Zonadhesin is essential for species specificity of sperm adhesion to the egg zona pellucida

Integrative analysis of single-nucleus RNA-seq and bulk RNA-seq reveals germline cells development dynamics and niches in the Pacific oyster gonad

Gametogenesis drives the maturation of germ cell precursors into functional gametes, facilitated by interactions with the niche environment. However, the molecular mechanisms, especially in invertebrates, remain incompletely understood. In this study, the gonadal microenvironment and gametogenic processes in the Pacific oyster, a model for diffuse gonadal organization and periodic gametogenesis, are investigated. We combine single-nucleus RNA-seq and bulk RNA-seq to analyze gonadal microenvironments in oysters. Twenty-three male and nineteen female gonadal cell clusters are identified, revealing four male and three female germ cell types, alongside follicular cells in females and Sertoli/Leydig cells in males. The NOTCH and BMP (bone morphogenetic protein) signaling pathways play a significant role in the male germline niche, suggesting similarities with mammalian germ cell microenvironment. This study offers valuable insights into germ cell developmental transitions and microenvironmental characteristics.

Membrane molecule bouncer regulates sperm binding activity in immature oocytes in the viviparous teleost species Poecilia reticulata (guppy)

Generally, in vertebrates, the first step toward fertilization is the ovulation of mature oocytes, followed by their binding to sperm cells outside of the ovary. Exceptionally, the oocytes of poeciliid fish are fertilized by sperm cells within the follicle, and the developmental embryo is subsequently released into the ovarian lumen before delivery. In the present study, we aimed to identify the factor(s) responsible for intrafollicular fertilization in a viviparous teleost species, Poecilia reticulata (guppy). Sperm tracking analysis in this regard indicated that in this species, sperm cells reached immature oocytes including the germinal vesicle, and the insemination assay indicated that the immature oocytes robustly adhered to the sperm cells; similar binding was not observed in Danio rerio (zebrafish) and Oryzias latipes (medaka). We also identified the Ly6/uPAR protein bouncer as the factor responsible for the observed sperm binding activity of the immature oocytes in this species. The recombinant bouncer peptide acted as an inhibitory decoy for the sperm-oocyte binding in guppy. On the other hand, ectopic expression of guppy bouncer in zebrafish oocytes resulted in interspecific sperm-oocyte binding. These results argue that bouncer is responsible for sperm-immature oocyte binding. Our findings highlight the unique reproductive strategies of guppy fish and enhance our understanding of the diverse reproductive mechanisms in vertebrates.

SMA20/PMIS2 Is a Rapidly Evolving Sperm Membrane Alloantigen with Possible Species-Divergent Function in Fertilization

Immunodominant alloantigens in pig sperm membranes include 15 known gene products and a previously undiscovered Mr 20,000 sperm membrane-specific protein (SMA20). Here we characterize SMA20 and identify it as the unannotated pig ortholog of PMIS2. A composite SMA20 cDNA encoded a 126 amino acid polypeptide comprising two predicted transmembrane segments and an N-terminal alanine- and proline (AP)-rich region with no apparent signal peptide. The Northern blots showed that the composite SMA20 cDNA was derived from a 1.1 kb testis-specific transcript. A BLASTp search retrieved no SMA20 match from the pig genome, but it did retrieve a 99% match to the Pmis2 gene product in warthog. Sequence identity to predicted PMIS2 orthologs from other placental mammals ranged from no more than 80% overall in Cetartiodactyla to less than 60% in Primates, with the AP-rich region showing the highest divergence, including, in the extreme, its absence in most rodents, including the mouse. SMA20 immunoreactivity localized to the acrosome/apical head of methanol-fixed boar spermatozoa but not live, motile cells. Ultrastructurally, the SMA20 AP-rich domain immunolocalized to the inner leaflet of the plasma membrane, the outer acrosomal membrane, and the acrosomal contents of ejaculated spermatozoa. Gene name search failed to retrieve annotated Pmis2 from most mammalian genomes. Nevertheless, individual pairwise interrogation of loci spanning Atp4a-Haus5 identified Pmis2 in all placental mammals, but not in marsupials or monotremes. We conclude that the gene encoding sperm-specific SMA20/PMIS2 arose de novo in Eutheria after divergence from Metatheria, whereupon rapid molecular evolution likely drove the acquisition of a species-divergent function unique to fertilization in placental mammals.

Genome-wide analyses identify 21 infertility loci and over 400 reproductive hormone loci across the allele frequency spectrum

Genome-wide association studies (GWASs) may help inform treatments for infertility, whose causes remain unknown in many cases. Here we present GWAS meta-analyses across six cohorts for male and female infertility in up to 41,200 cases and 687,005 controls. We identified 21 genetic risk loci for infertility (P≤5E-08), of which 12 have not been reported for any reproductive condition. We found positive genetic correlations between endometriosis and all-cause female infertility (rg=0.585, P=8.98E-14), and between polycystic ovary syndrome and anovulatory infertility (rg=0.403, P=2.16E-03). The evolutionary persistence of female infertility-risk alleles in EBAG9 may be explained by recent directional selection. We additionally identified up to 269 genetic loci associated with follicle-stimulating hormone (FSH), luteinising hormone, oestradiol, and testosterone through sex-specific GWAS meta-analyses (N=6,095-246,862). While hormone-associated variants near FSHB and ARL14EP colocalised with signals for anovulatory infertility, we found no rg between female infertility and reproductive hormones (P>0.05). Exome sequencing analyses in the UK Biobank (N=197,340) revealed that women carrying testosterone-lowering rare variants in GPC2 were at higher risk of infertility (OR=2.63, P=1.25E-03). Taken together, our results suggest that while individual genes associated with hormone regulation may be relevant for fertility, there is limited genetic evidence for correlation between reproductive hormones and infertility at the population level. We provide the first comprehensive view of the genetic architecture of infertility across multiple diagnostic criteria in men and women, and characterise its relationship to other health conditions.

