Protein phosphorylation and ions effects on salmonid sperm motility activation

Sperm motility is considered as a key factor allowing determination of semen quality and predicts fertilizing capacity. In many fish species, the spermatozoa are immotile in the testes and seminal plasma, and motility is induced when they are released in the aqueous environment. Initiation and activation of sperm motility are prerequisite processes for the contact and fusion of male and female gametes at fertilization. Many proteins are involved in the activation of sperm motility in many species. Cell signalling for the initiation of sperm motility in the salmonid fish has drawn much attention during the last two decades. In some species, protein phosphorylation process was shown to be involved in flagellar motility regulation. Hyperpolarization of the sperm membrane induces synthesis of cAMP (cyclic AMP), which triggers further cell signalling processes, such as cAMP-dependent protein phosphorylation that finally initiates sperm motility in salmonid fish. Ions such as Na+, K+ and Ca2+ play also an important role in the activation of sperm motility in many species, more specifically in salmonids. Salmonid fish sperm motility can be suppressed by millimolar concentrations of extracellular K+, and dilution of K+ upon spawning is enough to trigger the cAMP-dependent signalling cascade leading to motility initiation. This review aims to update the present knowledge about the roles of ions and protein phosphorylation process in the sperm motility activation in salmonid