Wolbachia as an Agent for Population Replacement in Anopheles Gambiae

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DESCRIPTION (provided by applicant): Failure of traditional methods to control malaria has stimulated efforts to create transgenic mosquitoes for malaria control. Transgenes must be actively driven into natural Anopheles populations to high frequency for transgenic strategies to be successful. Wolbachia are maternally inherited endosymbionts associated with cytoplasmic incompatibility (CI) i.e., reduced egg hatch when an infected male mates with an uninfected female. Matings of infected females are fertile regardless of the infection status of the male. CI confers a reproductive advantage to infected females and allows Wolbachia to spread rapidly through insect populations to high frequency. Transgenic traits tightly linked to Wolbachia are expected to be driven into the population by genetic hitchhiking, replacing the natural population with one that is refractory to parasite transmission. While Wolbachia infections are common in mosquitoes, they have never been observed in any species of Anopheles. Thus, Wolbachia-based strategies for malaria control require the artificial transfer of infection into Anopheles species responsible for parasite transmission. Artificial Wolbachia transfections have succeeded in several medically-important Aedes species but have not yet succeeded in Anopheline mosquitoes. Our in vitro studies show that the Anopheles gambiae genetic background is competent to harbor at least 3 diverse Wolbachia infections, and thus, previous unsuccessful Anopheles transfection attempts are likely due to technique rather than an intrinsic genetic block to infection. We will use recently-developed embryonic and adult injection techniques to establish Wolbachia infections in Anopheles gambiae and examine the interaction between Wolbachia and Anopheles at the phenotypic, genetic and population levels. By the end of the proposed research, we will 1) artificially transfect Anopheles gambiae with Wolbachia, 2) determine the effect of Wolbachia infection on expression of candidate Anopheles genes previously identified by cell line experiments and 3) evaluate the potential for Wolbachia to drive maternally-inherited transgenes into Anopheles gambiae cage populations. These results will lay the foundation for the successful deployment of genetically-modified mosquitoes for malaria control. Transgenic strategies for malaria control require the active spread of introduced transgenes to high frequency in natural Anopheles populations. Wolbachia endosymbionts can theoretically act as a mechanism to spread genes into populations. We propose to evaluate transfer Wolbachia infection into Anopheles gambiae and evaluate the symbiont as a candidate transgene drive system for malaria control.