Tssk6 is required for Izumo relocalization and gamete fusion in the mouse

Testis-specific serine kinase 6 (TSSK6) is abnormally expressed in colorectal cancer and promotes oncogenic behaviors

Cancer testis antigens (CTAs) are a collection of proteins whose expression is normally restricted to the gamete but abnormally activated in a wide variety of tumors. The CTA, Testis-specific serine kinase 6 (TSSK6), is essential for male fertility in mice. The functional relevance of TSSK6 to cancer, if any, has not previously been investigated. Here we find that TSSK6 is frequently anomalously expressed in colorectal cancer and patients with elevated TSSK6 expression have reduced relapse-free survival. Depletion of TSSK6 from colorectal cancer cells attenuates anchorage-independent growth, invasion, and growth in vivo. Conversely, overexpression of TSSK6 enhances anchorage independence and invasion in vitro as well as in vivo tumor growth. Notably, ectopic expression of TSSK6 in semi-transformed human colonic epithelial cells is sufficient to confer anchorage independence and enhance invasion. In somatic cells, TSSK6 co-localizes with and enhances the formation of paxillin and tensin-positive foci at the cell periphery, suggesting a function in focal adhesion formation. Importantly, TSSK6 kinase activity is essential to induce these tumorigenic behaviors. Our findings establish that TSSK6 exhibits oncogenic activity when abnormally expressed in colorectal cancer cells. Thus, TSSK6 is a previously unrecognized intervention target for therapy, which could exhibit an exceptionally broad therapeutic window.

Characterization of sexual maturity-associated N6-methyladenosine in boar testes

BACKGROUND

The health and size of the testes are crucial for boar fertility. Testicular development is tightly regulated by epigenetics. N6-methyladenosine (m6A) modification is a prevalent internal modification on mRNA and plays an important role in development. The mRNA m6A methylation in boar testicular development still needs to be investigated.

RESULTS

Using the MeRIP-seq technique, we identify and profile m6A modification in boar testes between piglets and adults. The results showed 7783 distinct m6A peaks in piglets and 6590 distinct m6A peaks in adults, with 2,471 peaks shared between the two groups. Enrichment of GO and KEGG analysis reveal dynamic m6A methylation in various biological processes and signalling pathways. Meanwhile, we conjointly analyzed differentially methylated and expressed genes in boar testes before and after sexual maturity, and reproductive related genes (TLE4, TSSK3, TSSK6, C11ORF94, PATZ1, PHLPP1 and PAQR7) were identified. Functional enrichment analysis showed that differential genes are associated with important biological functions, including regulation of growth and development, regulation of metabolic processes and protein catabolic processes.

CONCLUSION

The results demonstrate that m6A methylation, differential expression and the related signalling pathways are crucial for boar testicular development. These results suggest a role for m6A modification in boar testicular development and provided a resource for future studies on m6A function in boar testicular development.

The Cancer Testis Antigen Testis Specific Serine Kinase 6 (TSSK6) is abnormally expressed in colorectal cancer and promotes oncogenic behaviors

Cancer testis antigens (CTAs) are a collection of proteins whose expression is normally restricted to the gamete, but abnormally activated in a wide variety of tumors. The CTA, Testis specific serine kinase 6 (TSSK6), is essential for male fertility in mice. Functional relevance of TSSK6 to cancer, if any, has not previously been investigated. Here we find that TSSK6 is frequently anomalously expressed in colorectal cancer and patients with elevated TSSK6 expression have reduced relapse free survival. Depletion of TSSK6 from colorectal cancer cells attenuates anchorage independent growth, invasion and growth in vivo. Conversely, overexpression of TSSK6 enhances anchorage independence and invasion in vitro as well as in vivo tumor growth. Notably, ectopic expression of TSSK6 in semi-transformed human colonic epithelial cells is sufficient to confer anchorage independence and enhance invasion. In somatic cells, TSSK6 co-localizes with and enhances the formation of paxillin and tensin positive foci at the cell periphery, suggesting a function in focal adhesion formation. Importantly, TSSK6 kinase activity is essential to induce these tumorigenic behaviors. Our findings establish that TSSK6 exhibits oncogenic activity when abnormally expressed in colorectal cancer cells. Thus, TSSK6 is a previously unrecognized intervention target for therapy, which could exhibit an exceptionally broad therapeutic window.

Coiled-coil domain-containing 38 is required for acrosome biogenesis and fibrous sheath assembly in mice

During spermiogenesis, haploid spermatids undergo dramatic morphological changes to form slender sperm flagella and cap-like acrosomes, which are required for successful fertilization. Severe deformities in flagella cause a male infertility syndrome, multiple morphological abnormalities of the flagella (MMAF), while acrosomal hypoplasia in some cases leads to sub-optimal embryonic developmental potential. However, evidence regarding the occurrence of acrosomal hypoplasia in MMAF is limited. Here, we report the generation of base-edited mice knocked out for coiled-coil domain-containing 38 (Ccdc38) via inducing a nonsense mutation and find that the males are infertile. The Ccdc38-KO sperm display acrosomal hypoplasia and typical MMAF phenotypes. We find that the acrosomal membrane is loosely anchored to the nucleus and fibrous sheaths are disorganized in Ccdc38-KO sperm. Further analyses reveal that Ccdc38 knockout causes a decreased level of TEKT3, a protein associated with acrosome biogenesis, in testes and an aberrant distribution of TEKT3 in sperm. We finally show that intracytoplasmic sperm injection overcomes Ccdc38-related infertility. Our study thus reveals a previously unknown role for CCDC38 in acrosome biogenesis and provides additional evidence for the occurrence of acrosomal hypoplasia in MMAF.

IZUMO1 Receptor Localization during Hyaluronic Acid Selection in Human Spermatozoa

IZUMO1 is an acrosome transmembrane protein implicated in the adhesion and fusion of gametes. This study aims to describe the distribution of IZUMO1 in human sperm under different physiological conditions: before capacitation (NCS), at one-hour capacitation (CS1), after a hyaluronic acid (HA) selection test (mature, MS1 and immature, IS1), and induced acrosome reaction from one-hour-capacitated sperm (ARS1). The data obtained in NCS, CS1, and MS1 significantly highlight dotted fluorescence in the acrosomal region (P1) as the major staining pattern (~70%). Moreover, we describe a new distribution pattern (P2) with a dotted acrosomal region and a labelled equatorial region that significantly increases in HA-bound spermatozoa, suggesting the onset of the migration of IZUMO1. In contrast, unbound spermatozoa presented an increase in P3 (equatorial region labelled) and P4 (not labelled). Finally, costaining to observe IZUMO1 distribution and acrosome status was performed in ARS1. Interestingly, we reported a variety of combinations between the IZUMO1 staining patterns and the acrosomal stages. In conclusion, these data show as a novelty the diffusion of the IZUMO1 protein during different physiological conditions that could contribute to the improvement in sperm selection techniques.

