From the cellular to the molecular dimension: The actual challenge for human fertilization research

Gossypol-induced inhibition of plasminogen activator activity in human and ovine acrosomal extract

The effect of gossypol--a polycyclic compound isolated from cotton seeds--on the plasminogen activator activity of man and ram acrosomal extracts was explored in vitro. The action of gossypol on the plasminogen activator activity was investigated by a spectrophotometric method using the chromogenic substrate S-2251. Gossypol, a known antispermatogenic agent, was found to effectively inhibit human and ovine acrosomal plasminogen activator activity. The inhibition was dose-dependent. Plasminogen activator activity from man and ram extracts was completely inhibited by 350 mumol l-1 and 300 mumol l-1 of gossypol, respectively. In additional experiments, low, non-spermicidal concentrations of gossypol (2.5-40 mumol l-1) were found to significantly inhibit plasmin activity in a dose-dependent manner. The results suggest that inhibition of both acrosomal plasminogen activator and plasmin activity is a possible mechanism by which gossypol exerts its antifertility effect, since the plasminogen activator/plasmin system plays a role in the whole process of ovum fertilization.

Selective expression of a progesterone receptor on the human sperm surface

OBJECTIVE

To visualize progesterone (P) binding sites on the sperm surface, examine the relationship between hormone binding and hormone action (acrosome reaction), and determine the size of the hormone-responsive sperm subpopulation.

DESIGN

Kinetic analysis of P binding was combined with the assessment of the hormone effect using a fluorescent acrosomal marker.

SETTING

Private hospital, medical research center, and a university-based andrological laboratory.

PATIENTS, PARTICIPANTS

Sperm samples were from healthy volunteers with normal spermiogram values.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Progesterone binding was analyzed by fluorescence microscopy and flow cytometry using P coupled to fluorescein isothiocyanate-labeled bovine serum albumin. Tetramethylrhodamine isothiocyanate-labeled Pisum sativum agglutinin was used as acrosomal marker in double-labeling experiments.

RESULTS

After in vitro capacitation, only few spermatozoa (approximately 10%) were able to bind P to the cell surface, but most of these cells subsequently generated the acrosome reaction in response to hormone binding.

CONCLUSIONS

The expression of P receptor sites on the human sperm surface is a major factor controlling the P-induced acrosome reaction. Further studies are warranted to explore if defective expression of the receptor can compromise fertility.

Fertilization failure and dysfunctions as possible causes for human idiopathic infertility

Consideration of the most common currently practiced laboratory assays for human spermatozoal fertility are discussed, with reference to the relevance of such assays to success or failure in human in vitro fertilization (IVF). Such IVF therapy should be the definitive challenge for human spermatozoal fertilization ability. However, when fertilization fails, is polyspermic, or is suboptimal, then questions concerning the step or steps in the process of fertilization which are dysfunctional remain unanswered. Quite possibly new assays need to be devised to address these problems, while in the meantime our present laboratory assay systems need to be improved to discern those defects in fertilization which operate in many cases of human idiopathic infertility.

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.

Glycosaminoglycan-sulfate as plasma membrane component of pig spermatozoa

The effect of specific glycosaminoglycan-hydrolyzing enzymes on the ruthenium red staining of pig spermatozoa was studied. Washed spermatozoa were incubated at 35 degrees C in buffer or with neuraminidase 0.5 units/ml, heparinase 0.2 mg/ml, or chondroitinase ABC 2.0 units/ml. After incubation sperm cells were washed, stained with ruthenium red and studied under the electron microscope. Anionic sites in the surface of untreated spermatozoa follow regularly the plasma membrane, but present are numerous processes constituting what has been defined as the glycocalyx. Neuraminidase did not affect the distribution of ruthenium red on the surface of the spermatozoa, but eliminated almost completely the processes of the glycocalyx. Heparinase caused loss of the ruthenium red-stained sites on the membrane surface of pig spermatozoa with less influence on the dense processes of the glycocalyx. A similar loss of ruthenium red-stained sites was observed with nitrous acid treatment. A striking effect of treatment with chondroitinase ABC was the production of a typical acrosome reaction.

Human antral follicles: oocyte nucleus and the karyosphere formation (electron microscopic and autoradiographic data)

The functional organization of the nucleus in the oocytes from human antral follicles was examined by morphological and autoradiographic analysis methods at the light and electron microscopic level. According to the position of the nucleus, the level of its transcriptional activity, and the pattern of distribution of structures in it, oocytes fall into two groups. In the first one, the oocytes with the nucleus in the central position are characterized by the distribution of numerous structures all over the nucleus or by a different extent of aggregation of chromatin around the nucleolus. The nuclei of these oocytes are characterized by [3H]uridine incorporation, the label being localized over purely fibrillar, agranular nucleoli and over dispersed fibrillar chromatin adjacent to either the regions of densely packed chromatin or fibrillar-granular material of the nucleolus-like bodies. The latter, the same as condensed chromatin, do not incorporate [3H]uridine. In the second group, the nuclei are displaced towards the oocyte's periphery, and chromosomes surround the nucleolus as a continuous mass closely adjacent to its surface, thus forming a karyosphere. The karyosphere formation takes place on the background of cessation of nuclear transcriptional activity. A fully formed karyosphere represents a complex of closely associated inactivated structures: Nucleolus, chromosomes, and nucleolus-like bodies. The karyosphere nucleolus bears no granules and consists of densely packed finely fibrillar material (fibrils 3 nm thick). Two zones (central and peripheral) can be distinguished in a nucleolus. Nucleolus-like bodies, consisting of granules 20 nm in diameter embedded in finely fibrillar material, are often associated with chromosomes. In this study, data obtained by observations on the loss of association between the oocyte (with karyosphere) and corona radiata cells are evaluated. The relation of the karyosphere formation to the atresia process and the duration of karyosphere existence in human antral follicles are also discussed.