Proteomic analysis of boar seminal plasma: Putative markers for fertility based on capacity of semen preservation at 17°C

Boar seminal plasma (SP) proteins were associated with differences on sperm resistance to cooling at 17°C. However, information about seminal plasma proteins in boars classified by capacity of semen preservation and in vivo fertility remains lacking. Thus, the objective was to evaluate the SP proteome in boars classified by capacity of semen preservation and putative biomarkers for fertility. The ejaculates from high-preservation (HP) showed higher progressive motility during all 5 days than the low-preservation (LP) boars. There was no difference for farrowing rate between ejaculates from LP (89.7%) and HP boars (88.4%). The LP boars presented lower total piglets born (14.0 ± 0.2) than HP (14.8 ± 0.2; p < 0.01). A total of 257 proteins were identified, where 184 were present in both classes of boar, and 41 and 32 were identified only in LP and HP boars, respectively. Nine proteins were differently expressed: five were more abundant in HP (SPMI, ZPBP1, FN1, HPX, and C3) and four in LP boars (B2M, COL1A1, NKX3-2, and MPZL1). The HP boars had an increased abundance of SP proteins related to sperm resistance and fecundation process which explains the better TPB. LP boars had a higher abundance of SP proteins associated with impaired spermatogenesis.

Reproductive genomics of the mouse: implications for human fertility and infertility

Genetic analyses of mammalian gametogenesis and fertility have the potential to inform about two important and interrelated clinical areas: infertility and contraception. Here, we address the genetics and genomics underlying gamete formation, productivity and function in the context of reproductive success in mammalian systems, primarily mouse and human. Although much is known about the specific genes and proteins required for meiotic processes and sperm function, we know relatively little about other gametic determinants of overall fertility, such as regulation of gamete numbers, duration of gamete production, and gamete selection and function in fertilization. As fertility is not a binary trait, attention is now appropriately focused on the oligogenic, quantitative aspects of reproduction. Multiparent mouse populations, created by complex crossing strategies, exhibit genetic diversity similar to human populations and will be valuable resources for genetic discovery, helping to overcome current limitations to our knowledge of mammalian reproductive genetics. Finally, we discuss how what we know about the genomics of reproduction can ultimately be brought to the clinic, informing our concepts of human fertility and infertility, and improving assisted reproductive technologies.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Oral immunocontraceptive vaccines: A novel approach for fertility control in wildlife

The overabundant populations of wildlife have caused many negative impacts, such as human-wildlife conflicts and ecological degradation. The existing approaches like injectable immunocontraceptive vaccines and lethal methods have limitations in many aspects, which has prompted the advancement of oral immunocontraceptive vaccine. There is growing interest in oral immunocontraceptive vaccines for reasons including high immunization coverage, easier administration, frequent boosting, the ability to induce systemic and mucosal immune responses, and cost-effectiveness. Delivery systems have been developed to protect oral antigens and enhance the immunogenicity, including live vectors, microparticles and nanoparticles, bacterial ghosts, and mucosal adjuvants. However, currently, no effective oral immunocontraceptive vaccine is available for field trials because of the enormous development challenges, including biological and physicochemical barriers of the gastrointestinal tract, mucosal tolerance, pre-existing immunity, antigen residence time in the small intestine, species specificity and other safety issues. To overcome these challenges, this article summarizes achievements in delivery systems and contraceptive antigens in oral immunocontraceptive vaccines and explores the potential barriers for future vaccine design and application.

A novel role for ATP2B in ascidians: Ascidian-specific mutations in ATP2B contribute to sperm chemotaxis

Sperm chemotaxis, in which sperms are attracted to conspecific eggs via species-specific attractants, plays an important role in fertilization. This phenomenon has been observed in various animals and species-specific sperm attractants have been reported in some species. However, the mechanisms involved in the reception and recognition of the species-specific attractant by the sperms is poorly studied. Previously, we found that the plasma membrane-type Ca²⁺ /ATPase (PMCA) is the receptor for the sperm-activating and -attracting factor (SAAF) in the ascidian Ciona intestinalis. To determine the role of PMCA in species-specific sperm chemotaxis, we identified the amino acid sequences of PMCAs derived from six Phlebobranchia species. The testis-specific splice variant of PMCA was found to be present in all the species investigated and the ascidian-specific sequence was detected near the 3'-terminus. Moreover, dN/dS analysis revealed that the extracellular loops 1, 2, and 4 in ascidian PMCA underwent a positive selection. These findings suggest that PMCA recognizes the species-specific structure of SAAF at the extracellular loops 1, 2, and 4, and its testis-specific C-terminal region is involved in the activation and chemotaxis of ascidian sperms.

Testis-Specific Isoform of Na+-K+ ATPase and Regulation of Bull Fertility

An advanced understanding of sperm function is relevant for evidence-based male fertility prediction and addressing male infertility. A standard breeding soundness evaluation (BSE) merely identifies gross abnormalities in bulls, whereas selection based on single nucleotide polymorphisms and genomic estimated breeding values overlooks sub-microscopic differences in sperm. Molecular tools are important for validating genomic selection and advancing knowledge on the regulation of male fertility at an interdisciplinary level. Therefore, research in this field is now focused on developing a combination of in vitro sperm function tests and identifying biomarkers such as sperm proteins with critical roles in fertility. The Na+-K+ ATPase is a ubiquitous transmembrane protein and its α4 isoform (ATP1A4) is exclusively expressed in germ cells and sperm. Furthermore, ATP1A4 is essential for male fertility, as it interacts with signaling molecules in both raft and non-raft fractions of the sperm plasma membrane to regulate capacitation-associated signaling, hyperactivation, sperm-oocyte interactions, and activation. Interestingly, ATP1A4 activity and expression increase during capacitation, challenging the widely accepted dogma of sperm translational quiescence. This review discusses the literature on the role of ATP1A4 during capacitation and fertilization events and its prospective use in improving male fertility prediction.

