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Abstract
Mammalian spermatozoa acquire the capacity for motility and fertilization during the transit through the epididymis under the control of different factors, such as cAMP, intracellular pH, intracellular calcium and phosphorylation of sperm proteins. As the acquisition of functional competence including gaining motility during epididymal transit occurs in the complete absence of contemporaneous gene transcription and translation on the part of the spermatozoa, it is widely accepted that post-translational modifications are the only means by which spermatozoa can acquire functionality. Serine-threonine protein phosphatase 1 (PP1) together with their testis/sperm-specific interacting proteins might be involved in this regulatory mechanism. PP1α, PP1β/δ, PP1γ1 and PP1γ2 are all expressed in the testis whereas PP1γ2 is the only isoform expressed on spermatozoa. I2, I3, sds22, 14-3-3 and hsp90 are associated with PP1γ2 in spermatozoa located on the sperm head and tail. Activity of PP1γ2 and the binding pattern to these regulatory proteins changes in spermatozoa recruited from the caput and those from the cauda part of the epididymis. In this review, we summarize the possible roles of PP1 on spermatozoa during spermatogenesis and flagellar motility control. We suggest that PP1 might take part in the inhibition of the sperm motility activation by interacting with AKAPs and CAMKII. A hypothesized signaling pathway of mammalian sperm motility activation and PP1's function has been proposed.
Notes
Abbreviations: PPs: Protein serine/threonine phosphatases, PP1: Protein phosphatase 1, PIPs: PP1 interacting proteins, cAMP: Cyclic adenosine monophosphate, AKAP: A kinase anchor protein, CAMKII: Calmodulin kinase II, cdKs: Cyclin-dependent kinases, PKA: Protein kinase A, NLS: Nuclear localization signals, NTS: Nucleolar targeting signals, FSH: Follicular stimulating hormone, Spz1: Spermatogenic zip protein 1, GSK: Glycogen synthase kinase 3, DNA: Deoxyribonucleic acid, SARP: Several ankyrin repeat protein, ACE: Angiotensin-converting enzyme, Tesk: Testis-specific protein kinase, ADF: Actin-depolymerizing factor, MOs: Membranous organelles, ATP: Adenosin triphosphate