Chlamydomonas γ-tubulin mutations reveal a critical role of γ-TuRC in maintaining the stability of centriolar microtubules
Nakazawa, Y.; Horii, M.; Noga, A.; Koike, Y.; Kawai-Toyooka, H.; Dohra, H.; Yamaguchi, K.; Shigenobu, S.; Wakabayashi, K.-i.; Hirono, M.
10.1101/2025.03.18.643570 bioRxivShow abstract
The centriolar triplet microtubule consists of an A-tubule with 13 protofilaments, and B- and C-tubules, each with 10 protofilaments. Although the formation of the triplets has been shown to require {gamma}-tubulin, its specific role in the formation of each tubule remains elusive. We isolated two novel Chlamydomonas reinhardtii mutants, bld13-1 and bld13-2, each expressing {gamma}-tubulin with a single amino-acid substitution (T292I, E89D, respectively). Similar to known centriole-deficient mutants, both mutants exhibited defects in ciliary assembly, nuclear number, and the number and orientation of cytoplasmic microtubules. Genetic analyses of the mutants, along with expression of the mutant {gamma}-tubulins in the wild-type cells, showed that both mutants exert dominant-negative effects over wild-type {gamma}-tubulin. Interestingly, although the centrioles in these mutants retained the typical nine triplet structure, their triplets frequently lacked several protofilaments in specific regions of the A- and C-tubules. The protofilament loss occurs more frequently at the proximal end of the centriole. These structural defects strongly suggest that {gamma}-tubulin is essential for the stability of the A- and C-tubules of centriolar triplets.
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