Enigmas of mammalian gamete form and function

Phosphoproteomic analysis of the adaption of epididymal epithelial cells to corticosterone challenge

BACKGROUND

The epididymis has long been of interest owing to its role in promoting the functional maturation of the male germline. More recent evidence has also implicated the epididymis as an important sensory tissue responsible for remodeling of the sperm epigenome, both under physiological conditions and in response to diverse forms of environmental stress. Despite this knowledge, the intricacies of the molecular pathways involved in regulating the adaptation of epididymal tissue to paternal stressors remains to be fully resolved.

OBJECTIVE

The overall objective of this study was to investigate the direct impact of corticosterone challenge on a tractable epididymal epithelial cell line (i.e., mECap18 cells), in terms of driving adaptation of the cellular proteome and phosphoproteome signaling networks.

MATERIALS AND METHODS

The newly developed phosphoproteomic platform EasyPhos coupled with sequencing via an Orbitrap Exploris 480 mass spectrometer, was applied to survey global changes in the mECap18 cell (phospho)proteome resulting from sub-chronic (10-day) corticosterone challenge.

RESULTS

The imposed corticosterone exposure regimen elicited relatively subtle modifications of the global mECap18 proteome (i.e., only 73 out of 4171 [∼1.8%] proteins displayed altered abundance). By contrast, ∼15% of the mECap18 phosphoproteome was substantially altered following corticosterone challenge. In silico analysis of the corresponding parent proteins revealed an activation of pathways linked to DNA damage repair and oxidative stress responses as well as a reciprocal inhibition of pathways associated with organismal death. Corticosterone challenge also induced the phosphorylation of several proteins linked to the biogenesis of microRNAs. Accordingly, orthogonal validation strategies confirmed an increase in DNA damage, which was ameliorated upon selective kinase inhibition, and an altered abundance profile of a subset of microRNAs in corticosterone-treated cells.

CONCLUSIONS

Together, these data confirm that epididymal epithelial cells are reactive to corticosterone challenge, and that their response is tightly coupled to the opposing action of cellular kinases and phosphatases.

Cryopreservation Cooling Rate Impacts Post-Thaw Sperm Motility and Survival in Litoria booroolongensis

The cryopreservation and storage of gametes (biobanking) can provide a long-term, low-cost option for the preservation of population genetic diversity and is particularly impactful when applied to manage selective breeding within conservation breeding programs (CBPs). This study aimed to develop a sperm cryopreservation protocol for the critically endangered Booroolong frog (Litoria booroolongensis) to capture founder genetics within the recently established (est. 2019) CBP for this species. Hormone-induced sperm release was achieved using established protocols, and spermic urine samples were collected over a 6-h period. Pooled spermic urine samples (n = 3 males) were divided equally between two cryoprotectant (CPA) treatments and diluted by 1:5 (sperm:CPA) with either 15% (v/v) dimethyl sulfoxide + 1% (w/v) sucrose in simplified amphibian Ringer's (SAR; CPAA) or 10% (v/v) dimethylformamide + 10% (w/v) trehalose dihydrate in SAR (CPAB). The samples were cryopreserved in 0.25 mL straws using either a programmable freezer (FrA) or an adapted dry shipper method (FrB). The thawed samples were activated via dilution in water and assessed for viability and motility using both manual assessment and computer-assisted sperm analysis (CASA; 0 h, 0.5 h post-thaw). Upon activation, the survival and recovery of motility (total motility, forward progression and velocity) of cryopreserved sperm suspensions were higher for sperm preserved using FrB than FrA, regardless of CPA composition. This work supports our long-term goal to pioneer the integration of biobanked cryopreserved sperm with population genetic management to maximize restoration program outcomes for Australian amphibian species.

New horizons in human sperm selection for assisted reproduction

Male infertility is a commonly encountered pathology that is estimated to be a contributory factor in approximately 50% of couples seeking recourse to assisted reproductive technologies. Upon clinical presentation, such males are commonly subjected to conventional diagnostic andrological practices that rely on descriptive criteria to define their fertility based on the number of morphologically normal, motile spermatozoa encountered within their ejaculate. Despite the virtual ubiquitous adoption of such diagnostic practices, they are not without their limitations and accordingly, there is now increasing awareness of the importance of assessing sperm quality in order to more accurately predict a male's fertility status. This realization raises the important question of which characteristics signify a high-quality, fertilization competent sperm cell. In this review, we reflect on recent advances in our mechanistic understanding of sperm biology and function, which are contributing to a growing armory of innovative approaches to diagnose and treat male infertility. In particular we review progress toward the implementation of precision medicine; the robust clinical adoption of which in the setting of fertility, currently lags well behind that of other fields of medicine. Despite this, research shows that the application of advanced technology platforms such as whole exome sequencing and proteomic analyses hold considerable promise in optimizing outcomes for the management of male infertility by uncovering and expanding our inventory of candidate infertility biomarkers, as well as those associated with recurrent pregnancy loss. Similarly, the development of advanced imaging technologies in tandem with machine learning artificial intelligence are poised to disrupt the fertility care paradigm by advancing our understanding of the molecular and biological causes of infertility to provide novel avenues for future diagnostics and treatments.

