A targeted approach to the identification of candidate genes determining susceptibility to Plasmodium gallinaceum in Aedes aegypti

The malaria parasite, Plasmodium , has evolved an intricate life cycle that includes stages specific to a mosquito vector and to the vertebrate host. The mosquito midgut represents the first barrier Plasmodium parasites encounter following their ingestion with a blood meal from an infected vertebrate. Elucidation of the molecular interaction between the parasite and the mosquito could help identify novel approaches to preventing parasite development and subsequent transmission to vertebrates. We have used an integrated Bulked Segregant Analysis-Differential Display (BSA-DD) approach to target genes expressed that are in the midgut and located within two genome regions involved in determining susceptibility to P. gallinaceum in the mosquito Aedes aegypti. A total of twenty-two genes were identified and characterized, including five genes with no homologues in public sequence databases. Eight of these genes were mapped genetically to intervals on chromosome 2 that contain two quantitative trait loci (QTLs) that determine susceptibility to infection by P. gallinaceum. Expression analysis revealed several expression patterns, and ten genes were specifically or preferentially expressed in the midgut of adult females. Real-time PCR quantification of expression with respect to the time of blood meal ingestion and infection status in mosquito strains permissive and refractory for malaria revealed a differential expression pattern for seven genes. These represent candidate genes that may influence the ability of the mosquito vector to support the development of Plasmodium parasites. Here we describe their isolation and discuss their putative roles in parasite-mosquito interactions and their use as potential targets in strategies designed to block transmission of malaria.