From endocytosis to recycling, the plasma membranes dynamics of the apicomplexan parasite Toxoplasma gondii

Abstract text

The plasma membrane is at the interphase of the intracellular content and the environment. It plays a critical role in numerous functions from motility to cell communication. This is particularly true for the intracellular parasites, which are switching between drastically different environments during their life cycle. Endocytosis is an important key mechanism involved in the regulation of the plasma membrane surface protein and uptake of environmental molecule. In apicomplexan parasites, endocytosis has mainly been studied in the genus Plasmodium spp. Only recently, endocytosis has been successfully described in Toxoplasma gondii (T.gondii). The two types of endocytic mechanisms have been described in T.gondii: the uptake of proteins from the host cell and the uptake of plasma membrane proteins of the parasite. Previously, we showed the uptake of fluorescent lipids and antibodies in extracellular tachyzoites. We have now designed a new assay, which does not rely on exogenous material and allows us to image not only endocytosis but the whole plasma membrane dynamics. The gene coding for SAG1, one of the major surface antigens, was endogenously tagged with Halo. Using a new dual (spatial and/or temporal) labelling strategy, we were not only able to differentiate between internal and surface proteins, but also from mother and de-novo synthesised material during replication. We observed during replication that the plasma membrane from the mother is shared with the daughters, endocytosed, and recycled. We quantified this dynamics by tracking the changes in the fluorescence signals. Moreover, we identify for the first time that T. gondii generates extra plasma membrane "blebs" prior to the generation of the daughter cells as a reservoir for daughter cell hatching from the mother. In collaboration with the Waller"s laboratory, we have identified an important complex involved in endocytosis. Interestingly, inhibition of endocytosis also leads to a strong alteration of the plasma membrane dynamics. Taken together these data indicate that the reuptake of the plasma membrane is a critical step during replication.