Differential decondensation of class I (rat) and class II (mouse) spermatozoa nuclei by physiological concentrations of heparin and glutathione

FLUORESCENT BERBERINE BINDING AS A MARKER OF INTERNAL GLYCOSAMINOGLYCANS SULFATE IN BOVINE OOCYTES AND SPERM CELLS

The use of berberine as a biological marker of glycosamineglycans sulfate was employed to corroborate the presence of heparin in mammalian oocytes and sperm and its distribution in all the structures, or only in some specialized zones, of the male and female gametes. Oocytes and sperms were treated with 1.8 mM berberine for the presence of heparin and examined 10, 30, 60, and 120 minutes later. We have found that heparin is homogeneously distributed in all the zones of bovine oocytes and in sperm cells. When sperm cells are first treated with 80 microM of heparin and then berberine, 40% of them display in their post acrosomal region an intense yellow fluorescence. This may be in relation to the high amount of heparin binding sites due to the presence of the reticular membranous like system in this sperm region and in its possible role whereby gametes recognize and adhere to one another. Therefore, the use of berberine as a fluorescent marker of heparin represents clear proof of the presence of GAGs and their binding sites in the outside and inside of mammalian gametes, reinforcing the importance they play in the events of the process of fertilization.

Presence and release of bovine sperm histone H1 during chromatin decondensation by heparin-glutathione

During spermatogenesis, changes in sperm nuclear morphology are associated with the replacement of core somatic histones by protamines. Although protamines are the major nucleoproteins of mature sperm, not all species totally replace the histones. Histone H1, along with protamines, mediates chromatin condensation into an insoluble complex that is transcriptionally inactive. In vitro, heparin-reduced glutathione causes sperm decondensation, and the structures formed are morphologically similar to the in vivo male pronucleus. To study the participation of histone H1 in bovine sperm chromatin remodelling, we measured the presence and release of histone H1 by immunofluorescence, acetic acid-urea-triton-polyacrylamide gel electrophoresis, and immunoblotting. Nuclear decondensation was induced by 80 microM heparin and 15.0 mM reduced glutathione (GSH) for 7, 14, and 21 h at 37 degrees C. Additionally, nucleons, composed of nuclei isolated from the sperm, were decondensed with 20.0 microM heparin and 5.0 mM GSH for 4.0 h at 37 degrees C. Controls were incubated in buffer for similar periods of time. Immunofluorescent localization of histone H1 was carried out with mouse monoclonal antibody, and DNA localization was visualized by 0.001% quinacrine staining. Chromatin decondensation was accompanied by increased sperm nuclei and nucleon surface area. We observed that histone H1 was localized exclusively in the nuclei of intact sperm and nucleons. Histone H1 immunofluorescent intensity did not change in control samples but decreased over time in samples treated with heparin-GSH. There was a negative correlation between the surface area of sperm nuclei and immunohistochemical intensity of histone H1 (P < 0.05). Nucleon decondensation showed a similar relationship. By electrophoresis and immunoblotting, we verified the loss of histone H1 from the sperm and nucleons and its release into the incubation media. Based on these results, we propose that histone H1 is present in the bovine sperm nuclei. H1 depletion may participate in chromatin decondensation and nuclear swelling induced by heparin-GSH.

Arrangement of beta tubulin in bull spermatozoa during nuclei decondensation

Eukaryotic cells have internal scaffolding of microtubules cytoskeleton that gives them their characteristic shapes. We analyzed by immuno-fluorescence the shift and distribution of tubuline during in vitro bull sperm nuclei swelling by the action of heparin-reduced glutathione physiological decondensing agents. Sperm tubulin display a pattern that shows tubulin fluorescence all over the head, leaving the acrosome tip devoid of tubulin. In the second stage we can observe that the acrosomal zone is practically devoid of fluorescence and a net of fluorescent microtubules that seems to be anchored in the basal plate in the postacrosomal region. It is also possible to observe green spots of tubulin fluorescence in the nucleus periphery, that might represent clusters of chromatin hub-like bodies and/or the microtubule organizing center (MTOC). In the third stage, practically all tubulin moves backwards to the basal plate in the neck region of the sperm nuclei remaining in only the green fluorescence spots in the periphery of the swollen sperm nuclei. The results allow us to assume that tubulin mechanism rearrangement is considered to be necessary for the normal fertilization process.

Heparin and glutathione II: correlation between decondensation of bull sperm cells and its nucleons

The correlation between the kinetics of bull sperm nuclear and nucleon decondensation induced by the action of physiological concentrations of heparin/GSH was studied. Sperm and nucleon suspensions were incubated at 37 degrees C in salt medium, at a constant concentration of either heparin or GSH and increasing concentrations of the other reagent. Even though nucleons are pretreated with DTT/CTAB, when they are incubated alone with GSH for 96 h, they remain intact, no matter which concentration is employed, and it was impossible to observe the slightest sign of nuclei decondensation. Therefore, rupture of disulfide bridges is not the main mechanism to induce nuclei decondensation and perhaps the GSH role resides in potentate the heparin effect by increasing its negative charge. Nevertheless, nucleons reach 95% of chromatin decondensation in the presence of heparin plus GSH or heparin alone. The fact that the correlation between heparin and GSH concentrations needed to induce sperm nuclei decondensation was 3- to 4-fold greater that in nucleons might be due to the complete lack of nucleon membranes. Heparin/GSH seem to induce nuclei decondensation by an ionic chromatin charge neutralization mechanism.

