Sperm motility initiation by egg jelly of the anuran,Discoglossus pictusmay be mediated by sperm motility-initiating substance of the internally-fertilizing newt,Cynops pyrrhogaster

Abstract

SummaryThe egg jelly ofDiscoglossus pictuscontains sperm motility-activating activity, the molecular basis of which has not been studied.Discoglossus pictussperm initiated motility immediately after immersion in egg-jelly extract, as well as after immersion in hyposmotic solution, which initiates sperm motility in the external fertilization of anuran amphibians. Sequential treatment of theD. pictussperm with these two solutions revealed the predominant effect of hyposmolality in initiation of motility. The motility initiation induced by jelly extract was suppressed by a monoclonal antibody (mAb) that is specific for the 34 kDa sperm motility-initiating substance (SMIS) in the egg jelly of the newt,Cynops pyrrhogaster.Immunoblotting using the anti-SMIS mAb revealed several antigenic proteins that included major ones with sizes of 18- and 34-kDa inD. pictusjelly extract. Scanning electron microscopic observation revealed that granules of jelly matrix, in which SMIS localizes and which have a critical role in the internal fertilization ofC. pyrrhogaster, were not observed near the surface of theD. pictusegg jelly. These results suggest that sperm motility-activating activity in egg jelly ofD. pictusmay be mediated by SMIS homologous proteins that act through a mechanism that is partially different from that ofC. pyrrhogaster.