The centrosome in animals constitutes the cell's microtubule-organizing center that nucleates spindle assembly, and is characterized by a symmetrical array of nine microtubule triplets emanating from a cartwheel structure in the very proximal region of the centriole. Biogenesis of centrioles requires many regulatory proteins, including SAS-6, SAS-4/CPAP, and BLD10/CEP135, which are thought to constitute the core ancestral module involved in centriole assembly (1). The three proteins have distinct functions in centriole biogenesis. SAS-6 assembles to the cartwheel (2, 3) and BLD10/CEP135 forms the pinhead that connects the cartwheel spokes to the A-microtubules of the microtubule triplets (4, 5), whereas SAS-4/CPAP controls the elongation of centriolar microtubules (6 -9).Trypanosoma brucei, a flagellated protozoan and the causative agent of human sleeping sickness, does not have centrosomes, but it possesses the basal body as its microtubule-organizing center to nucleate the assembly of a motile flagellum. The basal body is characterized by an array of nine microtubule triplets, with the conserved SAS-6 protein forming the cartwheel structure (10), similar to that of the centrosome in metazoa. The flagellum is attached, along most of its length, to the cell body via a specialized cytoskeletal structure termed the flagellum attachment zone (FAZ), 2 which consists of three main domains: the structure connecting the paraflagellar rod (PFR) to the flagellar membrane, the structure connecting the flagellar membrane and the cell body membrane, and a cytoplasmic filament (often referred to as the FAZ filament) and its associated microtubule quartet (11)(12)(13)(14)(15)(16)(17). In addition to mediating flagellum-cell body attachment, the FAZ filament also defines the cytokinesis cleavage plane (11,12), with the distal tip of the new FAZ filament marking the site of cytokinesis initiation (18 -20). Moreover, during the cell cycle in the procyclic form, the elongation of the FAZ filament positions the newly assembled basal body toward the cell posterior (21), which is crucial for organelle segregation and cell division (10,(22)(23)(24)(25).Trypanosomatids, a group of kinetoplastid parasites consisting of T. brucei, Trypanosoma cruzi, and Leishmania spp., appear in a variety of different morphological forms during their life cycle and are distinguished by the relative position of the kinetoplast (mitochondrial DNA) and the nucleus and by the position, length, and cell body attachment of the flagellum (26). In the tsetse fly vector, T. brucei differentiates from the trypomastigote form to the epimastigote form, which undergoes asymmetrical cell division to produce a long epimastigote cell and a short epimastigote cell (26). How life cycle transitions in T. brucei are regulated is largely unknown, but recent work has begun to uncover the regulators involved in this process. ALBA3 and ALBA4, two closed related RNA-binding proteins, are the first factors found to be involved in life cycle transitions in T. brucei (27). Anothe...