CENTROSOME AND MICROTUBULE DYNAMICS DURING MEIOTIC PROGRESSION IN THE MOUSE OOCYTE

The disposition, function and fate of centrosomes were analysed in mouse oocytes undergoing in vitro meiotic maturation, using multiple-label fluorescence microscopy. Oocytes fixed at various points during meiotic progression were double labeled with either human centrosome-specific antibody, 5051, and anti-tubulin antibodies or 5051 and MPM-2 antibodies in order to evaluate the microtubule nucleation capacity and phosphorylation status of centrosomes during this process. Double labeling with anti-tubulin antibodies revealed two populations of centrosomes that undergo stage-specific changes in number, location and microtubule nucleation capacity in relation to spindle assembly and cytoplasmic events. Specifically, one population was consistently associated with chromatin throughout meiotic maturation whereas a second population of cytoplasmic centrosomes exhibited maximal numbers and nucleation capacity at prometaphase and anaphase of meiosis-I. Quantitative evaluation of cytoplasmic centrosomes indicated increased numbers during the transition from diakinesis to prometaphase and metaphase to anaphase and total disappearance during telophase. Colocalization studies with MPM-2 revealed that centrosomes were always phosphorylated. However, at metaphase of meiosis I and II the microtubule nucleation capacity of centrosomes was diminished. These results suggest the existence of two discrete populations of centrosomes in the mouse oocyte that are coordinately regulated to subserve aspects of microtubule organization relative to both nuclear and cytoplasmic events.