Invasion and egress cascade in intracellular protozoa: Part 2 (T. gondii)

As an apicomplexan member, T. gondii has a complex life cycle that involves multiplication within vertebrate and invertebrate hosts by specialized cell-invasive and egressed life cycle stages, called zoites. They are unique eukaryotic cells with characteristic four main sub-cellular structures. They include a specific inner membrane complex beneath the plasma membrane, an apical “conoid” to sustain parasite micro-tubular cytoskeleton, a plastid responsible for lipids synthesis, and specific secretory organelles; micronemes (MICs), rhoptries (ROs) and dense granules (DGs). The last is involved in maturation of the parasitophorous vacuole (PV), where the parasite multiplies; the first essential step after invasion and before egress. Similar to Plasmodium sp., successful invasion and egress cascade accounts mainly on efficient rapid invasion without alteration of host cell cytoskeleton, and multiplication within host cells inside its PV. However, Plasmodium sp. export proteins into host cell cytoplasm and plasma membrane utilizing PV as a trafficking vehicle. Instead, PV of T. gondii zoites utilized abundantly expressed DGs and ROs proteins to build up the intra-vacuolar membranous network (IVMN) for trafficking. The present editorial aims to clarify roles of proteins released from MICs, ROs and DGs in invasion and egress cascade of T. gondii.