Showing papers on "Sperm published in 1998"

Sperm competition and sexual selection

Abstract: General Themes: G.A. Parker, Sperm Competition and the Evolution of Ejaculates: Towards a Theory Base. A.P. Moller, Sperm Competition and Sexual Selection. W.G. Eberhard, Female Roles in Sperm Competition. J. Wright, Paternity and Paternal Care. Taxonomic Treatments: L.F. Delph and K. Havens, Pollen Competition in Flowering Plants. D.R. Levitan, Sperm Limitation, Gamete Competition and Sexual Selection in External Fertilizers. N.K. Michiels, Mating Conflicts and Sperm Competition in Simultaneous Hermaphrodites. B. Baur, Sperm Competition in Molluscs. M.A. Elgar, Sperm Competition and Sexual Selection in Spiders and Other Arachnids. L.W. Simmons and M.T. Siva-Jothy, Sperm Competition in Insects: Mechanisms and the Potential for Selection. C.W. Petersen and R.R. Warner, Sperm Competition in Fishes. T.R. Halliday, Sperm Competition in Amphibians. M. Olsson and T. Madsen, Sexual Selection and Sperm Competition in Reptiles. T.R. Birkhead, Sperm Competition in Birds: Mechanisms and Function. D.A. Taggart, W.G. Breed, P.D. Temple-Smith, A. Purvis, and G. Shimmin, Reproduction, Mating Strategies and Sperm Competition in Marsupials and Monotremes. M. Gomendio, A.H. Harcourt, and E.R.S. Roldan, Sperm Competition in Mammals. T.R. Birkhead and A.P. Moller, Sperm Competition, Sexual Selection and Different Routes to Fitness. Index.

Fertilization Defects in Sperm from Mice Lacking Fertilin β

Abstract: Fertilin, a member of the ADAM family, is found on the plasma membrane of mammalian sperm. Sperm from mice lacking fertilin beta were shown to be deficient in sperm-egg membrane adhesion, sperm-egg fusion, migration from the uterus into the oviduct, and binding to the egg zona pellucida. Egg activation was unaffected. The results are consistent with a direct role of fertilin in sperm-egg plasma membrane interaction. Fertilin could also have a direct role in sperm-zona binding or oviduct migration; alternatively, the effects on these functions could result from the absence of fertilin activity during spermatogenesis.

Regulation of protein phosphorylation during sperm capacitation

Abstract: After leaving the testis, mammalian spermatozoa from many species are morphologically differentiated but have acquired neither progressive motility nor the ability to fertilize a metaphase II-arrested egg. During epididymal transit, sperm acquire the ability to move progressively; however, they are still fertilization incompetent. Fertilization capacity is gained after residence in the female tract for a finite period of time. The physiological changes that confer on the sperm the ability to fertilize are collectively called ‘‘capacitation.’’ Capacitation was first described and defined independently by Chang [1, 2] and Austin [3, 4]. The definition of this poorly understood phenomenon has been modified and narrowed over the years. Although fertilization still represents the benchmark endpoint of a capacitated sperm, the ability of the sperm to undergo a regulated acrosome reaction (e.g., in response to the zona pellucida) can be taken as an earlier, upstream endpoint of this extratesticular maturational event. It must be stressed at this point that capacitation is also correlated with changes in sperm motility patterns, designated as sperm hyperactivation, in a number of species [5, 6]. There are examples of cases in which capacitation and hyperactivation can be dissociated experimentally [7], but one cannot yet argue that hyperactivation of motility represents an event completely independent of the capacitation process [6]. Therefore, when one attempts to understand the process of capacitation at the molecular level, it is necessary to consider events occurring both in the head (i.e., acrosome reaction) and in the tail (i.e., motility changes). The physiological site of capacitation in vivo is the oviduct or the uterus, depending on the species [5]. However, capacitation in vitro has been accomplished using cauda and/or ejaculated sperm incubated under a variety of conditions in defined media that mimic the electrolyte composition of the oviduct fluid. In most cases, these media contain energy substrates such as pyruvate, lactate, and glucose (depending on the species); a protein source that usually is serum albumin; NaHCO3; and Ca21. The action of these media components to promote capacitation at the molecular level is poorly understood and will be discussed in this review. This review is not intended to provide an ex-

