Mice lacking two sperm serine proteases, ACR and PRSS21, are subfertile, but the mutant sperm are infertile in vitro

GPI-anchored serine proteases: essential roles in development, homeostasis, and disease

The glycosylphosphatidylinositol (GPI)-anchored serine proteases, prostasin and testisin, have essential roles in diverse physiological functions including development, reproduction, homeostasis and barrier function of epithelia, angiogenesis, coagulation, and fibrinolysis. Important functions in pathological conditions such as cancer, kidney disease and cardiovascular disease have also been reported. In this review, we summarize current knowledge of the cellular and in vivo roles of prostasin and testisin in physiology and pathophysiology and explore the underlying molecular mechanisms. We discuss how new insights of their role in cancer and cardiovascular disease may facilitate translation into clinical settings in the future.

Fertilization mechanisms in hermaphroditic ascidians and nematodes: Common mechanisms with mammals and plants

Most animals have male and female, whereas flowering plants are hermaphrodites. Exceptionally, a small population of invertebrates, including ascidians and nematodes, has hermaphrodite in reproductive strategies. Several ascidians exhibit strict self-sterility (or self-incompatibility), similar to flowering plants. Such a self-incompatibility mechanism in ascidian has been revealed to be very similar to those of flowering plants. Here, we describe the mechanisms of ascidian fertilization shared with invertebrates and mammals, as well as with plants. In the nematode Caenorhabditis elegans, having self-fertile hermaphrodite and male, several genes responsible for fertilization are homologous to those of mammals. Thus, novel proteins responsible for fertilization will be easily disclosed by the analyses of sterile mutants. In this review, we focus on the same or similar reproductive strategies by shedding lights on the common mechanisms of fertilization, particularly in hermaphrodites.

Molecular Evolution of the Ovgp1 Gene in the Subfamily Murinae

OGP, encoded by the Ovgp1 gene, is the major non-serum oviductal protein in most mammals. In the genome of Rattus norvegicus, Ovgp1 has been identified as a pseudogene. However, Mus musculus presents a functional gene. As the rat and the mouse belong to the subfamily Murinae, Ovgp1 has probably been lost after their divergence. This study aims to determine when the pseudogenization event occurred and which proteins could replace its function. To attain that, the potential expression of members belonging to the GH18 family is investigated in the rat oviduct by means of molecular and proteomic analyses. Specific Ovgp1 regions are sequenced in different murine rodent species. The analysis reveals the presence of stop codons only in some species of the Rattini tribe, suggesting that the majority of the murine species present a functional gene. Thus, the pseudogenization of Ovgp1 could be dated back to around 10 Mya, after the divergence of the Rattini tribe. The expression of several genes and proteins of the GH18 family, such as Chia, Chit1, Chi3l1, and Chid1, are detected in the rat oviduct. This study opens the door for further research on GH18 family proteins that mimic the OGP functions in species where Ovgp1 is pseudogenized.

Age-associated aberrations of the cumulus-oocyte interaction and in the zona pellucida structure reduce fertility in female mice

One of the major age-related declines in female reproductive function is the reduced quantity and quality of oocytes. Here we demonstrate that structural changes in the zona pellucida (ZP) were associated with decreased fertilization rates from 34- to 38-week-old female mice, equivalent to the mid-reproductive of human females. In middle-aged mouse ovaries, the decline in the number of transzonal projections was accompanied by a decrease in cumulus cell-oocyte interactions, resulting in a deterioration of the oocyte quality. Scanning electron microscopy showed the ZP surface microfilament structure transitioning from rugged to smooth with aging, leading to decreased fertilization rates due to impaired sperm binding to the ZP. Moreover, the fertilization rate of middle-aged mice was restored to a comparable level to that of young mice by destabilizing the ZP in the presence of glutathione. These results suggest that the age-related structural changes in the ZP are key for successful fertilization at reproductive age.

Involvement of Metalloproteases in the Fertilization of the Ascidian Halocynthia roretzi

We previously reported that five astacin-like metalloproteases with thrombospondin type-1 repeats (Tasts) located on the sperm surface are a promising candidate as the protease involved in sperm penetration of the vitelline coat (VC) during fertilization of the ascidian Ciona intestinalis type A (Phlebobranchia). However, whether such a protease is involved in the fertilization of other ascidians is unknown. Here, we investigated the effects of four metalloprotease inhibitors on the fertilization of the ascidian Halocynthia roretzi (Stolidobranchia). Three metalloprotease inhibitors, GM6001, TAPI-0, and TAPI-1, strongly inhibited fertilization at 33 and 11 μM, whereas TAPI-2 weakly inhibited fertilization at 33 μM. In contrast, GM6001NC (negative control) had no effect on fertilization at 100 μM. Furthermore, GM6001 had no inhibitory effect on the fertilization of VC-deprived eggs. The metalloprotease appears to function at the middle or late stage of fertilization. Ten Tast genes were identified in the H. roretzi genome database, among which four genes (HrTast1, HrTast2b, HrTast2c, and HrTast3c) possessed a single transmembrane domain in the N-terminal region. These four genes are transcribed in the testis and ovary, as revealed by RT-PCR. Anti-HrTast2c IgG raised against a peptide corresponding to the Zn-binding consensus sequence weakly inhibited fertilization at 0.5 mg/mL. These results led us to propose that sperm astacin-like metalloproteases may be involved in sperm penetration of the VC during H. roretzi fertilization.

Intersection of Coagulation and Fibrinolysis by the Glycosylphosphatidylinositol (GPI)-Anchored Serine Protease Testisin

Hemostasis is a delicate balance between coagulation and fibrinolysis that regulates the formation and removal of fibrin, respectively. Positive and negative feedback loops and crosstalk between coagulation and fibrinolytic serine proteases maintain the hemostatic balance to prevent both excessive bleeding and thrombosis. Here, we identify a novel role for the glycosylphosphatidylinositol (GPI)-anchored serine protease testisin in the regulation of pericellular hemostasis. Using in vitro cell-based fibrin generation assays, we found that the expression of catalytically active testisin on the cell surface accelerates thrombin-dependent fibrin polymerization, and intriguingly, that it subsequently promotes accelerated fibrinolysis. We find that the testisin-dependent fibrin formation is inhibited by rivaroxaban, a specific inhibitor of the central prothrombin-activating serine protease factor Xa (FXa), demonstrating that cell-surface testisin acts upstream of factor X (FX) to promote fibrin formation at the cell surface. Unexpectedly, testisin was also found to accelerate fibrinolysis by stimulating the plasmin-dependent degradation of fibrin and enhancing plasmin-dependent cell invasion through polymerized fibrin. Testisin was not a direct activator of plasminogen, but it is able to induce zymogen cleavage and the activation of pro-urokinase plasminogen activator (pro-uPA), which converts plasminogen to plasmin. These data identify a new proteolytic component that can regulate pericellular hemostatic cascades at the cell surface, which has implications for angiogenesis, cancer biology, and male fertility.

