When unfertilized eggs of the sea urchin Hemicentrotus pulcherrimus were treated with the extracts from the sea algae Laminaria diabolica, fertilization envelope formation (FEF) was observed in 1.5 to 2 min without subsequent cleavage. The molecular mass of the FEF-inducing protein purified from the Laminaria extracts was estimated by gel-filtration to be 120 kDa, and it induced a 100% FEF at a concentration of 525 ng/ml (4.4 nM). The FEF activity of the purified protein was completely inhibited by GlcNAc, less effectively by GlcN, and not at all by various other sugars and amino-sugars, suggesting its nature as a lectin. Normal FEF and cleavage were observed when eggs were inseminated in the presence of GlcNAc. Immunohistochemical observations using antibodies against purified protein revealed its specific localization in the cells lining the wall of mucilaginous lacunae and in secretory products in the lumen. The purified protein did not activate the pretreated with verapamil or diltiazem, while ionomycin, a Ca2 -ionophore, did induce activation of the similarly pretreated eggs. These results indicate that the Laminaria lectin triggers a very initial step in the cascade of the egg cortical reactions leading to FEF, independently of those induced by sperm.