Rapid divergence of a gamete recognition gene promoted macroevolution of Eutheria

BACKGROUND

Speciation genes contribute disproportionately to species divergence, but few examples exist, especially in vertebrates. Here we test whether Zan, which encodes the sperm acrosomal protein zonadhesin that mediates species-specific adhesion to the egg's zona pellucida, is a speciation gene in placental mammals.

RESULTS

Genomic ontogeny reveals that Zan arose by repurposing of a stem vertebrate gene that was lost in multiple lineages but retained in Eutheria on acquiring a function in egg recognition. A 112-species Zan sequence phylogeny, representing 17 of 19 placental Orders, resolves all species into monophyletic groups corresponding to recognized Orders and Suborders, with <5% unsupported nodes. Three other rapidly evolving germ cell genes (Adam2, Zp2, and Prm1), a paralogous somatic cell gene (TectA), and a mitochondrial gene commonly used for phylogenetic analyses (Cytb) all yield trees with poorer resolution than the Zan tree and inferior topologies relative to a widely accepted mammalian supertree. Zan divergence by intense positive selection produces dramatic species differences in the protein's properties, with ordinal divergence rates generally reflecting species richness of placental Orders consistent with expectations for a speciation gene that acts across a wide range of taxa. Furthermore, Zan's combined phylogenetic utility and divergence exceeds those of all other genes known to have evolved in Eutheria by positive selection, including the only other mammalian speciation gene, Prdm9.

CONCLUSIONS

Species-specific egg recognition conferred by Zan's functional divergence served as a mode of prezygotic reproductive isolation that promoted the extraordinary adaptive radiation and success of Eutheria.

Oviducal gland transcriptomics of Octopus maya through physiological stages and the negative effects of temperature on fertilization

Background

Elevated temperatures reduce fertilization and egg-laying rates in the octopus species. However, the molecular mechanisms that control the onset of fertilization and egg-laying in the octopus' oviducal gland are still unclear; and the effect of temperature on the expression of key reproductive genes is unknown. This study aims to better understand the molecular bases of octopus fertilization and egg-laying, and how they are affected by elevated temperatures.

Method

RNA-seq of oviducal glands was performed for samples before, during, and after fertilization and their transcriptomic profiles were compared. Also, at the fertilization stage, the optimal and thermal-stress conditions were contrasted. Expression levels of key reproductive genes were validated via RT-qPCR.

Results

In mated females before egg-laying, genes required for the synthesis of spermine, spermidine, which may prevent premature fertilization, and the myomodulin neuropeptide were upregulated. Among the genes with higher expression at the fertilization stage, we found those encoding the receptors of serotonin, dopamine, and progesterone; genes involved in the assembly and motility of the sperm flagellum; genes that participate in the interaction between male and female gametes; and genes associated with the synthesis of eggshell mucoproteins. At temperatures above the optimal range for reproduction, mated females reduced the fertilization rate. This response coincided with the upregulation of myomodulin and APGW-amide neuropeptides. Also, genes associated with fertilization like LGALS3, VWC2, and Pcsk1 were downregulated at elevated temperatures. Similarly, in senescent females, genes involved in fertilization were downregulated but those involved in the metabolism of steroid hormones like SRD5A1 were highly expressed.

Prioritising positively selected variants in whole-genome sequencing data using FineMAV

Background

In population genomics, polymorphisms that are highly differentiated between geographically separated populations are often suggestive of Darwinian positive selection. Genomic scans have highlighted several such regions in African and non-African populations, but only a handful of these have functional data that clearly associates candidate variations driving the selection process. Fine-Mapping of Adaptive Variation (FineMAV) was developed to address this in a high-throughput manner using population based whole-genome sequences generated by the 1000 Genomes Project. It pinpoints positively selected genetic variants in sequencing data by prioritizing high frequency, population-specific and functional derived alleles.

Results

We developed a stand-alone software that implements the FineMAV statistic. To graphically visualise the FineMAV scores, it outputs the statistics as bigWig files, which is a common file format supported by many genome browsers. It is available as a command-line and graphical user interface. The software was tested by replicating the FineMAV scores obtained using 1000 Genomes Project African, European, East and South Asian populations and subsequently applied to whole-genome sequencing datasets from Singapore and China to highlight population specific variants that can be subsequently modelled. The software tool is publicly available at https://github.com/fadilla-wahyudi/finemav.

Conclusions

The software tool described here determines genome-wide FineMAV scores, using low or high-coverage whole-genome sequencing datasets, that can be used to prioritize a list of population specific, highly differentiated candidate variants for in vitro or in vivo functional screens. The tool displays these scores on the human genome browsers for easy visualisation, annotation and comparison between different genomic regions in worldwide human populations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-021-04506-9.

ACRBP (Sp32) is involved in priming sperm for the acrosome reaction and the binding of sperm to the zona pellucida in a porcine model

In boar sperm, we have previously shown that capacitation is associated with the appearance of the p32 tyrosine phosphoprotein complex. The principal tyrosine phosphoprotein involved in this complex is the acrosin-binding protein (ACRBP), which regulates the autoconversion of proacrosin to intermediate forms of acrosin in both boar and mouse sperm. However, the complete biological role of ACRBP has not yet been elucidated. In this study, we tested the hypothesis that tyrosine phophorylation and the presence of the ACRBP in the sperm head are largely necessary to induce capacitation, the acrosome reaction (AR) and sperm-zona pellucida (ZP) binding, all of which are necessary steps for fertilization. In vitro fertilization (IVF) was performed using matured porcine oocytes and pre-capacitated boar sperm cultured with anti-phosphotyrosine antibodies or antibodies against ACRBP. Anti-ACRBP antibodies reduced capacitation and spontaneous AR (P<0.05). Sperm-ZP binding declined in the presence of anti-phosphotyrosine or anti-ACRBP antibodies. The localisation of anti-ACRBP antibodies on the sperm head, reduced the ability of the sperm to undergo the AR in response to solubilized ZP or by inhibiting the sarco/endoplasmic reticulum Ca2+-ATPase. These results support our hypothesis that tyrosine phosphorylated proteins and ACRBP are present upon the sperm surface in order to participate in sperm-ZP binding, and that ACRBP upon the surface of the sperm head facilitates capacitation and the AR in the porcine.

