Distinct Malaria Parasite Sporozoites Reveal Transcriptional Changes That Cause Differential Tissue Infection Competence in the Mosquito Vector and Mammalian Host

Abstract

The malaria parasite sporozoite transmission stage develops and differentiates within parasite oocysts on the Anopheles mosquito midgut. Successful inoculation of the parasite into a mammalian host is critically dependent on the sporozoite's ability to first infect the mosquito salivary glands. Remarkable changes in tissue infection competence are observed as the sporozoites transit from the midgut oocysts to the salivary glands. Our microarray analysis shows that compared to oocyst sporozoites, salivary gland sporozoites upregulate expression of at least 124 unique genes. Conversely, oocyst sporozoites show upregulation of at least 47 genes (upregulated in oocyst sporozoites [UOS genes]) before they infect the salivary glands. Targeted gene deletion of UOS3, encoding a putative transmembrane protein with a thrombospondin repeat that localizes to the sporozoite secretory organelles, rendered oocyst sporozoites unable to infect the mosquito salivary glands but maintained the parasites' liver infection competence. This phenotype demonstrates the significance of differential UOS expression. Thus, the UIS-UOS gene classification provides a framework to elucidate the infectivity and transmission success of Plasmodium sporozoites on a whole-genome scale. Genes identified herein might represent targets for vector-based transmission blocking strategies (UOS genes), as well as strategies that prevent mammalian host infection (UIS genes).

ACKNOWLEDGMENTS

This work was funded by a grant from the Foundation for the National Institutes of Health through the Grand Challenges in Global Health Initiative and an SBRI institutional grant to S.H.I.K. Design and construction of the P. yoelii microarray were supported by the National Institutes of Health (to L.W.B.).

A potential conflict of interest is as follows: S.H.I.K. is an inventor listed on U.S. patent no. 7,22,179, U.S. patent no. 7,261,884, and international patent application PCT/US2004/043023, each titled “Live genetically attenuated malaria vaccine.”