gamma-Tubulin is present in acentriolar MTOCs during early mouse development

gamma-Tubulin, a recently discovered member of the tubulin superfamily, is a peri-centriolar component considered to be essential for microtubule nucleation. Mouse oocytes and early embryos lack centrioles until the blastocyst stage. Thus, early mouse embryos allowed us to study the location of gamma-tubulin in animal cells in the absence of centrioles. For this, we used an antiserum directed against a specific peptide of the gamma-tubulin sequence, which is conserved among species. This serum has been characterised both in PtK2 and mouse cells. We found that it specifically-stained the spindle poles and the cytoplasmic microtubule organizing centers in metaphase II oocytes and the spindle poles in mitosis during the cleavage stages. In contrast, no interphase staining could be detected during cleavage. Since the overall level of gamma-tubulin did not decrease during interphase, as shown by immunoblotting experiments, this absence of staining during interphase is probably due to a cytoplasmic dispersion of gamma-tubulin. A single dot-like interphase reactivity appeared at the 32-cell stage. In parallel, electron microscopy studies allowed us to detect centrioles for the first time at the 64-cell stage. The possible roles of gamma-tubulin in microtubule nucleation and in centrosome maturation are discussed.