[Studies on protein tyrosine phosphorylation in mouse oocyte maturation]

Effects of an inhibitor of tyrosine protein kinases, genistein, and anti-phosphotyrosine monoclonal antibody on mouse oocyte maturation in vitro were examined. Genistein inhibited germinal vesicle breakdown (GVBD) in a dose dependent manner (ED50:20 micrograms/ml), and the inhibitory effect was completely reversible. The level of oocyte cAMP just before GVBD was not affected by the addition of genistein to the culture medium. The addition of 30 micrograms/ml genistein to the medium after 45 min culture in the absence of dibutyryl cAMP (dbcAMP) resulted in 50% inhibition of GVBD. Activator of protein kinase C, 12-O-tetradecanoylphorbol-13-acetate (5 ng/ml) or dbcAMP (40 microM) inhibited GVBD synergistically with genistein (15 micrograms/ml). The meiotic maturation was significantly inhibited in the oocytes injected with anti-phosphotyrosine monoclonal antibody compared with the control oocytes injected with phosphate buffered saline. Genistein attenuated phosphorylation of the maturation-associated phosphoproteins which was demonstrated by means of one dimensional gel electrophoresis. Oocytes cultured with 30 micrograms/ml genistein showed a decreased rate of the first polar body emission (15 to 20%), and the inhibitory effect was dose dependent. The majority of oocytes (80 to 90%) inhibited from emitting the first polar body by genistein exhibited maturation arrest at metaphase 1. These data suggest that protein tyrosine phosphorylation may be implicated in the regulation of mouse oocyte maturation.