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Initiation and activation of sperm motility are prerequisite processes for the contact and fusion of male and female gametes at fertilization. The phenomena are under the regulation of CAMP and Ca2+ in vertebrates and invertebrates. Mammalian sperm requires Ca2+and cyclic AMP for the activation of sperm motility. Cell signaling for the initiation and activation of sperm motility has been well studied in the ascidians, Ciona intestinalis and C. savignyi and salmonid fishes. In Ciona, whose cell signaling for activation of sperm motility has been established, the sperm-activating and -attracting factor released from unfertilized egg requires extracellular Ca2+ for activating sperm motility and eliciting chemotactic behavior of the activated sperm toward the egg. On the other hand, the cyclic AMP-dependent phosphorylation of protein is essential for the initiation of sperm motility in salmonid fishes. A decrease in the environmental Ti concentration surrounding the spawned sperm causes a li efflux and Ca2+ influx through the specific K+ channel and dihydropyridine-sensitive L-/T- type Ca2+ channel, respectively, thereby leading to the membrane hyperpolarization and Ca2+ influx. The membrane hyperpolarization synthesizes cyclic AMP, which triggers the luther Process of cell signaling, i.e., cyclic AMP-dependent protein phosphorylation, to initiate sperm motility in salmond fishes.almond fishes.
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