Gantz/Bier paper on CRISPR/Cas9 mutagenic chain reaction

The Scientist notes some potential issues:

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However, there are concerns about the technique, such as the possibility that permanently integrated and expressed CRISPR/Cas9 machinery could cut and replace DNA in off-target parts of the genome. “I think having both of the elements continuously expressed at a high level is just asking for a problem to arise,” said Sekelsky. Gantz, who is testing this possibility, said that this might not be a problem in the small Drosophila genome, but could affect mammals. Eventually, the system may incorporate an element that can turn Cas9 off once it is no longer needed, suggested Bier.

The biggest concern—one the authors raised in their paper—is that, if not properly contained, the rapidly propagating mutations created by the powerful MCR technique could affect wild populations. “An absolute caveat that has to be imposed on any experiments that take place strictly in the laboratory is that these animals would have 100 percent containment,” Bier said.

“Certainly, I share the same concerns,” Liu said. Overall, however, he is “quite optimistic about this technology.”

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Of the general approach, the article noted

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The CRISPR/Cas9 system requires two components: a guide RNA that matches the region of the genome to be cleaved, and an enzyme, Cas9, that cuts the DNA. Often, these two elements are transiently expressed in the cells or organism of interest, orintegrated separately into the genomes of animals that are then mated together, such that their progeny will activate the DNA cleavage. Once the DNA is cut, the cell’s machinery repairs the genome, adding in replacement DNA containing the desired mutation.

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Citation to paper

V. M. Gantz and E. Bier, “The mutagenic chain reaction: A method for converting heterozygous to homozygous mutations,” Science, doi:10.1126/science.aaa5945, 2015.