Analysis of blood-induced Anopheles gambiae midgut proteins and sexual stage Plasmodium falciparum interaction reveals mosquito genes important for malaria transmission

Plasmodium invasion of mosquito midguts is a mandatory step for malaria transmission. The roles of mosquito midgut proteins and parasite interaction during malaria transmission are not clear. This study aims to identify mosquito midgut proteins that interact with and affect P. falciparum invasion. Based on gene expression profiles and protein sequences, 76 mosquito secretory proteins that are highly expressed in midguts and up-regulated by blood meals were chosen for analysis. About 61 candidate genes were successfully cloned from Anopheles gambiae and expressed in insect cells. ELISA analysis showed that 25 of the insect cell-expressed recombinant mosquito proteins interacted with the P. falciparum-infected cell lysates. Indirect immunofluorescence assays confirmed 17 of them interacted with sexual stage parasites significantly stronger than asexual stage parasites. Knockdown assays found that seven candidate genes significantly changed mosquitoes' susceptibility to P. falciparum. Four of them (AGAP006268, AGAP002848, AGAP006972, and AGAP002851) played a protective function against parasite invasion, and the other three (AGAP008138, FREP1, and HPX15) facilitated P. falciparum transmission to mosquitoes. Notably, AGAP008138 is a unique gene that only exists in Anopheline mosquitoes. These gene products are ideal targets to block malaria transmission.