Microtubule Patterning during Meiotic Maturation in Mouse Oocytes Is Determined by Cell Cycle-Specific Sorting and Redistribution of γ-Tubulin

AbstractThe topography of microtubule assembly events during meiotic maturation of animal oocytes demands tight spatial control and temporal precision. To better understand what regulates the timing and location of microtubule assembly, synchronously maturing mouse oocytes were evaluated with respect to γ-tubulin, pericentrin, and total tubulin polymer fractions at specific stages of meiotic progression. γ-Tubulin remained associated with cytoplasmic centrosomes through diakinesis of meiosis-1. Following chromatin condensation and perinuclear centrosome aggregation, γ-tubulin relocated to a nuclear lamina-bounded compartment in which meiosis-1 spindle assembly occurred. γ-Tubulin was stably associated with the meiotic spindle from prometaphase-1 through to anaphase-2, but also exhibited cell cycle-specific relocalization to cytoplasmic centrosomes. Specifically, anaphase onset of both meiosis-1 and -2 was characterized by the concomitant appearance of γ-tubulin and microtubule nucleation in subcortical centrosomes. Brief pulses of taxol applied at specific cell cycle stages enhanced detection of γ-tubulin compartmentalization, consistent with a γ-tubulin localization-dependent spatial restriction of microtubule assembly during meiotic progression. In addition, a taxol pulse during meiotic resumption impaired subsequent γ-tubulin sorting, resulting in monopolar spindle formation and cell cycle arrest in meiosis-1; despite cell cycle arrest, polar body extrusion occurred roughly on schedule. Therefore, sorting of γ-tubulin is involved in both the timing of location of meiotic spindle assembly as well as the coordination of karyokinesis and cytokinesis in mouse oocytes