Ligands and Receptors Involved in the Sperm-Zona Pellucida Interactions in Mammals

Sperm-zona pellucida (ZP) interaction, involving the binding of sperm surface ligands to complementary carbohydrates of ZP, is the first direct gamete contact event crucial for subsequent gamete fusion and successful fertilization in mammals. It is a complex process mediated by the coordinated engagement of multiple ZP receptors forming high-molecular-weight (HMW) protein complexes at the acrosomal region of the sperm surface. The present article aims to review the current understanding of sperm-ZP binding in the four most studied mammalian models, i.e., murine, porcine, bovine, and human, and summarizes the candidate ZP receptors with established ZP affinity, including their origins and the mechanisms of ZP binding. Further, it compares and contrasts the ZP structure and carbohydrate composition in the aforementioned model organisms. The comprehensive understanding of sperm-ZP interaction mechanisms is critical for the diagnosis of infertility and thus becomes an integral part of assisted reproductive therapies/technologies.

The enigmatic sperm proteins in mammalian fertilization: an overview†

Mammalian fertilization involves a physical interaction between a sperm and an egg followed by molecular interactions amongst their various cell surface molecules. These interactions are initially mediated on the egg's outermost matrix, zona pellucida (ZP), and then its plasma membrane. To better understand this process, it is pertinent to find the corresponding molecules on sperm that interact with ZP or the egg's plasma membrane. Although currently, we have some knowledge about the binding partners for egg's plasma membrane on sperm, yet the ones involved in an interaction with ZP have remained remarkably elusive. This review provides comprehensive knowledge about the various sperm proteins participating in mammalian fertilization and discusses the possible reasons for not being able to identify the strong sperm surface candidate (s) for ZP adhesion. It also hypothesizes the existence of a multi-protein complex(s), members of which participate in oviduct transport, cumulus penetration, zona adhesion, and adhesion/fusion with the egg's plasma membrane; with some protein(s) having multiple roles during this process. Identification of these proteins is crucial as it improves our understanding of the process and allows us to successfully treat infertility, develop contraceptives, and improve artificial reproductive technologies.

Porcine model for the study of sperm capacitation, fertilization and male fertility

Mammalian fertilization remains a poorly understood event with the vast majority of studies done in the mouse model. The purpose of this review is to revise the current knowledge about semen deposition, sperm transport, sperm capacitation, gamete interactions and early embryonic development with a focus on the porcine model as a relevant, alternative model organism to humans. The review provides a thorough overview of post-ejaculation events inside the sow's reproductive tract including comparisons with humans and implications for human fertilization and assisted reproductive therapy (ART). Porcine methodology for sperm handling, preservation, in vitro capacitation, oocyte in vitro maturation, in vitro fertilization and intra-cytoplasmic sperm injection that are routinely used in pig research laboratories can be successfully translated into ART to treat human infertility. Last, but not least, new knowledge about mitochondrial inheritance in the pig can provide an insight into human mitochondrial diseases and new knowledge on polyspermy defense mechanisms could contribute to the development of new male contraceptives.

Protamine and other proteins in sperm and seminal plasma as molecular markers of bull fertility

Fertility is the most important aspect in the efforts to increase livestock populations. Protamine and various proteins in sperm and seminal plasma are the results of the molecular analysis which can be used as a marker of fertility. Each of the proteins plays an important role in the normal function of sperm, starting from the formation of sperm structure, motility, capacitation, cell protection, acrosome reactions, successful fertilization, egg activation, and embryonic development. Finally, these molecular components can be a marker of fertility and can help to diagnose the cases of infertility/subfertility in livestock in the field.

Species-specific mechanisms during fertilization

The perpetuation and preservation of distinct species rely on mechanisms that ensure that only interactions between gametes of the same species can give rise to viable and fertile offspring. Species-specificity can act at various stages, ranging from physical/behavioral pre-copulatory mechanisms, to pre-zygotic incompatibility during fertilization, to post-zygotic hybrid incompatibility. Herein, we focus on our current knowledge of the molecular mechanisms responsible for species-specificity during fertilization. While still poorly understood, decades of research have led to the discovery of molecules implicated in species-specific gamete interactions, starting from initial sperm-egg attraction to the binding of sperm and egg. While many of these molecules have been described as species-specific in their mode of action, relatively few have been demonstrated as such with definitive evidence. Thus, we also raise remaining questions that need to be addressed in order to characterize gamete interaction molecules as species-specific.

The molecular mechanisms mediating mammalian fertilization

Fertilization is a key biological process in which the egg and sperm must recognize one another and fuse to form a zygote. Although the process is a continuum, mammalian fertilization has been studied as a sequence of steps: sperm bind and penetrate through the zona pellucida of the egg, adhere to the egg plasma membrane and finally fuse with the egg. Following fusion, effective blocks to polyspermy ensure monospermic fertilization. Here, we review how recent advances obtained using genetically modified mouse lines bring new insights into the molecular mechanisms regulating mammalian fertilization. We discuss models for these processes and we include studies showing that these mechanisms may be conserved across different mammalian species.

