The Sperm TRP-3 Channel Mediates the Onset of a Ca2+ Wave in the Fertilized C. elegans Oocyte

Abstract

Sperm induce Ca2+ waves in the fertilized egg by introducing soluble factors or by surface interactions, which activate egg Ca2+ channels. Involvement of sperm Ca2+ channels is predicted by the conduit model; however, this model has not been validated. In Caenorhabditis elegans, the sperm-specific TRP family Ca2+ channel TRP-3 mediates sperm-oocyte fusion. Here, using high-speed in vivo imaging and image analyses, we show that sperm induce an immediate local Ca2+ rise followed by a Ca2+ wave in fertilized C. elegans oocytes. Oocytes fertilized by rare trp-3 escaper sperm showed a lack of local rise and a delay in onset of the Ca2+ wave. Sperm Ca2+ imaging suggests that the local rise is not due to the bolus introduction of stored Ca2+. These results suggest that, along with its primary function in sperm-oocyte fusion, TRP-3 induces Ca2+ waves in fertilized oocytes, consistent with the conduit model.