Deficiency of cancer/testis antigen gene CT55 causes male infertility in humans and mice

The Cancer/Testis Antigen (CTA) genes comprise a group of genes whose expression under physiological conditions is restricted to the testis but is activated in many human cancers. Depending on the particular expression pattern, the CTA genes are speculated to play a role in spermatogenesis, but evidence is limited thus far. Here, we reported patients with a hemizygous nonsense mutation in cancer-testis antigen 55 (CT55) suffering from male infertility with extreme disruption in sperm production, morphology, and locomotion. Specifically, the insufficiency of sperm individualization, excessive residue of unnecessary cytoplasm, and defects in acrosome development were evident in the spermatozoa of the patients. Furthermore, mouse models with depletion of Ct55 showed accelerated infertility with age, mimicking the defects in sperm individualization, unnecessary cytoplasm removal, and meanwhile exhibiting the disrupted cumulus-oocyte complex penetration. Mechanistically, our functional experiments uncovered CT55 as a new autophagic manipulator to regulate spermatogenesis via selectively interacting with LAMP2 and GABARAP (which are key regulators in the autophagy process) and further fine-tuning their expression. Therefore, our findings revealed CT55 as a novel CTA gene involved in spermatogenesis due to its unprecedented autophagy activity.

1α,25-dihydroxyvitamin D3 supplementation alleviates perfluorooctanesulfonate acid-induced reproductive injury in male mice: Modulation of Nrf2 mediated oxidative stress response

Perfluorooctanesulfonate acid (PFOS) is a typical persistent organic pollutant that widely exists in the environment. To clarify the toxic effects and mechanisms of PFOS and to find effective intervention strategies have been attracted global attention. Here, we investigated the effects of PFOS on the male reproductive system and explored the potential protective role of 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂ D₃ ). Our results showed that 1α,25(OH)₂ D₃ intervention significantly improved PFOS-induced sperm quality decline and testicular damage. Moreover, 1α,25(OH)₂ D₃ aggrandized the total antioxidant capacity. Furthermore, after PFOS exposure, the transcription factor nuclear factor erythroid-related factor 2 (Nrf2) was adaptively increased together with its target genes, such as HO-1, NQO1, and SOD2. Meanwhile, 1α,25(OH)₂ D₃ ameliorated PFOS-induced augment of Nrf2 and target genes. These findings indicated that 1α,25(OH)₂ D₃ might attenuate PFOS-induced reproductive injury in male mice via Nrf2-mediated oxidative stress.

Testis-specific serine protease PRSS54 regulates acrosomal granule localization and sperm head morphogenesis in mice

Serine proteases (PRSS) constitute nearly one-third of all proteases, and many of them have been identified to be testis-specific and play significant roles during sperm development and male reproduction. PRSS54 is one of the testis-specific PRSS in mouse and human but its physiological function remains largely unclear. In the present study, we demonstrate in detail that PRSS54 exists not only in testis but also in mature sperm, exhibiting a change in protein size from 50 kDa in testis to 42 kDa in sperm. Loss of PRSS54 in mice results in male subfertility, acrosome deformation, defective sperm-zona penetration, and phenotypes of male subfertility and acrosome deformation can be rescued by Prss54 transgene. Ultrastructure analyses by transmission electronic microscopy further reveal various morphological abnormalities of Prss54-/- spermatids during spermiogenesis, including unfused vacuoles in acrosome, detachment and eccentrical localization of the acrosomal granules, and asymmetrical elongation of the nucleus. Subcellular localization of PRSS54 display that it appears in the acrosomal granule at the early phase of acrosome biogenesis, then extends along the inner acrosomal membrane, and ultimately presents in the acrosome region of the mature sperm. PRSS54 interacts with acrosomal proteins ZPBP1, ZPBP2, ACRBP and ZP3R, and loss of PRSS54 affects the distribution of these proteins in testis and sperm, although their protein levels are largely unaffected. Moreover, Prss54-/- sperm are more sensitive to acrosome reaction inducers. These data indicate that PRSS54 is an acrosomal protein and plays an important role in regulating acrosome biogenesis, sperm function and male fertility.

Insights into the source, mechanism and biotechnological applications of hyaluronidases

It has long been found that hyaluronidases exist in a variety of organisms, playing their roles in various biological processes including infection, envenomation and metabolic regulation through degrading hyaluronan. However, exploiting them as a bioresource for specific applications had not been extensively studied until the latest decades. In recent years, new application scenarios have been developed, which extended the field of application, and emphasized the research value of hyaluronidase. This critical review comprehensively summarizes existing studies on hyaluronidase from different source, particularly in their structures, action patterns, and biological functions in human and mammals. Furthermore, we give in-depth insight into the resource mining and protein engineering process of hyaluronidase, as well as strategies for their high-level production, indicating that mixed strategies should be adopted to obtain well-performing hyaluronidase with efficiency. In addition, advances in application of hyaluronidase were summarized and discussed. Finally, prospects for future researches are proposed, highlighting the importance of further investigation into the characteristics of hyaluronidases, and the necessity of investigating their products for the development of their application value.

Serine protease inhibitor disrupts sperm motility leading to reduced fertility in female mice†

Inhibition of the sperm transport process in the female reproductive tract could lead to infertility. We previously showed that a pan-serine protease inhibitor, 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF), blocked semen liquefaction in vivo and resulted in a drastic decrease in the number of sperm in the oviduct of female mice. In this study, we used a mouse model to test the efficacy of AEBSF as a reversible contraceptive, a sperm motility inhibitor, and a spermicide. Additionally, this study evaluated the toxicity of AEBSF on mouse vaginal tissues in vivo and human endocervical cells in vitro. We found that female mice treated with AEBSF had significantly less pups born per litter as well as fertilization rates in vivo compared to the vehicle control. We then showed that AEBSF reduced sperm motility and fertilization capability in vitro in a dose-dependent manner. Furthermore, AEBSF also exhibited spermicidal effects. Lastly, AEBSF treatment in female mice for 10 min or 3 consecutive days did not alter vaginal cell viability in vivo, similar to that of the vehicle and non-treated controls. However, AEBSF decreased cell viability of human ectocervical (ECT) cell line in vitro, suggesting that cells in the lower reproductive tract in mice and humans responded differently to AEBSF. In summary, our study showed that AEBSF can be used as a prototype compound for the further development of novel non-hormonal contraceptives for women by targeting sperm transport in the female reproductive tract.

