CRISPR gene editing has successfully been used to develop inheritance control in mice. By shifting the gene editing window to align more with the timing of meiosis, researchers have now been able to affect the mechanism of gene conversation in both males and females.
The achievement was reported initially in the December 23, 2021 journal PLOS Biology and co-authored by Alexander Weitzel, Hannah Grunwald, Ceri Weber, Rimma Levina, Valentino Gantz, Stephen Hedrick, Ethan Bier, and Kimberly Cooper.
This builds on previous research that used CRISPR gene editing to influence the inheritance of genes in female mice. In 2019, Grunwald and Cooper demonstrated the ability to control which genes are inherited from one generation to the next. At the time, they were only able to replicate the study in female mice.
Although gene editing conversion in one parent might be enough to increase the probability of gene inheritance, the researchers say, successful gene editing in both parents significantly increases the odds.
“For these gene conversion strategies to work in any context—in the lab or in wild populations—you need the mechanism of gene conversion to work in both males and females,” said Cooper, associate professor in the Section of Cell and Developmental Biology, Division of Biological Sciences in a news release. “It seems as though the reason this process was previously working in females is because we were closer to the female meiotic window. Now that we’ve moved Cas9 expression to within the meiotic window in males, it works in them too.”
Scientists use an active genetic DNA element to copy genetic information in mice. Known as a CopyCat, regulatory DNA of SPo11 (the gene known to be part of meiosis in both males and females) was used to control Cas9 protein that cuts DNA.
Timing became critical. Researchers had to stay with the timing window for male meiosis and female meiosis. This creates some challenges as lower expression levels for Cas9 expression existed. “Hitting that meiosis sweet spot was important for male gene conversion,” said Cooper.
While still in the early stages, this has the potential for editing and developing new models for research, such as therapeutic design for pharmaceuticals, investigation of disease, or controlling invasive species. The study’s authors say this may provide both long-term results in nature and more immediate benefits in the lab.
In a paper published on the same day in Nature Protocols, Grunwald, Witzel, and Cooper wrote: “Although substantial technical hurdles remain, overcoming these could lead to strategies that might decrease the spread of rodent-borne Lyme disease or eliminate invasive populations of mice and rats that devastate island ecology. Perhaps more immediately achievable at moderate gene conversion efficiency, applications in a laboratory setting could produce complex genotypes that reduce the time and cost in both dollars and animal lives compared with Mendelian inheritance strategies.”
The authors also suggest that a more robust expression of Cas9 in the earlier stages of meiosis may improve the efficiency of gene conversion and further increase the “super-mendelian” inheritance rate for both sexes.
This achievement is just one more example of how researchers are using gene editing to advance science. CRISPR gene editing is opening the door for genomic design and evaluation of guide RNA sequences across a wide spectrum.
Adapted from a naturally occurring genome editing system found in bacteria, researchers create a small piece of RNA that acts as a guide sequence in CRISPR gene editing. This guide binds itself to a specific target in the DNA sequence within a genome and to the Cas9 enzyme. This modified RNS is used to recognize the sequence and cut it at the target location.
Once the DNA is cut, scientists can add or delete pieces of the genetic material or replace existing segments with customized sequences.