences, society should approach this technology with caution, and the same authors of the eLife paper have also published a policy forum paper in Science opening the conversation about how this technology should be regulated.

    In addition to the Scientific American blog post linked above, PBS also has a good, popular press summary of the papers: http://www.pbs.org/wgbh/nova/next/evolution/crispr-gene-drives/
     
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  2. jcsd
  3. Greg Bernhardt

    Staff: Admin

    Very nice! Thanks for sharing Ygggdrasil!
     
  4. Ygggdrasil

    Ygggdrasil 1,530
    Science Advisor

    Two studies published today provide experimental demonstration of gene drive technologies in fruit flies and yeast (two commonly used experimental organisms in biology). Both these studies make use of CRISPR/Cas9 genome editing system. Here's an exerpt from a news article in Science:

    (http://news.sciencemag.org/biology/2015/03/chain-reaction-spreads-gene-through-insects)

    Here are the studies:
    Gantz and Bier. The mutagenic chain reaction: A method for converting heterozygous to homozygous mutations. Science. Published online March 19, 2015. doI:10.1126/science.aaa5945
    DiCarlo et al. RNA-guided gene drives can efficiently and reversibly bias inheritance in wild yeast. bioRxiv, posted March 19, 2015. doi:10.1101/013896 (this was posted in the non-peer reviewed bioRxiv pre-print server, but it comes from a reputable group with expertise in the area)

    These studies have stirred much debate among scientists because they are capable of making large scale changes to our environment. Both groups employed safeguards in their research to prevent accidental release of their technologies into their environment, but the barrier to creating gene drives is not very high, and many research groups around the world likely have the capabilities to build similar systems. What sorts of restrictions should we place on this type of research? Should systems like these be used in the wild to, for example, combat malaria, and what criteria should we use to make that determination?
     
  5. mfb

    Staff: Mentor

    A very interesting report.

    Sounds like something that would spread so incredibly fast that I wonder why it has not occured naturally at some point, or at least why it is not so common we see it today.

    If I understand the method correctly, you need a specific CRISPR complex for a specific gene you want to spread? And then you also need one gene for this specific CRISPR complex - and that has to spread faster as well?
     
    Last edited: Mar 20, 2015
  6. Ygggdrasil

    Ygggdrasil 1,530
    Science Advisor

    Here's a diagram from the Science paper describing how it works:

    [​IMG]
    CRISPR/Cas9 is a complex between a protein called Cas9 and an RNA containing specific structural features that allow it to bind to Cas9 (called the guide RNA or gRNA). A specific part of the gRNA sequence tells the Cas9 protein which sequences to cut, and by changing that sequence in the gRNA, researchers can "program" CRISPR/Cas9 to a specific sequence of DNA. When CRISPR/Cas9 cuts the DNA on one chromosome, it activates the DNA repair pathways in the cell. These DNA repair pathways grab the homologous chromosome (remember, we have two copies of each chromosome), finds a region with a similar sequence to the damaged region, then copies the sequence from the homologous chromosome onto the damaged chromosome. So, everything between the two homology arms of the gene drive (HA1 & HA2 in the figure), which would include the Cas9 gene, the gRNA, and whatever else you include, gets copied onto the other chromosome. Thus, the Cas9, gRNA, and other additional sequences all spread together.

    You would need a specific gRNA for each specific gene you would want to spread, but the same Cas9 works for any gRNA. The study done in yeast by George Church's lab made a gene drive containing only the homology arms, the gRNA, and the target gene they wanted to spread. They supplied the Cas9 in a separate plasmid so that they could better control the process.

    That's a good question. The CRISPR/Cas9 system comes from bacteria and these bacteria control the system such that it does not target the bacterium's own DNA (it acts as a defense against viral DNA), so potentially these things have never popped up in eukaryotes (which have the homologous repair system that helps to copy gene drives).
     
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  7. Filip Larsen

    Filip Larsen 996
    Gold Member

  8. Runaway diversity scares me. 12 new viruses this year 144 next year perhaps 20,000 the year after? To introduce a new ecosystem which could devastate the one that exists just sounds risky right off the bat. Especially one based on mass mutation of species.
     
  9. I think how fast it would spread depends at least in part on the gene(s) in question. If they gene harms the organism to much it wont be able to pass it on, and there is also Sexual Selection to think about.
     
    Last edited: Mar 25, 2015 at 5:42 PM
  10. wabbit

    wabbit 470
    Gold Member

    But it still seems it could spread even if it confers a sgnificant disadvantage (within limits). Prsumably that s what makes it attractive as a weapon against some mosquitoes and such, but also it sounds potentially disastrous especially if it finds a way to cross species some time after having been released in the wild. Scary stuff,
     
  11. This could also be used in eugenics in humans ? In this case it is really a thing to avoid
     
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