Dynamics of the global tyrosine phosphorylation during capacitation and acquisition of the ability to fuse with oocytes in human spermatozoa.
Phosphorylation of tyrosine residues in cellular proteins represents a major event during sperm capacitaton, but its relationship with the acquisition of sperm-fertilizing ability is still unclear. In this study we explored the relationship between the kinetics of the global tyrosine phosphorylation, monitored with a flow cytometric assay, and the acquisition of the human sperm ability to fuse with oocytes, evaluated with the progesterone-enhanced hamster egg penetration test. Sperm tyrosine phosphorylation appeared to be an early event in the capacitation process, with a 3.6-fold mean increase within 1 h of capacitation, but at this time sperm-oocyte fusion was extremely poor compared with that observed at 5 h of capacitation. Capacitation in calcium-free medium produced a 2-fold mean increase in tyrosine phosphorylation compared with that seen in complete capacitation medium both at 1 h and 5 h of capacitation, whereas sperm-oocyte fusion significantly increased only at 1 h, remaining unchanged at 5 h of capacitation. The cAMP analog, N,2-O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP), prevented the inhibitory effect of seminal plasma on tyrosine phosphorylation but not on sperm-oocyte fusion. In conclusion, these results suggest that the acquisition of sperm-fertilizing ability is always associated with an increase of the global tyrosine phosphorylation, but tyrosine phosphorylation does not necessarily reflect the acquisition of the sperm-fertilizing ability. Flow cytometry assay, a reliable technique to quickly quantify the global levels of the human sperm tyrosine phosphorylation, could be useful for a further elucidation of the biological meaning of this process, with the perspective of its clinical use as a measure of the sperm-fertilizing potential.
Barbonetti
A
A
Department of Internal Medicine, University of L'Aquila, 67100 L'Aquila, Italy.
Vassallo
M R C
MR
Cinque
B
B
Antonangelo
C
C
Sciarretta
F
F
Santucci
R
R
D'Angeli
A
A
Francavilla
S
S
Francavilla
F
F
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D006224:Cricetinae; D000242:Cyclic AMP / Q000494:pharmacology; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods; D005434:Flow Cytometry / Q000379:methods; D006801:Humans; D007700:Kinetics; D008297:Male; D009865:Oocytes / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012661:Semen / Q000502:physiology; D013075:Sperm Capacitation / Q000187:drug effects / Q000502:physiology*; D013084:Sperm-Ovum Interactions / Q000187:drug effects / Q000502:physiology*; D013094:Spermatozoa / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D013379:Substrate Specificity
D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D002118:Calcium