Effects of protein kinase C stimulation and free Ca2+ rise in mammalian egg activation.
Protein phosphorylation activity, chromosome segregation, and cortical granule exocytosis (CGE) have been studied in mouse eggs activated parthenogenetically by specific PKC stimulators such as 4 beta-phorbol 12-myristate 13-acetate (PMA) and 1-oleyl-2-acetylglycerol (OAG), or by agents inducing an immediate increase in cytosolic calcium concentration ([Ca2+]i) such as ethanol and Ca-ionophore A23187. When protein phosphorylation activity of mouse eggs was analyzed 10 min after different activation treatments, the phosphorylation of a 32 kDa polypeptide was a feature common to all different parthenogenetic agents used. The appearance of such labeling was independent of an increasing [Ca2+]i, as indicated by direct measurements of 1) cytosolic Ca2+ concentration with fura-2 and 2) exogenous Ca2+ entrance into activated eggs. Emission of the second polar body was blocked in PMA-elicited parthenogenones, whereas it was apparently normal in OAG-treated eggs, unless the eggs were continuously exposed to OAG. CGE was almost immediate in ethanol-activated eggs, but in PMA-treated cells, it occurred significantly later, with a timing corresponding to that found for the appearance of sustained Ca2+ oscillations in this system. Here, we propose that in mammalian eggs 1) PKC stimulation represents an early regulatory step in egg activation; 2) this kinase activity is turned off before the second meiotic cleavage; and 3) cytosolic free Ca2+ rise is essential for CGE occurrence.
Colonna
R
R
Dipartimento di Scienze e Technologie Biomediche, University of L'Aquila, Italy.
Tatone
C
C
Malgaroli
A
A
Eusebi
F
F
Mangia
F
F
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002875:Chromosomes / Q000187:drug effects / Q000502:physiology; D003434:Crossing Over, Genetic; D015180:Electrophoresis, Gel, Two-Dimensional; D000431:Ethanol / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005260:Female; D051379:Mice; D010063:Ovum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010312:Parthenogenesis / Q000187:drug effects; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D013268:Stimulation, Chemical; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015044:Zona Pellucida / Q000187:drug effects
D000431:Ethanol; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium