Effect of vanadate on the chromatin configuration in pig GV-oocytes

Vanadate, an inhibitor of tyrosine phosphatases, has been reported to prevent germinal vesicle breakdown in mammalian oocytes. We examined the effect of vanadate on the chromatin configuration of fully grown pig oocytes. In the presence of human menopausal gonadotropin (hMG), vanadate (0.5-5 mM) resulted in a dose-dependent change in oocyte chromatin in germinal vesicles from the condensed state to a decondensed filamentous or stringy configuration. The effect of vanadate and hMG on chromatin configuration could be replicated with 2 mM dibutyryl cyclic AMP (dbcAMP) in place of hMG. Western blot analysis showed that vanadate caused a massive accumulation in the oocytes of tyrosine-phosphorylated proteins with a range of molecular weights that was enhanced by both hMG and dbcAMP in a similar manner. These results suggest that inhibition of tyrosine phosphatase(s) in the presence of an effective level of cAMP induces a change in chromatin configuration of pig oocytes.