2 - Sperm Motility Activation and Chemoattraction

Abstract

This chapter provides a general discussion on sperm motility activation and chemoattraction. Under natural circumstances in sexually reproducing species, sperm motility is critical to fertilization and thus, for the continuation of a species. Several events important for successful fertilization in many species rely on adequate sperm motility—namely, (1) Penetration of the extracellular matrix surrounding eggs, (2) directed motility in response to factors released from the egg or closely associated structures, and, (3) migration through the female reproductive tract or within an environment such as water or seawater. In general, sperm motility is activated at ejaculation as a consequence of changes in intracellular ion concentrations. The external signals that initiate these events, and thus flagellar beating, differ among species according to the environment in which fertilization occurs. Sperm chemoattraction is defined as the movement of spermatozoa in response to a chemical signal toward the source of that signal. This form of motility is reported in many evolutionarily diverse species. This chapter concludes that sperm motility is a complex phenomenon that is responsive to the external cellular environment. Factors regulating motility such as changes in extracellular ion concentrations and secreted products from the male and/or female reproductive systems, activate sperm cell signaling involving changes in cyclic nucleotides, calcium, and protein phosphorylation/dephosphorylation in diverse species. In the conceptual model of sperm motility, the aspects describing both the plasma membrane and the final axoneme are poorly defined.