Sea urchin fertilization stimulates CaM kinase-II (multifunctional [type II] Ca super(2+)/CaM kinase) activity and association with p34 super(cdc2)

Upon fertilization, the sea urchin (Strongylocentrotus purpuratus) egg synthesizes proteins which impart a Ca super(2+) dependence to M-phase onset. A potential target of this Ca super(2+) dependence may be CaM kinase-II (the multifunctional [type II] Ca super(2+)/calmodulin [CaM]-dependent protein kinase) which is necessary for nuclear envelope breakdown in fertilized sea urchin eggs. This study was intended to determine whether sea urchin CaMK-II is activated after fertilization and whether it interacts with other known M-phase regulators, such as p34 super(cdc2). We report that total CaMK-II activity, measured by solution assays, increase after fertilization, peaking just prior to cleavage. Interestingly, total CaMK-II activity continues to fluctuate, peaking again prior to second and third cleavage. Gel assays also reveal enhanced levels of the 56 and 62 kDa potential CaMK-II phosphoproteins after fertilization. Finally, CaMK-II activity and only the 62 kDa phosphoprotein physically associate with p34 super(cdc2), but again only after fertilization. These changes in CaMK-II activity and p34 super(cdc2)-association after fertilization may ensure that Ca super(2+) signals are targeted to the M-phase machinery at the appropriate developmental times.