MAMMALIAN SPERM DNA SUSCEPTIBILITY TO IN-SITU DENATURATION ASSOCIATEDWITH THE PRESENCE OF DNA STRAND BREAKS AS MEASURED BY THE TERMINAL DEOXYNUCLEOTIDYL TRANSFERASE ASSAY

Sperm from four mammalian species were analyzed by the sperm chromatin structure assay (SCSA) and the terminal deoxynucleotidyl transferase assay (TdTA) using flow cytometry. The SCSA quantitates the susceptibi lity of sperm nuclear DNA to in situ acid denaturation, while the TdTA quantitates the presence of endogenous DNA strand breaks in sperm nuc lear chromatin. Correlations were seen between the percentage of sperm cells showing susceptibility to in situ acid denaturation and the per centage of cells showing the presence of DNA strand breaks for humans (r = 0.56, P = 0.004), rams (r = 0.84, P < 0.001), bulls (r = 0.78, P < 0.001), and stallions (r = 0.65, P < 0.001). No significant differen ces were seen when using fresh or frozen samples for either assay. The se results suggest that sperm cells that are more susceptible to in si tu DNA denaturation may have a greater number of accessible endogenous DNA strand breaks. We hypothesize that the DNA strand breaks produced in the normal transition from a somatic cell histone complex to a pro tamine complex are not ligated properly, resulting in residual DNA str and breaks and altered chromatin structure. Alternatively, altered chr omatin structure could lead to the accessibility of the endogenous DNA strand breaks.