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.

Octopus maya white body show sex-specific transcriptomic profiles during the reproductive phase, with high differentiation in signaling pathways

White bodies (WB), multilobulated soft tissue that wraps the optic tracts and optic lobes, have been considered the hematopoietic organ of the cephalopods. Its glandular appearance and its lobular morphology suggest that different parts of the WB may perform different functions, but a detailed functional analysis of the octopus WB is lacking. The aim of this study is to describe the transcriptomic profile of WB to better understand its functions, with emphasis on the difference between sexes during reproductive events. Then, validation via qPCR was performed using different tissues to find out tissue-specific transcripts. High differentiation in signaling pathways was observed in the comparison of female and male transcriptomic profiles. For instance, the expression of genes involved in the androgen receptor-signaling pathway were detected only in males, whereas estrogen receptor showed higher expression in females. Highly expressed genes in males enriched oxidation-reduction and apoptotic processes, which are related to the immune response. On the other hand, expression of genes involved in replicative senescence and the response to cortisol were only detected in females. Moreover, the transcripts with higher expression in females enriched a wide variety of signaling pathways mediated by molecules like neuropeptides, integrins, MAPKs and receptors like TNF and Toll-like. In addition, these putative neuropeptide transcripts, showed higher expression in females' WB and were not detected in other analyzed tissues. These results suggest that the differentiation in signaling pathways in white bodies of O. maya influences the physiological dimorphism between females and males during the reproductive phase.

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.

The Ly6/uPAR protein Bouncer is necessary and sufficient for species-specific fertilization

Fertilization is fundamental for sexual reproduction, yet its molecular mechanisms are poorly understood. We found that an oocyte-expressed Ly6/uPAR protein, which we call Bouncer, is a crucial fertilization factor in zebrafish. Membrane-bound Bouncer mediates sperm-egg binding and is thus essential for sperm entry into the egg. Remarkably, Bouncer not only is required for sperm-egg interaction but is also sufficient to allow cross-species fertilization between zebrafish and medaka, two fish species that diverged more than 200 million years ago. Our study thus identifies Bouncer as a key determinant of species-specific fertilization in fish. Bouncer's closest homolog in tetrapods, SPACA4, is restricted to the male germline in internally fertilizing vertebrates, which suggests that our findings in fish have relevance to human biology.

Gamete compatibility genes in mammals: candidates, applications and a potential path forward

Fertilization represents a critical stage in biology, where successful alleles of a previous generation are shuffled into new arrangements and subjected to the forces of selection in the next generation. Although much research has been conducted on how variation in morphological and behavioural traits lead to variation in fertilization patterns, surprisingly little is known about fertilization at a molecular level, and specifically about how genes expressed on the sperm and egg themselves influence fertilization patterns. In mammals, several genes have been identified whose products are expressed on either the sperm or the egg, and which influence the fertilization process, but the specific mechanisms are not yet known. Additionally, in 2014 an interacting pair of proteins was identified: 'Izumo' on the sperm, and 'Juno' on the egg. With the identification of these genes comes the first opportunity to understand the molecular aspects of fertilization in mammals, and to identify how the genetic characteristics of these genes influence fertilization patterns. Here, we review recent progress in our understanding of fertilization and gamete compatibility in mammals, which should provide a helpful guide to researchers interested in untangling the molecular mechanisms of fertilization and the resulting impacts on population biology and evolutionary processes.

Functional Amyloids in Reproduction

Amyloids are traditionally considered pathological protein aggregates that play causative roles in neurodegenerative disease, diabetes and prionopathies. However, increasing evidence indicates that in many biological systems nonpathological amyloids are formed for functional purposes. In this review, we will specifically describe amyloids that carry out biological roles in sexual reproduction including the processes of gametogenesis, germline specification, sperm maturation and fertilization. Several of these functional amyloids are evolutionarily conserved across several taxa, including human, emphasizing the critical role amyloids perform in reproduction. Evidence will also be presented suggesting that, if altered, some functional amyloids may become pathological.

The egg coat zona pellucida 3 glycoprotein - evolution of its putative sperm-binding region in Old World murine rodents (Rodentia: Muridae)

In eutherian mammals, before fertilisation can occur the spermatozoon has to bind to, and penetrate, the egg coat, the zona pellucida (ZP). In the laboratory mouse there is good evidence that the primary sperm-binding site is a protein region encoded by Exon 7 of the ZP3 gene and it has been proposed that binding is species specific and evolves by sexual selection. In the present study we investigate these hypotheses by comparing Exon 6 and 7 sequences of ZP3 in 28 species of murine rodents of eight different divisions from Asia, Africa and Australasia, in which a diverse array of sperm morphologies occurs. We found considerable nucleotide (and corresponding amino acid) sequence divergence in Exon 7, but not in Exon 6, across these species, with evidence for positive selection at five codon positions. This molecular divergence does not appear to be due to reinforcement to reduce hybridisation, nor does it correlate with divergence in sperm head morphology or tail length, thus it is unlikely to be driven by inter-male sperm competition. Other forms of post-copulatory sexual selection therefore appear to have resulted in the molecular divergence of this region of ZP3 in this highly speciose group of mammals.

