Protamine in the rat, its fate in vivo, and its degradation in vitro by egg homogenate

Fertilization and embryonic developmental capacity of epididymal and testicular sperm and immature spermatids and spermatocytes

Spermatogenesis in mammalian species begins after birth. The gonocytes, arrested at G2 of the cell cycle in the foetus, resume mitotic proliferation after birth. As identified in the mouse, the gonocytes migrate towards the periphery of the seminiferous cords at day 4 to day 6 after birth and are located in close contact with the basal lamina. From this stage the gonocytes are referred to as primitive type A spermatogonia. These cells continue mitotic proliferation and differentiate to form type B spermatogonia. By day 10 after birth, many of the type B spermatogonia have formed preleptotene primary spermatocytes which undergo a final phase of DNA synthesis (leptotene) prior to entering meiotic prophase (zygotene).

In vitro decondensation of the sperm chromatin in Holothuria tubulosa (sea cucumber) not affecting proteolysis of basic nuclear proteins

Sea urchin and sea star oocyte extracts contain proteolytic activities that are active against sperm basic nuclear proteins (SNBP). This SNBP degradation has been related to the decondensation of sperm chromatin as a possible model to male pronuclei formation. We have studied the presence of this proteolytic activity in Holothuria tubulosa (sea cucumber) and its possible relationship with sperm nuclei decondensation. The mature oocyte extracts from H. tubulosa contain a proteolytic activity to SNBP located in the macromolecular fraction of the egg-jelly layer. SNBP degradation occurred both on sperm nuclei and on purified SNBP, histones being more easily degraded than protein Ø(o) (sperm-specific protein). SNBP degradation was found to be dependent on concentration, incubation time, presence of Ca(2+), pH, and this activity could be a serine-proteinase. Thermal denaturalization of the oocyte extracts (80 degrees C, 10-15 min) inactivates its proteolytic activity on SNBP but does not affect sperm nuclei decondensation. These results would suggest that sperm nuclei decondensation occurs by a mechanism different from SNBP degradation. Thus, the sperm nuclei decondensation occurs by a thermostable factor(s) and the removal of linker SNBP (H1 and protein Ø(o)) will be a first condition in the process of sperm chromatin remodeling.

Development of sperm granulomas in the epididymides of L-cysteine-treated rats

We investigated the histopathological effects of excess L-cysteine on the male rat reproductive tract during sexual maturation. Male 6-week-old Sprague-Dawley rats were injected intraperitoneally daily with L-cysteine, 1,000 mg/kg body weight, for 1, 2, 3, and 4 weeks. L-Cysteine-treated rats developed sperm granulomas in the epididymides at an incidence of 0% (0/6), 50% (3/6), 83% (5/6), and 100% (6/6) in rats examined at study weeks 1, 2, 3, and 4, respectively. These sperm granulomas were unilateral or bilateral, and most frequently involved the proximal cauda region of the epididymides. Interestingly, small ducts, indicative of immaturity, were seen frequently in L-cysteine-treated rats. These findings suggest that the maturation of epididymides in L-cysteine-treated rats might be delayed. Additionally, dilated ducts and interstitial edema, suggestive of an increase in intraluminal pressure, were seen often in the epididymides of L-cysteine-treated rats. Labeling spermatozoa and epithelial cells with monobromobimane indicated no influence of the thiol-disulfide status of L-cysteine to the epididymides. The testes and prostate glands also showed no effects, suggesting that inhibited epididymis maturation was not a result of hormonal deficiencies. We speculate that defective development of the ducts might result in aberrant fluid flow, leading to ductal rupture in the epididymides. In that case, sperm granulomas might form around leaked spermatozoa.