Expression of Testis-specific Serine/Threonine Kinases during the Reproductive and Nonreproductive Seasons and Their Localization in Mature Spermatozoa of Tree Shrews (Tupaia belangeri)

Tree shrews display obvious reproductive cycles, and sexually mature male tree shrews produce little or no sperm with extremely low motility during the nonreproductive season; the mechanism underlying this phenomenon remains unknown. Because testis-specific serine/threonine kinases (TSSK) are specifically expressed in the testis and male germ cells of mammals, we hypothesized that they may have an important role in spermatogenesis or sperm function regulation in tree shrews. In addition, the expression, distribution, subcellular localization, and dynamic changes of TSSK in tree shrew sperm are unclear. Here we show that during the reproductive season, the seminiferous tubules were significantly larger as compared with the nonreproductive season and contained mature sperm and other germ cells. The mRNA expression of Tssk genes in testis was significantly higher than that in other tissues, and the mRNA level in the testis during the reproductive season was significantly higher than that in nonreproductive season. In addition, the mRNA level of Tssk3 in the testis and sperm was significantly higher than that of other members. Specifically, Tssk1 mRNA was distributed in the acrosome and throughout the flagellum of tree shrew sperm, Tssk2 was present in the acrosome, Tssk3 was localized to postacrosomal region and relocated to the main part of the flagellum after capacitation, and Tssk6 was distributed in the acrosome and postacrosomal region. These results indicate that the TSSK are important regulating reproductive function in tree shrews.

Structural specializations of the sperm tail

Sperm motility is crucial to reproductive success in sexually reproducing organisms. Impaired sperm movement causes male infertility, which is increasing globally. Sperm are powered by a microtubule-based molecular machine-the axoneme-but it is unclear how axonemal microtubules are ornamented to support motility in diverse fertilization environments. Here, we present high-resolution structures of native axonemal doublet microtubules (DMTs) from sea urchin and bovine sperm, representing external and internal fertilizers. We identify >60 proteins decorating sperm DMTs; at least 15 are sperm associated and 16 are linked to infertility. By comparing DMTs across species and cell types, we define core microtubule inner proteins (MIPs) and analyze evolution of the tektin bundle. We identify conserved axonemal microtubule-associated proteins (MAPs) with unique tubulin-binding modes. Additionally, we identify a testis-specific serine/threonine kinase that links DMTs to outer dense fibers in mammalian sperm. Our study provides structural foundations for understanding sperm evolution, motility, and dysfunction at a molecular level.

Analyzing the effect of heparin on in vitro capacitation and spermatozoal RNA population in goats

Heparin is a glycosaminoglycan polymer that is commonly used as an anticoagulant. Heparin also induces in vitro capacitation in spermatozoa, although its molecular mechanism is elusive. This study investigated the effect of heparin on in vitro capacitation and spermatozoal RNA (spRNA) population in goats. Goat spermatozoa were treated with 20 μM heparin for 0-6 h and evaluated for motility, capacitation, acrosome reaction, and spRNA population by RNA sequencing (RNA-seq). It was observed that heparin enhanced sperm motility up to 6 h of incubation (p < 0.05). Heparin also induced capacitation and acrosome reaction within 4 h. RNA-seq identified 1254 differentially expressed genes (DEGs) between heparin-treated and control spermatozoa. Most DEGs (1251 nos.) were upregulated and included 1090 protein-coding genes. A few genes (PRND, ITPR1, LLCFC1, and CHRM2) showed >5-fold increased expression in heparin-treated spermatozoa compared to the control. The upregulated genes were found to be involved in cAMP-PKA, PI3-Akt, calcium, MAPK signaling, and oxidative stress pathways. DCFDA staining confirmed the increased oxidative stress in heparin-treated spermatozoa compared to the control (p < 0.05). In conclusion, the results of the present study suggest that heparin enhances sperm motility and induces capacitation by upregulation of the spRNA population and oxidative stress pathway.

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.

Cytochalasin D restores nuclear size acting on F-actin and IZUMO1 localization in low-quality spermatozoa

In spermatozoa, the nuclear F-actin supports the acroplaxome, a subacrosomal structure involved in the correct exposure of several acrosomal membrane proteins; among them, the glycoprotein IZUMO1 is the major protein involved in sperm-oocyte fusion. Nuclear F-actin is also involved in sperm head shaping and chromosome compartmentalization. To date, few notions regarding the bivalent role of F-actin on sperm chromatin organization and IZUMO1 positioning have been reported. In our work, we characterized subcellular organization of F-actin in human high- and low-quality spermatozoa (A- and B-SPZ), respectively, showing that F-actin over-expression in sperm head of B-SPZ affected IZUMO1 localization. A correct IZUMO1 repositioning following in vitro induction of F-actin depolymerization, by cytochalasin D treatment, occurred. Interestingly, F-actin depolymerization was also associated with a correct acrosome repositioning, thus to favor a proper acrosome reaction onset, with changes in sperm nuclear size parameters and histone acetylation rate reaching high-quality conditions. In conclusion, the current work shows a key role of F-actin in the control of IZUMO1 localization as well as chromatin remodeling and acetylation events.

Intra and intercellular signals governing sperm maturation

After their production in the testis, spermatozoa do not have the capacity to move progressively and are unable to fertilise an oocyte. They sequentially acquire these abilities following their maturation in the epididymis and their capacitation/hyperactivation in the female reproductive system. As gene transcription is silenced in spermatozoa, extracellular factors released from the epididymal epithelium and from secretory glands allow spermatozoa to acquire bioactive molecules and to undergo intrinsic modifications. These modifications include epigenetic changes and post-translational modifications of endogenous proteins, which are important processes in sperm maturation. This article emphasises the roles played by extracellular factors secreted by the epididymis and accessory glands in the control of sperm intercellular signallings and fertilising abilities.

Comparative analysis of the testes from wild-type and Alkbh5-knockout mice using single-cell RNA sequencing

The RNA demethylase ALKBH5 is regarded as the “eraser” in N6-methyladenosine modification. ALKBH5 deficiency causes male infertility in mice; however, the mechanisms that confer disruption of spermatogenesis are not completely clear. In this study, we profiled testis samples from wild-type and Alkbh5-knockout mice using single-cell RNA sequencing. We obtained single-cell RNA sequencing data of 5,596 and 6,816 testis cells from a wild-type and a knockout mouse, respectively. There were differences detected between the transcriptional profiles of the groups at various germ cell developmental stages. This ranged from the development of spermatogonia to sperm cells, in macrophages, Sertoli cells, and Leydig cells. We identified the differentially expressed genes related to spermatogenesis in germ cells and somatic cells (Sertoli cells and Leydig cells) and evaluated their functions and associated pathways, such as chromatin-related functional pathways, through gene ontology enrichment analysis. This study provides the first single-cell RNA sequencing profile of the testes of ALKBH5-deficient mice. This highlights that ALKBH5 is an important gene for germ cell development and spermatogenesis and offers new molecular mechanistic insights. These findings could provide the basis for further research into the causes and treatment of male infertility.

