Gamma Tubulin is Localized to a New Organelle, The Multivesicular Aggregate, In Mammalian Oocytes

Abstract

Oocyte meiotic maturation occurs without the aid of centrioles in the mouse; instead the division spindles are organized by a number of microtubule organizing centers (MTOC). Immunofluorescence microscopy using anti-γ tubulin shows that multiple MTOCs migrate to surround the central nucleus (germinal vesicle, GV) during early maturation.. However, at the EM level, recognizable MTOCs have never been seen prior to the nucleation of microtubules (MT) which occurs near the time of nuclear envelope breakdown. Recently, I described multivesicular aggregates (MVAs) as the organelles most likely to represent immature MTOCs prior to MT nucleation4. These are first seen at time zero by EM as two large aggregates in the cortex, with sizes averaging 10um. MVA subsequently fragment into smaller units as they migrate centrally.Materials and Methods: Female ICR mice were injected IP with 100 iu of chorionic gonadotropin (Sigma) to stimulate follicle growth, and ovaries were removed 48 hours later.