10 – Sperm Competition in Insects: Mechanisms and the Potential for Selection

Abstract: The chapter focuses on the understanding of the mechanisms of sperm competition, which are essential for interpreting nonrandom patterns of paternity and for predicting the types of adaptations that sperm competition can generate. P2 values are often used to infer the mechanism of underlying patterns of sperm utilization: intermediate values are taken as indicative of sperm mixing while higher values of P2 are taken as evidence for sperm precedence or sperm displacement. The bimodal distribution of P2 values seen in Lepidoptera is an excellent example of how little the mean value of P2 can tell us about the patterns of sperm competition. Patterns of sperm competition can change markedly with changes in the intervals between copulations. It is clear that males can adjust the numbers of sperm ejaculated into females, depending on female quality and/or the risks of sperm competition. Thus, patterns of sperm utilization depend on the behavior of males. Alternatively, they also depend on the responses of females to males that vary in their quality as mates. Variation in the numbers of sperm inseminated into the female prior to the final mating can have marked effects on the patterns of sperm utilization.

Oxidative damage to DNA in human spermatozoa does not preclude pronucleus formation at intracytoplasmic sperm injection.

Abstract: We present the first evidence that genetically damaged human spermatozoa are able to form normal pronuclei in oocytes after intracytoplasmic sperm injection (ICSI). The role of reactive oxygen species (ROS) as a cause of chromatin and DNA damage is well recognized. The same class of molecule can be found in the semen of males with severe infertility, who remained infertile until the advent of ICSI. In this study we have investigated the role of ROS in the induction of chromatin damage, DNA strand breakage and the subsequent ability of spermatozoa to decondense and form pronuclei after ICSI. Spermatozoa from normozoospermic men participating in our research programme were exposed to oxidizing environments created by co-incubation with hydrogen peroxide, reduced nicotinamide adenine dinucleotide phosphate (NADPH) or activated white cells. The subsequent ability of the spermatozoa to decondense in vitro was examined using sequential incubations in EDTA, dithiothreitol and sodium dodecyl sulphate, and the amounts of DNA strand breakage were assessed using an in-situ nick translation protocol. Finally, cells exposed to hydrogen peroxide, NADPH and activated leukocytes were microinjected into hamster oocytes, and their ability to decondense and form normal pronuclei was determined. The results indicate that human sperm chromatin becomes cross-linked under conditions of oxidative stress and exhibits increased DNA strand breakage, yet the rate of pronucleus formation is no different from that of untreated control cells. The ability of genetically damaged spermatozoa to achieve normal fertilization following ICSI has implications for the practice of this form of assisted conception therapy.

Angiotensin-converting enzyme and male fertility

Abstract: The angiotensin-converting enzyme (ACE; EC 3.4.15.1) gene (Ace) encodes both a somatic isozyme found in blood and several other tissues, including the epididymis, and a testis-specific isozyme (testis ACE) found only in developing spermatids and mature sperm. We recently used gene targeting to disrupt the gene coding for both ACE isozymes in mice and reported that male homozygous mutants mate normally but have reduced fertility; the mutant females are fertile. Here we explore the male fertility defect. We demonstrate that ACE is important for achieving in vivo fertilization and that sperm from mice lacking both ACE isozymes show defects in transport within the oviducts and in binding to zonae pellucidae. Males generated by gene targeting that lack somatic ACE but retain testis ACE are normally fertile, establishing that somatic ACE in males is not essential for their fertility. Furthermore, male and female mice lacking angiotensinogen have normal fertility, indicating that angiotensin I is not a necessary substrate for testis ACE. Males heterozygous for the mutation inactivating both ACE isozymes sire wild-type and heterozygous offspring at an indistinguishable frequency, indicating no selection against sperm carrying the mutation.

