Characterization of gamma-tubulin filaments in mammalian cells

Overexpression of gamma-tubulin leads to the formation of filaments, but nothing is known about such filaments with regard to possible presence in cells, structure and probable dynamics. Here, we used mammalian cell lines to investigate the ability of gamma-tubulin to form filaments. We found that gamma-tubulin produces fibers called gamma-tubules in a GTP-dependent manner and that gamma-tubules are made up of pericentrin and the gamma-tubulin complex proteins 2, 3, 5 and 6. Furthermore, we noted that the number of cells with cytosolic gamma-tubules is increased in non-dividing cells. Our experiments showed that gamma-tubules are polar structures that have a low regrowth rate compared to microtubules. Also, we observed that gamma-tubules were disassembled by treatment with cold, colcemid, citral di-methyl acetal, dimethyl fumarate or mutation of gamma-tubulin GTPase domain, but were increased in number by treatment with taxol or by stable expression of the gamma-tubulin(1-333) GTPase domain. Our results demonstrate that gamma-tubulin forms filaments, and such assembly is facilitated by the GTPase domain of gamma-tubulin.