Regulation of blastocoele formation by intracellular calcium release is mediated through a phospholipase C-dependent...

Calcium signaling plays a critical role in the regulation of mouse preimplantation development, in part through the activation of calmodulin. Calcium transients in mouse morulae appear to be generated predominantly through the production of inositol 1,4,5-trisphosphate (IP3) by phospholipase C (PLC). IP3 receptors predominate in mouse embryos as regulators of calcium release. Exposure to the PLC inhibitors ET-18-OCH3 or U73122 resulted in a dose-dependent, reversible inhibition of cavitation, while the inactive analogue U73343 did not alter the rate of cavitation, as compared to that in controls. U73122 inhibited the release of calcium from intracellular stores after exposure to ethanol or lysophosphatidic acid, suggesting that PLC is required for blastocoele formation in the mouse and that calcium signaling may be PLC-dependent. In addition to IP3, PLC activation generates diacylglycerol, which stimulates protein kinase C (PKC) and could also alter the rate of embryonic development. However, activation of PKC with phorbol ester or synthetic diacylglycerol was not sufficient to accelerate development, although embryo culture in medium containing PKC inhibitors did delay cavitation. Exposure to a PKC inhibitor during ethanol-induced calcium signaling did not attenuate the ensuing acceleration of cavitation. These results demonstrate that a PLC-mediated signaling pathway is required for blastocoele formation and that the generation of IP3, but not diacylglycerol, is critical for accelerating preimplantation development.