Morphological events at the time of oocyte maturation and sperm–egg interactions during fertilisation in a dasyurid marsupial

In marsupials there have been several studies on oocyte maturation and sperm–egg interactions at the time of fertilisation, but controversy exists as to when and how some of the processes occur. Here we present a summary of relevant data from a species of dasyurid marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata). The findings show that in oocytes of developing ovarian follicles cortical granules are produced with many of the granules sometimes initially congregating around the cytoplasmic vacuoles before migrating to the proximity of the oocyte cell membrane. During fertilisation the spermatozoon binds to the zona pellucida that surrounds the oocyte with its tail lying parallel to the long axis of the head. As the spermatozoon passes through the zona pellucida it is surrounded by the zona matrix and, when entering the egg cytoplasm, a localised area of elevated ooplasm occurs around the spermatozoon. Also, unlike a recent claim to the contrary, the head of the spermatozoon travels a considerable distance into the egg cytoplasm before chromatin decondensation occurs, an event that probably minimises the chances of chromatin disruption by the sperm tail at the time of its incorporation.

Energy Metabolism and Hyperactivation of Spermatozoa from Three Mouse Species under Capacitating Conditions

Mammalian sperm differ widely in sperm morphology, and several explanations have been presented to account for this diversity. Less is known about variation in sperm physiology and cellular processes that can give sperm cells an advantage when competing to fertilize oocytes. Capacitation of spermatozoa, a process essential for mammalian fertilization, correlates with changes in motility that result in a characteristic swimming pattern known as hyperactivation. Previous studies revealed that sperm motility and velocity depend on the amount of ATP available and, therefore, changes in sperm movement occurring during capacitation and hyperactivation may involve changes in sperm bioenergetics. Here, we examine differences in ATP levels of sperm from three mouse species (genus Mus), differing in sperm competition levels, incubated under non-capacitating and capacitating conditions, to analyse relationships between energetics, capacitation, and swimming patterns. We found that, in general terms, the amount of sperm ATP decreased more rapidly under capacitating conditions. This descent was related to the development of a hyperactivated pattern of movement in two species (M. musculus and M. spicilegus) but not in the other (M. spretus), suggesting that, in the latter, temporal dynamics and energetic demands of capacitation and hyperactivation may be decoupled or that the hyperactivation pattern differs. The decrease in ATP levels during capacitation was steeper in species with higher levels of sperm competition than in those with lower levels. Our results suggest that, during capacitation, sperm consume more ATP than under non-capacitating conditions. This higher ATP consumption may be linked to higher velocity and lateral head displacement, which are associated with hyperactivated motility.

Sperm bauplan and function and underlying processes of sperm formation and selection

The spermatozoon is a highly differentiated and polarized cell, with two main structures: the head, containing a haploid nucleus and the acrosomal exocytotic granule, and the flagellum, which generates energy and propels the cell; both structures are connected by the neck. The sperm's main aim is to participate in fertilization, thus activating development. Despite this common bauplan and function, there is an enormous diversity in structure and performance of sperm cells. For example, mammalian spermatozoa may exhibit several head patterns and overall sperm lengths ranging from ∼30 to 350 µm. Mechanisms of transport in the female tract, preparation for fertilization, and recognition of and interaction with the oocyte also show considerable variation. There has been much interest in understanding the origin of this diversity, both in evolutionary terms and in relation to mechanisms underlying sperm differentiation in the testis. Here, relationships between sperm bauplan and function are examined at two levels: first, by analyzing the selective forces that drive changes in sperm structure and physiology to understand the adaptive values of this variation and impact on male reproductive success and second, by examining cellular and molecular mechanisms of sperm formation in the testis that may explain how differentiation can give rise to such a wide array of sperm forms and functions.

Comparative genomics reveals molecular mechanisms underlying health and reproduction in cryptorchid mammals

BACKGROUND

Mammals have wide variations in testicular position, with scrotal testes in some species and ascrotal testes in others. Although cryptorchidism is hazardous to human health, some mammalian taxa are natural cryptorchids. However, the evolution of testicular position and the molecular mechanisms underlying the maintenance of health, including reproductive health, in ascrotal mammals are not clear.

RESULTS

In the present study, comparative genomics and evolutionary analyses revealed that genes associated with the extracellular matrix and muscle, contributing to the development of the gubernaculum, were involved in the evolution of testicular position in mammals. Moreover, genes related to testicular position were significantly associated with spermatogenesis and sperm fertility. These genes showed rapid evolution and the signature of positive selection, with specific substitutions in ascrotal mammals. Genes associated with testicular position were significantly enriched in functions and pathways related to cancer, DNA repair, DNA replication, and autophagy.