Egress of sperm autoantigen from seminiferous tubules maintains systemic tolerance

Autoimmune responses to meiotic germ cell antigens (MGCA) that are expressed on sperm and testis occur in human infertility and after vasectomy. Many MGCA are also expressed as cancer/testis antigens (CTA) in human cancers, but the tolerance status of MGCA has not been investigated. MGCA are considered to be uniformly immunogenic and nontolerogenic, and the prevailing view posits that MGCA are sequestered behind the Sertoli cell barrier in seminiferous tubules. Here, we have shown that only some murine MGCA are sequestered. Nonsequestered MCGA (NS-MGCA) egressed from normal tubules, as evidenced by their ability to interact with systemically injected antibodies and form localized immune complexes outside the Sertoli cell barrier. NS-MGCA derived from cell fragments that were discarded by spermatids during spermiation. They egressed as cargo in residual bodies and maintained Treg-dependent physiological tolerance. In contrast, sequestered MGCA (S-MGCA) were undetectable in residual bodies and were nontolerogenic. Unlike postvasectomy autoantibodies, which have been shown to mainly target S-MGCA, autoantibodies produced by normal mice with transient Treg depletion that developed autoimmune orchitis exclusively targeted NS-MGCA. We conclude that spermiation, a physiological checkpoint in spermatogenesis, determines the egress and tolerogenicity of MGCA. Our findings will affect target antigen selection in testis and sperm autoimmunity and the immune responses to CTA in male cancer patients.

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.

Gamete activation: basic knowledge and clinical applications

Background

The first clues to the process of gamete activation date back to nearly 60 years ago. The mutual activation of gametes is a crucial event during fertilization. In the testis and ovaries, spermatozoa and oocytes are in a state of meiotic and metabolic quiescence and require reciprocal signals in order to undergo functional changes that lead to competence for fertilization. First, the oocyte activates sperm by triggering motility, chemoattraction, binding and the acrosome reaction, culminating with the fusion of the two plasma membranes. At the end of this cascade of events, collectively known as sperm capacitation, sperm-induced oocyte activation occurs, generating electrical, morphological and metabolic modifications in the oocyte.

Objective and rationale

The aim of this review is to provide the current state of knowledge regarding the entire process of gamete activation in selected specific animal models that have contributed to our understanding of fertilization in mammals, including humans. Here we describe in detail the reciprocal induction of the two activation processes, the molecules involved and the mechanisms of cell interaction and signal transduction that ultimately result in successful embryo development and creation of a new individual.

Search methods

We carried out a literature survey with no restrictions on publication date (from the early 1950s to March 2016) using PubMed/Medline, Google Scholar and Web of Knowledge by utilizing common keywords applied in the field of fertilization and embryo development. We also screened the complete list of references published in the most recent research articles and relevant reviews published in English (both animal and human studies) on the topics investigated.

Outcomes

Literature on the principal animal models demonstrates that gamete activation is a pre-requisite for successful fertilization, and is a process common to all species studied to date. We provide a detailed description of the dramatic changes in gamete morphology and behavior, the regulatory molecules triggering gamete activation and the intracellular ions and second messengers involved in active metabolic pathways in different species. Recent scientific advances suggest that artificial gamete activation may represent a novel technique to improve human IVF outcomes, but this approach requires caution.

Wider implications

Although controversial, manipulation of gamete activation represents a promising tool for ameliorating the fertilization rate in assisted reproductive technologies. A better knowledge of mechanisms that transform the quiescent oocyte into a pluripotent cell may also provide new insights for the clinical use of stem cells.

Mechanisms of fertilization elucidated by gene-manipulated animals

Capacitation and the acrosome reaction are key phenomena in mammalian fertilization. These phenomena were found more than 60 years ago. However, fundamental questions regarding the nature of capacitation and the timing of the acrosome reaction remain unsolved. Factors were postulated over time, but as their roles were not verified by gene-disruption experiments, widely accepted notions concerning the mechanism of fertilization are facing modifications. Today, although in vitro fertilization systems remain our central research tool, the importance of in vivo observations must be revisited. Here, primarily focusing on our own research, I summarize how in vivo observations using gene-manipulated animals have elucidated new concepts in the mechanisms of fertilization.

Remodeling of the plasma membrane in preparation for sperm-egg recognition: roles of acrosomal proteins

The interaction of sperm with the egg's extracellular matrix, the zona pellucida (ZP) is the first step of the union between male and female gametes. The molecular mechanisms of this process have been studied for the past six decades with the results obtained being both interesting and confusing. In this article, we describe our recent work, which attempts to address two lines of questions from previous studies. First, because there are numerous ZP binding proteins reported by various researchers, how do these proteins act together in sperm–ZP interaction? Second, why do a number of acrosomal proteins have ZP affinity? Are they involved mainly in the initial sperm–ZP binding or rather in anchoring acrosome reacting/reacted spermatozoa to the ZP? Our studies reveal that a number of ZP binding proteins and chaperones, extracted from the anterior sperm head plasma membrane, coexist as high molecular weight (HMW) complexes, and that these complexes in capacitated spermatozoa have preferential ability to bind to the ZP. Zonadhesin (ZAN), known as an acrosomal protein with ZP affinity, is one of these proteins in the HMW complexes. Immunoprecipitation indicates that ZAN interacts with other acrosomal proteins, proacrosin/acrosin and sp32 (ACRBP), also present in the HMW complexes. Immunodetection of ZAN and proacrosin/acrosin on spermatozoa further indicates that both proteins traffic to the sperm head surface during capacitation where the sperm acrosomal matrix is still intact, and therefore they are likely involved in the initial sperm–ZP binding step.

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".