Nucleons, I: A model for studying the mechanism of sperm nucleus swelling in vitro

The nucleon, a highly organized chromatin structure, was studied to learn if its swelling takes place by the action of heparin/GSH, without the participation of any mechanism provided by sperm membranes, subcellular organelles, or other proteins foreign to the sperm nucleus. Sperm suspensions of guinea pigs and rats were incubated with 9 mM DTT and 1% CTAB. The nucleons obtained from washed epididymal spermatozoa appear under a phase-contrast microscope to preserve their original nucleus shape and to completely lack the acrosome, middle piece, and tail. In an electron microscope, nucleon thin sections show a slight nuclear chromatin decompressed from the periphery toward the center. An outstanding result was that the nucleon swelling pattern by heparin/GSH showed the same classic organization into hub-like nuclear bodies joined by a network of chromatin fibers ranging in thickness from 25 to 1.5 nm. Under the conditions of this study there was no need of any membrane or subcellular structure. At stage IV, all the thick fibers disappear, leaving only thin bead fibers on a string. With respect to nuclear swelling there is no doubt that the sperm chromatin is organized in a special form that decides a specific required pattern of unpacking.

The correlation of sperm chromatin decondensation following in vitro exposure to heparin and sperm penetration rates

PURPOSE

The aim of this study was to evaluate the possible correlation of low-dose heparin-induced decondensation of sperm chromatin with sperm concentration, motility, morphology, membrane hypoosmotic response, ejaculate volume, and the ability of sperm to penetrate zona-free hamster oocytes.

METHODS

Twenty-two donors of known fertility and 105 patients undergoing evaluation at an andrology laboratory were evaluated by standard World Health Organization semen analysis techniques and a modified sperm penetration assay (SPA). An aliquot was also incubated for 60 min and Ham's F10 medium containing 50 USP/ml heparin. The percentage of sperm undergoing chromatin decondensation was evaluated and correlated to SPA rates and semen quality parameters.

RESULTS

No significant correlation was observed between semen parameters and decondensation rates. A nonsignificant (P = 0.11) inverse correlation (P = -0.21) was observed between SPA rates and chromatin decondensation. Significant (P < 0.001) differences were observed in the decondensation rate of donors (3.7 +/- 0.6), patients with normal SPA rates (7.8 +/- 1.5), and patients with decreased SPA rates (21.7 +/- 1.8). The decondensation rates were significantly different (P < 0.01) between patients with a normal SPA rate and patients with a decreased SPA rate.

CONCLUSIONS

These data indicate a significant inverse relationship between the SPA rate, which has previously been shown to correlate highly with fertilization ability and heparin-induced sperm chromatin decondensation.

DNA unpacking in guinea pig sperm chromatin by heparin and reduced glutathione

The kinetics of nuclear decondensation and DNA unpacking induced by the action of a physiological concentration of heparin and glutathione of guinea pig spermatozoa was studied. Sperm (acrosomeless) suspensions were incubated at several different temperatures (37, 40, 43, and 46 degrees C), with a constant concentration of either heparin (50 microM) or reduced glutathione (12.5 mM) and increasing concentrations of the other reagent. Nuclei spermatozoa remained highly condensed when incubated in the medium alone or in either GSH or heparin alone for up to 72 h. Swelling of nuclei spermatozoa was initially observed during the first 20 min of incubation. The sperm nuclei initiate decompaction at the central part of the nuclear structure while at the periphery there remain numerous residues of densely packed chromatin. The swollen chromatin pattern presents the characteristic organization into "hub-like" nuclear bodies that measured 10-100 nm diameter joined by a network of chromatin fibers. At full nuclei decondensation chromatin end fibers are loose, probably meaning that DNA is not organized into loop domains. DNA presence was verified by the use of ethidium bromide and acridine orange.

Effect of heparin-reduced glutathione on hamster sperm DNA unpacking and nuclear swelling

This study examined the kinetics of sperm nuclear decondensation induced by the action of physiological concentrations of heparin and glutathione in hamster sperm nuclei as a chromatin model that contains protamine P1 and P2. Sperm suspension was incubated at different temperatures (37, 40, 43, and 46 degrees C) in media, keeping constant the concentration of either heparin or GSH and increasing concentrations of the other reagent. Spermatozoa nuclei without any treatment, incubated for 72 h, appear densely condensed. Swelling of hamster spermatozoa nuclei was observed after 30 min of incubation in the presence of efficient concentrations of heparin-GSH. The extent of this time lag was significantly reduced at higher temperatures. DNA presence was verified by the use of ethidium bromide, acridine orange, and Feulgen stain. Phase-contrast microscopy shows that nuclear decondensation begins at the equatorial levels, with DNA highly condensed at the acrosome pole, and the basal pole as the DNA attachment point. Electron microscopy observations showed that hamster sperm nuclei initiates its decompaction at the peripheral regions and this behavior remains until late stages of decondensation, nevertheless, the chromatin is organized into "hub-like" nuclear bodies that measured 10-100 nm in diameter, joined by a network of chromatin fibers with apparent reduction in number. At the decondensation full stage, the network seems to be wide open with a reduced number of hub-like nuclear bodies present in the interlace. DNA is not organized into topologically constrained loop domains and is attached to the basal plate instead of to the nuclear matrix or any other structure.