Final Report Summary - ANOPATH (Genetics of mosquito resistance to pathogens.)
The focus of the AnoPath project is mosquito genetic variation and its role in susceptibility to pathogens and disease transmission. The project goal is to characterize the underlying genomic architecture of pathogen resistance in Anopheles mosquitoes, vectors of human malaria and viral disease. We developed new deep sequence-based mapping tools to detect genetic loci that influence mosquito susceptibility to natural and model pathogens. This work led to the hypothesis that that genetic polymorphism of noncoding regulatory elements such as transcription enhancers and micro RNAs explains an important fraction of vector phenotypic variation for malaria infection in nature. We generated the first comprehensive genome-wide map of enhancers in Anopheles and detected the influence of genetic variation on enhancer activity levels. Fine-mapping by whole genome sequencing of individual mosquitoes for the major genomic malaria control locus refined the locus interval to a small amount of mostly noncoding sequence containing candidate enhancers, which may explain the major effect of genetic control in Anopheles for Plasmodium infection. Application of mapping tools identified multiple new genetic loci that mediate protection of Anopheles against the human malaria Plasmodium falciparum, with functional identification of underlying candidate genes. Working in the Anopheles field population in West Africa, we identified a pattern of genetic differentiation that highlights genes with protective activity against Plasmodium and other pathogens. Using this genetic pattern, we identified multiple novel malaria-protective mosquito genes, as well as new protein binding interactions between them. The results suggest that a repertoire of interacting immune proteins can form a range of functionally diverse immune complexes that confer protection against a spectrum of pathogens. Among these pathogens are viruses, but the viruses found in Anopheles in nature, their virome, is not well known, nor is the role of RNA-interference and other Anopheles antiviral pathways in the transmission of viruses. It is important to understand antiviral mechanisms in potential new arbovirus vectors such as Anopheles mosquitoes in order to assess risks associated with emergence and cross-species arbovirus spread. Using a pathogenic arbovirus naturally transmitted by Anopheles, we observed that the initial first-line antiviral defense mediated by the vector midgut barrier after the bloodmeal requires different mechanisms than protection against later infection stages, after the virus disseminates into the main body compartment. The presence of live midgut bacterial flora is required for full viral infectivity to Anopheles, in contrast to malaria infection, where presence of the midgut bacterial flora is required for protection against infection. This reciprocal protective effect, where high susceptibility to one pathogen is correlated with low susceptibility to the other, indicates protection trade-offs in immunity. Related to this work, we have identified numerous novel viruses in Anopheles field samples from Senegal and Cambodia, and developed some of them as new laboratory models to study mosquito-virus biology.