βγ subunits of heterotrimeric G-proteins contribute to Ca2+ release at fertilization in the sea urchin

A cytoplasmic Ca2+ transient is required for egg activation at fertilization in all animals. The pathway leading to release of Ca2+ from the endoplasmic reticulum in echinoderms includes activation of a SRC homolog, followed by phospholipase Cgamma activation, and formation of inositol trisphosphate. However, the upstream activators or modulators of this signaling pathway are not known. We recently identified four Galpha subunits of heterotrimeric G-proteins present in the sea urchin egg, and here we find that activation of G-proteins of the Galphas and Galphaq type, but not Galphai or Galpha12 type, is required for normal Ca2+ dynamics at fertilization. The effects of these G-proteins are mediated by the Gbetagamma subunits, occur upstream of the cytoplasmic Ca2+ release, and influence both the amplitude of Ca2+ release and the duration of the lag phase. We propose integration of the G-protein input into the framework of signaling at sea urchin fertilization.