Sea urchin sperm receptors for egg peptides

Peptides released from sea urchin eggs bind to and activate receptors in the sperm plasma membrane. The activated receptors cause multiple physiological changes in the sperm cell, including increased synthesis of cyclic GMP, that result in kinetic and directional changes in motility. Egg peptides appear to activate spermatozoa only from sea urchins in the same taxonomic order. The amino acid sequences of two different apparent receptors for the peptides reveal that one is a receptor/guanylyl cyclase. The mechanism by which the other putative receptor signals, if in fact it signals, is not known. Mammalian receptors homologous to both types of sperm-activating peptide receptors have been found in somatic cells. Thus, proteins that carry out communication between gametes of ancient invertebrates may be considered prototypes for the evolution of signaling molecules in animals that are morphologically more complex.