Proteomic Characterization of Pig Sperm Anterior Head Plasma Membrane Reveals Roles of Acrosomal Proteins in ZP3 Binding

The sperm anterior head plasma membrane (APM) is the site where sperm first bind to the zona pellucida (ZP). This binding reaches the maximum following the sperm capacitation process. To gain a better understanding of the sperm-ZP binding mechanisms, we compared protein profiles obtained from mass spectrometry of APM vesicles isolated from non-capacitated and capacitated sperm. The results revealed that ZP-binding proteins were the most abundant group of proteins, with a number of them showing increased levels in capacitated sperm. Blue native gel electrophoresis and far-western blotting revealed presence of high molecular weight (HMW) protein complexes in APM vesicles of both non-capacitated and capacitated sperm, but the complexes (∼750-1300 kDa) from capacitated sperm possessed much higher binding capacity to pig ZP3 glycoprotein. Proteomic analyses indicated that a number of proteins known for their acrosome localization, including zonadhesin, proacrosin/acrosin and ACRBP, were components of capacitated APM HMW complexes, with zonadhesin being the most enriched protein. Our immunofluorescence results further demonstrated that a fraction of these acrosomal proteins was transported to the surface of live acrosome-intact sperm during capacitation. Co-immunoprecipitation indicated that zonadhesin, proacrosin/acrosin and ACRBP interacted with each other and they may traffic as a complex from the acrosome to the sperm surface. Finally, the significance of zonadhesin in the binding of APM HMW complexes to pig ZP3 was demonstrated; the binding ability was decreased following treatment of the complexes with anti-zonadhesin antibody. Our results suggested that acrosomal proteins, especially zonadhesin, played roles in the initial sperm-ZP binding during capacitation.

The challenges involved in elucidating the molecular basis of sperm-egg recognition in mammals and approaches to overcome them

Sexual reproduction is used by many different organisms to create a new generation of genetically distinct progeny. Cells originating from separate sexes or mating types segregate their genetic material into haploid gametes which must then recognize and fuse with each other in a process known as fertilization to form a diploid zygote. Despite the central importance of fertilization, we know remarkably little about the molecular mechanisms that are involved in how gametes recognize each other, particularly in mammals, although the proteins that are displayed on their surfaces are almost certainly involved. This paucity of knowledge is largely due to both the unique biological properties of mammalian gametes (sperm and egg) which make them experimentally difficult to manipulate, and the technical challenges of identifying interactions between membrane-embedded cell surface receptor proteins. In this review, we will discuss our current knowledge of animal gamete recognition, highlighting where important contributions to our understanding were made, why particular model systems were helpful, and why progress in mammals has been particularly challenging. We discuss how the development of mammalian in vitro fertilization and targeted gene disruption in mice were important technological advances that triggered progress. We argue that approaches employed to discover novel interactions between cell surface gamete recognition proteins should account for the unusual biochemical properties of membrane proteins and the typically highly transient nature of their interactions. Finally, we describe how these principles were applied to identify Juno as the egg receptor for sperm Izumo1, an interaction that is essential for mammalian fertilization.

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.

Functional amyloids in the mouse sperm acrosome

The acrosomal matrix (AM) is an insoluble structure within the sperm acrosome that serves as a scaffold controlling the release of AM-associated proteins during the sperm acrosome reaction. The AM also interacts with the zona pellucida (ZP) that surrounds the oocyte, suggesting a remarkable stability that allows its survival despite being surrounded by proteolytic and hydrolytic enzymes released during the acrosome reaction. To date, the mechanism responsible for the stability of the AM is not known. Our studies demonstrate that amyloids are present within the sperm AM and contribute to the formation of an SDS- and formic-acid-resistant core. The AM core contained several known amyloidogenic proteins, as well as many proteins predicted to form amyloid, including several ZP binding proteins, suggesting a functional role for the amyloid core in sperm-ZP interactions. While stable at pH 3, at pH 7, the sperm AM rapidly destabilized. The pH-dependent dispersion of the AM correlated with a change in amyloid structure leading to a loss of mature forms and a gain of immature forms, suggesting that the reversal of amyloid is integral to AM dispersion.

Mechanism of fertilization: a modern view

Despite numerous studies on mammalian fertilization, the mechanisms of fertilization—including the timing of acrosome reaction—remain largely unknown; more accurately described, the classical theory built upon years of layered experimental data is being challenged by recent conflicting evidence provided by gene-manipulated animals. Although in vitro fertilization remains our central research tool, the classical theory’s decline reminds us of the importance of in vivo observations. Here, I describe the essential roles of gene-manipulated animals in elucidating the mechanism of fertilization and the pitfalls of in vitro fertilization studies trapping many researchers.

Antisperm antibodies: invaluable tools toward the identification of sperm proteins involved in fertilization

The identification of sperm proteins involved in fertilization has been the subject of numerous investigations. Much interest has been dedicated to naturally occurring antisperm antibodies (ASA) and their impact in fertility. Their presence in men and women has been associated with 2-50% of infertility cases. ASA may impair pre- and post-fertilization steps. Experimental models have been developed using sperm proteins as immunogens to evaluate their involvement in sperm function. Our team has pursued investigations to assess ASA presence in biological fluids from patients consulting for infertility and their effect on fertilization. We found ASA in follicular fluids with ability of inducing the acrosome reaction and blocking sperm-zona pellucida interaction and used them to identify sperm entities involved in these events. We generated and utilized antibodies against proacrosin/acrosin to characterize the sperm protease system. We implemented an ELISA to detect proacrosin/acrosin antibodies in human sera and evaluated their impact upon fertility by developing in vitro assays and a gene immunization model. This review presents a summary of ASA history, etiology, current approaches for detection and effects upon fertility. ASA (naturally occurring, generated by animal immunization and/or of commercial origin) are invaluable tools to understand the molecular basis of fertilization, better diagnose/treat immunoinfertility and develop immunocontraceptive methods.

Unresolved questions concerning mammalian sperm acrosomal exocytosis

In recent years, the study of mammalian acrosomal exocytosis has produced some major advances that challenge the long-held, general paradigms in the field. Principally, the idea that sperm must be acrosome-intact to bind to the zona pellucida of unfertilized eggs, based largely on in vitro fertilization studies of mouse oocytes denuded of the cumulus oophorus, has been overturned by experiments using state-of-the-art imaging of cumulus-intact oocytes and fertilization experiments where eggs were reinseminated by acrosome-reacted sperm recovered from the perivitelline space of zygotes. In light of these results, this minireview highlights a number of unresolved questions and emphasizes the fact that there is still much work to be done in this exciting field. Future experiments using recently advanced technologies should lead to a more complete and accurate understanding of the molecular mechanisms governing the fertilization process in mammals.