CONCLUSIONS

Our results revealed that alterations in gubernaculum development contributed to the evolution of testicular position in mammals and provided the first support for two hypotheses for variation in testicular position in mammals, the "cooling hypothesis", which proposes that the scrotum provides a cool environment for acutely heat-sensitive sperm and the "training hypothesis", which proposes that the scrotum develops the sperm by exposing them to an exterior environment. Further, we identified cancer resistance and DNA repair as potential protective mechanisms in natural cryptorchids. These findings provide general insights into cryptorchidism and have implications for health and infertility both in humans and domestic mammals.

Contribution of epididymal epithelial cell functions to sperm epigenetic changes and the health of progeny

BACKGROUND

Spermatozoa acquire their motility and fertilizing abilities during their maturation through the epididymis. This process is controlled by epididymal epithelial cells that possess features adapted to sense and respond to their surrounding environment and to communicate with spermatozoa. During the past decade, new intercellular communication processes have been discovered, including the secretion and transport of molecules from the epithelium to spermatozoa via extracellular vesicles (EVs), as well as sensing of the intraluminal milieu by cellular extensions.

OBJECTIVE AND RATIONALE

This review addresses recent findings regarding epididymal epithelial cell features and interactions between spermatozoa and the epididymal epithelium as well as epigenetic modifications undergone by spermatozoa during transit through the epididymal microenvironment.

SEARCH METHODS

A systematic search was conducted in Pubmed with the keyword 'epididymis'. Results were filtered on original research articles published from 2009 to 2021 and written in the English language. One hundred fifteen original articles presenting recent advancements on the epididymis contribution to sperm maturation were selected. Some additional papers cited in the primary reference were also included. A special focus was given to higher mammalian species, particularly rodents, bovines and humans, that are the most studied in this field.

OUTCOMES

This review provides novel insights into the contribution of epididymal epithelium and EVs to post-testicular sperm maturation. First, new immune cell populations have been described in the epididymis, where they are proposed to play a role in protecting the environment surrounding sperm against infections or autoimmune responses. Second, novel epididymal cell extensions, including dendrites, axopodia and primary cilia, have been identified as sensors of the environment surrounding sperm. Third, new functions have been outlined for epididymal EVs, which modify the sperm epigenetic profile and participate in transgenerational epigenetic inheritance of paternal traits.

WIDER IMPLICATIONS

Although the majority of these findings result from studies in rodents, this fundamental research will ultimately improve our knowledge of human reproductive physiopathologies. Recent discoveries linking sperm epigenetic modifications with paternal environmental exposure and progeny outcome further stress the importance of advancing fundamental research on the epididymis. From this, new therapeutic options for infertile couples and better counseling strategies may arise to increase positive health outcomes in children conceived either naturally or with ART.

Molecular insights into the divergence and diversity of post-testicular maturation strategies

Competition to achieve paternity has coerced the development of a multitude of male reproductive strategies. In one of the most well-studied examples, the spermatozoa of all mammalian species must undergo a series of physiological changes as they transit the male (epididymal maturation) and female (capacitation) reproductive tracts prior to realizing their potential to fertilize an ovum. However, the origin and adaptive advantage afforded by these intricate processes of post-testicular sperm maturation remain to be fully elucidated. Here, we review literature pertaining to the nature and the physiological role of epididymal maturation and subsequent capacitation in comparative vertebrate taxa including representative species from the avian, reptilian, and mammalian lineages. Such insights are discussed in terms of the framework they provide for helping to understand the evolutionary significance of post-testicular sperm maturation.

Sperm morphology of the Rattini – are the interspecific differences due to variation in intensity of intermale sperm competition?

It is widely accepted that in mammals a causal relationship exists between postcopulatory sexual selection and relative testes mass of the species concerned, but how much it determines sperm size and shape is debatable. Here we detailed for the largest murine rodent tribe, the Rattini, the interspecific differences in relative testes mass and sperm form. We found that residual testes mass correlates with sperm head apical hook length as well as its angle, together with tail length, and that within several lineages a few species have evolved highly divergent sperm morphology with a reduced or absent apical hook and shorter tail. Although most species have a relative testes mass of 1–4%, these derived sperm traits invariably co-occur in species with much smaller relative testes mass. We therefore suggest that high levels of intermale sperm competition maintain a sperm head with a long apical hook and long tail, whereas low levels of intermale sperm competition generally result in divergent sperm heads with a short or non-existent apical hook and shorter tail. We thus conclude that sexual selection is a major selective force in driving sperm head form and tail length in this large tribe of murine rodents.

The Molecules of Sperm Exocytosis

Exocytosis is a fundamental process used by eukaryotic cells to release biological compounds and to insert lipids and proteins in the plasma membrane. Specialized secretory cells undergo regulated exocytosis in response to physiological signals. Sperm exocytosis or acrosome reaction (AR) is essentially a regulated secretion with special characteristics. We will focus here on some of these unique features, covering the topology, kinetics, and molecular mechanisms that prepare, drive, and regulate membrane fusion during the AR. Last, we will compare acrosomal release with exocytosis in other model systems.

