Researchers from the University of California San Diego have constructed a new genetic toolkit using CRISPR technology to innovate gene drives for Culex mosquitoes and other pathogen-carrying vectors.
With the advent of the CRISPR genetic editing tool, scientists have been able to drive forward advancements in gene drives, which refers to the process of using genetic engineering to manipulating the probability that a specific characteristic is propagated to an organism’s offspring. Usually, it is used to increase the probability of favourable genes being transmitted to progeny, and decrease the chances of less favourable ones.
One of the major applications of gene drives is targeting carriers of diseases like Anopheles and Aedes mosquitoes that spread malaria, dengue, and many others. However, amongst the several mosquito species of interest for gene drives, Culex mosquitoes, the carriers of the West Nile virus, St. Louis encephalitis, and Japanese encephalitis, have received much less attention despite being the culprit of many elephantiasis cases in Asian and African regions.
To address this, researchers from the University of California San Diego have developed several genetic editing tools that will lay the groundwork for future Culex gene drives. Due to the minimal work done on Culex gene drives, researchers Xuechun Feng, Valentino Gantz, and their colleagues at Harvard Medical School and National Emerging Infectious Diseases Laboratories had to work from the ground up by first carefully studying the Culex genome before developing their Culex-targeting Cas9/guide-RNA expression toolkit.
The CRISPR-Cas9 technology comprises two main components – a guide RNA and a caspase enzyme. It acts in a similar fashion as scissors, whereby target genes are located using a guide RNA sequence and the caspase enzyme is used to cut the DNA segments for insertion or deletion of these target genes.
Through extensive investig-ation, the group continuously improved upon their toolkit to ensure that the CRISPR components can effectively and accurately induce the correct genetic expressions. Once complete, the team proceeded to concentrate on the gene drive effort. After extensive modifications and adjustments, their novel kit was found to demonstrate remarkable applicability for Culex, showing great potential to disable pathogen-transmitting genes in these mosquitoes.
"My co-authors and I believe that our work will be impactful for scientists working on the biology of the Culex disease vector since new genetic tools are deeply needed in this field," explained Gantz, an assistant research scientist in the Division of Biological Sciences at UC San Diego. "We also believe the scientific community beyond the gene drive field will welcome these findings since they could be of broad interest."
From this study, the team also noted the severe lack of gene editing tools for other vector species. As such, they made special efforts to ensure that their tools are versatile and adaptable for future work in other insect pests and disease vectors.
For now, the team is ready to apply their new tools to derive a gene drive in Culex mosquitoes that can be used to stop pathogen transmission or suppress the population to prevent biting.
Source: Feng et al. (2021). Optimized CRISPR tools and site-directed transgenesis towards gene drive development in Culex quinquefasciatus mosquitoes. Nature Communications, 12(1), 1-13.