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 Cγ activation, and formation of inositol trisphosphate. However, the upstream activators or modulators of this signaling pathway are not known. We recently identified four Gα subunits of heterotrimeric G-proteins present in the sea urchin egg, and here we find that activation of G-proteins of the Gαs and Gαq type, but not Gαi or Gα12 type, is required for normal Ca²⁺ dynamics at fertilization. The effects of these G-proteins are mediated by the Gβγ 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.