Protease propeptide structures, mechanisms of activation, and functions

Proteases are a diverse group of hydrolytic enzymes, ranging from single-domain catalytic molecules to sophisticated multi-functional macromolecules. Human proteases are divided into five mechanistic classes: aspartate, cysteine, metallo, serine and threonine proteases, based on the catalytic mechanism of hydrolysis. As a protective mechanism against uncontrolled proteolysis, proteases are often produced and secreted as inactive precursors, called zymogens, containing inhibitory N-terminal propeptides. Protease propeptide structures vary considerably in length, ranging from dipeptides and propeptides of about 10 amino acids to complex multifunctional prodomains with hundreds of residues. Interestingly, sequence analysis of the different protease domains has demonstrated that propeptide sequences present higher heterogeneity compared with their catalytic domains. Therefore, we suggest that protease inhibition targeting propeptides might be more specific and have less off-target effects than classical inhibitors. The roles of propeptides, besides keeping protease latency, include correct folding of proteases, compartmentalization, liganding, and functional modulation. Changes in the propeptide sequence, thus, have a tremendous impact on the cognate enzymes. Small modifications of the propeptide sequences modulate the activity of the enzymes, which may be useful as a therapeutic strategy. This review provides an overview of known human proteases, with a focus on the role of their propeptides. We review propeptide functions, activation mechanisms, and possible therapeutic applications.

Acrosin is essential for sperm penetration through the zona pellucida in hamsters

During natural fertilization, mammalian spermatozoa must pass through the zona pellucida before reaching the plasma membrane of the oocyte. It is assumed that this step involves partial lysis of the zona by sperm acrosomal enzymes, but there has been no unequivocal evidence to support this view. Here we present evidence that acrosin, an acrosomal serine protease, plays an essential role in sperm penetration of the zona. We generated acrosin-knockout (KO) hamsters, using an in vivo transfection CRISPR/Cas9 system. Homozygous mutant males were completely sterile. Acrosin-KO spermatozoa ascended the female genital tract and reached ovulated oocytes in the oviduct ampulla, but never fertilized them. In vitro fertilization (IVF) experiments revealed that mutant spermatozoa attached to the zona, but failed to penetrate it. When the zona pellucida was removed before IVF, all oocytes were fertilized. This indicates that in hamsters, acrosin plays an indispensable role in allowing fertilizing spermatozoa to penetrate the zona. This study also suggests that the KO hamster system would be a useful model for identifying new gene functions or analyzing human and animal disorders because of its technical facility and reproducibility.

Sperm-egg interaction and fertilization: past, present, and future

Fifty years have passed since the findings of capacitation and acrosome reaction. These discoveries and the extensive effort of researchers led to the success of in vitro fertilization, which has become a top choice for patients at infertility clinics today. The effort to understand the mechanism of fertilization is ongoing, but the small number of eggs and similarly small quantity of spermatozoa continue to hinder biochemical experiments. The emergence of transgenic animals and gene disruption techniques has had a significant effect on fertilization research. Factors considered important in the early years were shown not to be essential and were replaced by newly found proteins. However, there is much about sperm-egg interaction which remains to be learned before we can outline the mechanism of fertilization. In fact, our understanding of sperm-egg interaction is entering a new stage. Progress in transgenic spermatozoa helped us to observe the behavior of spermatozoa in vivo and/or at the moment of sperm-egg fusion. These advancements are discussed together with the paradigm-shifting research in related fields to help us picture the direction which fertilization research may take in the future.

Fluoride Interferes with the Sperm Fertilizing Ability via Downregulated SPAM1, ACR, and PRSS21 Expression in Rat Epididymis

Fluoride is a widespread environmental pollutant that can induce low sperm quality and fertilizing ability; however, the underlying mechanism still remains unclear. Hence, we aimed to investigate the influence of fluoride on the sperm fertilizing ability via some key proteins in the epididymis. For this, 40 adult rats were assigned randomly into four groups. The control group was given distilled water, while the other three groups were given 25, 50, and 100 mg of NaF/L via drinking water for 56 days, respectively. After 1 day, epididymides were processed for sperm-egg binding, RNA extraction, western blot, and immunofluorescence analysis. Fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer. A further study revealed that fluoride altered the expression levels of genes and proteins related to acrosome reaction in vivo, including SPAM1, ACR, and PRSS21. However, fluoride only affected the expression of the ACR protein only in the epididymis but not in the testis. Fluoride also affected the expression levels of the membrane proteins CD9 and CD81 of epididymosomes in the epididymis. From the results, it can be concluded that fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer, which could be one of the reasons for decreased fertility ability in males treated with fluoride. These results provide some theoretical guidance and new ideas for treatments of low fertility, infertility, and other reproductive diseases.

Behavior of ACRBP-deficient mouse sperm in the female reproductive tract

Gene-knockout mice lacking ACRBP, a proacrosin-binding protein localized in the acrosome of sperm, have been shown to exhibit male subfertility, owing to abnormal formation of the acrosome. In this study, to elucidate the mechanism contributing to the subfertility phenotype, we examined the behavior of ACRBP-deficient mouse sperm in the female reproductive tract. When sperm that had migrated into the uterus and oviduct after mating were counted, the number of ACRBP-deficient sperm was noticeably smaller in the oviduct of mice post mating. However, ACRBP-deficient sperm recovered from the oviduct possessed morphologically normal head shape and retained normal motility. Importantly, ACRBP-deficient sperm displayed a marked reduction in the ability to successfully gain access to unfertilized oocytes. These data suggest that male subfertility of ACRBP-deficient mice may be attributed to incompleteness of the acrosome reaction rather than impairment in sperm migration from the uterus to the oviduct.

The serine protease testisin is present on the surface of capacitated stallion spermatozoa and interacts with key zona pellucida binding proteins

BACKGROUND AND OBJECTIVES

Serine proteases are emerging as important players in the spermatozoon's acquisition of functional competence. This study aimed to characterize the serine protease testisin (PRSS21) in stallion spermatozoa, examining its surface expression, possible origins in the testis and epididymis, and changes in response to capacitation and acrosome reaction, as well as its capacity to form high molecular weight complexes and interact with other proteins.

