Decondensation of Bull and Human Sperm Nuclei by Dithiothreitol and/or Heparin

Abstract

Various concentrations of dithiothreitol (DTT) and/or heparin were examined for their ability to induce in vitro decondensation of bovine and human sperm nuclei. Bull sperm nuclei decondensed when DTT (10 mM) and heparin (10 μg /ml) were added simultaneously or when heparin (100 μg/ml) was added after the pretreatment with DTT (100 mM). Neither DTT (500 mM) nor heparin (10 mg/ml) alone, even at high concentration, could induce decondensation of bull sperm nuclei. In contrast, human sperm nuclei decondensed when DTT alone (10 mM) or heparin alone (1 mg/ml) was added. Pretreatment of human sperm with DTT (0.1 mM) decreased the concentration of heparin required for decondensation to 10 μg/ml, a concentration incapable of inducing decondensation by itself. Overall, higher concentrations of DTT and heparin were required for bovine than for human sperm for nuclear decondensation to occur. The difference in nuclear decondensation between bull and human sperm in response to DTT and heparin is likely related to the differences between the two species in the DNA-protamine complex of sperm nuclei.