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 C activation, and formation of inositol trisphosphate. However, the upstream activators or modulators of this signaling pathway are not known. We recently identified four G subunits of heterotrimeric G-proteins present in the sea urchin egg, and here we find that activation of G-proteins of the Gs and Gq type, but not Gi or G12 type, is required for normal Ca²⁺ dynamics at fertilization. The effects of these G-proteins are mediated by the G 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.