Involvement of microtubules and microfilaments in the control of the nuclear movement during maturation of mouse oocyte.

We confirm that the centrifugal migration of the chromosomes in maturing mouse oocytes depends on a microfilament-mediated process. We investigated the role of the cytoskeleton in the germinal vesicle (GV) behavior of oocytes prevented from resuming meiosis by either activators of protein kinase A or activators of protein kinase C. A time-lapse microcinematography study demonstrates that GV immobilization by isobutylmethylxanthine (IBMX) is overcome by colcemid (COL), nocodazole (NOC), and taxol and that cytochalasin D (CCD) reversibly immobilizes the GV of oocytes treated with either IBMX + COL (or NOC) or 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, known to allow a programmed GV cortical translocation. An immunofluorescence analysis shows that the disorganization of a perinuclear microtubule network is the very first cytological clue of maturation. IBMX promotes its persistence while NOC, COL, and taxol induce its immediate disappearance. It is concluded that elements of the cytoplasmic microtubular complex (CMTC) are passively involved in the control of the setting up of a "centrifugal displacement property" (CDP) by counteracting a motive force provided by the microfilament cytoskeleton. Finally, TPA induces a clearcut reorganization instead of a total disorganization of the CMTC. This reorganization is, however, sufficient to allow the microfilaments to drive the GV displacement.