A developmentally regulated Rab11 homologue inTrypanosoma bruceiis involved in recycling processes

Abstract

Endocytosis in the parasitic protozoan Trypanosoma brucei, a deeply divergent eukaryote, is implicated as important in both general cellular function and virulence, and is strongly developmentally regulated. We report the characterisation of a previously undefined endosomal compartment in T. brucei based on identification of a new trypanosome gene (TbRAB11) homologous to Rab11/Ypt31. 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 expression profile. In procyclic form parasites TbRAB11 localised to a compartment positioned close to the basal body, similar to mammalian Rab11. By contrast, in bloodstream form parasites, TbRAB11-containing structures were more extensive and the TbRAB11 compartment extended towards the posterior face of the nucleus, was more elaborate and was not always adjacent to the basal body. Colocalisation studies by light and confocal microscopy demonstrated that TbRAB11 was located on a compartment that did not correspond to other established trypanosomal organelles or markers. Using concanavalin A internalisation and temperature block procedures, TbRAB11 was observed on endomembranes anterior to the flagellar pocket that are juxtaposed to the collecting tubules. TbRAB11 colocalised with the trypanosomal transferrin receptor and internalised antivariant surface glycoprotein. Further, we show that the collecting tubules contain TbRAB5A, suggesting that they are the trypanosomatid early endosome. Hence, TbRAB11 is present on endosomal structures that contain recycling cargo molecules and is under developmental regulation, suggesting a role in stage-dependent endocytic processes.

Lessons from the deep: mechanisms behind diversification of eukaryotic protein complexes

“…Rabs are identity markers coordinating vesicle fusion through interactions with tethering complexes, and facilitate transport through cytoskeletal elements (Stenmark, 2009 ; Kjos et al ., 2018 ). Rab11 controls a major recycling pathway returning molecules to the cell surface after internalisation, a role conserved in trypanosomatids (Jeffries, Morgan & Field, 2001 ; Umaer, Bush & Bangs, 2018 ). In metazoans, Rab11 functions are mediated in part via coiled‐coil Rab11‐family interacting proteins (FIPs) and additional interactions with Sec15, a subunit of the exocyst, a heterooctameric complex responsible for late stages of exocytosis (Synek, Sekereš & Zárský, 2014 ).…”

The old and the new about the contractile vacuole of Trypanosoma cruzi

“…Rab11 is a small GTPase involved in the regulation of trafficking from the trans ‐Golgi network to the plasma membrane (Rab11a), as well as in the endocytic recycling of membrane components (Rab11b) (Campa & Hirsch, 2017). In Trypanosoma brucei , it regulates the endocytic recycling of variant surface glycoproteins (VSGs) and other surface components (Jeffries et al, 2001; Umaer et al, 2018). In Dictyostelium , Rab11 is localized in the CVC, where it regulates its biogenesis and trafficking (Du et al, 2008; Harris et al, 2001).…”