Heterologous murine and bovine IVF using bottlenose dolphin (Tursiops truncatus) spermatozoa

Assisted reproductive technologies are of great importance for increasing the genetic diversity in captive animals. The use of bovine or murine oocytes in heterologous IVF provides advantages compared to homologous IVF in nondomestic animals, such as the accessibility to oocytes and the availability of well-developed in vitro maturation systems. The aim of this study was to determine the heterologous IVF parameters using cryopreserved dolphin spermatozoa and zona-intact bovine or murine oocytes and to examine the nuclear chromatin status of the dolphin spermatozoa. All the processes involved in the fertilization including embryo cleavage were observed by confocal microscopy and hybrid embryo formation was confirmed by polymerase chain reaction. Heterologous bovine IVF showed no polyspermy, lower percentages of pronuclear formation, and a lower cleavage rate compared to homologous IVF group (34.8% vs. 89.3%). Heterologous murine IVF showed a lower cleavage rate than homologous IVF (9.6% vs. 77.1%). With respect to dolphin sperm chromatin, it was more stable, i.e. more resistant to EDTA-SDS decondensation than the bovine sperm chromatin. This study revealed the stability of the dolphin sperm chromatin and the ability of the dolphin spermatozoa to penetrate zona-intact bovine and murine oocytes, leading to hybrid embryo formation.

Live birth rates after MESA or TESE in men with obstructive azoospermia: is there a difference?

STUDY QUESTION

How do live birth rates compare after intracytoplasmic sperm injection (ICSI) for men with obstructive azoospermia when using sperm derived from testicular sperm extraction (TESE) versus microsurgical epididymal sperm aspiration (MESA)?

SUMMARY ANSWER

Our study suggests that proximal epididymal sperm (from MESA) result in higher live birth rates as compared with testicular sperm (from TESE) in couples where the man has obstructive azoospermia due to congenital bilateral absence of the vas deferens (CBAVD) or vasectomy.

WHAT IS KNOWN ALREADY

For couples with obstructive azoospermia, MESA (epididymal sperm) and TESE (testicular sperm) have generally been assumed to be equivalent for use in ICSI. But this assumption has never been confirmed, and this view has important clinical and basic scientific consequences.

STUDY DESIGN, SIZE, DURATION

This was a retrospective study of a consecutive cohort of 374 men with obstructive azoospermia and normal spermatogenesis, who underwent IVF and ICSI using either epididymal sperm or testicular sperm in the period 2000-2009.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study included men undergoing MESA or TESE at St. Luke's Hospital for obstructive azoospermia due to CBAVD or vasectomy.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 280 couples underwent MESA and 94 underwent TESE with ICSI. The live birth rate was 39% after MESA-ICSI and 24% after TESE-ICSI. The MESA-ICSI cycles also resulted in a significantly higher implantation rate and significantly higher clinical and ongoing pregnancy rates than the TESE-ICSI cycles. There was no significant difference in results between fresh or frozen sperm for both MESA and TESE. When adjusted for the available confounders, the odds ratio for live birth was significantly in favour of MESA-ICSI versus TESE-ICSI (OR 1.82; 95% CI 1.05-3.67). The only significant confounders were female age and ovarian reserve.

LIMITATIONS, REASONS FOR CAUTION

This is a retrospective cohort study and not a randomized clinical trial.

WIDER IMPLICATIONS OF THE FINDINGS

Our study suggests that some aspect of sperm maturation after the sperm leaves the testicle to enter the epididymis is required for the most optimal results, even when ICSI is used for fertilization.

STUDY FUNDING/COMPETING INTERESTS

No funding was used and there are no competing interests.

Spermatozoa of the old endemic rodents of Australia - the possible functional significance of their ventral processes

Spermatozoa of the plains mouse (Pseudomys australis), like those of most Australian old endemic rodents, contain, in addition to an apical hook, two further processes that extend from the upper concave surface of the head, the ventral processes. This study shows that these processes contain thiol-rich cytoskeletal proteins, which presumably help to maintain their rigidity during sperm transport, together with the overlying cell membrane having abundant intramembranous proteins. To determine the possible functional significance of these processes, an in vitro study of spermatozoon-zona binding was undertaken. The findings suggest that initial sperm binding occurs by way of the cell membrane over the acrosome of the apical hook and that, subsequently, the lateral surfaces of the ventral processes also become tightly bound to the zona matrix. These ventral processes may therefore have evolved to increase sperm adhesion to the outer zona surface and/or to enhance stabilisation of the spermatozoon at the time of zona binding and initial penetration of the egg coat.

