Maternal gamma (γ)‐tubulin is involved in microtubule reorganization during bovine fertilization and parthenogenesis

In this study, γ‐tubulin distribution was determined chronologically in conjunction with microtubule dynamics during bovine fertilization and parthenogenesis. In unfertilized bovine oocytes, γ‐tubulin was identified in the cytoplasm, mainly in the cortex and concentrated in the meiotic spindle. Following sperm penetration, γ‐tubulin in the cytoplasm was recruited by a sperm component. During pronuclear apposition, γ‐tubulin was localized as spots at the spindle poles. γ‐tubulin spots were observed in blastomeres of embryos cleaved in vitro. Following electrical stimulation, γ‐tubulin and microtubule matrix were noted in oocyte cortex. In the late pronuclear stage, considerably less γ‐tubulin and microtubules were detected in the cytoplasm. At the mitotic metaphase of parthenotes, γ‐tubulin was recruited to the condensed chromatin and concentrated in the spindle. The γ‐tubulin spots were not detected until the 8‐cell stage of parthenotes. This suggests that maternal γ‐tubulin is recruited by a sperm component to reconstitute the zygotic centrosome. In the absence of sperm components, the cell cycle‐related assembly of γ‐tubulin organizes microtubule nucleation for positioning the pronucleus and spindle protein of mitotic metaphase during the first cell cycle of bovine parthenotes. Mol. Reprod. Dev. 64: 438–445, 2003. © 2003 Wiley‐Liss, Inc.