The Role of Sperm Proteins IZUMO1 and TMEM95 in Mammalian Fertilization: A Systematic Review

Gamete membrane fusion is a critical cellular event in sexual reproduction. In addition, the generation of knockout models has provided a powerful tool for testing the functional relevance of proteins thought to be involved in mammalian fertilization, suggesting IZUMO1 and TMEM95 (transmembrane protein 95) as essential proteins. However, the molecular mechanisms underlying the process remain largely unknown. Therefore, the aim of this study was to summarize the current knowledge about IZUMO1 and TMEM95 during mammalian fertilization. Hence, three distinct databases were consulted—PubMed, Scopus and Web of Science—using single keywords. As a result, a total of 429 articles were identified. Based on both inclusion and exclusion criteria, the final number of articles included in this study was 103. The results showed that IZUMO1 is mostly studied in rodents whereas TMEM95 is studied primarily in bovines. Despite the research, the topological localization of IZUMO1 remains controversial. IZUMO1 may be involved in organizing or stabilizing a multiprotein complex essential for the membrane fusion in which TMEM95 could act as a fusogen due to its possible interaction with IZUMO1. Overall, the expression of these two proteins is not sufficient for sperm–oocyte fusion; therefore, other molecules must be involved in the membrane fusion process.

Mysteries and unsolved problems of mammalian fertilization and related topics

Mammalian fertilization is a fascinating process that leads to the formation of a new individual. Eggs and sperm are complex cells that must meet at the appropriate time and position within the female reproductive tract for successful fertilization. I have been studying various aspects of mammalian fertilization over 60 years. In this review, I discuss many different aspects of mammalian fertilization, some of my laboratory's contribution to the field, and discuss enigmas and mysteries that remain to be solved.

High Resolution Proteomic Analysis of Subcellular Fractionated Boar Spermatozoa Provides Comprehensive Insights Into Perinuclear Theca-Residing Proteins

The perinuclear theca (PT) is a highly condensed, largely insoluble protein structure that surrounds the nucleus of eutherian spermatozoa. Recent reports have indicated that the PT unexpectedly houses several somatic proteins, such as core histones, which may be important post-fertilization during re-modelling of the male pronucleus, yet little is known regarding the overall proteomic composition of the PT. Here, we report the first in depth, label-free proteomic characterization of the PT of boar spermatozoa following the implementation of a long-established subcellular fractionation protocol designed to increase the detection of low abundance proteins. A total of 1,802 proteins were identified, a result that represents unparalleled depth of coverage for the boar sperm proteome and exceeds the entire annotated proteome of the Sus scrofa species so far. In the PT structure itself, we identified 813 proteins and confirmed the presence of previously characterized PT proteins including the core histones H2A, H2B, H3 and H4, as well as Ras-related protein Rab-2A (RAB2A) and Rab-2B (RAB2B) amongst other RAB proteins. In addition to these previously characterized PT proteins, our data revealed that the PT is replete in proteins critical for sperm-egg fusion and egg activation, including: Izumo family members 1–4 (IZUMO1-4) and phosphoinositide specific phospholipase ζ (PLCZ1). Through Ingenuity Pathway Analysis, we found surprising enrichment of endoplasmic reticulum (ER) proteins and the ER-stress response in the PT. This is particularly intriguing as it is currently held that the ER structure is lost during testicular sperm maturation. Using the String and Cytoscape tools to visualize protein-protein interactions revealed an intricate network of PT protein complexes, including numerous proteasome subunits. Collectively, these data suggest that the PT may be a unique site of cellular homeostasis that houses an abundance of protein degradation machinery. This fits with previous observations that the PT structure dissociates first within the oocyte post-fertilization. It remains to be explored whether proteasome subunits within the PT actively assist in the protein degradation of paternal cell structures post-fertilization and how aberrations in PT protein content may delay embryonic development.

Sperm proteins ODF2 and PAWP as markers of fertility in breeding bulls

Low fertility is the single most important factor limiting livestock reproductive performance, adversely affecting the cattle industry and causing millions of dollars of economic loss. In the livestock industry, male fertility is of crucial importance for the reproductive performance of livestock. However, there is a lack of reliable biomarkers to predict bull fertility in artificial insemination service. The objective of this study was to identify sperm proteins as biomarkers for bull fertility. To discover candidate sperm quality biomarkers, sperm proteome profiling was conducted in extreme high- and extreme low-fertile bulls selected from a pool of 1000 AI sires with varied fertility. Thirty-two differentially expressed proteins were identified. Among them, high levels of sperm outer dense fiber of sperm tails 2 (ODF2) and post-acrosomal assembly of sperm head protein (PAWP/WBP2NL) represented the most extreme differences in quantity between high- and low-fertility bulls. Protein immunodetection and flow cytometry used to validate these putative fertility markers in a combined cohort of 154 AI sires. Both ODF2 and PAWP correlated significantly with fertility. In conclusion, ODF2 and PAWP can be used to assess semen quality and predict sire fertility.

Significance and Relevance of Spermatozoal RNAs to Male Fertility in Livestock

Livestock production contributes to a significant part of the economy in developing countries. Although artificial insemination techniques brought substantial improvements in reproductive efficiency, male infertility remains a leading challenge in livestock. Current strategies for the diagnosis of male infertility largely depend on the evaluation of semen parameters and fail to diagnose idiopathic infertility in most cases. Recent evidences show that spermatozoa contains a suit of RNA population whose profile differs between fertile and infertile males. Studies have also demonstrated the crucial roles of spermatozoal RNA (spRNA) in spermatogenesis, fertilization, and early embryonic development. Thus, the spRNA profile may serve as unique molecular signatures of fertile sperm and may play pivotal roles in the diagnosis and treatment of male fertility. This manuscript provides an update on various spRNA populations, including protein-coding and non-coding RNAs, in livestock species and their potential role in semen quality, particularly sperm motility, freezability, and fertility. The contribution of seminal plasma to the spRNA population is also discussed. Furthermore, we discussed the significance of rare non-coding RNAs (ncRNAs) such as long ncRNAs (lncRNAs) and circular RNAs (circRNAs) in spermatogenic events.

TSSK3, a novel target for male contraception, is required for spermiogenesis

We have previously shown that members of the family of testis-specific serine/threonine kinases (TSSKs) are post-meiotically expressed in testicular germ cells and in mature sperm in mammals. The restricted post-meiotic expression of TSSKs as well as the importance of phosphorylation in signaling processes strongly suggest that TSSKs have an important role in germ cell differentiation and/or sperm function. This prediction has been supported by the reported sterile phenotype of the TSSK6 knock-out (KO) mice and of the double TSSK1/TSSK2 KO. The aim of this study was to develop KO mouse models of TSSK3 and to validate this kinase as a target for the development of a male contraceptive. We used CRISPR/Cas9 technology to generate the TSSK3 KO allele on B6D2F1 background mice. Male heterozygous pups were used to establish three independent TSSK3 KO lines. After natural mating of TSSK3 KO males, females that presented a plug (indicative of mating) were monitored for the following 24 days and no pregnancies or pups were found. Sperm numbers were drastically reduced in all three KO lines and, remarkably, round spermatids were detected in the cauda epididymis of KO mice. From the small population of sperm recovered, severe morphology defects were detected. Our results indicate an essential role of TSSK3 in spermiogenesis and support this kinase as a suitable candidate for the development of novel nonhormonal male contraceptives.

