Calcium-Independent, Egg Age-Dependent Parthenogenic Activation of Mouse Eggs by Staurosporine.

Abstract

The effect of protein kinase inhibitors on the activation events of mouse eggs at different ages and the dependence on Ca2+ were studied. Inhibition of protein kinase(s) by staurosporine with concentration over 2 μM first induced the destruction of meiotic spindle and then the nuclear formation in metaphase II eggs, but did not stimulate the cortical granule exocytosis; staurosporine with concentration below 0.2 μM and protein kinase C inhibitor sphingosine at concentrations of 10-100 μM did not activate mouse eggs. The activation of mouse eggs by staurosporine was egg age-dependent, but calcium-independent. The number of nucleoli in the formed nucleus or naked nucleoli in the ooplasm was dose- and egg age-dependent. To further evaluate the nuclear and cytoplasmic activation by staurosporine, interphase eggs were processed for electron microscopy and it was found that most nucleoli were highly condenced like those in the pronucleus, but vacuolated or ring-shaped ones also appeared, which implied the activation of egg genome. In addition, staurosporine also induced the formation of Golgi complexes around the nucleus. The nuclear formation induced by staurosporine was completely overcome by okadaic acid. These results suggest that inhibition of staurosporine-sensitive protein kinase(s) other than protein kinase A and C is responsible for the transition from metaphase to interphase in an egg age-dependent but calcium-independent manner in mouse eggs.