MATERIALS AND METHODS

The role of serine proteases in spontaneous capacitation and acrosome reaction of stallion spermatozoa was established using the serine protease inhibitor, AEBSF. Testisin localization, before and after exposure of stallion spermatozoa to capacitating conditions and calcium ionophore, was examined using live cell immunofluorescence and flow cytometry. Immunohistochemistry of testicular and epididymal tissues was used to further dissect the origins of sperm testisin. Testisin's participation in high molecular weight protein complexes and identification of its interacting partner proteins were investigated using Blue Native PAGE, co-immunoprecipitation, and mass spectrometry, with interrogation of protein-protein interaction databases and gene ontology analysis of partner proteins used to further explore the potential roles of the testisin-containing complex in sperm function.

RESULTS

Testisin surface expression increased significantly in capacitated spermatozoa (p < 0.001), increased further following acrosome reaction (p < 0.01), and was localized to the equatorial region of the sperm head. Testisin was also detected in luminal fluid within the caput and corpus regions of the epididymis, epididymal spermatozoa, and epididymal epithelial cells. Testisin formed several multiprotein complexes; co-immunoprecipitation revealed interactions of testisin with a multitude of zona pellucida-binding proteins, including ZPBP, ZAN, acrosin, several heat-shock proteins, and components of the TCP1 complex.

CONCLUSION

Testisin appears to form part of the zona pellucida-binding complex in stallion spermatozoa and may be involved in the proteolytic cascade that prepares the sperm surface for interaction with the oocyte.

A delayed sperm penetration of cumulus layers by disruption of acrosin gene in rats

Acrosin, the trypsin-like serine protease in the sperm acrosome, was long viewed as a key enzyme required for zona pellucida penetration to fertilize eggs. However, gene disruption experiments in mice surprisingly showed that acrosin-disrupted males were fertile. Thus, the acrosin was considered to be not an essential enzyme for fertilization in mice. However, the involvement of acrosin in fertilization has been suggested in various species such as rat, bull, and pig. Moreover, it has been reported that serine protease (including acrosin) activity in mice is significantly weaker compared to other species, including rats. We analyzed the role of acrosin by disrupting the rat acrosin gene. It was found that, unlike in mice, acrosin was almost the sole source of serine protease in rat spermatozoa. Nevertheless, the acrosin-disrupted males were not infertile. However, the litter size from acrosin-disrupted males was decreased compared to heterozygous mutant rats. Further investigation using an in vitro fertilization system revealed that the acrosin-disrupted spermatozoa possessed an equal ability to penetrate the zona pellucida with wild-type spermatozoa, but the cumulus cell dispersal was slower compared to wild-type and heterozygous spermatozoa. This delay was presumed to be the cause of the small litter size of acrosin-disrupted male rats.

Membrane-Anchored Serine Proteases: Host Cell Factors in Proteolytic Activation of Viral Glycoproteins

Over one third of all known proteolytic enzymes are serine proteases. Among these, the trypsin-like serine proteases comprise one of the best characterized subfamilies due to their essential roles in blood coagulation, food digestion, fibrinolysis, or immunity. Trypsin-like serine proteases possess primary substrate specificity for basic amino acids. Most of the well-characterized trypsin-like proteases such as trypsin, plasmin, or urokinase are soluble proteases that are secreted into the extracellular environment. At the turn of the millennium, a number of novel trypsin-like serine proteases have been identified that are anchored in the cell membrane, either by a transmembrane domain at the N- or C-terminus or via a glycosylphosphatidylinositol (GPI) linkage. Meanwhile more than 20 membrane-anchored serine proteases (MASPs) have been identified in human and mouse, and some of them have emerged as key regulators of mammalian development and homeostasis. Thus, the MASP corin and TMPRSS6/matriptase-2 have been demonstrated to be the activators of the atrial natriuretic peptide (ANP) and key regulator of hepcidin expression, respectively. Furthermore, MASPs have been recognized as host cell factors activating respiratory viruses including influenza virus as well as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) coronaviruses. In particular, transmembrane protease serine S1 member 2 (TMPRSS2) has been shown to be essential for proteolytic activation and consequently spread and pathogenesis of a number of influenza A viruses in mice and as a factor associated with severe influenza virus infection in humans.

This review gives an overview on the physiological functions of the fascinating and rapidly evolving group of MASPs and a summary of the current knowledge on their role in proteolytic activation of viral fusion proteins.

Factors controlling sperm migration through the oviduct revealed by gene-modified mouse models

Mammalian fertilization is comprised of many steps including sperm survival in the uterus, sperm migration in the female reproductive tract, physiological and morphological changes to the spermatozoa, and sperm-egg interaction in the oviduct. In vitro studies have revealed essential factors for these fertilization steps for over half a century. However, the molecular mechanism of fertilization has recently been revised by the emergence of genetically modified animals. Here, we focus on essential factors for sperm fertilizing ability and describe recent advances in our knowledge of the mechanisms of mammalian fertilization, especially of sperm migration from the uterus into the oviduct.

Knockout of Murine Mamld1 Impairs Testicular Growth and Daily Sperm Production but Permits Normal Postnatal Androgen Production and Fertility

MAMLD1 has been implicated in testicular function in both human and mouse fetuses. Although three patients with MAMLD1 mutations were reported to have hypergonadotropic hypogonadism in their teens, the functional significance of MAMLD1 in the postnatal testis remains unclear. Here, we analyzed the phenotype of Mamld1 knockout (KO) male mice at reproductive ages. The reproductive organs of KO male mice were morphologically unremarkable, except for relatively small testes. Seminiferous tubule size and number of proliferating spermatogonia/spermatocytes were reduced in the KO testis. Daily sperm production of KO mice was mildly attenuated, whereas total sperm counts in epididymal semen remained normal. Sperm motility and morphology, as well as androgen levels in serum and testicular tissues and the number of pups born from cross-mated wildtype (WT) female mice, were comparable between WT and KO male mice. These results indicate that MAMLD1 contributes to the maintenance of postnatal testicular growth and daily sperm production but is dispensable for androgen biosynthesis and fertility. MAMLD1 likely plays supporting roles in multiple and continuous steps of male reproduction.