What should it take to describe a substance or product as 'sperm-safe'

BACKGROUND

Male reproductive potential continues to be adversely affected by many environmental, industrial and pharmaceutical toxins. Pre-emptive testing for reproductive toxicological (side-)effects remains limited, or even non-existent. Many products that come into direct contact with spermatozoa lack adequate testing for the absence of adverse effects, and numerous products that are intended for exposure to spermatozoa have only a general assumption of safety based on the absence of evidence of actual harm. Such assumptions can have unfortunate adverse impacts on at-risk individuals (e.g. couples who are trying to conceive), illustrating a clear need for appropriate up-front testing to establish actual 'sperm safety'.

METHODS

After compiling a list of general areas within the review's scope, relevant literature and other information was obtained from the authors' personal professional libraries and archives, and supplemented as necessary using PubMed and Google searches. Review by co-authors identified and eliminated errors of omission or bias.

RESULTS

This review provides an overview of the broad range of substances, materials and products that can affect male fertility, especially through sperm fertilizing ability, along with a discussion of practical methods and bioassays for their evaluation. It is concluded that products can only be claimed to be 'sperm-safe' after performing objective, properly designed experimental studies; extrapolation from supposed predicate products or other assumptions cannot be trusted.

CONCLUSIONS

We call for adopting the precautionary principle, especially when exposure to a product might affect not only a couple's fertility potential but also the health of resulting offspring and perhaps future generations.

Mouse sperm acquire a new structure on the apical hook during epididymal maturation

Spermatozoa emerging from the testis undergo a maturation process in the epididymis during which they change morphologically, biochemically and physiologically to gain motility and the ability to fertilize ova. We examined mouse epididymal sperm with immunostaining and transmission electron microscopy (EM) and identified a previously unknown structure on the apical hook. The structure has a coiled configuration around 11 nm in thickness and is present at the tip of each corner of the triangular-rod shaped perforatorium. Surveying sperm isolated from various regions of the epididymis indicated that mouse sperm acquire the hook rim (HR) structure during its passage through the proximal two-thirds of the caput epididymidis. The structure withstands vigorous sonication and harsh chemical treatments and remains intact after the acrosome reaction. Its location and sturdiness suggest a function in protecting the apical hook from mechanical wear during fertilization. Our EM images of epididymal sperm also revealed additional novel structures as well as lateral asymmetry of the sperm head, indicating that mouse sperm head has a structure more complex than previously recognized.

The nerve of ovulation-inducing factor in semen

A component in seminal fluid elicits an ovulatory response and has been discovered in every species examined thus far. The existence of an ovulation-inducing factor (OIF) in seminal plasma has broad implications and evokes questions about identity, tissue sources, mechanism of action, role among species, and clinical relevance in infertility. Most of these questions remain unanswered. The goal of this study was to determine the identity of OIF in support of the hypothesis that it is a single distinct and widely conserved entity. Seminal plasma from llamas and bulls was used as representative of induced and spontaneous ovulators, respectively. A fraction isolated from llama seminal plasma by column chromatography was identified as OIF by eliciting luteinizing hormone (LH) release and ovulation in llamas. MALDI-TOF revealed a molecular mass of 13,221 Da, and 12-23 aa sequences of OIF had homology with human, porcine, bovine, and murine sequences of β nerve growth factor (β-NGF). X-ray diffraction data were used to solve the full sequence and structure of OIF as β-NGF. Neurite development and up-regulation of trkA in phaeochromocytoma (PC(12)) cells in vitro confirmed NGF-like properties of OIF. Western blot analysis of llama and bull seminal plasma confirmed immunorecognition of OIF using polyclonal mouse anti-NGF, and administration of β-NGF from mouse submandibular glands induced ovulation in llamas. We conclude that OIF in seminal plasma is β-NGF and that it is highly conserved. An endocrine route of action of NGF elucidates a previously unknown pathway for the direct influence of the male on the hypothalamo-pituitary-gonadal axis of the inseminated female.

Seminal plasma and its effect on ruminant spermatozoa during processing

Seminal plasma can both inhibit and stimulate sperm function, making its use as a supportive medium somewhat contradictory. These effects are directed by the multifunctional action of numerous inorganic and organic components, but it is the direct association of seminal plasma proteins with the sperm membrane that is thought to exert the most significant response. In vitro handling of spermatozoa in preparation for artificial insemination may involve washing, dilution, cooling, freezing, re-warming and sex-sorting. These processes can alter proteins of the sperm surface and reduce seminal plasma in the sperm environment. This, among other factors, may destabilize the sperm membrane and reduce the fertilizable lifespan of spermatozoa. Such handling-induced damage may be prevented or reversed through supplementation of seminal plasma, but the effectiveness of this technique differs with species, and the source and subsequent treatment of both spermatozoa and seminal plasma. Seminal plasma appears to act as a protective medium during in vitro processing of ram spermatozoa, but this does not appear to be the case for bull spermatozoa. The reasons for this divergent effect will be discussed with particular emphasis on the influence of the major proteins of ruminant seminal plasma, known as BSP proteins. The biochemical and biophysical properties of these proteins are well documented, and this information has provided greater insight into the signalling pathways of capacitation and the protective action of extender components.

