Tyrosine phosphorylation of cytochrome c as a signaling event in frozen thawed buffalo spermatozoa at the cross-roads of capacitation and apoptosis.

Considering the importance of cytochrome c in both life and death, it was of significant interest to investigate the expression of cytochrome c, its tyrosine phosphorylation status and immunolocalization patterns in a frozen-thawed buffalo sperm cell in comparison to in vitro capacitated [heparin (10 μg/ml) induced, for 4h] and stress [apoptotic (10 μM staurosporine), oxidative (25 μM H2O2) and osmotic (180 mM NaCl) for 4h] induced conditions. Proteins were subjected to immunoblotting and probed by using monoclonal anti-phosphotyrosine antibodies. A significant (p<0.05) increase in expression of tyrosine phosphorylated cytochrome c was observed in capacitated buffalo sperm in comparison to frozen-thawed samples. cAMP protein kinase-A dependent and extracellular signal-regulated kinase independent tyrosine phosphorylation of cytochrome c was found during in vitro capacitation of buffalo spermatozoa. Localized increase in cytochrome c and tyrosine phosphorylated proteins were observed in frozen thawed and capacitated sperm. The information generated in this study can be used to understand the molecular mechanism of regulation of an apoptotic protein (cytochrome c) by tyrosine phosphorylation (a capacitation marker) in a frozen thawed sperm cell which could be a good target to combat apoptosis.