Serum Inhibin B as a Marker of Spermatogenesis

Abstract: Inhibin B is produced by Sertoli cells, provides negative feedback on FSH secretion, and may prove to be an important marker for the functioning of seminiferous tubules. The purpose of the present study was to examine the relationship between the spermatogenic function of the testis of subfertile men and the plasma concentrations of inhibin B and FSH. These parameters were estimated in a group of 218 subfertile men. Serum inhibin B levels were closely correlated with the serum FSH levels (r 5 20.78, P , 0.001), confirming the role of inhibin B as feedback signal for FSH production. The spermatogenic function of the testis was evaluated by determining testicular volume and total sperm count. Inhibin B levels were significantly correlated with the total sperm count and testicular volume (r 5 0.54 and r 5 0.63, respectively; P , 0.001). Testicular biopsies were obtained in 22 of these men. Inhibin B was significantly correlated with the biopsy score (r 5 0.76, P , 0.001). Receiver operating characteristic analysis revealed a diagnostic accuracy of 95% for differentiating competent from impaired spermatogenesis for inhibin B, whereas for FSH, a value of 80% was found. We conclude that inhibin B is the best available endocrine marker of spermatogenesis in subfertile men. (J Clin Endocrinol Metab 83: 3110–3114, 1998)

Cryptic female choice: criteria for establishing female sperm choice.

Abstract: In this paper, I consider the criteria necessary to demonstrate the postcopulatory ability of females to favor the sperm of one conspecific male over another, that is, sperm choice. In practice it is difficult to distinguish between sperm competition and sperm choice, and sperm choice can be demonstrated only if the effects of sperm competition can be controlled. Few studies have used experimental protocols that do this, so evidence for sperm choice is limited. Moreover, in those studies in which sperm choice occurs, it does so to avoid incompatible genetic combinations and is therefore unlikely to result in directional sexual selection.

Ploidy induction and sex control in fish

Abstract: In fish, pre-embryonic events such as insemination, second polar body extrusion and first mitotic cleavage are manipulable and render 37 different types of ploidy induction possible. A classification of physical, chemical, and biological inductors of ploidy is provided. The amazing ability of fish to tolerate genomes from haploid to heptaploid, genomic contributions from the male or female parent alone, and unequal contributions from parents belonging to the same or different species is highlighted; surprisingly, a single species is amenable for 8–12 different types of ploidy induction. Advantages and limitations of different methods and live or preserved tissues for ploidy confirmation are assessed. Live haploids have been induced in Oreochromis mossambicus. With an ability to synthesize rRNAs and metabolic enzymes such as LDH, the haploid embryos are capable of normal translation and transcription, but suffer mass mortality at hatching, perhaps due to expression of lethal mutant genes. Induction of gynogenesis involves egg activation by irradiated homologous or heterologous sperm, and diploidization by retention of the second polar body (meiotic gynogenesis), or suppression of the first mitotic cleavage (mitotic gynogenesis). UV-irradiation inactivates sperm DNA maximally and avoids chromosome fragmentation. Egg activation by UV-irradiated heterologous sperm under dark conditions, and diploidization by pressure shock result in the highest survival of gynogens; meiotic gynogens survive better than mitotic gynogens. The need for confirmation of genetic purity of mitotic gynogens by one or more methods is emphasized. In different species, survival, growth and fertility improve when gynogens are generated successively for two or more generations. Combinations of induction of ploidy and hormonal sex reversal in gynogens renders the scope for generating all-male or all-female populations. In some gynogenetic species genetic homozygosity leads to growth suppression from 3 to 60% however, meiotic gynogens of Clarias macrocephalus and Paralicthys olivaceus display 18 and 35% faster growth. Hypotheses for the unexpected occurrence of males among natural and artificially induced gynogenetic populations are assessed. In a few species, reproductive performance of gynogens is not equivalent to normal females. Maximal elimination of egg genome by UV-radiation, induction of androgenesis using 2n sperm of a tetraploid, facilitation of dispermy using heterologous eggs, and activation by cryopreserved sperm are land-mark events in the history of androgenesis. In male-heterogametic species, androgenesis may produce supermales to establish broodstock for consistent production of all-male populations. In combination with cryopreservation of sperm, androgenesis may prove to be the best method for conservation of fish genomes. As many as 11 different types of triploids are inducible; and most of them require the retention of the second polar body. The yield and survival of triploids are higher than those of gynogens and these values decrease with the kind of inductor used in the following order: pressure < cold < heat shock. Usually triploidy confers sterility, especially in females, and accelerates growth during post-maturation, when reared solitarily in some (Tinca tinca, Oreochromis Mossambicus) or communally (with diploids) in other species (Oncorhynchus mykiss). The presence of two sets of maternal chromosomes does not disturb the manifestation of morphological sexual characters; however, unexpected sex ratios observed in some triploids indicate a preponderance of females in natural populations and a dominance of males in artificially induced populations. In some species, a certain percentage of female triploids are fertile. Possible pathways, through which the natural fertile triploids may form the base for evolution of tetraploids and origin of diploid new species are suggested. Triploids, especially females, suffer delayed maturity, a low gonado-somatic index, and disrupted gametogenesis due to cytogenetic and endocrine incompatibilities; males do not suffer endocrine incompatibility. Three possible pathways, through which oogenesis may be completed in these fertile triploid species, are indicated. Triploid hybridization between salmonids, which can tolerate salinity changes (e.g. chum and pink salmons) and which cannot tolerate early transfer to sea water but are desired for their meat quality (e.g. Atlantic, chinook and coho salmons) is commercially important. Triploid conspecific salmonids grow faster than diploid conspecifics or triploid hybrids. Protocols for the combination of induced ploidy and hormonal sex reversal to generate all-male, all-female or all-sterile triploid populations are described. In triploids, the increase in nuclear DNA per cell is 1.3 to 1.7 times that of diploids, which results in corresponding volumetric increase of a cell. This, in turn, imposes corresponding decreases in total cell surface area and cell number of a tissue or a triploid individual; however, such a decrease in cell surface area does not impair metabolic processes like oxygen uptake and food utilization. Data for effective temperature required to induce cold or heat shock to retain the second polar body suggest that an elevation of 18, 15 and 14 °C successfully retains the polar body in salmonids, cyprinids and cichlids; the corresponding values for the depression of temperature are 11, 19 and 21 °C, respectively. Seven different kinds of tetraploidy are inducible; however, live, feeding tetraploids have been induced in ten species only. Causes for embryonic or post-embryonic mortality of tetraploids are discussed. Increasing maternal genomic contribution and heterologous insemination appear to enhance tetraploid survival. Survival and growth of Oncorhynchus mykiss progressively improve in F1 and F2 tetraploid progenies. In a rare strain of the loach, Misgurnus anguillicaudatus, pentaploids, hexaploids and heptaploids have been successfully induced. An individual polyploid loach (3n) simultaneously spawns small, intermediate and large eggs carrying n, 2n and 3n genomes. It is not clear how during oogenesis the passage of n, 2n and 3n genomes is regulated into small, intermediate and large eggs. However, evidence from other fish species is accumulating for the simultaneous production of at least two kinds of eggs by a single female. Studies on ploidy induction have shown the magnitude of the complicated genetic mechanisms that control sex determination in fish.

