TbVps34, the trypanosome orthologue of Vps34, is required for Golgi complex segregation

Phosphoinositides are important regulators of numerous cellular functions. The yeast class III phosphatidylinositol 3-kinase Vps34p, and its human orthologue hVPS34, are implicated in control of several key pathways, including endosome to lysosome transport, retrograde endosome to Golgi traffic, multivesicular body formation, and autophagy. We have identified the Vps34p orthologue in the African trypanosome, TbVps34. Knockdown of TbVps34 expression by RNA interference induces a severe growth defect, with a post-mitotic block to cytokinesis accompanied by a variety of morphological abnormalities. GFP2xFYVE, a chimeric protein that specifically binds phosphatidylinositol 3-phosphate, localizes to the trypanosome endosomal system and is delocalized under TbVps34 RNA interference (RNAi), confirming that TbVps34 is an authentic phosphatidylinositol 3-kinase. Expression of GFP2xFYVE enhances the TbVps34 RNAi-associated growth defect, suggesting a synthetic interaction via competition for phosphatidylinositol 3-phosphate-binding sites with endogenous FYVE domain proteins. Endocytosis of a fluid phase marker is unaffected by TbVps34 RNAi, but receptor-mediated endocytosis of transferrin and transport of concanavalin A to the lysosome are both impaired, confirming a role in membranous endocytic trafficking for TbVps34. TbVps34 knockdown inhibits export of variant surface glycoprotein, indicating a function in exocytic transport. Ultrastructural analysis revealed a highly extended Golgi apparatus following TbVps34 RNAi, whereas expression of the Golgi marker red fluorescent protein-GRASP (Grp1 (general receptor for phosphoinositides-1)-associated scaffold protein) demonstrated that trypanosomes are able to duplicate the Golgi complex but failed to complete segregation during mitosis, despite faithful replication and segregation of basal bodies and the kinetoplast. These observations implicate TbVps34 as having a role in coordinating segregation of the Golgi complex at cell division.