Secretory Organelle Function in the Plasmodium Sporozoite

The Sporozoite's Journey Depends on the Secretory Organelles Sporozoites (see Glossary), together with red-blood-cell-infectious merozoites and mosquitomidgut-infectious ookinetes, are the invasive forms of the malaria parasite's life cycle. Their task is the successful transmission from the mosquito to the mammalian host with the ultimate goal of achieving productive infection of hepatocytes. This is not a simple endeavor as the liver is Plasmodium sporozoites exhibit a complex infection biology in the mosquito and mammalian hosts. The sporozoite apical secretory organelles, the micronemes and rhoptries, store protein mediators of parasite/host/vector interactions and must secrete them in a temporally and spatially well orchestrated manner. Micronemal proteins are critical for sporozoite motility throughout its journey from the mosquito midgut oocyst to the mammalian liver, and also for cell traversal (CT) and hepatocyte invasion. Rhoptry proteins, until recently thought to be only important for hepatocyte invasion, appear to also play an unexpected role in motility and in the interaction with mosquito tissue. Therefore, navigating the different microenvironments with secretion likely requires the sporozoite to have a more complex system of secretory organelles than previously appreciated.