Proteins of the malaria parasite sexual stages: expression, function and potential for transmission blocking strategies

The sexual phase of the malaria pathogen, Plasmodium falciparum, culminates in fertilization within the midgut of the mosquito and represents a crucial step in the completion of the parasite's life-cycle and transmission of the disease. Two decades ago, the first sexual stage-specific surface proteins were identified, among them Pfs230, Pfs48/45, and Pfs25, which were of scientific interest as candidates for the development of transmission blocking vaccines. A decade later, gene information gained from the sequencing of the P. falciparum genome led to the identification of numerous additional sexual-stage proteins with antigenic properties and novel enzymes that putatively possess regulatory functions during sexual-stage development. This review aims to summarize the sexual-stage proteins identified to date, to compare their stage specificities and expression patterns and to highlight novel regulative mechanisms of sexual differentiation. The prospective candidacy of select sexual-stage proteins as targets for transmission blocking strategies will be discussed.