Investigation of the molecular mechanisms of malarial ookinete invasion into the mosquite midgut epithelium in the rodent mararial parasite, Plasmodium berghei

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To search for genes playing roles in malarial infection of the mosquito vector, we constructed EST databases of the vector stages of rodent malarial parasite. We selected some genes from these databases and prepared knock-out parasites of each gene. As criteria for selection, we adopted presence of the N-terminal signal peptide, because this indicates that the gene products may play a role in parasite interactions with the vector mosquito. In this study, we identified some genes that play a critical role in malarial parasite infection of mosquito organs. One of them encodes 21kDa protein with a secretory protein-lilke structure and is necessay for ookinete invasion into the midgut epithelium. We performed immuno-electeon microscopy and found that this protein is localized in the micronemes. Other one encodes an attachment protein-like molecule and is expressed by the sporozoite in the oocyst but not by the salivary gland sporozoite. By disruption of this gene, we demonstrated that it is essential for the malarial parasite to infect the mosquito salivary gland.