Sperm nuclear packing and regulation during spermatogenesis and fertilization

Taken together, our in vitro studies demonstrated the following: First, species-specific proteolytic degradation of protamine occurs when isolated sperm nuclei are incubated in vitro with disulfide-reducing agent, caused by proteinase that can be removed with salt from the isolated sperm nuclei; second, protamine degradation occurs prior to and during thiol-induced nuclear decondensation and release of DNA template restrictions in vitro; third, salt-extracted proteinases can be recombined with proteinase-free nuclei to again produce species-specific proteolytic protamine degradation and sperm nuclear decondensation; and fourth, differences in the protamine substrates and not in the proteinases underlie the species specificity of protamine degradation seen in the three species - the proteinases associated with isolated hamster, rabbit and guinea pig sperm nuclei apparently have endoproteinase activity at simular or identical amino acid residues. However, our in vitro studies did not distinguish between the possibility that proteinase activity associated with isolated sperm nuclei is associated with sperm chromatin in situ, and the alternative possibility that proteolytic activity is of acrosomal origin, becoming bound to the chromatin during experimental manipulation of the spermatozoa. Additionally, and most important, it could not be determined from these studies whether proteolysis is involved in the decondensation of the sperm nucleus during fertilization and, if so, whether the proteinase is derived from the sperm or egg. Studies which address these important issues are currently underway.