Submitted February 7, 2008
Returned for revision March 26, 2008
Accepted June 9, 2008
Gamete Biology
Dynamics of the Global Tyrosine Phosphorylation During Capacitation and Acquisition of the Ability to Fuse with Oocytes in Human Spermatozoa
A. Barbonetti ,
M.R.C. Vassallo ,
B. Cinque ,
C. Antonangelo ,
F. Sciarretta ,
R. Santucci ,
A. D'Angeli ,
S. Francavilla ,
and
F. Francavilla *
* To whom correspondence should be addressed. E-mail: francavi{at}cc.univaq.it.
Abstract
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 hour (h)-capacitation, but, at this time, sperm/oocyte fusion was extremely poor as compared to that observed at 5h-capacitation. Capacitation in calcium-free medium, produced a 2-fold mean increase in tyrosine phosphorylation as compared to that seen in complete capacitation medium both at 1h and 5h capacitation, whereas, sperm/oocyte fusion significantly increased only at 1h, remaining unchanged at 5h capacitation. The cAMP analogue, dbcAMP, prevented the inhibitory effect of seminal plasma on tyrosine phosphorylation but not that on sperm/oocyte fusion. In conclusion, these results suggest that the acquisition of sperm fertilizing ability is always associated to 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.
Key words:
Sperm capacitation •
flow cytometry •
human spermatozoa •
sperm/oocyte fusion •
tyrosine phosphorylation