16 - Sperm Competition in Mammals

Abstract: The chapter focuses on the fact that as compared to other mammals, including primates, humans are behaviorally, anatomically, and physiologically monandrous. However, sometimes multimale matings within the window of life-span of sperm and ovum also occur. Moreover, humans show adaptations to the possibility of sperm competition. The issue of sperm competition in humans still needs predictions that separate sperm competition from the alternative hypotheses. On the basis of this information, it can be inferred, that in eutherian mammals, the sperm fertile life-span tends to be short. In addition, there are no sperm-storage organs, the interactions between sperm and the female tract are complex and competition between ejaculates is in the nature of scramble competition not contesting competition. Sperm face major barriers within the female tract and the timing of mating in relation to ovulation determines male success at fertilization to a great extent. Thus, mechanisms of sperm competition in mammals appear to differ to a great extent from other taxa, in which sperm are stored within the female tract for long periods of time.

Larger sperm outcompete smaller sperm in the nematode Caenorhabditis elegans.

Abstract: Sperm competition is generally thought to drive the evolution of sperm miniaturization. Males gain advantage by transferring more sperm, which they produce by dividing limited resources into ever smaller cells. Here, we describe the opposite effect of size on the competitiveness of amoeboid sperm in the hermaphroditic nematode Caenorhabditis elegans. Larger sperm crawled faster and displaced smaller sperm, taking precedence at fertilization. Larger sperm took longer to produce, however, and so were more costly than smaller sperm. Our results provide evidence of a mechanism to support recent theoretical and comparative studies that suggest sperm competition can favour not small, but large sperm.

The effect of oral selenium supplementation on human sperm motility.

