A developmentally regulated Rab11 homologue in Trypanosoma brucei is involved in recycling processes

Endocytosis in the parasitic protozoan Trypanosoma brucei, a deeply diverge nt eukaryote, is implicated as important in both general cellular function and virulence, and is strongly developmentally regulated. We report the cha racterisation of a previously undefined endosomal compartment in T brucei b ased on identification of a new trypanosome gene (TbRAB11) homologous to Ra b11/Ypt3l. Northern and western analyses indicated that TbRAB11 expression was significantly upregulated in the bloodstream stage of the parasite, the first trypanosome Rab to be identified with a developmentally regulated ex pression profile. In procyclic form parasites TbRAB11 localised to a compar tment positioned close to the basal body, similar to mammalian Rab11. By co ntrast, in bloodstream form parasites, TbRAB11-containing structures were m ore extensive and the TbRAB11 compartment extended towards the posterior fa ce of the nucleus, was more elaborate and was not always adjacent to the ba sal body. Colocalisation studies by light and confocal microscopy demonstra ted that TbRAB11 was located on a compartment that did not correspond to ot her established trypanosomal organelles or markers. Using concanavalin A in ternalisation and temperature block procedures, TbRAB11 was observed on end omembranes anterior to the flagellar pocket that are juxtaposed to the coll ecting tubules. TbRAB11 colocalised with the trypanosomal transferrin recep tor and internalised anti-variant surface glycoprotein. Further, we show th at the collecting tubules contain TbRAB5A, suggesting that they are the try panosomatid early endosome. Hence, TbRAB11 is present on endosomal structur es that contain recycling cargo molecules and is under developmental regula tion, suggesting a role in stage-dependent endocytic processes.