Cyclic FEE Peptide Improves Human Sperm Movement Parameters without Modification of Their Energy Metabolism

Cyclic fertilin peptide (cFEE: phenylalanine, glutamic acid; glutamic acid) improves gamete interaction in humans. We investigate whether it could be via improvement of sperm movement parameters and their mitochondrial ATP production. Sperm movement parameters were studied using computer-assisted sperm analysis (CASA) in sperm samples from 38 patients with normal sperm in medium supplemented with cyclic fertilin against a control group. Sperm mitochondrial functions were studied using donor’s sperm, incubated or not with cFEE. It was evaluated by the measurement of their ATP production using bioluminescence, their respiration by high resolution oxygraphy, and of mitochondrial membrane potential (MMP) using potentiometric dyes and flow cytometry. cFEE significantly improved sperm movement parameters and percentage of hyperactivated sperm. Impact of inhibitors showed OXPHOS as the predominant energy source for sperm movement. However, cFEE had no significant impact on any of the analyzed mitochondrial bioenergetic parameters, suggesting that it could act via a more efficient use of its energy resources.

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

BACKGROUND

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

OBJECTIVE AND RATIONALE

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

SEARCH METHODS

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

OUTCOMES

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

WIDER IMPLICATIONS

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

The cell biology of fertilization: Gamete attachment and fusion

Fertilization is defined as the union of two gametes. During fertilization, sperm and egg fuse to form a diploid zygote to initiate prenatal development. In mammals, fertilization involves multiple ordered steps, including the acrosome reaction, zona pellucida penetration, sperm-egg attachment, and membrane fusion. Given the success of in vitro fertilization, one would think that the mechanisms of fertilization are understood; however, the precise details for many of the steps in fertilization remain a mystery. Recent studies using genetic knockout mouse models and structural biology are providing valuable insight into the molecular basis of sperm-egg attachment and fusion. Here, we review the cell biology of fertilization, specifically summarizing data from recent structural and functional studies that provide insights into the interactions involved in human gamete attachment and fusion.

KinOrtho: a method for mapping human kinase orthologs across the tree of life and illuminating understudied kinases

BACKGROUND

Protein kinases are among the largest druggable family of signaling proteins, involved in various human diseases, including cancers and neurodegenerative disorders. Despite their clinical relevance, nearly 30% of the 545 human protein kinases remain highly understudied. Comparative genomics is a powerful approach for predicting and investigating the functions of understudied kinases. However, an incomplete knowledge of kinase orthologs across fully sequenced kinomes severely limits the application of comparative genomics approaches for illuminating understudied kinases. Here, we introduce KinOrtho, a query- and graph-based orthology inference method that combines full-length and domain-based approaches to map one-to-one kinase orthologs across 17 thousand species.

RESULTS

Using multiple metrics, we show that KinOrtho performed better than existing methods in identifying kinase orthologs across evolutionarily divergent species and eliminated potential false positives by flagging sequences without a proper kinase domain for further evaluation. We demonstrate the advantage of using domain-based approaches for identifying domain fusion events, highlighting a case between an understudied serine/threonine kinase TAOK1 and a metabolic kinase PIK3C2A with high co-expression in human cells. We also identify evolutionary fission events involving the understudied OBSCN kinase domains, further highlighting the value of domain-based orthology inference approaches. Using KinOrtho-defined orthologs, Gene Ontology annotations, and machine learning, we propose putative biological functions of several understudied kinases, including the role of TP53RK in cell cycle checkpoint(s), the involvement of TSSK3 and TSSK6 in acrosomal vesicle localization, and potential functions for the ULK4 pseudokinase in neuronal development.

CONCLUSIONS

In sum, KinOrtho presents a novel query-based tool to identify one-to-one orthologous relationships across thousands of proteomes that can be applied to any protein family of interest. We exploit KinOrtho here to identify kinase orthologs and show that its well-curated kinome ortholog set can serve as a valuable resource for illuminating understudied kinases, and the KinOrtho framework can be extended to any protein-family of interest.

Targeted knock-in mice with a human mutation in GRTH/DDX25 reveals the essential role of phosphorylated GRTH in spermatid development during spermatogenesis

Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) is a testis specific member of the DEAD-box family of RNA helicases expressed in meiotic and haploid germ cells which plays an essential role in spermatogenesis. There are two species of GRTH the 56 kDa non-phospho and 61 kDa phospho forms. Our early studies revealed a missense mutation (R242H) of GRTH in azoospermic men that when expressed in COS1-cells lack the phospho-form of GRTH. To investigate the role of the phospho-GRTH species in spermatogenesis, we generated a GRTH knock-in (KI) transgenic mice with the R242H mutation. GRTH-KI mice are sterile with reduced testis size, lack sperm with spermatogenic arrest at round spermatid stage and loss of the cytoplasmic phospho-GRTH species. Electron microscopy studies revealed reduction in the size of chromatoid bodies (CB) of round spermatids (RS) and germ cell apoptosis. We observed absence of phospho-GRTH in the CB of RS. Complete loss of chromatin remodeling and related proteins such as TP2, PRM2, TSSK6 and marked reduction of their respective mRNAs and half-lives were observed in GRTH-KI mice. We showed that phospho-GRTH has a role in TP2 translation and revealed its occurrence in a 3' UTR dependent manner. These findings demonstrate the relevance of phospho-GRTH in the structure of the chromatoid body, spermatid development and completion of spermatogenesis and provide an avenue for the development of a male contraceptive.

Cleavage of SPACA1 regulates assembly of sperm-egg membrane fusion machinery in mature spermatozoa†

The acrosome reaction is a multi-step event essential for physiological fertilization. During the acrosome reaction, gamete fusion-related factor IZUMO1 translocates from the anterior acrosome to the equatorial segment and assembles the gamete fusion machinery. The morphological changes in the acrosome reaction process have been well studied, but little is known about the molecular mechanisms of acrosome reorganization essential for physiological gamete membrane fusion. To elucidate the molecular mechanisms of IZUMO1 translocation, the steps of the acrosome reaction during that process must be clarified. In this study, we established a method to detect the early steps of the acrosome reaction and subdivided the process into seven populations through the use of two epitope-defined antibodies, anti-IZUMO1 and anti-SPACA1, a fertilization-inhibiting antibody. We found that part of the SPACA1 C-terminus in the periacrosomal space was cleaved and had begun to disappear when the vesiculation of the anterior acrosome occurred. The IZUMO1 epitope externalized from the acrosomal lumen before acrosomal vesiculation and phosphorylation of IZUMO1 occurred during the translocation to the equatorial segment. IZUMO1 circumvented the area of the equatorial segment where the SPACA1C-terminus was still localized. We therefore propose an IZUMO1 translocation model and involvement of SPACA1.