Sperm nuclear activation during fertilization

The delivery of the paternal genome to the egg is a primary goal of fertilization. In preparation for this step, the nucleus of the developing spermatozoon undergoes extensive morphological and biochemical transformations during spermatogenesis to yield a tightly compacted sperm nucleus. These modifications are essentially reversed during fertilization. As a result, the incorporated sperm nucleus undergoes many steps in the egg cytoplasm as it develops into a male pronucleus. The sperm nucleus (1) loses its nuclear envelope, (2) undergoes nucleoprotein remodeling, (3) decondenses and increases in size, (4) becomes more spherical, (5) acquires a new nuclear envelope, and (6) becomes functionally competent to synthesize DNA and RNA. These changes are coordinate with meiotic processing of the maternal chromatin, and often result in behaviors asynchronous with the maternal chromatin. For example, in eggs fertilized during meiosis, the sperm nucleus decondenses while the maternal chromatin remains condensed. A model is presented that suggests some reasons why this puzzling behavior exists. Defects in any of the processes attending male pronuclear development often result in infertility. New assisted reproductive technologies have been developed that ensure delivery of the sperm nucleus to the egg cytoplasm so that a healthy embryo is produced. An emerging challenge is to further characterize the molecular mechanisms that control sperm nuclear transformations and link these to causes of human infertility. Further understanding of this basic process promises to revolutionize our understanding of the mystery of the beginning of new life.

Effects of castration on thiol status in rat spermatozoa and epididymal fluid

Mammalian spermatozoa gain their fertilizing ability as they mature in the epididymis, a process which is accompanied by oxidation of sperm protein thiols. Since sperm maturation is dependent upon normal androgenic support to the epididymis, the present work was designed to study the effects of castration on thiol status. Spermatozoa and epididymal fluid were isolated from the epididymides of male rats 5 days after castration or after 11 daily injections of the antiandrogen, cyproterone acetate. Spermatozoa and epididymal fluid were labeled with the fluorescent thiol labeling agent monobromobimane. Intact spermatozoa were evaluated by fluorescence microscopy, protein thiols were analyzed by electrophoresis, and fertilizing ability was examined after insemination of sperm suspension into the uterine horns of immature superovulated female rats. We found that both treatments resulted in an increase in cauda sperm thiols as shown by increased fluorescence in the intact spermatozoa. Protamines and nonbasic proteins were found to have increased levels of reactive thiols. The protein profiles of epididymal fluid from castrated rats were different from those of the controls, and the fluorescence patterns corresponded to the protein profiles. Our results indicate that testosterone withdrawal leads to inhibition of sperm thiol oxidation.

Chromatin remodeling in mammalian zygotes

With sperm-egg fusion at the time of fertilization the gamete nuclei are remodeled from genetically quiescent structures into pronuclei capable of DNA synthesis. Features of this process that are critical to insure the genetic integrity of the zygote and the success of subsequent embryonic development include: oocyte responses that prevent polyspermy; completion of the 2nd meiotic division by the oocyte; exchange of proteins in the sperm nucleus; and, remodelling of the oocyte chromosomes and sperm nucleus into functional pronuclei. Elucidation of the biological and molecular mechanisms underlying zygote formation and chromatin remodeling should enhance our understanding of the potential vulnerability of the zygote to toxicant-induced damage.

Male pronuclei formation release of phosphorylation of histone H-3 during decondensation of human sperm nuclei activated in vitro by heparin

The release and phosphorylation/dephosphorylation mechanisms of human spermatozoa histone during nuclei in vitro decondensation by heparin was studied. Washed sperm cells were incubated in the presence of 32P and in the absence or presence of heparin. The results showed an increase in the incorporation of 32P of 20 times greater in the presence of heparin than in the absence of heparin (the control sample). In some cases the incorporation of 32P into histones was confirmed by its isolation. To validate these results a phosphorylation kinetic of isolated sperm histone, used as a substrate, was performed. The amount of 32P was not a linear function of time, and maximal phosphorylation was reached in 60 min. A measurement of 32P incorporated as a function of the amount of histone, shows a linear relationship of up to 50 micrograms of protein, with a rapid saturation thereafter with the incorporation of 220 nm and with a KD = 442 x 10(-6) mol/L. 32P incorporation, independent of exogenous cAMP, was related to alkaline pH but was totally dependent on temperature--with a maximum of 37 degrees C. The only histone released was histone H-3. Phosphorylation/dephosphorylation is involved during male pronuclei formation.