Singular features of fertilization and their impact on the male reproductive system in eutherian mammals

Therian (marsupial and eutherian) mammals have evolved a suite of novel reproductive features – seen variously in their gametes, the steps of fertilization and the male reproductive tract – whose adaptive significance remains unclear. Present evidence for the better-understood eutherian mammals suggests that the ‘prime mover’ in their evolution has been the character of the egg coat, with other such features being adaptations to the consequences of this. Its elastic thickness allows the zona pellucida to stretch to a variable degree and yet remain around the blastocyst during much or all of its expansion before implantation, but its character represents an unusual challenge for spermatozoa. Novel aspects of the acrosome related to this challenge enable it to maintain a relatively prolonged binding after the onset of the acrosome reaction, and the structure, shape and behaviour of the sperm head point to physical thrust as a major element of zona penetration – with the unique configuration of gamete fusion as a sequela of this strategy. In the male, such adaptations are reflected in sperm head formation in the testis and in sperm maturation in the epididymis involving at least the sperm head's structure, plasmalemma and acrosome. This complexity allied to a slow epididymal sperm transport, a relatively modest sperm production and the brief life span of mature spermatozoa kept above the cauda epididymidis could account for the evolution of the sperm storage function – a development seemingly linked, in turn, to the need for sperm capacitation and scrotal evolution.

The cell biology of mammalian fertilization

Fertilization is the process by which eggs and spermatozoa interact, achieve mutual recognition, and fuse to create a zygote, which then develops to form a new individual, thus allowing for the continuity of a species. Despite numerous studies on mammalian fertilization, the molecular mechanisms underpinning the fertilization event remain largely unknown. However, as I summarize here, recent work using both gene-manipulated animals and in vitro studies has begun to elucidate essential sperm and egg molecules and to establish predictive models of successful fertilization.

Partial deletion of chromosome 8 β-defensin cluster confers sperm dysfunction and infertility in male mice

β-defensin peptides are a family of antimicrobial peptides present at mucosal surfaces, with the main site of expression under normal conditions in the male reproductive tract. Although they kill microbes in vitro and interact with immune cells, the precise role of these genes in vivo remains uncertain. We show here that homozygous deletion of a cluster of nine β-defensin genes (DefbΔ9) in the mouse results in male sterility. The sperm derived from the mutants have reduced motility and increased fragility. Epididymal sperm isolated from the cauda should require capacitation to induce the acrosome reaction but sperm from the mutants demonstrate precocious capacitation and increased spontaneous acrosome reaction compared to wild-types but have reduced ability to bind the zona pellucida of oocytes. Ultrastructural examination reveals a defect in microtubule structure of the axoneme with increased disintegration in mutant derived sperm present in the epididymis cauda region, but not in caput region or testes. Consistent with premature acrosome reaction, sperm from mutant animals have significantly increased intracellular calcium content. Thus we demonstrate in vivo that β-defensins are essential for successful sperm maturation, and their disruption leads to alteration in intracellular calcium, inappropriate spontaneous acrosome reaction and profound male infertility.

β-defensins are small molecules, considered primarily to be antimicrobials and important in the first defence response to invading organisms. They are predominantly produced at surfaces in contact with the outside environment and these include skin, airway and reproductive tract. We show here that when we delete from the mouse a subset of nine β-defensin genes, surprisingly the main consequence is that the male mice are completely infertile. When normal sperm leave the male and enter the female reproductive tract they are triggered to undergo a reaction that alters the membrane properties of the sperm and allows fertilisation. We show here that sperm isolated from the male mice, that no longer make these β-defensins, are prematurely ready to fertilise an egg. It is far too early for this to happen and as a consequence the sperm are severely reduced in their ability to move and have a major defect in the structure of their tail. We provide evidence that the reason this has happened is due to a dysregulation of calcium transport. This work is important for understanding defensin gene function in a living organism and may enable the design of novel contraceptives with additional antibiotic ability.

Regulatory T cells and vasectomy

CD4+ CD25+ regulatory T cells (Tregs) strongly influence the early and late autoimmune responses to meiotic germ cell antigens (MGCA) and the gonadal immunopathology in vasectomized mice. This is supported by the published and recently acquired information presented here. Within 24h of unilateral vasectomy (uni-vx) the ipsilateral epididymis undergoes epithelial cell apoptosis followed by necrosis, severe inflammation, and granuloma formation. Unexpectedly, vasectomy alone induced MGCA-specific tolerance. In contrast, uni-vx plus simultaneous Treg depletion resulted in MGCA-specific autoimmune response and bilateral autoimmune orchitis. Both tolerance and autoimmunity were strictly linked to the early epididymal injury. We now discovered that testicular autoimmunity in uni-vx mice did not occur when Treg depletion was delayed by one week. Remarkably, this delayed Treg depletion also prevented tolerance induction. Therefore, tolerance depends on a rapid de novo Treg response to MGCA exposed after vasectomy. Moreover, tolerance was blunted in mice genetically deficient in PD-1 ligand, suggesting the involvement of induced Treg. We conclude that pre-existing natural Treg prevents post-vasectomy autoimmunity, whereas vasectomy-induced Treg maintains post-vasectomy tolerance. We further discovered that vasectomized mice were still resistant to autoimmune orchitis induction for at least 12-16 months; thus, tolerance is long-lasting. Although significant sperm autoantibodies of low titers became detectable in uni-vx mice at 7 months, the antibody titers fluctuated over time, suggesting a dynamic "balance" between the autoimmune and tolerance states. Finally, we observed severe epididymal fibrosis and hypo-spermatogenesis at 12 months after uni-vx: findings of highly critical clinical significance.