Comparative Transcriptomic Analysis of Spermatozoa From High- and Low-Fertile Crossbred Bulls: Implications for Fertility Prediction

Crossbred bulls produced by crossing Bos taurus and Bos indicus suffer with high incidence of infertility/subfertility problems; however, the etiology remains poorly understood. The uncertain predictability and the inability of semen evaluation techniques to maintain constant correlation with fertility demand for alternate methods for bull fertility prediction. Therefore, in this study, the global differential gene expression between high- and low-fertile crossbred bull sperm was assessed using a high-throughput RNA sequencing technique with the aim to identify transcripts associated with crossbred bull fertility. Crossbred bull sperm contained transcripts for 13,563 genes, in which 2,093 were unique to high-fertile and 5,454 were unique to low-fertile bulls. After normalization of data, a total of 776 transcripts were detected, in which 84 and 168 transcripts were unique to high-fertile and low-fertile bulls, respectively. A total of 176 transcripts were upregulated (fold change > 1) and 209 were downregulated (<1) in low-fertile bulls. Gene ontology analysis identified that the sperm transcripts involved in the oxidative phosphorylation pathway and biological process such as multicellular organism development, spermatogenesis, and in utero embryonic development were downregulated in low-fertile crossbred bull sperm. Sperm transcripts upregulated and unique to low-fertile bulls were majorly involved in translation (biological process) and ribosomal pathway. With the use of RT-qPCR, selected sperm transcripts (n = 12) were validated in crossbred bulls (n = 12) with different fertility ratings and found that the transcriptional abundance of ZNF706, CRISP2, TNP2, and TNP1 genes was significantly (p < 0.05) lower in low-fertile bulls than high-fertile bulls and was positively (p < 0.05) correlated with conception rate. It is inferred that impaired oxidative phosphorylation could be the predominant reason for low fertility in crossbred bulls and that transcriptional abundance of ZNF706, CRISP2, TNP2, and TNP1 genes could serve as potential biomarkers for fertility in crossbred bulls.

Deletion of the PDZ-binding kinase (Pbk) gene does not affect male fertility in mice

The PDZ-binding kinase (PBK) protein is localised exclusively in spermatogenic cells, such as spermatogonia, spermatocytes and round spermatids, of the adult testis. However, its role in male fertility remains unknown. Analysis of adult Pbk-knockout (KO) male mice showed no significant difference in the weight of the testes, epididymis and seminal vesicle compared with adult wild-type (WT) mice. There were no significant differences in testis morphology, tubule diameter and the number of offspring born to females mated with KO or WT male mice. Sperm number, motility and morphology did not differ significantly between KO and WT mice. The oocyte fertilisation rate and embryo development following IVF were comparable between groups fertilised using spermatozoa from KO versus WT mice (P>0.05). Further analysis revealed that the phosphorylation of the mitogen-activated protein kinases (MAPKs) p38 kinase, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinases was dysregulated in the testis of KO mice. In conclusion, Pbk-KO male mice are fertile and their spermatozoa and testis do not show any morphological and functional abnormalities despite the dysregulated phosphorylation of MAPKs. It is likely that functional redundancy of PBK and overlapping substrate specificities of the MAPK superfamily compensated for the loss of PBK from the testis.

Expression of the Testis-Specific Serine/Threonine Kinases Suggests Their Role in Spermiogenesis of Bay Scallop Argopecten irradians

Members of the testis-specific serine/threonine kinases (Tssk) family play critical roles in spermatogenesis in vertebrates. But in mollusks, research on Tssk family is still lagging. In this study, we systematically identified Tssk family based on the genomic and transcriptomic data from a commercially important scallop Argopecten irradians and detected the spatiotemporal expression in adult gonads. Five members were identified, with the gene length varying from 1,068 to 10,729 bp and the protein length ranging from 294 to 731 aa. All the Tssks possess a serine/threonine protein kinase catalytic (S_TKc) domain. Phylogenetic analysis revealed existence of four homologs of vertebrate Tssk1/2, Tssk3, Tssk4, Tssk5, and absence of Tssk6 in the scallop. The remaining gene (Tssk7) formed an independent clade with Tssks of other mollusks and arthropods, indicating that it may be a new member of Tssk family unique to protostomes. By investigating the expression of Tssks in four developmental stages of testes and ovaries, we found all five Tssks were primarily expressed in mature testis. In situ hybridization experiment revealed the five Tssks were localized in the spermatids and spermatozoa. The testis-predominant expression of Tssk family suggests Tssks may play pivotal roles in spermiogenesis in the scallop. Our study provides basic information on the characteristics and expression profiles of Tssk family of A. irradians. To our knowledge, it represents the first comprehensive analysis of Tssk family in mollusks.

Comparative transcriptome analysis of three gonadal development stages reveals potential genes involved in gametogenesis of the fluted giant clam (Tridacna squamosa)

BACKGROUND

Gonad development and differentiation is an essential function for all sexually reproducing species, and many aspects of these developmental processes are highly conserved among the metazoa. However, the mechanisms underlying gonad development and gametogenesis remain unclear in Tridacna squamosa, a large-size bivalve of great ecological value. They are protandrous simultaneous hermaphrodites, with the male gonad maturing first, eventually followed by the female gonads. In this study, nine gonad libraries representing resting, male and hermaphrodite stages in T. squamosa were performed to identify the molecular mechanisms.

RESULTS

Sixteen thousand four hundred ninety-one unigenes were annotated in the NCBI non-redundant protein database. Among the annotated unigenes, 5091 and 7328 unigenes were assigned to Gene Ontology categories and the Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway database, respectively. A total of 4763 differentially expressed genes (DEGs) were identified by comparing male to resting gonads, consisting of 3499 which were comparatively upregulated in males and 1264 which were downregulated in males. Six hundred-ninteen DEGs between male and hermaphroditic gonads were identified, with 518 DEGs more strongly expressed in hermaphrodites and 101 more strongly expressed in males. GO (Gene Ontology) and KEGG pathway analyses revealed that various biological functions and processes, including functions related to the endocrine system, oocyte meiosis, carbon metabolism, and the cell cycle, were involved in regulating gonadal development and gametogenesis in T. squamosa. Testis-specific serine/threonine kinases 1 (TSSK1), TSSK4, TSSK5, Doublesex- and mab-3-related transcription factor 1 (DMRT1), SOX, Sperm surface protein 17 (SP17) and other genes were involved in male gonadal development in Tridacna squamosal. Both spermatogenesis- (TSSK4, spermatogenesis-associated protein 17, spermatogenesis-associated protein 8, sperm motility kinase X, SP17) and oogenesis-related genes (zona pellucida protein, Forkhead Box L2, Vitellogenin, Vitellogenin receptor, 5-hydroxytryptamine, 5-hydroxytryptamine receptor) were simultaneously highly expressed in the hermaphroditic gonad to maintain the hermaphroditism of T. squamosa.

CONCLUSION

All these results from our study will facilitate better understanding of the molecular mechanisms underlying giant clam gonad development and gametogenesis, which can provided a base on obtaining excellent gametes during the seed production process for giant clams.

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.

