Female gamete membrane glycoproteins potentially involved in gamete recognition in Ectocarpus siliculosus (Phaeophyceae)

Abstract

In the plasma membrane-enriched fraction of female gametes of Ectocarpus siliculosus (Phaeophyceae) four sex-specific glycoproteins (P2–3, P5, P16) exposing N- acetylglucosamine (GlcNAc) residues were detected in vitro. In immunoblots these proteins were labelled with the GlcNAc complementary lectin wheat germ agglutinin (WGA) conjugated to digoxigenin. P2 also cross-reacted with the mannose-specific Galanthus nivalis agglutinin (GNA). Previously, a key and lock mechanism of gamete recognition was demonstrated in vivo: fertilization can be selectively inhibited by a WGA pretreatment of female gametes, or by GlcNAc pretreated male gametes. Lectins with different carbohydrate requirements such as GNA do not affect fertilization in vivo. Thus, the remaining glycoproteins P3, P5 and P16 seem to be involved in cell-cell recognition during fertilization, and possibly one of them functions as the male receptor in the plasma membrane of female gametes. Membrane proteins of both gamete types showed higher differences than cytosolic proteins or proteins extracted from whole cells when examined by high resolution two-dimensional gel electrophoresis.