The molecular basis and reproductive function(s) of copulatory plugs

In many animals, male ejaculates coagulate to form what has been termed a copulatory plug, a structure that varies in size and shape but often fills and seals the female's reproductive tract. The first published observation of a copulatory plug in a mammal was made more than 160 years ago, and questions about its formation and role in reproduction continue to endear evolutionary and population geneticists, behavioral ecologists, and molecular, reproductive, and developmental biologists alike. Here, we review the current knowledge of copulatory plugs, focusing on rodents and asking two main questions: how is it formed and what does it do? An evolutionary biology perspective helps us understand the latter, potentially leading to insights into the selective regimes that have shaped the diversity of this structure. Mol. Reprod. Dev. 83: 755-767, 2016 © 2016 Wiley Periodicals, Inc.

Targeting the membrane-anchored serine protease testisin with a novel engineered anthrax toxin prodrug to kill tumor cells and reduce tumor burden

The membrane-anchored serine proteases are a unique group of trypsin-like serine proteases that are tethered to the cell surface via transmembrane domains or glycosyl-phosphatidylinositol-anchors. Overexpressed in tumors, with pro-tumorigenic properties, they are attractive targets for protease-activated prodrug-like anti-tumor therapies. Here, we sought to engineer anthrax toxin protective antigen (PrAg), which is proteolytically activated on the cell surface by the proprotein convertase furin to instead be activated by tumor cell-expressed membrane-anchored serine proteases to function as a tumoricidal agent. PrAg's native activation sequence was mutated to a sequence derived from protein C inhibitor (PCI) that can be cleaved by membrane-anchored serine proteases, to generate the mutant protein PrAg-PCIS. PrAg-PCIS was resistant to furin cleavage in vitro, yet cytotoxic to multiple human tumor cell lines when combined with FP59, a chimeric anthrax toxin lethal factor-Pseudomonas exotoxin fusion protein. Molecular analyses showed that PrAg-PCIS can be cleaved in vitro by several serine proteases including the membrane-anchored serine protease testisin, and mediates increased killing of testisin-expressing tumor cells. Treatment with PrAg-PCIS also potently attenuated the growth of testisin-expressing xenograft tumors in mice. The data indicates PrAg can be engineered to target tumor cell-expressed membrane-anchored serine proteases to function as a potent tumoricidal agent.

The Acrosomal Matrix

The acrosome, a single exocytotic vesicle on the head of sperm, has an essential role in fertilization, but the exact mechanisms by which it facilitates sperm-egg interactions remain unresolved. The acrosome contains dozens of secretory proteins that are packaged into the forming structure during spermatogenesis; many of these proteins are localized into specific topographical areas of the acrosome, while others are more diffusely distributed. Acrosomal proteins can also be biochemically classified as components of the acrosomal matrix, a large, relatively insoluble complex, or as soluble proteins. This review focuses on recent findings using genetically modified mice (gene knockouts and transgenic "green acrosome" mice) to study the effects of eliminating acrosomal matrix-associated proteins on sperm structure and function. Some gene knockouts produce infertile phenotypes with obviously missing, specific activities that affect acrosome biogenesis during spermatogenesis or interfere with acrosome function in mature sperm. Mutations that delete some components produce fertile phenotypes with subtler effects that provide useful insights into acrosomal matrix function in fertilization. In general, these studies enable the reassessment of paradigms to explain acrosome formation and function and provide novel, objective insights into the roles of acrosomal matrix proteins in fertilization. The use of genetically engineered mouse models has yielded new mechanistic information that complements recent, important in vivo imaging studies.

Biogenesis of sperm acrosome is regulated by pre-mRNA alternative splicing of Acrbp in the mouse

Proper biogenesis of a sperm-specific organelle, the acrosome, is essential for gamete interaction. An acrosomal matrix protein, ACRBP, is known as a proacrosin-binding protein. In mice, two forms of ACRBP, wild-type ACRBP-W and variant ACRBP-V5, are generated by pre-mRNA alternative splicing of Acrbp Here, we demonstrate the functional roles of these two ACRBP proteins. ACRBP-null male mice lacking both proteins showed a severely reduced fertility, because of malformation of the acrosome. Notably, ACRBP-null spermatids failed to form a large acrosomal granule, leading to the fragmented structure of the acrosome. The acrosome malformation was rescued by transgenic expression of ACRBP-V5 in ACRBP-null spermatids. Moreover, exogenously expressed ACRBP-W blocked autoactivation of proacrosin in the acrosome. Thus, ACRBP-V5 functions in the formation and configuration of the acrosomal granule during early spermiogenesis. The major function of ACRBP-W is to retain the inactive status of proacrosin in the acrosome until acrosomal exocytosis.

Individual differences in the distribution of sperm acrosome-associated 1 proteins among male patients of infertile couples; their possible impact on outcomes of conventional in vitro fertilization

The aims of this study were to show the existence of individual differences in the distribution of sperm acrosome-associated 1 (SPACA1) among male patients of infertile couples and to examine their possible impact on the outcomes of conventional in vitro fertilization (IVF). The spermatozoa were collected from male patients of infertile couples, washed by centrifugation, collected by the swim-up method, and then used for clinical treatments of conventional IVF. The surplus sperm samples were fixed and stained with an anti-SPACA1 polyclonal antibody for the immunocytochemistry. In the clinical IVF treatments, fertilization rates and blastocyst development rates were evaluated. The immunocytochemical observations revealed that SPACA1 were localized definitely in the acrosomal equatorial segment and variedly in the acrosomal principal segment. Specifically, the detection patterns of SPACA1 in the acrosomal principal segment could be classified into three categories: (A) strong, (B) intermediate or faint, and (C) almost no immunofluorescence. The SPACA1 indexes were largely different among male patients with the wide range from 13 to 199 points. The SPACA1 indexes were significantly correlated with developmental rates of embryos to blastocysts (r = 0.829, P = 0.00162), although they were barely associated with fertilization rates at 19 h after insemination (r = 0.289, P = 0.389). These results suggest that the distribution of SPACA1 in sperm affects the outcomes of conventional IVF. In conclusion, this study provides initial data to promote large-scale clinical investigation to demonstrate that the SPACA1 indexes are valid as molecular biomarkers that can predict the effectiveness of conventional IVF of infertile couples.