Abstract: Objectives To determine whether the decline in selenium intake and selenium status in men in the West of Scotland might be a contributory factor to male subfertility. Patients and methods Two semen samples were collected from patients attending a subfertility clinic and those patients with samples showing reduced motility were invited to participate in an ethically approved double-blind clinically controlled trial with informed consent. Sixty-nine patients were recruited and received either placebo, selenium alone or selenium plus vitamins A, C and E daily for 3 months. A further semen sample was collected at the end of the trial. Plasma selenium status was determined at the beginning and end of the trial period, as was total sperm density and motility. Results Plasma selenium concentrations were significantly (P<0.001) higher in both selenium-treated groups than in controls. No significant effect of treatment on sperm density was recorded. Sperm motility increased in both selenium-treated groups, in contrast to a slight decline in the placebo group, but the difference was not significant. However, as the provision of additional vitamins had no effect on any variable measured it was considered justified to combine the two selenium-treated groups and compare them with the placebo treatment. On this basis, selenium treatment significantly (P<0.002) increased plasma selenium concentrations and sperm motility (P=0.023) but sperm density was again unaffected. Five men (11%) achieved paternity in the treatment group, in contrast to none in the placebo group. Conclusion This trial confirms the result of an earlier study, that selenium supplementation in subfertile men with low selenium status can improve sperm motility and the chance of successful conception. However, not all patients responded; 56% showed a positive response to treatment. The low selenium status of patients not supplemented again highlights the inadequate provision of this essential element in the Scottish diet.

Predictive value of normal sperm morphology: a structured literature review

Abstract: The aim of the study was to conduct a structured review of the literature published on the use of normal sperm morphology, as an indicator of male fertility potential in the in-vitro fertilization (IVF) situation, and to establish the universal predictive value of this semen parameter. Published literature in which normal sperm morphology was used to predict fertilization and pregnancy, during the period 1978-1996, was reviewed. A total of 216 articles were identified by the sourcing methodology, but only 49 provided data that could be tabulated and analysed. Of these, only 18 provided sufficient data for statistical analysis. Fifteen studies used the strict criteria to evaluate sperm morphology, two used World Health Organization (WHO) guidelines and one used both the strict criteria and the WHO guidelines. All the studies (n = 10) using the 5 and 14% normal sperm morphology thresholds (strict criteria) produced positive predictive values for IVF success. In the prediction of pregnancy, 82% (9/11) and 75% (6/8) of the studies produced positive predictive values when using the 5% and 14% thresholds respectively. Aggregating the data produced around the 5% normal sperm morphology threshold (strict criteria), the overall fertilization rates were 59.3% (1979/3337; per oocyte) for the 4% group, and the overall pregnancy rates were 15.2% (60/395; per cycle) and 26.0% (355/1368; per cycle) respectively. The no-transfer rates across the 5% threshold were 24.0% (86/359; per cycle) in the 4% group. The inclusion of an accurately evaluated normal sperm morphology count as an integral part of the standard semen analysis makes this analysis still the most cost-effective means of evaluating the male factor.

Sperm competition in birds

Abstract: Sperm competition in birds occurs when a female is inseminated by more than one male during a single breeding cycle. Despite most birds being socially monogamous, sperm competition is widespread and results in frequent extra-pair paternity. Sperm competition is a fundamental part of sexual selection since it results in differential reproductive success among males. Male adaptations to sperm competition include relatively large testes, large sperm stores and long spermatozoa, mate guarding and frequent pair copulations. Females show no obvious morphological adaptations to sperm competition but, by controlling whether copulations are successful, they probably determine its frequency and extent. Despite this, the evolutionary benefits females acquire from extra-pair fertilizations are poorly understood. Experiments in which females are inseminated with equal numbers of spermatozoa from two males usually show last male sperm precedence. Understanding the mechanism of sperm competition requires understanding of why the last male to inseminate a female fertilizes a disproportionate number of eggs. The data from sperm competition studies on the domestic fowl, turkeys and zebra finches are consistent only with a passive sperm loss model of sperm competition. The mechanism is as follows: after insemination, spermatozoa enter the sperm storage tubules located in the oviduct, from which they are lost at a constant rate over days or weeks. All else being equal, the interval between two inseminations determines the probability of fertilization: the second of two inseminations fertilizes most eggs simply because, by the time fertilization occurs, fewer of these spermatozoa have been lost. Other factors also affect the outcome of sperm competition: the timing of insemination relative to oviposition, the differential fertilizing capacity of males and differences in the numbers of spermatozoa inseminated; as a consequence, last male sperm precedence is not automatic. On the basis of the mechanism of sperm competition, the optimal strategy for both males and females to maximize their likelihood of extra-pair fertilization is to copulate with an extra-pair partner as close as possible to the onset of oviposition.

