γ-Tubulin Functions in the Nucleation of a Discrete Subset of Microtubules in the Eukaryotic Flagellum.

McKean, Paul G. and Baines, Andrea and Vaughan, Sue and Gull, Keith (2003) γ-Tubulin Functions in the Nucleation of a Discrete Subset of Microtubules in the Eukaryotic Flagellum. Current Biology, 13 (7). pp. 598-602. ISSN 0960-9822

Abstract

γ-tubulin is an essential part of a multiprotein complex that nucleates the minus end of microtubules. Although the function of γ-tubulin in nucleating cytoplasmic and mitotic microtubules from organizing centers such as the centrosome and spindle pole body is well documented [1, 2 and 3], its role in microtubule nucleation in the eukaryotic flagellum is unclear. Here, we have used Trypanosoma brucei to investigate possible functions of γ-tubulin in the formation of the 9 + 2 flagellum axoneme. T. brucei possesses a single flagellum and forms a new flagellum during each cell cycle. We have used an inducible RNA interference (RNAi) approach to ablate expression of γ-tubulin, and, after induction, we observe that the new flagellum is still formed but is paralyzed, while the old flagellum is unaffected. Electron microscopy reveals that the paralyzed flagellum lacks central pair microtubules but that the outer doublet microtubules are formed correctly. These differences in microtubule nucleation mechanisms during flagellum growth provide insights into spatial and temporal regulation of γ-tubulin-dependent processes within cells and explanations for the organization and evolution of axonemal structures such as the 9 + 0 axonemes of sensory cells and primary cilia.