Plasminogen Improves Mouse IVF by Interactions with Inner Acrosomal Membrane-Bound MMP2 and SAMP14

Spermatozoa must penetrate the outer investments of the oocyte, the cumulus oophorus and the zona pellucida (ZP), in order for fertilization to occur. This may require exposure of enzymes on the sperm's inner acrosomal membrane (IAM), one of which is matrix metalloproteinase (MMP) 2, to factors in oviductal fluid. Plasminogen is present in oviductal fluid and activates MMP2 in somatic tissues. The objectives of this study were: 1) to examine possible interactions between plasminogen and IAM-bound plasminogen activator receptor (SAMP14) and -MMP2, 2) to demonstrate plasminogen's presence in the extracellular environment at the site of fertilization, and 3) to provide evidence that plasminogen plays a role in fertilization. Zymographs of sonicated bull and rat sperm extracts incubated with plasmin and/or plasminogen (plasmin/ogen) showed acceleration of initiation of MMP2 activity in concentrations as low as 1 μg/ml. Immunohistochemical and immunofluorescence analysis of plasmin/ogen revealed its presence in the cytoplasm of mouse ovarian and oviductal oocytes, oviductal epithelium, around the ZP, and amongst the cumulus cells. We modified the standard in vitro fertilization (IVF) approach to more closely mimic natural fertilization by reducing sperm concentration during insemination by ∼100× and also comparing cumulus-intact and denuded oocytes. In mice, addition of plasminogen in IVF medium significantly improved fertilization, while MMP2 antibody significantly inhibited sperm penetration in these conditions. IVF improvement by plasminogen was blocked by SAMP14 antibody. Furthermore, MMP2 antibody inhibition was coincident with a failure by spermatozoa to disperse the cumulus oophorus. We provide evidence that plasminogen on its own and through an MMP2-related mechanism improves the ability of oocytes to be fertilized, and demonstrate its effect in sperm penetration of oocyte investments.

Acrosome markers of human sperm

Molecular biomarkers that can assess sperm acrosome status are very useful for evaluating sperm quality in the field of assisted reproductive technology. In this review, we introduce and discuss the localization and function of acrosomal proteins that have been well studied. Journal databases were searched using keywords, including "human acrosome", "localization", "fertilization-related protein", "acrosomal membrane", "acrosomal matrix", "acrosome reaction", "knockout mouse", and "acrosome marker".

Genetic and phenotypic influences on copulatory plug survival in mice

Across a diversity of animals, male seminal fluid coagulates upon ejaculation to form a hardened structure known as a copulatory plug. Previous studies suggest that copulatory plugs evolved as a mechanism for males to impede remating by females, but detailed investigations into the time course over which plugs survive in the female's reproductive tract are lacking. Here, we cross males from eight inbred strains to females from two inbred strains of house mice (Mus musculus domesticus). Plug survival was significantly affected by male genotype. Against intuition, plug survival time was negatively correlated with plug size: long-lasting plugs were small and relatively more susceptible to proteolysis. Plug size was associated with divergence in major protein composition of seminal vesicle fluid, suggesting that changes in gene expression may play an important role in plug dynamics. In contrast, we found no correlation to genetic variation in the protein-coding regions of five genes thought to be important in copulatory plug formation (Tgm4, Svs1, Svs2, Svs4 and Svs5). Our study demonstrates a complex relationship between copulatory plug characteristics and survival. We discuss several models to explain unexpected variation in plug phenotypes.

Network analyses of sperm-egg recognition and binding: ready to rethink fertility mechanisms?

The rapid growth of published literature makes biomedical text mining increasingly invaluable for unpacking implicit knowledge hidden in unstructured text. We employed biomedical text mining and biological networks analyses to research the process of sperm egg recognition and binding (SERB). We selected from the literature the molecules expressed either on spermatozoa or on oocytes thought to be involved in SERB and, using an automated literature search software (Agilent Literature Search), we realized a network, SERBN, characterized by a hierarchical scale free and a small world topology. We used an integrated approach, either based on selection of hubs or by a cluster analysis, to discern the key molecules of SERB. We found that in most cases some of them are not directly situated on spermatozoa and oocyte, but are dispersed in oviductal fluid or embedded in exosomes present in the perivitelline space. To confirm and validate our results, we performed further analyses using STRING and Reactome FI software. Our findings underscore that the fertility is not a property of gametes in isolation, but rather depends on the functional integrity of the entire reproductive system. These observations collectively underscore the importance of integrative biology in exploring biological systems and in rethinking of fertility mechanisms in the light of this innovative approach.

Effects of acrosomal conditions of frozen-thawed spermatozoa on the results of artificial insemination in Japanese Black cattle

The purposes of this study were to examine the relationship between male artificial insemination (AI) fertility and sperm acrosomal conditions assessed by new and conventional staining techniques and to identify possible reproductive dysfunctions causing low conception rates in AI using frozen-thawed spermatozoa with poor acrosomal conditions in Japanese Black bulls. We investigated individual differences among bulls in the results concerning (1) acrosomal conditions of frozen-thawed spermatozoa as assessed by not merely peanut agglutinin-lectin staining (a conventional staining technique) but also immunostaining of acrosomal tyrosine-phosphorylated proteins (a new staining technique), (2) routine AI using frozen-thawed spermatozoa as assessed by pregnancy diagnosis, (3) in vivo fertilization of frozen-thawed spermatozoa and early development of fertilized eggs as assessed by superovulation/AI-embryo collection tests and (4) in vitro fertilization of frozen-thawed spermatozoa with oocytes. The percentages of frozen-thawed spermatozoa with normal acrosomal conditions assessed by the abovementioned staining techniques were significantly correlated with the conception rates of routine AI, rates of transferable embryos in superovulation/AI-embryo collection tests and in vitro fertilization rates. These results are consistent with new suggestions that the distribution of acrosomal tyrosine-phosphorylated proteins as well as the acrosomal morphology of frozen-thawed spermatozoa are AI fertility-associated markers that are valid for the prediction of AI results and that low conception rates in AI using frozen-thawed spermatozoa with poor acrosomal conditions result from reproductive dysfunctions in the processes between sperm insemination into females and early embryo development, probably failed fertilization of frozen-thawed spermatozoa with oocytes.