Partial Sperm beta1 Integrin Subunit Deletion Proves its Involvement in Mouse Gamete Adhesion/Fusion

We have previously shown, using antibodies, that the sperm alpha6beta1 integrin is involved in mouse gamete fusion in vitro. Here we report the conditional knockdown of the sperm Itgb1 gene. It induced a drastic failure of sperm fusogenic ability with sperm accumulation in the perivitelline space of in vitro inseminated oocytes deleted or not for the Itgb1 gene. These data demonstrate that sperm, but not oocyte, beta1 integrin subunit is involved in gamete adhesion/fusion. Curiously, knockdown males were fertile in vivo probably because of the incomplete Cre-mediated deletion of the sperm Itgb1 floxed gene. Indeed, this was shown by Western blot analysis and confirmed by both the viability and litter size of pups obtained by mating partially sperm Itgb1 deleted males with females producing completely deleted Itgb1 oocytes. Because of the total peri-implantation lethality of Itgb1 deletion in mice, we assume that sperm that escaped the Itgb1 excision seemed to be preferentially used to fertilize in vivo. Here, we showed for the first time that the deletion, even partial, of the sperm Itgb1 gene makes the sperm unable to normally fertilize oocytes. However, to elucidate the question of the essentiality of its role during fertilization, further investigations using a mouse expressing a recombinase more effective in male germ cells are necessary.

RNA-Seq analysis reveals functionally relevant coding and non-coding RNAs in crossbred bull spermatozoa

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RNA-Seq analysis was done to characterize the transcriptome of crossbred bull spermatozoa.

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Among the 13,814 transcripts detected, 431 had FPKM > 1 and 13,673 had FPKM > 0 or < 1.

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Coding and non-coding RNAs account for 13,145 (95.15%) and 152 (1.1%), respectively.

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Sperm transcripts were mainly related to ribosome, oxidative phosphorylation and spliceosome pathways.

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qPCR analysis showed individual variations in transcriptional abundance of selected genes.

Sperm, which are believed to be transcriptionally and translationally inactive, synthesize RNA and proteins before there is gradual disappearance of the ribosome during chromatin compaction. Sperm transfer several functionally relevant transcripts to the oocyte, controlling maternal-zygotic transition and embryonic development. The present study was undertaken to profile and analyze sperm transcripts comprehensively using Next Generation Ribonucleic acid sequencing technology in Holstein Friesian x Tharparkar crossbred bulls. The results from global transcriptomic profiling revealed transcripts for 13,814 genes; of which 431 transcripts were expressed with >1 FPKM and 13,383 transcripts were expressed with >0 or <1 FPKM. The abundant mRNA transcripts of crossbred bull sperm were PRM1 and HMGB4. Gene ontology of transcripts with>1 FPKM revealed there was a major involvement in the structural constituent of ribosomes and translation. Results from pathway enrichment indicated the connection between ribosome, oxidative phosphorylation and spliceosome pathways and the transcripts of crossbred bull spermatozoa. The transcriptional abundance of selected genes, validated using RT-qPCR, indicated significant variations between bulls. Collectively, it may be inferred that the transcripts in crossbred bull sperm were heavily implicated in functions such as the structural constituent of ribosomes and translation, and pathways such as ribosome, oxidative phosphorylation and spliceosome. Further studies using larger sample sizes are required to understand the possible implications of transcriptomic variations on semen quality and fertility.

Cryopreservation and its effects on motility and gene expression patterns and fertilizing potential of bovine epididymal sperm

Despite encountering new challenges in using epididymal sperm recovered from cauda epididymides, this accessible and, in some species, worthwhile sample makes inevitable the further development of a suitable cryopreservation protocol. In this study, sperm was recovered from the epididymis of 4°C overnight stored slaughtered bulls' testes and the effects of cryopreservation on the bovine epididymal sperm motility (with CASA) and gene expression patterns (with quantitative Real time-PCR) were evaluated. Moreover the fertilizing potential of cryopreserved epididymal sperm was used in in vitro fertilization (IVF). After freezing and thawing of epididymal sperm, total and slow progressive sperm motility, VCL, VAP, MAD, ALH and BCF were significantly decreased (p < .05), while in the parameters of fast progressive motility, VSL, LIN, WOB and STR there were not any significant variations in the frozen sperm compared to fresh (non-frozen) counterpart. The assessment of abundance of transcripts encoding motility (TSSK6) and fertility (PRM1 and PRM2)-related genes in epididymal sperm, showed that these transcripts were affected by freezing especially in slow progressive motility status (p < .01). Furthermore, cleavage and blastocyst rate did not present any significant differences between bovine embryos produced in vitro by fresh or frozen-thawed epididymal sperm. It can be concluded that epididymal sperm has enough freezability after overnight testes storage, and cryopreservation could not affect the percentage of in vitro produced embryos in spite of the changes of relative abundance of some transcripts and direction progressive motility pattern of sperm.

Testis-specific serine kinase protein family in male fertility and as targets for non-hormonal male contraception†

Male contraception is a very active area of research. Several hormonal agents have entered clinical trials, while potential non-hormonal targets have been brought to light more recently and are at earlier stages of development. The general strategy is to target genes along the molecular pathways of sperm production, maturation, or function, and it is predicted that these novel approaches will hopefully lead to more selective male contraceptive compounds with a decreased side effect burden. Protein kinases are known to play a major role in signaling events associated with sperm differentiation and function. In this review, we focus our analysis on the testis-specific serine kinase (TSSK) protein family. We have previously shown that members of the family of TSSKs are postmeiotically expressed in male germ cells and in mature mammalian sperm. The restricted postmeiotic expression of TSSKs as well as the importance of phosphorylation in signaling processes strongly suggests that TSSKs have an important role in germ cell differentiation and/or sperm function. This prediction has been supported by the reported sterile phenotype of the Tssk6 knockout (KO) mice and of the double Tssk1 and Tssk2 KO mice and by the male subfertile phenotype observed in a Tssk4 KO mouse model.

FAK regulates actin polymerization during sperm capacitation via the ERK2/GEF-H1/RhoA signaling pathway

Actin polymerization is a crucial process during sperm capacitation. We have recently described the participation of FAK during actin polymerization in guinea pig spermatozoa. However, the mechanism by which FAK mediates these processes is unknown. Our previous data have shown that MAPK1 (hereafter referred to as ERK2) is activated during the first minutes of capacitation, and inhibition of ERK2 blocked actin polymerization and the acrosome reaction. In this current study, we found that FAK is involved in ERK2 activation - as FAK was phosphorylated at tyrosine residue 925 and bound to Grb2 - and that inhibition of FAK results in a significant decrease of ERK2 activation. We also confirmed the presence of Rho guanine nucleotide exchange factor 2 (ARHGEF2, hereafter referred to as GEF-H1), which is able to associate with RhoA during capacitation. RhoA activation and its participation in actin polymerization were also analyzed. Inhibition of FAK or ERK1/2 impeded GEF-H1 phosphorylation, RhoA activation, and the association between GEF-H1 and RhoA. Finally, we observed the presence of fibronectin on the sperm surface, its role in sperm-sperm interaction as well as participation of β-integrin in the activation of ERK2. Our results show that the signaling pathway downstream of fibronectin, via integrin, FAK, Grb2, MEK1/2, ERK2, GEF-H1 and RhoA regulates the actin polymerization associated with spermatozoa capacitation.

