Developmental arrest of the human malaria parasite Plasmodium falciparum within the mosquito midgut via CTRP gene disruption

Apicomplexan protozoa possess a family of micronemal and cell surface-associated proteins, each comprised a combination of cell-adhesive vertebrate von Willebrand factor (vWF)-like A domains and thrombospondin (TSP) type 1-like domains. The human malaria parasite Plasmodium falciparum has in the extracellular portion of the CS protein TRAP-related protein (CTRP) six tandemly arrayed A domains followed by seven TSP type 1-like domains, whereas a second member of this family, thrombospondin-related anonymous protein (TRAP), contains a single vWF-like A domain and a single TSP type 1-like domain. Here we show that CTRP transcripts are present within the infected mosquito midgut and that CTRP protein is expressed with a punctate distribution and a predominance at the apical end of mosquito midgut-stage ookinetes. This expression pattern is analogous to micronemal expression of TRAP in Plasmodium sporozoites. Disruption of the CTRP gene by homologous recombination in cultures of the human malaria parasite P. falciparum demonstrates that CTRP is essential for mosquito midgut development. Oocyst formation was never observed following membrane feeds of CTRP disruptant lines to Anopheline mosquitoes, despite the development of mature ookinetes. We propose that CTRP is involved in essential recognition or motility processes at the ookinete cell surface within the mosquito midgut.