Protein-Carbohydrate Interaction between Sperm and the Egg-Coating Envelope and Its Regulation by Dicalcin, a Xenopus laevis Zona Pellucida Protein-Associated Protein

Protein-carbohydrate interaction regulates multiple important processes during fertilization, an essential biological event where individual gametes undergo intercellular recognition to fuse and generate a zygote. In the mammalian female reproductive tract, sperm temporarily adhere to the oviductal epithelium via the complementary interaction between carbohydrate-binding proteins on the sperm membrane and carbohydrates on the oviductal cells. After detachment from the oviductal epithelium at the appropriate time point following ovulation, sperm migrate and occasionally bind to the extracellular matrix, called the zona pellucida (ZP), which surrounds the egg, thereafter undergoing the exocytotic acrosomal reaction to penetrate the envelope and to reach the egg plasma membrane. This sperm-ZP interaction also involves the direct interaction between sperm carbohydrate-binding proteins and carbohydrates within the ZP, most of which have been conserved across divergent species from mammals to amphibians and echinoderms. This review focuses on the carbohydrate-mediated interaction of sperm with the female reproductive tract, mainly the interaction between sperm and the ZP, and introduces the fertilization-suppressive action of dicalcin, a Xenopus laevis ZP protein-associated protein. The action of dicalcin correlates significantly with a dicalcin-dependent change in the lectin-staining pattern within the ZP, suggesting a unique role of dicalcin as an inherent protein that is capable of regulating the affinity between the lectin and oligosaccharides attached on its target glycoprotein.

Proteolytic activation of the protease-activated receptor (PAR)-2 by the glycosylphosphatidylinositol-anchored serine protease testisin

Protease-activated receptors (PARs) are a family of seven-transmembrane, G-protein-coupled receptors that are activated by multiple serine proteases through specific N-terminal proteolytic cleavage and the unmasking of a tethered ligand. The majority of PAR-activating proteases described to date are soluble proteases that are active during injury, coagulation, and inflammation. Less investigation, however, has focused on the potential for membrane-anchored serine proteases to regulate PAR activation. Testisin is a unique trypsin-like serine protease that is tethered to the extracellular membrane of cells through a glycophosphatidylinositol (GPI) anchor. Here, we show that the N-terminal domain of PAR-2 is a substrate for testisin and that proteolytic cleavage of PAR-2 by recombinant testisin activates downstream signaling pathways, including intracellular Ca(2+) mobilization and ERK1/2 phosphorylation. When testisin and PAR-2 are co-expressed in HeLa cells, GPI-anchored testisin specifically releases the PAR-2 tethered ligand. Conversely, knockdown of endogenous testisin in NCI/ADR-Res ovarian tumor cells reduces PAR-2 N-terminal proteolytic cleavage. The cleavage of PAR-2 by testisin induces activation of the intracellular serum-response element and NFκB signaling pathways and the induction of IL-8 and IL-6 cytokine gene expression. Furthermore, the activation of PAR-2 by testisin results in the loss and internalization of PAR-2 from the cell surface. This study reveals a new biological substrate for testisin and is the first demonstration of the activation of a PAR by a serine protease GPI-linked to the cell surface.

TMPRSS13 deficiency impairs stratum corneum formation and epidermal barrier acquisition

Membrane-anchored serine proteases serve as important regulators of multiple developmental and homoeostatic processes in mammals. TMPRSS13 (transmembrane protease, serine 13; also known as mosaic serine protease large-form, MSPL) is a membrane-anchored serine protease with unknown biological functions. In the present study, we used mice with the Tmprss13 gene disrupted by a β-galactosidase-neomycin fusion gene insertion to study the expression and function of the membrane-anchored serine protease. High levels of Tmprss13 expression were found in the epithelia of the oral cavity, upper digestive tract and skin. Compatible with this expression pattern, Tmprss13-deficient mice displayed abnormal skin development, leading to a compromised barrier function, as measured by the transepidermal fluid loss rate of newborn mice. The present study provides the first biological function for the transmembrane serine protease TMPRSS13.

Molecular and cellular mechanisms of sperm-oocyte interactions opinions relative to in vitro fertilization (IVF)

One of the biggest prerequisites for pregnancy is the fertilization step, where a human haploid spermatozoon interacts and penetrates one haploid oocyte in order to produce the diploid zygote. Although fertilization is defined by the presence of two pronuclei and the extraction of the second polar body the process itself requires preparation of both gametes for fertilization to take place at a specific time. These preparations include a number of consecutive biochemical and molecular events with the help of specific molecules and with the consequential interaction between the two gametes. These events take place at three different levels and in a precise order, where the moving spermatozoon penetrates (a) the outer vestments of the oocyte, known as the cumulus cell layer; (b) the zona pellucida (ZP); where exocytosis of the acrosome contents take place and (c) direct interaction of the spermatozoon with the plasma membrane of the oocyte, which involves a firm adhesion of the head of the spermatozoon with the oocyte plasma membrane that culminates with the fusion of both sperm and oocyte membranes (Part I). After the above interactions, a cascade of molecular signal transductions is initiated which results in oocyte activation. Soon after the entry of the first spermatozoon into the oocyte and oocyte activation, the oocyte’s coat (the ZP) and the oocyte’s plasma membrane seem to change quickly in order to initiate a fast block to a second spermatozoon (Part II). Sometimes, two spermatozoa fuse with one oocyte, an incidence of 1%–2%, resulting in polyploid fetuses that account for up to 10%–20% of spontaneously aborted human conceptuses. The present review aims to focus on the first part of the human sperm and oocyte interactions, emphasizing the latest molecular and cellular mechanisms controlling this process.

Roles of intracellular cyclic AMP signal transduction in the capacitation and subsequent hyperactivation of mouse and boar spermatozoa

It is not until accomplishment of a variety of molecular changes during the transit through the female reproductive tract that mammalian spermatozoa are capable of exhibiting highly activated motility with asymmetric whiplash beating of the flagella (hyperactivation) and undergoing acrosomal exocytosis in the head (acrosome reaction). These molecular changes of the spermatozoa are collectively termed capacitation and promoted by bicarbonate, calcium and cholesterol acceptors. Such capacitation-promoting factors can stimulate intracellular cyclic AMP (cAMP) signal transduction in the spermatozoa. Meanwhile, hyperactivation and the acrosome reaction are essential to sperm fertilization with oocytes and are apparently triggered by a sufficient increase of intracellular Ca²⁺ in the sperm flagellum and head, respectively. Thus, it is necessary to investigate the relationship between cAMP signal transduction and calcium signaling cascades in the spermatozoa for the purpose of understanding the molecular basis of capacitation. In this review, I cover updated insights regarding intracellular cAMP signal transduction, the acrosome reaction and flagellar motility in mammalian spermatozoa and then account for possible roles of intracellular cAMP signal transduction in the capacitation and subsequent hyperactivation of mouse and boar spermatozoa.

