The core of the mammalian centriole contains γ-tubulin

Background: The microtubule network, upon which transport occurs in higher cells, is formed by the polymerization of a and 3 tubulin. The third major tubulin isoform, y 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 y tubulin must be restored to stripped centrioles to regenerate the centrosomal functions of duplication and microtubule nucleation. Results: We have re-examined the localization of y tubulin in isolated and in situ mammalian centrosomes using a novel immunocytochemical technique that preserves antigenicity and morphology while allowing increased accessibility. As expected, a tubulin was localized in cytoplasmic and centriolar barrel microtubules and in the associated pericentriolar material. Foci of y 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 y tubulin was a structure within the proximal end of the centriolar barrel. The distributions were complementary, in that ao tubulin was excluded from the core of the centriole, and y tubulin was excluded from the microtubule barrel. Conclusions: We have shown that y tubulin is localized both in the pericentriolar material and in the core of the mammalian centriole. This result suggests that y 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.