Spermatozoa lacking Fertilization Influencing Membrane Protein (FIMP) fail to fuse with oocytes in mice

As the human body is composed of 60 trillion cells that originate from a fertilized egg, sperm–oocyte fusion is the initial event of our life. Few sperm–oocyte fusion factors have been unveiled to date, and only IZUMO1 has been identified as a sperm-specific fusion-mediating protein. Here, we identified the testis-specific 4930451I11Rik gene important for male fertility, playing a role in sperm–oocyte fusion during fertilization. Based on its functional role, we renamed this gene fertilization influencing membrane protein (Fimp). We discovered a factor responsible for sperm–oocyte fusion in mammals, and this knowledge could be used to develop in vitro and in vivo infertility treatments as well as male contraceptives.

Sperm–oocyte fusion is a critical event in mammalian fertilization, categorized by three indispensable proteins. Sperm membrane protein IZUMO1 and its counterpart oocyte membrane protein JUNO make a protein complex allowing sperm to interact with the oocyte, and subsequent sperm–oocyte fusion. Oocyte tetraspanin protein CD9 also contributes to sperm–oocyte fusion. However, the fusion process cannot be explained solely by these three essential factors. In this study, we focused on analyzing a testis-specific gene 4930451I11Rik and generated mutant mice using the CRISPR/Cas9 system. Although IZUMO1 remained in 4930451I11Rik knockout (KO) spermatozoa, the KO spermatozoa were unable to fuse with oocytes and the KO males were severely subfertile. 4930451I11Rik encodes two isoforms: a transmembrane (TM) form and a secreted form. Both CRISPR/Cas9-mediated TM deletion and transgenic (Tg) rescue with the TM form revealed that only the TM form plays a critical role in sperm–oocyte fusion. Thus, we renamed this TM form Fertilization Influencing Membrane Protein (FIMP). The mCherry-tagged FIMP TM form was localized to the sperm equatorial segment where the sperm–oocyte fusion event occurs. Thus, FIMP is a sperm-specific transmembrane protein that is necessary for the sperm–oocyte fusion process.

Physiological role of actin regulation in male fertility: Insight into actin capping proteins in spermatogenic cells

BACKGROUND

During spermatogenesis, cytoskeletal elements are essential for spermatogenic cells to change morphologically and translocate in the seminiferous tubule. Actin filaments have been revealed to be concentrated in specific regions of spermatogenic cells and are regulated by a large number of actin-binding proteins. Actin capping protein is one of the essential actin regulatory proteins, and a recent study showed that testis-specific actin capping protein may affect male infertility.

METHODS

The roles of actin during spermatogenesis and testis-specific actin capping protein were reviewed by referring to the previous literature.

MAIN FINDINGS RESULTS

Actin filaments are involved in several crucial phases of spermatogenesis including acrosome biogenesis, flagellum formation, and nuclear processes such as the formation of synaptonemal complex. Besides, an implication for capacitation and acrosome reaction was also suggested. Testis-specific actin capping proteins are suggested to be associated with the removal of excess cytoplasm in mice. By the use of high-throughput sperm proteomics, lower protein expression of testis-specific actin capping protein in infertile men was also reported.

CONCLUSION

Actin is involved in the crucial phases of spermatogenesis, and the altered expression of testis-specific actin capping proteins is suggested to be a cause of male infertility in humans.

Sperm SPACA6 protein is required for mammalian Sperm-Egg Adhesion/Fusion

Three genes are known to be essential for gamete adhesion/fusion (Cd9, Izumo1 and Juno). Here, we confirmed that Spaca6 null males are infertile and showed that their sperm accumulate in the perivitelline space but are unable to fuse with oocyte. Like IZUMO1, SPACA6 which is expressed by human sperm, is remained on the equatorial segment after acrosomal reaction and is involved in human fertilization since an anti-SPACA6 antibody inhibited it. Despite the similarity of the phenotypes caused by Spaca6 and Izumo1 knockouts, these are not redundant and the essential relocation of IZUMO1 is not affected by the lack of SPACA6. We propose a model in which IZUMO1 and SPACA6 would be part of a molecular complex necessary for gamete fusion and that their concomitant presence would be required for the recruitment of another essential molecular actor, such as a fusogen, for the fusion to take place.

HIPK4 is essential for murine spermiogenesis

Mammalian spermiogenesis is a remarkable cellular transformation, during which round spermatids elongate into chromatin-condensed spermatozoa. The signaling pathways that coordinate this process are not well understood, and we demonstrate here that homeodomain-interacting protein kinase 4 (HIPK4) is essential for spermiogenesis and male fertility in mice. HIPK4 is predominantly expressed in round and early elongating spermatids, and Hipk4 knockout males are sterile, exhibiting phenotypes consistent with oligoasthenoteratozoospermia. Hipk4 mutant sperm have reduced oocyte binding and are incompetent for in vitro fertilization, but they can still produce viable offspring via intracytoplasmic sperm injection. Optical and electron microscopy of HIPK4-null male germ cells reveals defects in the filamentous actin (F-actin)-scaffolded acroplaxome during spermatid elongation and abnormal head morphologies in mature spermatozoa. We further observe that HIPK4 overexpression induces branched F-actin structures in cultured fibroblasts and that HIPK4 deficiency alters the subcellular distribution of an F-actin capping protein in the testis, supporting a role for this kinase in cytoskeleton remodeling. Our findings establish HIPK4 as an essential regulator of sperm head shaping and potential target for male contraception.

Perfect date-the review of current research into molecular bases of mammalian fertilization

Fertilization is a multistep process during which two terminally differentiated haploid cells, an egg and a sperm, combine to produce a totipotent diploid zygote. In the early 1950s, it became possible to fertilize mammalian eggs in vitro and study the sequence of cellular and molecular events leading to embryo development. Despite all the achievements of assisted reproduction in the last four decades, remarkably little is known about the molecular aspects of human conception. Current fertility research in animal models is casting more light on the complexity of the process all our lives start with. This review article provides an update on the investigation of mammalian fertilization and highlights the practical implications of scientific discoveries in the context of human reproduction and reproductive medicine.

Genetic Factors Affecting Sperm Chromatin Structure

Spermatozoa genome has unique features that make it a fascinating field of investigation: first, because, with oocyte genome, it can be transmitted generation after generation; second, because of genetic shuffling during meiosis, each spermatozoon is virtually unique in terms of genetic content, with consequences for species evolution; and finally, because its chromatin organization is very different from that of somatic cells or oocytes, as it is not based on nucleosomes but on nucleoprotamines which confer a higher order of packaging. Histone-to-protamine transition involves many actors, such as regulators of spermatid gene expression, components of the nuclear envelop, histone-modifying enzymes and readers, chaperones, histone variants, transition proteins, protamines, and certainly many more to be discovered.In this book chapter, we will present what is currently known about sperm chromatin structure and how it is established during spermiogenesis, with the aim to list the genetic factors that regulate its organization.

