Tr. Jeffries et al., A developmentally regulated Rab11 homologue in Trypanosoma brucei is involved in recycling processes, J CELL SCI, 114(14), 2001, pp. 2617-2626
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.