PROCAINE-INDUCED MATURATION OF XENOPUS OOCYTES IS MEDIATED BY A TRANSIENT ACTIVATION OF M-PHASE PROMOTING FACTOR

We have recently shown that the incubation of Xenopus laevis oocytes i n procaine-containing solutions induced germinal vesicle breakdown wit hout white spot formation and, in some cases, with the appearance of s pindle and chromosomes in the cytoplasm. The present study was perform ed to determine whether M-phase promoting factor was involved in this unusual maturation. Procaine failed to induce maturation in the presen ce of 6-dimethylamino purine or roscovitine, which are both known to i nhibit p34(cdc2) kinase. Histone H1 kinase activity was detected in pr ocaine-treated oocytes but it was always lower than in progesterone-tr eated controls. A shift in p34(cdc2) was observed in oocytes that had been exposed to procaine for 16h, but it was not detected in those exp osed for 24h. Finally, cytoplasm transfer experiments demonstrated tha t the maturation promoting activity that occurred in oocytes incubated in procaine for 16h could induce maturation of recipient stage VI ooc ytes. This transferable activity was weaker than that from progesteron e-treated controls since only 30% of the recipients underwent germinal vesicle breakdown and only a few spindles were observed, which were n ot always correctly located. Taken together these results demonstrate that M-phase promoting factor is involved in the procaine maturing eff ect despite some differences compared with progesterone-treated oocyte s which might explain the particular type of maturation induced by thi s substance. The discovery of the mechanisms by which procaine is able to activate M-phase promoting factor might now help in the understand ing of some steps in progesterone-induced maturation that have still t o be elucidated.