Determination of active, non-zymogen acrosin, proacrosin and total acrosin in different andrological patients

A spectrophotometric assay is described which, due to improved extraction conditions, allows quantitative determination of enzymatically active, non-zymogen acrosin, proacrosin and total acrosin activity from human sperm acrosomes. Acrosomal proteinase activity is assessed by acid extraction of the sperm pellet and the suspension medium before and after snap-freezing, followed by zymogen autoactivation. Release of acrosin from the acrosome can be used as a sensitive biochemical marker to characterize acrosomal membrane stability, severe disturbance of which may be the cause of impaired male fertility. Acrosin activities in different populations of semen specimens are reported and compared to data available in the literature. Different degrees of acrosomal membrane alterations are observed in men with oligozoospermia, tetratozoospermia and polyzoospermia. Particularly in oligozoospermia, a significant increase of active, non-zymogen acrosin points to severe acrosomal membrane alterations and, in addition, to a premature activation of proacrosin, which may impair fertilization in certain individuals. Finally, acrosin activity is shown to be significantly influenced by the time of sexual abstinence. It is concluded that determination of acrosin may be a useful indicator of the fertility potential in men.

Antigens on rat spermatozoa with a potential role in fertilization

Eight monoclonal antibodies (McAbs), directed against antigens on rat cauda epididymal spermatozoa, were tested for their capacity to interfere with fertilization in vitro as a means of identifying molecules with a potential role in sperm-egg recognition and fusion. Antigens recognized by the McAbs were visualized on live spermatozoa by indirect immunofluorescence (IIF) and characterized by immunoblotting. Five McAbs (designated 1B5, 2C4, 4B5, 5B1, and 8C4) recognized antigens specifically on the sperm acrosome and three (designated 2B1, 2D6, and 6B2) bound to the flagellum. Of the eight McAbs investigated, three (2B1, 2C4, and 6B2) were effective in blocking fertilization in vitro when added as culture supernatants to mixtures of sperm and eggs. McAb 6B2 was inhibitory due to its ability to agglutinate spermatozoa. McAbs 2B1 and 2C4 did not agglutinate capacitated spermatozoa, had no observable effect on motility, and yet blocked fertilization in a dose-dependent manner. McAb 2C4 did not give a reaction on immunoblots, but the 2B1 antigen was identified as an Mr 40 kD glycoprotein. McAb 2B1 appeared to block fertilization at the level of zona binding, whereas the effects of 2C4 were directed more against zona penetration and/or fusion with the vitellus. When sperm-egg complexes were stained with 2C4 or 2B1 McAbs and viewed by IIF, all spermatozoa that were attached to the zona showed fluorescence on the head. These results suggest that different antigens on the rat sperm head participate in different aspects of the fertilization process and that during capacitation there is either exposure of these antigens or else they migrate to their site of action from the flagellum.

Chromatin topology during the transformation of the mouse sperm nucleus into pronucleus in vivo

Time relationships of sperm chromatin dispersion and sperm nucleoprotein replacement have been studied in vivo, by an in situ cytochemical approach. We used the Feulgen reaction to reveal DNA, which allow us to record both processes simultaneously, on the basis of the return after fertilization to haploid Feulgen values after sperm nucleoprotein replacement with somatic histones. We have shown that sperm nucleoprotein replacement occurs at around anaphase II, whereas sperm chromatin dispersion is massive between the anaphase and telophase II oocyte phases. The morphological pattern of sperm chromatin dispersion supports the idea that the process involves the whole sperm chromatin mass simultaneously, with the region located between the implantation fossa and the postacrosomial region the last to swell.

DNA synthesis following microinjection of heterologous sperm and somatic cell nuclei into hamster oocytes

We have investigated the ability of the hamster oocyte to initiate DNA synthesis in nuclei differing in basic protein content. DNA synthesis was studied by autoradiography in oocytes that had been incubated in 3H-thymidine after being parthenogenetically activated by sham microinjection, or microinjected with hamster, mouse, rabbit, or fish sperm nuclei, or hamster hepatocyte nuclei. Within 6 hr of sham or nucleus microinjection, nuclei of each type underwent transformation into pronuclei and synthesized DNA. These results demonstrated that the hamster egg can access and utilize its own and each type of template provided, whether homologous or heterologous. However, pronuclei derived from hamster sperm nuclei were more likely to be synthesizing DNA at 6 hr than pronuclei derived from sperm nuclei of other species. We conclude that the mechanisms employed by the hamster oocyte to transform hamster sperm nuclei into pronuclei and to effect DNA synthesis in these nuclei are not specific for the hamster sperm nucleus. Nevertheless, these mechanisms apparently operate more efficiently when the hamster sperm nucleus, rather than a heterologous sperm nucleus, is present.