The role of the BBSome in Trypanosoma brucei

In humans, 7 genes causing the cilia-related disorder Bardet-Biedl syndrome (BBS) encode proteins that form a complex, named the BBSome. The highly conserved 7 BBSome components facilitate ciliary membrane biogenesis by sorting and transporting specific membrane proteins to the ciliary membrane. The BBSome subunits are also conserved in the protozoan parasite Trypanosoma brucei, the causative agent of African sleeping sickness. T. brucei has been used as a model organism providing huge insight into basal body/flagella biology; it is therefore a good candidate for further analysis of BBSome function. Even though it has been suggested that BBSome traffics specific ciliary membrane proteins to the ciliary membrane in mammalian cells, we still do not know whether the function is universal or present in T. brucei. In my thesis, I have focused on the most conserved BBSome protein, BBS5, to characterize its localisation and function in flagella formation in T. brucei. Through bioinformatics, I identified that BBS5 was predicted to possess a predicted lipid binding domain which is not present in the other BBSome components, and that the diseases causing residues are most conserved in BBS5. Moreover, I generated a cell line in which endogenous BBS5 was tagged with TY-epitope and GFP to assess the localisation, which was found to be in transition zone of the flagellum. In order to investigate the function of BBS5 in the flagellum formation, RNAi mediated knockdown of BBS5 was then performed. Knockdown of BBS5 did not cause any defect in cell morphology and flagellum formation, indicating that BBS5 is not required for flagellum formation in T. brucei. This thesis provides the first insight into the localisation of BBS5 in T. brucei, and may shed the light on the importance of the transition zone proteins in T. brucei, where selection of proteins to enter the flagellum membrane may take place.