Epididymal protein Rnase10 is required for post-testicular sperm maturation and male fertility

Eutherian spermatozoa are dependent on the environment of the proximal epididymis to complete their maturation; however, no specific epididymal factors that mediate this process have so far been identified. Here, we show that targeted disruption of the novel gene Rnase10 encoding a secreted proximal epididymal protein in the mouse results in a binding defect in spermatozoa and their inability to pass through the uterotubal junction in the female. The failure to gain the site of fertilization in the knockout spermatozoa is associated with a gradual loss of ADAM3 and ADAM6 proteins during epididymal transit. In the distal epididymis, these spermatozoa appear to lack calcium-dependent associations with the immobilizing glutinous extracellular material and are released as single, vigorously motile cells that display no tendency for head-to-head agglutination and lack affinity to the oviductal epithelium. In sperm-egg binding assay, they are unable to establish a tenacious association with the zona pellucida, yet they are capable of fertilization. Furthermore, these sperm show accelerated capacitation resulting in an overall in vitro fertilizing ability superior to that of wild-type sperm. We conclude that the physiological role of sperm adhesiveness is in the mechanism of restricted sperm entry into the oviduct rather than in sperm-egg interaction.—Krutskikh, A., Poliandri, A., Cabrera-Sharp, V., Dacheux, J. L., Poutanen, M., Huhtaniemi, I. Epididymal protein Rnase10 is required for post-testicular sperm maturation and male fertility.

Oocytes use the plasminogen-plasmin system to remove supernumerary spermatozoa

BACKGROUND

The role of the plasminogen-plasmin (PLG-PLA) system in fertilization is unknown, although its dysfunction has been associated with subfertility in humans. We have recently detected and quantified plasminogen in the oviductal fluid of two mammals and showed a reduction in sperm penetration during IVF when plasminogen is present. The objective of this study was to describe the mechanism by which PLG-PLA system regulates sperm entry into the oocyte.

METHODS AND RESULTS

By combining biochemical, functional, electron microscopic, immunocytochemical and live cell imaging methods, we show here that (i) plasminogen is activated into the protease plasmin, by gamete interaction; (ii) urokinase-type and tissue-type plasminogen activators are present in oocytes, but they are not of cortical granule origin; (iii) sperm binding to oocytes triggers the releasing of plasminogen activators and (iv) the generated plasmin causes sperm detachment from the zona pellucida.

CONCLUSIONS

Our results describe a novel mechanism for the success or failure of fertilization in mammals, by which molecules present in the oviductal environment are activated by molecules originating within the gametes. We anticipate that therapeutic up- or down-regulation of this physiological mechanism may be used to help in conception or as a contraceptive tool. Since components of the PLG-PLA system are already available as drugs for heart attacks or cancer therapies, basic research on this novel function would be rapidly transferable for clinical application.

Sperm surface changes and physiological consequences induced by sperm handling and storage

Spermatozoa interact with their immediate environment and this contact remodels the sperm surface in preparation for fertilisation. These fundamental membrane changes will be critically covered in this review with special emphasis on the very specific surface destabilisation event, capacitation. This process involves very subtle and intricate modifications of the sperm membrane including removal of suppression (decapacitation) factors and changes in the lateral organisation of the proteins and lipids of the sperm surface. Processing of sperm for assisted reproduction (storage, sex-sorting, etc.) subjects spermatozoa to numerous stressors, and it is possible that this processing overrides such delicate processes resulting in sperm instability and cell damage. To improve sperm quality, novel mechanisms must be used to stabilise the sperm surface during handling. In this review, different types of membrane stress are considered, as well as novel surface manipulation methods to improve sperm stability.

Sperm morphology in the Malagasy rodents (Muroidea: Nesomyinae)

The morphology of the spermatozoon of representative species of the subfamily Nesomyinae (Muroidea: Nesomyidae), a monophyletic group of rodents endemic to Madagascar, was examined by light and electron microscopy to determine the sperm head shape and tail length across the species. Marked interspecific differences were found to occur in both the form of the sperm head and length of the tail. The species that possess a sperm head with an apical hook, which largely contains acrosomal material, generally displayed longer sperm tails, and a species with a spatulate sperm head had the shortest tail. The association between sperm head shape and tail length mirrors that previously found in Eurasian and Australasian murine rodents. Thus, the repeated association between sperm head shape and tail length across these groups of muroid rodents clearly indicates a functional relationship between these two features. A comparison of sperm morphology of the nesomyines to that of related muroid rodents on the mainland of Africa suggests that the possession of an apical hook is the ancestral condition.

