"Gene drive" may not work

Scientists are concerned about the development of resistance to GM CRISPR technology

Sergey Vasiliev, Naked Science

The CRISPR/Cas9 gene modification technique is borrowed from the immune system of bacteria that use these molecules to fight viruses. It demonstrates such accuracy and efficiency of work that in recent years scientists have been seriously talking about using GM to combat natural pests and disease carriers. To do this, methods of "gene drive" are being developed that promote the spread of the desired gene in the population – for example, making the offspring partially sterile or unsuitable for the transmission of infection.

In addition to such a gene, the genetic drive system must contain a gene encoding the Cas9 protein that cuts DNA, as well as fragments of guide RNA that indicate the exact location of the nuclease protein. Philipp Messer and his colleagues from Cornell University supplemented this set with a fluorescent protein genome, which allowed them to easily track the spread of CRISPR complexes in a population of laboratory fruit flies. The scientists cite the results in an article published by the journal PLOS Genetics.

Such a genetic drive system quickly spreads the gene in the population. If the crossing occurred between parents, of which only one carries a CRISPR "kit", then it will start working in a fertilized egg. In theory, Cas9 will make a break in exactly the right part of the DNA, after which the cell repair systems will fill the resulting space by copying the missing links from the CRISPR "kit" on the homologous (paired) chromosome. However, in real experiments, everything is not always perfect, and the system may work with errors.

Messer and his colleagues have shown that in some cases, Cas9 nuclease is produced in excess, cutting the target chromosome again and again. In other variants, errors occurred during or before fertilization – one way or another, but the spread of the "kit" in the population slowed down, or even stopped altogether. The rate of resistance development in different strains varied greatly, ranging from five to 56 percent, which make the use of technology almost meaningless.

"This 'resistance' will easily destroy almost any intentional attempts to use the gene drive," the researchers summarize, "and poses a big problem for many of its promising applications." Its existence was known before, but now, having considered the spread of stability in an experiment for the first time, scientists are taking it much more seriously.

It is worth adding that several methods of countering the development of such stability have already been proposed and even experimentally tested. A separate article is devoted to this, which Messer and his co-authors presented on the preprint service BioRxiv.org (Champer et al., Reducing resistance allele formation in CRISPR gene drives). In particular, it demonstrates the potential of parallel use of several guide RNAs.

Portal "Eternal youth" http://vechnayamolodost.ru  21.07.2017