Seminal vesicle protein SVS2 is required for sperm survival in the uterus

In mammals, sperm migrate through the female reproductive tract to reach the egg; however, our understanding of this journey is highly limited. To shed light on this process, we focused on defining the functions of seminal vesicle secretion 2 (SVS2). SVS2(-/-) male mice produced sperm but were severely subfertile, and formation of a copulatory plug to cover the female genital opening did not occur. Surprisingly, even when artificial insemination was performed with silicon as a substitute for the plug, sperm fertility in the absence of SVS2 remained severely reduced because the sperm were already dead in the uterus. Thus, our results provide evidence that the uterus induces sperm cell death and that SVS2 protects sperm from uterine attack.

Modes of acrosin functioning during fertilization

Mammalian fertilization is a complex process that involves gamete recognition, penetration, and fusion. Biochemical studies that identified the role of acrosome components during sperm-ova interaction especially the zona pellucida (ZP) provided major advances in sperm cell biology. Acrosin (a typical serine protease) functions during fertilization in several significant ways which include: a) activation of acrosome components, b) secondary binding with the ZP, and c) hydrolysis of the ZP. However, studies using knockout (KO) acrosin-deficient mice cast doubt on the traditional role of acrosin in fertilization. The KO acrosin-deficient mice exhibit normal fecundity except for delayed fertilization. Despite the doubt cast on the traditional role of acrosin by the KO acrosin-deficient mouse studies, acrosin still remains a major protease involved in multiple processes of fertilization. In this review, we assess the functional profile of acrosin and briefly summarize recent findings on proteases involved in fertilization. We propose a refined scheme for the functional role of acrosin in fertilization. We particularly emphasize the role of acrosin in acrosome exocytosis and activation of other acrosome components based on advanced technology like structural X-ray analysis.

Three testis-specific paralogous serine proteases play different roles in murine spermatogenesis and are involved in germ cell survival during meiosis

Spermatogenesis is a complex process that generates spermatozoa; its molecular mechanisms are not completely understood. Here we focused on the functions of three testis-specific serine proteases: Prss42/Tessp-2, Prss43/Tessp-3, and Prss44/Tessp-4. These protease genes, which constitute a gene cluster on chromosome 9F2-F3, were presumed to be paralogs and were expressed only in the testis. By investigating their mRNA distribution, we found that all three genes were expressed in primary and secondary spermatocytes. However, interestingly, the translated proteins were produced at different locations. Prss42/Tessp-2 was found in the membranes and cytoplasm of secondary spermatocytes and spermatids, whereas Prss43/Tessp-3 was present only in the membranes of spermatocytes and spermatids. Prss44/Tessp-4 was detected in the cytoplasm of spermatocytes and spermatids. To assess the roles of these proteases in spermatogenesis, we used organ culture of mouse testis fragments. Adding antibodies against Prss42/Tessp-2 and Prss43/Tessp-3 resulted in meiotic arrest at the stage when each protease was beginning to be translated. Furthermore, the number of apoptotic cells dramatically increased after the addition of these antibodies. These results strongly suggest that the three paralogous Prss/Tessp proteases play different roles in spermatogenesis and that Prss42/Tessp-2 and Prss43/Tessp-3 are required for germ cell survival during meiosis.

Safety, efficacy and efficiency of laser-assisted IVF in subfertile mutant mouse strains

In the present report we studied the safety, efficacy and efficiency of using an infrared laser to facilitate IVF by assessing fertilization, development and birth rates after laser-zona drilling (LZD) in 30 subfertile genetically modified (GM) mouse lines. We determined that LZD increased the fertilization rate four to ten times that of regular IVF, thus facilitating the derivation of 26 of 30 (86.7%) GM mouse lines. Cryopreserved two-cell stage embryos derived by LZD-assisted IVF were recovered and developed to blastocysts in vitro at the same rate as frozen-thawed embryos derived by regular IVF. Surprisingly after surgical transfer to pseudopregnant recipients the birth rate of embryos derived by LZD-assisted IVF was significantly lower than that of embryos derived by regular IVF. However this result could be completely mitigated by the addition of 0.25 M sucrose to the culture medium during LZD which caused the oocyte to shrink in volume relative to the perivitelline space. By increasing the distance from the laser target site on the zona pellucida, we hypothesize that the hyperosmotic effect of sucrose reduced the potential for laser-induced cytotoxic thermal damage to the underlying oocytes. With appropriate preparation and cautious application, our results indicate that LZD-assisted IVF is a safe, efficacious and efficient assisted reproductive technology for deriving mutant mouse lines with male factor infertility and subfertility caused by sperm-zona penetration defects.

Dynamic regulation of sperm interactions with the zona pellucida prior to and after fertilisation

Recent findings have refined our thinking on sperm interactions with the cumulus–oocyte complex (COC) and our understanding of how, at the molecular level, the sperm cell fertilises the oocyte. Proteomic analyses has identified a capacitation-dependent sperm surface reordering that leads to the formation of functional multiprotein complexes involved in zona–cumulus interactions in several mammalian species. During this process, multiple docking of the acrosomal membrane to the plasma membrane takes place. In contrast with the dogma that the acrosome reaction is initiated when spermatozoa bind to the zona pellucida (ZP), it has been established recently that, in mice, the fertilising spermatozoon initiates its acrosome reaction during its voyage through the cumulus before it reaches the ZP. In fact, even acrosome-reacted mouse spermatozoa collected from the perivitelline space can fertilise another ZP-intact oocyte. The oviduct appears to influence the extracellular matrix properties of the spermatozoa as well as the COC. This may influence sperm binding and penetration of the cumulus and ZP, and, in doing so, increase monospermic while decreasing polyspermic fertilisation rates. Structural analysis of the ZP has shed new light on how spermatozoa bind and penetrate this structure and how the cortical reaction blocks sperm–ZP interactions. The current understanding of sperm interactions with the cumulus and ZP layers surrounding the oocyte is reviewed with a special emphasis on the lack of comparative knowledge on this topic in humans, as well as in most farm mammals.

The oviduct: functional genomic and proteomic approach

The mammalian oviduct is an anatomical part of the female reproductive tract, which plays several important roles in the events related to fertilization and embryo development. This review examines and compares several studies related to the proteomic and transcriptomic profile of the oviduct in different domestic animals. This information could be important for clarifying the role of oviductal factors in different events regulating fertilization and early embryo development, as well as for improving synthetic media for in vitro maturation/in vitro fertilization/embryo culture techniques (IVM/IVF/EC).