Sperm nuclear DNA damage and altered chromatin structure: effect on fertilization and embryo development

Abstract: In the first part of this report we investigate whether chromatin anomalies in human spermatozoa can influence fertilization after intracytoplasmic sperm injection (ICSI). We have examined the sperm chromatin packaging quality using the chromomycin A3 (CMA3) fluorochrome and the presence of DNA damage in spermatozoa using in-situ nick translation. When comparing the spermatozoa of patients undergoing in-vitro fertilization (IVF) and ICSI distinct differences are evident in that ICSI males have a higher CMA3 fluorescence, indicating spermatozoa with loosely packed chromatin, and more spermatozoa containing endogenous DNA nicks. When examining the unfertilized oocytes of ICSI patients we found that men who had a high percentage of anomalies in their chromatin, i.e. > 30% CMA3 fluorescence and > 10% nicks, had more than double the number of unfertilized oocytes containing spermatozoa that had remained condensed. The observation that failed fertilized oocytes, injected with spermatozoa from patients with a higher percentage of sperm nuclear anomalies, contain more condensed spermatozoa indicates that a selection process against these spermatozoa may be in place at the time of fertilization. In the second part of the study we show that spare ICSI embryos have significantly lower rates of development to the blastocyst stage compared with those developed after routine IVF. These results show that a greater understanding of the molecular basis of male infertility is therefore needed to broaden our knowledge on the effect that abnormal spermatozoa have on fertilization and embryo development.

Analysis of mouse oocyte activation suggests the involvement of sperm perinuclear material.

Abstract: The mouse oocyte can be activated by injection of a single, intact mouse spermatozoon or its isolated head. Isolated tails are unable to activate the oocyte. Active sperm-borne oocyte-activating factor(s) (SOAF) appears during transformation of the round spermatid into the spermatozoon. The action of SOAF is not highly species-specific: mouse oocytes are activated by injection of spermatozoa from foreign species, such as the hamster, rabbit, pig, human, and even fish. Some SOAF can be extracted by simple freeze-thawing of (hamster) spermatozoa; additional SOAF is obtained by sequential treatment of spermatozoa with Triton X-100 and SDS. Electron microscopic examination of sperm heads during SOAF extraction suggests that the relatively insoluble SOAF is associated with perinuclear material. When microsurgically injected into oocytes, Triton X-100-treated sperm heads (with perinuclear material, but without any membranes) can activate the oocytes, leading to normal embryonic development. Whereas perinuclear components have been believed to play a purely structural role, these data suggest an additional function for them in oocyte activation.

Iatrogenic DNA damage induced in human spermatozoa during sperm preparation: protective significance of seminal plasma.

Abstract: Before the advent of intracytoplasmic sperm injection (ICSI) semen preparation techniques focused on the need to sustain the fertilizing potential of the spermatozoa particularly by reducing oxidative stress. However, for severely oligozoospermic patients treated by ICSI, sperm preparation protocols are used which aim to maximize sperm recovery rather than sperm function. In this study we have examined the impact of different sperm preparation techniques on oxidative stress, sperm motion and DNA integrity. Reactive oxygen species (ROS) generation was monitored using luminol-dependent chemiluminescence, seminal antioxidant activity was assessed using a total reactive antioxidant potential (TRAP) assay while sperm motility and DNA damage were evaluated using computer assisted semen analysis and in-situ nick translation respectively. The results demonstrate a significant increase in the levels of ROS generated by samples prepared by swim-up from a washed pellet compared with spermatozoa isolated directly from seminal plasma. This oxidative stress was associated with a highly significant increase in the level of DNA damage sustained by the spermatozoa while the quality of sperm motility remained largely unchanged. These results suggest that if repeated centifugation protocols are to be used to prepare spermatozoa, strategies should be developed for minimizing collateral DNA damage.

