The core of the mammalian centriole contains gamma-tubulin.

Abstract

The microtubule network, upon which transport occurs in higher cells, is formed by the polymerization of alpha and beta tubulin. The third major tubulin isoform, gamma tubulin, is believed to serve a role in organizing this network by nucleating microtubule growth on microtubule-organizing centers, such as the centrosome. Research in vitro has shown that gamma tubulin must be restored to stripped centrioles to regenerate the centrosomal functions of duplication and microtubule nucleation. We have re-examined the localization of gamma tubulin in isolated and in situ mammalian centrosomes using a novel immunocytochemical technique that preserves antigenicity and morphology while allowing increased accessibility. As expected, alpha tubulin was localized in cytoplasmic and centriolar barrel microtubules and in the associated pericentriolar material. Foci of gamma tubulin were observed at the periphery of the organized pericentriolar material, as reported previously, often near the termini of microtubules. A further and major location of gamma tubulin was a structure within the proximal end of the centriolar barrel. The distributions were complementary, in that alpha tubulin was excluded from the core of the centriole, and gamma tubulin was excluded from the microtubule barrel. We have shown that gamma tubulin is localized both in the pericentriolar material and in the core of the mammalian centriole. This result suggests that gamma tubulin has a role in the centriolar duplication process, perhaps as a template for growth of the centriolar microtubules, in addition to its established role in the nucleation of astral microtubules.