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suREJ proteins: new signalling molecules in sea urchin spermatozoa

In Strongylocentrotus purpuratus, the fucose sulphate polymer (FSP) of egg jelly induces the sperm acrosome reaction (AR; Vacquier & Moy, 1997). Protease treatment of sperm renders the cells insensitive to FSP, indicating that sperm membrane receptors mediate the signal transduction events underlying the AR. Monoclonal antibodies to a 210 kDa membrane glycoprotein induce Ca2+ influx into sperm and trigger the AR (Trimmer et al., 1986; Moy et al., 1996). Purified 210 kDa protein binds species-specifically to egg jelly and blocks AR induction by antibody (Podell & Vacquier, 1985; Moy et al., 1996). FSP binds to the 210 kDa protein attached to Sepharose (Vacquier & Moy, 1997). Monoclonal antibodies localise the 210 kDa protein on the plasma membrane over the acrosome and also on the sperm flagellum. The 210 kDa protein has the attributes of a sperm receptor for egg jelly and is henceforth named suREJ1 (Moy et al., 1996). We describe here the three REJ proteins found thus far in S. purpuratus sperm.