Stage‐specific changes in protein phosphorylation accompanying meiotic maturation of mouse oocytes and fertilization of mouse eggs

Abstract

Characteristic changes in the patterns of protein phosphorylation occur during meiotic maturation of mouse oocytes from the time subsequent to germinal vesicle breakdown, through metaphase II, and following fertilization. These changes occur during both in vitro or in vivo maturation or fertilization. Three major classes of changes in total phosphoprotein synthesis are observed. In the first class, protein phosphorylations increase from the germinal vesicle stage until just after germinal vesicle breakdown and then decrease during progression to metaphase II and after fertilization. The second class is characterized by decreases in protein phosphorylation during maturation with subsequent increases in phosphorylation of these proteins after fertilization. The third class is characterized by protein phosphorylations that remain relatively constant during maturation but increase after fertilization; phosphotyrosine phosphoproteins comprise the major species. The radiolabeled protein and phosphoprotein composition of isolated germinal vesicles was also examined, and a phosphoprotein of M_r29,000 is found exclusively associated with the germinal vesicle. Since we have shown previously that 12‐O‐tetradecanoyl phorbol 13‐acetate inhibits fertilization (Y. Endo, R.M. Schultz, and G.S. Kopf, submitted), we examined the effects of this compound on the phosphoprotein patterns of metaphase II eggs. 12‐O‐Tetradecanoyl phorbol 13‐acetate treatment stimulates the phosphorylation of a specific phosphoprotein of M_r80,000.