Pathogenic arboviruses, including dengue, chikungunya, yellow fever, and Zika, are all spread by the mosquito Aedes aegypti. Researchers at the University of California, Riverside (UCR), have now developed transgenic strains of this mosquito that stably express the Cas9 enzyme in their germline, making CRISPR genome editing fast and efficient and opening up the potential to develop “gene drive” strategies for controlling mosquito populations in the wild.
As an initial proof of concept, the researchers, headed by Omar Akbari, Ph.D., an assistant professor of entomology in UCR’s College of Natural and Agricultural Sciences, disrupted different genes in the Cas9-expressing mosquito embryos, which affected vision, flight, and blood feeding. “Overall, our results demonstrate that our simplified transgenic Cas9 system has improved capacity to rapidly induce highly efficient and specific targeted genome modifications, including gene disruptions, deletions, and insertions,” the researchers write in their published paper in the Proceedings of the National Academy of Sciences (PNAS) (“Germline Cas9 Expression Yields Highly Efficient Genome Engineering in a Major Worldwide Disease Vector, Aedes aegypti”).
The CRISPR/Cas9 system has been exploited for precision genome engineering in many different organisms. The technology uses short guide RNAs (sgRNAs) that bind to Cas9 and direct the enzyme to the specified DNA sequence, where double-stranded breaks are made.
There are a variety of methods for applying CRISPR-mediated genome engineering. Approaches based on directly injecting purified sgRNAs combined with either purified Cas9 RNA, recombinant Cas9 protein, or Cas9 expression plasmids have all been successful in a variety of organisms, including mosquitoes, the researchers point out. However, success rates vary, and previous attempts to use genome editing to prevent mosquitoes from spreading pathogens have been hampered by low mutation rates, poor survival rates of the transgenic insects, and inefficient transmission of disrupted genes to offspring.
Cas9 Expression in Mosquito Germlines Could Help Prevent Disease Spread