Studies on signal transduction during early development of amphibian(Rana dybowskii) eggs

Abstract

Phospholipase C(PLC) mediated signal transduction mechanism leading to the initiation of DNA replication in fertilizing amphibian egg was investigated. Staurosporine, a protein kinase C(PKC) inhibitor, treated Rana dybowskii eggs showed high frequency of abnormal cleavages and decreased DNA polymerase $\alpha$ activity. Inositol 1,4,5-triphosphate($P_3$) and diacylglycerol (DAG) which are the products of phosphatidylinositol 4,5-bis-phosphate($PIP_2$) hydrolysis by PLC was also observed. Numorous phosphoproteins were observed in proliferating eggs. The phosphorylation of these protein are not likely to be the substrate of PKC, since calphostin C treatment to the eggs did not change the phosphorylation level of these proteins. Rather, phosphorylation involved with contorol mechanism of cell division in proliferating eggs seems to be carried out by calcium independent protein kinases. EGTA treatment to egg extract resulted in phosphorylation of 70 kD protein in 15 minutes after fertilization, and 98 kD AND 49 kD proteins were phosphorylated at mid-or late-S-phase of the first cell cycle. The data suggest that the phosphorylation of these three proteins might be associated with the intiation of cell division or progress of cell cycle.