Chapter 17 - Effectors produced by rhoptries and dense granules: an intense conversation between parasite and host in many languages

Abstract

Other than the final divisions that lead to a mature oocyst, all the developmental stages of Toxoplasma gondii reproduce inside a host cell. The particular niche they occupy is formed by an invagination of the host plasma membrane (HPM) during invasion, resulting in a parasitophorous vacuole (PV) within which the parasites will grow and divide. The PV is a special environment that presents the parasites with the opportunity to coopt host cell functions through the use of secreted “effectors.” The chapter by Lebrun et al. discusses how the PV is formed and how the PV membrane (PVM) is modified to be a crucial place of dialogue between parasite and host cell. In this chapter, we focus on the parasite effectors that are translocated either across the HPM during invasion or across the PVM once the parasites have taken up residence inside the cell. Those transiting across the HPM during invasion generally originate in the apical, club-shaped rhoptries, while those that cross the PVM after invasion originate in the parasite’s dense granules. The number of such identified effectors continues to grow as does the list of remarkable ways, in which they coopt host cell functions for the parasite’s own purposes. Finally, we also discuss the limited knowledge on how these two classes of effectors move across the various membranes they respectively transit.