Relationships between intracellular pH, protein synthesis, and actin assembly during parthenogenetic activation of sea urchin eggs

Abstract

The relationship between the rate of protein synthesis and the state of assembly of actin was investigated in parthenogenetically activated and fertilized green sea urchin (Strongylocentrotus droebachiensis) eggs. Artificial agents known to raise the intracellular pH (pHi) without affecting the internal calcium concentration were used. Incubation of the eggs with ammonia, procaine, or 12-O-tetradecanoylphorbol 13-acetate (TPA, a protein kinase C activator) resulted in an increase of the protein synthesis rate. At low amounts of ammonia and procaine, this increase was concentration dependent. Higher concentrations of these amine compounds were inhibitory to protein synthesis. Also, chromosome condensation was optimal only in the eggs treated with low concentrations of ammonia or procaine, and was never observed in the TPA-treated eggs. None of these treatments induced detectable changes of the initial amount of G-actin observed in the resting cell, as measured by the deoxyribonuclease I assay. In parallel, no changes of the F-actin content were detected, as determined by quantitative fluorometric measurements of rhodamine–phalloidin labeled eggs. On the other hand, fertilized eggs that showed a higher rate of protein synthesis than parthenogenetically activated eggs were also characterized by a decrease in the total cellular concentration of G-actin. Thus, whereas protein synthesis and chromosome condensation may proceed in the absence of any polymerization of actin in the parthenogenetically activated eggs, it cannot be excluded that actin assembly could be linked to this metabolic activity in the fertilized egg.