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 microt ubule nucleation. Mouse oocytes and early embryos lack centrioles unti l the blastocyst stage. Thus, early mouse embryos allowed us to study the location of gamma-tubulin in animal cells in the absence of centri oles. For this, we used an antiserum directed against a specific pepti de of the gamma-tubulin sequence, which is conserved among species. Th is serum has been characterised both in PtK2 and mouse cells. We found that it specifically stained the spindle poles and the cytoplasmic mi crotubule organizing centers in metaphase II oocytes and the spindle p oles in mitosis during the cleavage stages. In contrast, no interphase staining could be detected during cleavage. Since the overall level o f gamma-tubulin did not decrease during interphase, as shown by immuno blotting experiments, this absence of staining during interphase is pr obably 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 f irst time at the 64-cell stage. The possible roles of gamma-tubulin in microtubule nucleation and in centrosome maturation are discussed.