Protein tyrosine phosphorylation of the human sperm head during capacitation: immunolocalization and relationship with acquisition of sperm-fertilizing ability

Abstract

The occurrence of tyrosine phosphorylation (TP) in the sperm head during capacitation has been poorly investigated, and no data exist on the relationship of its dynamics with the acquisition of sperm fertilizing ability. This study localized TP of head proteins in human spermatozoa during capacitation and explored its relationship with acquisition of the ability to display progesterone (P)-stimulated acrosome reactions (ARs) and to penetrate zona-free hamster oocytes. By immunofluorescence, TP immunoreactivity was revealed in the acrosomal region of formaldehyde-fixed/unpermeabilized samples, whereas it was abolished in fixed/permeabilized samples, in which TP immunoreactivity was high in the principal piece. No TP immunoreactivity was detectable in unfixed spermatozoa. Head TP immunoreactivity was localized externally to the acrosome, close to the cytoplasmic membrane, as assessed by transmission electron microscopy. The increase in head TP was an early event during capacitation, occurring within 1 h in capacitating conditions. At this time, the P-stimulated ARs were also increased, whereas egg penetration was as poor as in uncapacitated spermatozoa. At 5 h of capacitation, the extent of neither head TP nor the P-induced ARs were greater than that at 1 h, whereas egg penetration had significantly increased. Seminal plasma inhibited head TP, P-induced ARs and egg penetration. None of these inhibitory effects, unlike those on tail TP, were prevented by the cAMP analogue dbcAMP (N,2-O-dibutyryladenosine 3',5'-cyclic monophosphate). In conclusion, head TP is a subsurface event occurring early during capacitation and is closely related to acquisition of the ability to display P-stimulated ARs, whereas the ability to fuse with oolemma and to decondense is a later capacitation-related event.

Extracellular Regulation of Sperm Transmembrane Adenylyl Cyclase by a Forward Motility Stimulating Protein

“…In both the cases, tyrosine phosphorylation site have been found on sperm head. Similar observations regarding site of tyrosine phosphorylation in spermatozoa have been reported for human and boar system, too [52] , [53] . We postulate that the signaling cascade which originates with FMSF-receptor interaction and leads to tyrosine phosphorylation on sperm head may induce other intracellular molecular entities to transmit the signal to manifest movement of sperm tail.…”

Epididymal and ejaculated sperm differ on their response to the cryopreservation and capacitation processes in mouflon (Ovis musimon)

“…Epididymal sperm showed phosphorylation mostly in the apical region of the acrosome (pattern IV-a) while ejaculated sperm showed phosphorylation in the whole acrosome (pattern IV-b) which suggests differences on the phosphorylated acrosomal proteins. Head PTP has been associated with capacitation 85 which supports the higher PTP quantification observed in ejaculated sperm.…”

Acetylproteomic Analysis Reveals Functional Implications of Lysine Acetylation in Human Spermatozoa (sperm)

“…during capacitation (60,61) to enable sperm to display capacitation, to undergo acrosome reactions, and to penetrate zona-free oocytes. Therefore, acetylation profiles of different types of human sperm can lay a solid basis for the discovery of novel biomarkers if site-specific antibodies could be developed to verify the different modifications of key functional proteins in future.…”