Comparative study of the kinetics of the acrosome reaction and survival of human spermatozoa in various media

The in-vitro kinetics of the acrosome reaction and the survival of human spermatozoa were studied under different capacitating conditions. Human preovulatory follicular fluid (FF), isotonic BWW (N-BWW) and hypertonic BWW (H-BWW) were tested. Motile sperm selected by migration in these media were examined after 1, 3, 5 and 22 h of incubation under 5% CO2. The kinetics of the reaction in the population of live, morphologically normal sperm was dependent on both the culture medium and time of incubation. In the first hour, the mean percentage of acrosome-reacted sperm in H-BWW and FF was significantly greater than in N-BWW. The proportion of reacted cells increased significantly after 3 h in N-BWW (P = 0.001), after 5 h in FF (P = 0.03) and after 22 h in H-BWW (P = 0.01). A significant decrease in sperm viability was registered at 3 and 22 h of incubation (P less than 0.002) in all media. These results demonstrate that both H-BWW and FF stimulate the acrosome reaction while survival is optimal in the latter.

Subcellular immunochemical localization of acrosin in human spermatozoa during the acrosome reaction and zona pellucida penetration

The changes in acrosin immunoreactivity in human spermatozoa undergoing spontaneous or chemically induced acrosome reactions were studied by electron microscopic immunocytochemistry with an acrosin-specific monoclonal antibody. Migration of limited amounts of acrosin to the sperm surface was the earliest event characterizing the beginning of the acrosome reaction. The acrosome of such spermatozoa remained morphologically intact, swelled, or showed intraacrosomal vesiculation without any disruption of the plasma and acrosomal membrane integrity. Massive release of acrosin coincided with the fusion of the plasma and outer acrosomal membranes. However, even fully acrosome-reacted spermatozoa always retained some acrosin on the exposed inner acrosomal membrane and in the equatorial segment of the acrosome. This residual acrosin was also detected on spermatozoa within the zona pellucida of human oocytes inseminated in vitro, while the previously released bulk of acrosin remained attached to the surface of the zona pellucida at the site of sperm entry. These findings are compatible with multiple functions of acrosin in human sperm-egg interaction, including sperm-zona pellucida binding, dispersal of acrosomal contents, and facilitation of zona pellucida penetration.

The relationship between the motility and morphology of spermatozoa in human semen

High-speed videomicrography was used to assess simultaneously the morphology and motility of seminal spermatozoa from 10 fertile donors and 10 patients being evaluated for infertility. In both donors and patients, morphologically normal spermatozoa were more likely to be motile and had significantly higher straight line velocity, greater rolling frequency and flagellar beat frequency than abnormally shaped cells. For donors and patients there were highly significant, linear correlations (R = 0.7 to R = 0.98) between the movement characteristics of morphologically normal and abnormal spermatozoa within an ejaculate. A greater percentage of normal donor spermatozoa were motile than were the normal spermatozoa from patients (56% vs. 28%, respectively, P less than 0.005) and normal donor spermatozoa also swam faster than normal patient spermatozoa (49.1 +/- 3.2 microns/sec vs. 37.4 +/- 4.3 microns/sec, mean +/- sem, respectively, P less than 0.05). Overall, a multivariate analysis of variance, including straight line velocity, rolling frequency, beat frequency, and flagellar beat amplitude, demonstrated that these movement characteristics were significantly greater for the normal cells from donors than for the normal spermatozoa from patients. These biologic distinctions notwithstanding, the discrimination between semen from donors and patients was not improved when only morphologically normal cells were analyzed for motility.

Effect of urea and detergents on the ability of human spermatozoa to penetrate zona-free hamster oocytes

Washing of human spermatozoa with either BWW alone or with the same buffer containing 0.1 M urea, 0.005% SDS or 0.001% NP40 affected the penetration ability of the gametes into zona-free hamster oocytes to various degrees. In contrast, human spermatozoa washed with BWW buffer containing 0.3 M urea had an increased ability to fuse with the heterologous oocytes when compared to controls capacitated with BWW/BSA. Moreover, the presence or absence of BSA in the insemination medium did not further modify this enhanced penetration pattern. The BWW, BWW/0.1 M urea and BWW/SDS treatments apparently mimicked some of the in vitro capacitation properties of albumin-containing media; the BWW/0.3 M urea treatment overpowered the capacitation and acrosomal reaction extent obtained with BWW+BSA. In all samples the motility of the spermatozoa washed with BWW buffer alone or containing various additives (but no albumin) was significantly decreased if compared to the motility of semen samples washed with albumin containing media. However, each sperm sample behaved differently when exposed to a given buffer.

Distribution of sterols and anionic lipids in human sperm plasma membrane: effects of in vitro capacitation

Filipin, a membrane beta-hydroxysterol probe, and polymyxin B (PXB), a probe for anionic lipids, were used to study human sperm plasma membrane (PM) with particular reference to changes induced by capacitation in vitro. In washed but noncapacitated spermatozoa the density of filipin/sterol complexes (FSC) was uniformly high in the PM overlying the acrosome, without any differences between its anterior and equatorial regions. The postacrosomal region was poor in FSC. The exclusion of FSC from small areas of the PM covering the two acrosomal regions and reduction of their number in the postacrosomal region were the main changes induced by sperm capacitation. Unlike filipin, PXB produced a capacitation-independent reaction pattern characterized by a high reactivity of the PM covering the anterior portion of the acrosome, probably conferring to this region its potential fusigenicity temporarily antagonized by the elevated sterol content. Only an exceptional and slight PXB binding was seen in the nonfusigenic equatorial and postacrosomal regions.