Major Proteins of Bovine Seminal Plasma and High-Density Lipoprotein Induce Cholesterol Efflux from Epididymal Sperm

Abstract: One of the hypotheses to explain the mechanism of capacitation involves the loss of sperm membrane cholesterol. Here, we studied whether or not the major proteins of bovine seminal plasma designated as BSP-A1, -A2, -A3, and -30-kDa (collectively called BSP proteins), which are implicated in sperm capacitation, induce cholesterol efflux. When epididymal sperm were labeled with [3H]cholesterol and incubated with bovine seminal plasma (0.05-2%) or BSP proteins (20-120 microg/ml) for 8 h, the sperm lost [3H]cholesterol (3.6-fold and 3-fold, respectively). The same results in the presence of BSP-A1/-A2 were obtained (3.5-fold) by direct determination of cholesterol on unlabeled epididymal sperm. Analysis of efflux particles by ultracentrifugation on a sucrose gradient revealed a single symmetrical peak of radioactivity at 1.14 g/ml. Immunoblotting of the fractions obtained from size-exclusion chromatography of the efflux particles showed that a portion of the BSP proteins were associated with [3H]cholesterol. Heparin (12 microg/ml) alone did not stimulate cholesterol efflux. In contrast, high-density lipoprotein (HDL, 100 microg/ml) alone stimulated cholesterol efflux up to 3.1-fold after 8 h. When labeled epididymal sperm were preincubated for 20 min with BSP-A1/-A2 (120 microg/ml), washed, and incubated with HDL (100 microg/ml) for 8 h, the total cholesterol efflux of the sperm suspension was 51.8 +/- 5.0% compared to 39.3 +/- 1.2% when HDL alone was used. These results indicate that BSP proteins and HDL play an important role in the sperm sterol efflux that occurs during capacitation. Furthermore, the heparin-induced sperm capacitation did not involve the efflux of sperm membrane cholesterol.

Blastocyst development from supernumerary embryos after intracytoplasmic sperm injection: a paternal influence?

Abstract: The success of intracytoplasmic sperm injection (ICSI) warrants further study on the role of paternal factors in early human embryogenesis. To investigate whether poor sperm parameters can influence embryo development, we examined the development of ICSI-fertilized embryos to the blastocyst stage. We present results of blastocyst development from supernumerary ICSI embryos after co-culture on monkey kidney epithelial cells. In addition, we compare the development of supernumerary embryos to the blastocyst stage after ICSI and in-vitro fertilization (IVF). Of 168 supernumerary ICSI embryos, 45 (26.8%) developed to blastocysts. Sperm concentration and morphology did not influence blastocyst development. In contrast, blastocysts arose from spermatozoa that had a significantly higher (P = 0.015) forward progressive motility compared with spermatozoa from those patients who failed to produce blastocysts (42.7% versus 28.2%, respectively). Overall the rate of embryo development to the blastocyst stage after ICSI was lower (26.8%) than that after IVF (47.3%). When the rate of blastocyst development was calculated for patients with three or more supernumerary embryos, it remained significantly higher for the IVF patients than for the ICSI patients (45.6% versus 30.0%). There was no significant difference in the mean cell number and quality of the supernumerary embryos between the IVF and ICSI patients. This study confirms previous reports that have postulated that abnormal spermatozoa may manifest a negative paternal effect on preimplantation embryo development.

A role for oestrogens in the male reproductive system

Abstract: Oestrogen is considered to be the 'female' hormone, whereas testosterone is considered the 'male' hormone. However, both hormones are present in both sexes. Thus sexual distinctions are not qualitative differences, but rather result from quantitative divergence in hormone concentrations and differential expressions of steroid hormone receptors. In males, oestrogen is present in low concentrations in blood, but can be extraordinarily high in semen, and as high as 250 pg ml(-1) in rete testis fluids, which is higher than serum oestradiol in the female. It is well known that male reproductive tissues express oestrogen receptors, but the role of oestrogen in male reproduction has remained unclear. Here we provide evidence of a physiological role for oestrogen in male reproductive organs. We show that oestrogen regulates the reabsorption of luminal fluid in the head of the epididymis. Disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility. This finding raises further concern over the potential direct effects of environmental oestrogens on male reproduction and reported declines in human sperm counts.