Discussion

The flagella connector (FC) of the protozoan parasite Trypanosoma brucei is a mobile transmembrane junction connecting the tip of the growing flagellum to the side of the old flagellum during cell division. This association has been implicated in inheritance of the cell pattern. We developed a novel biochemical and proteomic approach for studying discrete cytoskeletal structures and identified 8 FC constituents. Immunogold and fluorescence labelling showed that these proteins localize to specific FC subdomains. Depletion of the constituents by RNAi led to a precocious loss of flagella connection. Moreover, it revealed that the principal mechanistic components of the structure are two types of kinesins cross-connected via the FC transmembrane junction, which comprises kinetoplastid-specific proteins. Intriguingly, the FC also contains two conserved ULK kinases, the mammalian orthologs of which are implicated in ciliogenesis and the plant orthologs in cell division. Finally, our biochemical approach also led to identification of several constituents of the enigmatic axonemal capping structure, suspected to regulate axonemal growth and present at tips of both new and old flagella. Our results show that the FC and the axonemal capping structure are biochemically distinct, despite both localizing to the new flagellum tip.