Maternal Exogastrula-Inducing Peptides (EGIPs) and Their Changes during Development in the Sea Urchin Anthocidaris crassispina

Exogastrula-inducing activity was examined in eggs and embryos of the sea urchin Anthocidaris crassispina at various stages. During fractionation on a column of DEAE-cellulose, the exogastrula-inducing activity was found in the flow-through fraction at all developmental stages. In particular, the activity present in the flow-through fraction of unfertilized eggs represents the presence of maternal exogastrula-inducing peptides (EGIPs). The flow-through fractions from the column of DEAE-cellulose were applied to a column of Sephadex G-100 and the activities in the eluate were assayed. The active low-molecular-weight fraction was obtained in all cases with the exception of pluteus larvae, extracts of which contained another active fraction. Immunoblots of protein samples from eggs and embryos probed with antiserum against EGIP-D indicated that there is a major immunoreactive protein that migrates with an apparent molecular weight of about 6 kDa in all cases with the exception of pluteus larvae, and that there are two major immunoreactive proteins that migrate with apparent molecular weights of 6 kDa and 35 kDa, respectively, in pluteus larvae.