Ovulation, fertilization, and early embryonic development in the menstruating fruit bat, Carollia perspicillata

To characterize periovulatory events, reproductive tracts were collected at 12 hr intervals from captive-bred, short-tailed fruit bats, Carollia perspicillata, on days 1-3 post coitum and examined histologically. Most bats bred readily. Graafian follicles developed large antra and exhibited preovulatory expansion of the cumulus oophorus. Ovulation had occurred in some on the morning, and in most by the evening, of day 1. The single ovum was released as a secondary oocyte and fertilized in the oviductal ampulla. Ovulated secondary oocytes were loosely associated with their cumulus cells, which were lost around the initiation of fertilization. Supernumerary spermatozoa were occasionally noted attached to the zonae pellucidae of oviductal ova, but never within the perivitelline space. By day 2, most ova had reached the pronuclear stage and by day 3, early cleavage stages. Several lines of evidence indicate that C. perspicillata is a spontaneous ovulator with a functional luteal phase. Most newly mated females had recently formed, but regressing corpora lutea, and thickened (albeit menstrual) uteri despite having been housed with males only for brief periods (<23 days). Menstruation is usually periovulatory in this species. Furthermore, the interval between successive estrus periods in most mated females that failed to establish ongoing pregnancies at the first was 21-27 days. Menstruation involved substantial endometrial desquamation, plus associated bleeding, and generally extended to the evening of day 3, the last time point studied. In nearly all females with a recent corpus luteum (n = 24 of 25; 96%), the preovulatory or newly ruptured follicle was in the opposite ovary.

Selectivity in the transport of spermatozoa to oviductal reservoirs in the menstruating fruit bat, Carollia perspicillata

To better document the timing of ovulation and fertilization, female reproductive tracts were collected every 12 h from captive-bred fruit bats (Carollia perspicillata) on days 1–3 postcoitum and examined histologically. This also permitted observations on sperm transport, storage, and disposition. As the animals had previously been sexually segregated, most had been cycling and possessed menstrual uteri at the time of collection. Menstruation is periovulatory in this species. A widespread, headfirst orientation of spermatozoa to the uterine mucosa was observed in specimens apparently collected soon after insemination. Thereafter, however, this relationship was limited in most cases to the area around the entrance of each uterotubal junction (UTJ). A small number of spermatozoa also colonized the UTJs, which functioned as temporary sperm reservoirs on days 1–2. AlthoughC. perspicillatais monovular, no consistent differences were observed between the two oviducts in the pattern of sperm storage and release. Very few sperm were ever observed in the isthmus or ampulla (the site of fertilization). Menstrual debris (including fine particulate matter) and leukocytes present in the uterine cavity in most tracts did not gain access to the UTJ with the spermatozoa. Smooth muscle and abundant elastic fibers in the wall of the intramural UTJ, as well as receptors on its luminal epithelial cells, may play roles in the selective transport of spermatozoa to the fertilization site. While some spermatozoa are phagocytosed in the uterine lumen or by epithelial cells in the UTJ, the fate of most is probably expulsion into the vagina.

Oviductal secretions: will they be key factors for the future ARTs?

A variety of evolutionary processes has led to the development of different organs to ensure that internal fertilization occur successfully. Fallopian tubes are a particularly interesting example of such organs. Some of the key events during fertilization and early embryo development occur in the oviduct. Knowledge of the different components described in the oviduct is extensive. Oviductal components include hormones, growth factors and their receptors that have important roles in the physiology of the oviduct and embryo development. Other oviductal factors protect the gamete and the embryos against oxidative stress and pathogens. Different proteins and enzymes are present in the oviductal fluid and have the ability to interact with the oocyte and the sperm before the fertilization occurs. Of special interest is the oviduct-specific glycoprotein (OVGP1), a glycoprotein that is conserved in different mammals, and its association with the zona pellucida (ZP). Interaction of the oocyte with oviductal secretions leads us to emphasize the concept of 'ZP maturation' within the oviduct. The ZP changes produced in the oviduct result in an increased efficiency of the in vitro fertilization technique in some animal models, contributing in particular to the control of polyspermy and suggesting that a similar role could be played by oviductal factors in human beings. Finally, attention should be given to the presence in the oviductal fluid of several embryotrophic factors and their importance in relation to the in vivo versus in vitro developmental ability of the embryos.

Effect of FSH and progesterone on human spermatozoa cytosolic calcium

Ejaculated spermatozoa must undergo a number of modifications before fertilizing the oocyte: among these the capacitation and the acrosome reaction. Calcium signals play an essential role in these functional and structural modifications. Mature spermatozoa have few organelles and a very small cytoplasmic volume but maintain the homeostasis of [Ca(2+)](c) with great accuracy. We study Ca(2+) mobilization in human spermatozoa exposed to FSH and progesterone by measuring the [Ca(2+)](c) with the FURA-2AM method and report for the first time that the exposure to FSH (up to 98ng/ml) produced an increase of [Ca(2+)](c) to an extent comparable to that observed with 1muM progesterone. FSH and progesterone increase the spermatozoa [Ca(2+)](c) by acting primarily on calcium entry from the external medium. The effects of the two hormones on [Ca(2+)](c) were similar but not identical; the pre-treatment of progesterone blocks the effects of FSH, but not vice-versa. The increase of [Ca(2+)](c) due to FSH was more sensitive to nifedipine (VOCCs inhibitor) than that of progesterone. The effects of these hormones on calcium homeostasis may be relevant for sperm activation.

Effects of heat stress on mammalian reproduction

Heat stress can have large effects on most aspects of reproductive function in mammals. These include disruptions in spermatogenesis and oocyte development, oocyte maturation, early embryonic development, foetal and placental growth and lactation. These deleterious effects of heat stress are the result of either the hyperthermia associated with heat stress or the physiological adjustments made by the heat-stressed animal to regulate body temperature. Many effects of elevated temperature on gametes and the early embryo involve increased production of reactive oxygen species. Genetic adaptation to heat stress is possible both with respect to regulation of body temperature and cellular resistance to elevated temperature.

Male infertility, female fertility and extrapair copulations

Females that are socially bonded to a single male, either in a social monogamy or in a social polygyny, are often sexually polyandrous. Extrapair copulations (EPC) have often been suggested or rejected, on both empirical and theoretical grounds, as an important mechanism that enables females to avoid fertility risks in case their socially bonded male is infertile. Here, we explore this possibility in two steps. First, we present a mathematical model that assumes that females have no precopulatory information about male fertility, and shows that a female EPC strategy increases female reproductive success only if certain specific conditions are upheld in the nature of male infertility. In particular, these conditions require both (i) that fertile sperm precedence (FSP) is absent or incomplete within ejaculates of the same male (i.e. that an infertile male is, at least partly, truly infertile), and (ii) the existence of FSP among ejaculates of different males (such that infertile spermatozoa of the infertile male are at a disadvantage when competing against spermatozoa of a fertile male). Second, to evaluate their potential role in the evolution of female EPC, we review the abundance and FSP patterns of the different male infertility types. The conclusion is drawn that some common infertility types, such as poor sperm count or motility, contribute to the evolution of female EPC, whereas other common infertility types, such as sperm depletion or allocation in a social monogamy (but not in a social polygyny), and in particular male driven polyspermy, do not. Also, a deeper look at the arms race between sperm fertilization efficiency and female barriers to sperm may answer the non-trivial question: "why are some types of infertility so common?"

Oviduct-specific glycoprotein and heparin modulate sperm-zona pellucida interaction during fertilization and contribute to the control of polyspermy

Polyspermy is an important anomaly of fertilization in placental mammals, causing premature death of the embryo. It is especially frequent under in vitro conditions, complicating the successful generation of viable embryos. A block to polyspermy develops as a result of changes after sperm entry (i.e., cortical granule exocytosis). However, additional factors may play an important role in regulating polyspermy by acting on gametes before sperm-oocyte interaction. Most studies have used rodents as models, but ungulates may differ in mechanisms preventing polyspermy. We hypothesize that zona pellucida (ZP) changes during transit of the oocyte along the oviductal ampulla modulate the interaction with spermatozoa, contributing to the regulation of polyspermy. We report here that periovulatory oviductal fluid (OF) from sows and heifers increases (both, con- and heterospecifically) ZP resistance to digestion with pronase (a parameter commonly used to measure the block to polyspermy), changing from digestion times of approximately 1 min (pig) or 2 min (cattle) to 45 min (pig) or several hours (cattle). Exposure of oocytes to OF increases monospermy after in vitro fertilization in both species, and in pigs, sperm-ZP binding decreases. The resistance of OF-exposed oocytes to pronase was abolished by exposure to heparin-depleted medium; in a medium with heparin it was not altered. Proteomic analysis of the content released in the heparin-depleted medium after removal of OF-exposed oocytes allowed the isolation and identification of oviduct-specific glycoprotein. Thus, an oviduct-specific glycoprotein-heparin protein complex seems to be responsible for ZP changes in the oviduct before fertilization, affecting sperm binding and contributing to the regulation of polyspermy.

Testis size, sperm characteristics and testosterone concentrations in four species of shrews (Mammalia, Soricidae)

The aim of this study was to establish and compare the sperm characteristics in four shrew species in the context of the sperm competition hypothesis. As expected, the large relative testis size in promiscuous species was associated with a high number of cauda epididymal spermatozoa and a high concentration of circulating testosterone. In addition, in Sorex and Neomys, species with high intensity of sperm competition, the spermatozoa stored in cauda epididymis were characterized by high percentage of progressive motility whereas in Crocidura and Suncus, the cauda epididymal spermatozoa were motile but with very low percentage of progressive motility. This capability is achieved only following the passage through the vas gland, a specialized region for sperm storage located along the vas deferens in these shrew species. The hypothesis that sperm competition is positively correlated with spermatozoa length could not be confirmed. In Crocidura and Suncus, the total sperm length is increased by the large sperm head due to a big acrosome. This trait, specific to the subfamily Crocidurinae, may results from a selective pressure independent of the context of sperm competition, related to a specific, but as yet unclear role, for the acrosome during the fertilization.