Dimorphism of sex and gonad-development-related genes in male and female lined seahorse, Hippocampus erectus, based on transcriptome analyses

Seahorse is characterized by its male pregnancy and sex-role reversal. To better understand the sexual dimorphism of male and female seahorses based on essential genes, we performed systematic transcriptome studies for both genders. A total of 157,834,590 cleaned reads were obtained and assembled into 129,268 transcripts and 31,764 could be annotated. Results showed that 176 up-regulated and 391 down-regulated transcripts were identified in the male seahorses compared with those in females. Genes involved in sex differentiation, such as dmrt1, sox9, fem1 and vasa, were identified and characterized. Moreover, the essential genes involved in reproductive molecular pathway were identified and analyzed in seahorses. In conclusion, the present study provides an archive for the future systematic research on seahorse sex differentiation.

Super-resolution imaging of live sperm reveals dynamic changes of the actin cytoskeleton during acrosomal exocytosis

Filamentous actin (F-actin) is a key factor in exocytosis in many cell types. In mammalian sperm, acrosomal exocytosis (denoted the acrosome reaction or AR), a special type of controlled secretion, is regulated by multiple signaling pathways and the actin cytoskeleton. However, the dynamic changes of the actin cytoskeleton in live sperm are largely not understood. Here, we used the powerful properties of SiR-actin to examine actin dynamics in live mouse sperm at the onset of the AR. By using a combination of super-resolution microscopy techniques to image sperm loaded with SiR-actin or sperm from transgenic mice containing Lifeact-EGFP, six regions containing F-actin within the sperm head were revealed. The proportion of sperm possessing these structures changed upon capacitation. By performing live-cell imaging experiments, we report that dynamic changes of F-actin during the AR occur in specific regions of the sperm head. While certain F-actin regions undergo depolymerization prior to the initiation of the AR, others remain unaltered or are lost after exocytosis occurs. Our work emphasizes the utility of live-cell nanoscopy, which will undoubtedly impact the search for mechanisms that underlie basic sperm functions.This article has an associated First Person interview with the first author of the paper.

Monitoring dimeric status of IZUMO1 during the acrosome reaction in living spermatozoon

The acrosome reaction (AR) is indispensable for successful spermatozoon-oocyte fusion. Recent studies have indicated that sperm IZUMO1 gradually gathers in the equatorial segment (EQ), which is the initiation site of sperm-egg fusion, after the AR. In addition, by examining the binding process of oocytes and Izumo1-expressing cultured cells to reconstitute the early steps of fertilization, we previously demonstrated that robust IZUMO1-dependent adhesion specifically occurs at the contact site along with the dimerization of IZUMO1. However, when IZUMO1 dimerizes after the AR in living spermatozoon is unknown. Here, we report dynamics of IZUMO1 dimerization during the AR in spermatozoa by combining transgenic mice and time-lapse imaging using a set of bimolecular fluorescence complementation (BiFC) probes. Surprisingly, dimeric IZUMO1 was already formed at the acrosomal cap region before the AR and redistributed into the EQ after the AR. We categorized the translocation of the dimer into two types: Type 1, the near-simultaneous appearance of BiFC signals with IZUMO1-mCherry; and Type 2, the delayed formation of dimer in the EQ. Those findings suggest that, before encountering oocytes, spermatozoa are prepared to boost their affinity with JUNO.

Chang's meaning of capacitation: A molecular perspective

Dr. Min Chue Chang's contributions to the field of reproductive biology set the stage for the development of the contraceptive pill and in vitro fertilization. Throughout his publications, Dr. Chang was also able to transmit his view of the fertilization process in ways that organized research for newer generations of reproductive biologists. Particularly relevant for the achievement of in vitro fertilization in mammals was the discovery that the sperm required a period of residence in the female tract to become fertilization-competent; Dr. Chang and Dr. Austin, in Australia, independently reported this process, now known as sperm capacitation. This review discusses Dr. Chang's views on capacitation, and puts them in the context of recent advances in the understanding of the molecular basis of this process. Mol. Reprod. Dev. 83: 860-874, 2016 © 2016 Wiley Periodicals, Inc.

Molecular changes and signaling events occurring in spermatozoa during epididymal maturation

After leaving the testis, spermatozoa have not yet acquired the ability to move progressively and are unable to fertilize oocytes. To become fertilization competent, they must go through an epididymal maturation process in the male, and capacitation in the female tract. Epididymal maturation can be defined as those changes occurring to spermatozoa in the epididymis that render the spermatozoa the ability to capacitate in the female tract. As part of this process, sperm cells undergo a series of biochemical and physiological changes that require incorporation of new molecules derived from the epididymal epithelium, as well as post-translational modifications of endogenous proteins synthesized during spermiogenesis in the testis. This review will focus on epididymal maturation events, with emphasis in recent advances in the understanding of the molecular basis of this process.

Effects of latrunculin A on the relocation of sperm IZUMO1 during gamete interaction in mouse

The sperm protein IZUMO1 plays a central role in gamete fusion. In mouse sperm, IZUMO1 is enriched at the acrosomal cap before the acrosome reaction, and at the equatorial segment following this reaction; its relocation is dependent on filamentous actin. How actin polymerization affects IZUMO1 relocation during gamete interaction remains unknown. The present study addressed these processes using latrunculin A (LatA), an inhibitor of actin polymerization. We report that 25 µM LatA blocked actin polymerization in the capacitated sperm head, resulting in a marked decrease in sperm with relocated IZUMO1 during the A23187-induced acrosome reaction and cumulus layer penetration. Treated sperm also exhibited reduced zona pellucida penetration and fertilizing capacity. Interestingly, LatA-treated sperm present in the perivitelline space of eggs did not show impaired IZUMO1 relocation. Thus, IZUMO1 relocation represents one method by which eggs may select for or rescue sperm that are competent to undergo gamete adhesion/fusion. These data support the hypothesis that dynamic movement of IZUMO1 is essential for gamete fusion during mouse fertilization.

TSSK6 is required for γH2AX formation and the histone-to-protamine transition during spermiogenesis

Spermiogenesis includes transcriptional silencing, chromatin condensation and extensive morphological changes as spermatids transform into sperm. Chromatin condensation involves histone hyperacetylation, transitory DNA breaks, histone H2AX (also known as H2AFX) phosphorylation at Ser139 (γH2AX), and replacement of histones by protamines. Previously, we have reported that the spermatid protein kinase TSSK6 is essential for fertility in mice, but its specific role in spermiogenesis is unknown. Here, we show that TSSK6 expression is spatiotemporally coincident with γH2AX formation in the nuclei of developing mouse spermatids. RNA-sequencing analysis demonstrates that genetic ablation of Tssk6 does not impact gene expression or silencing in spermatids. However, loss of TSSK6 blocks γH2AX formation, even though the timing and level of the transient DNA breaks is unaltered. Further, Tssk6-knockout sperm contained increased levels of histones H3 and H4, and protamine 2 precursor and intermediate(s) indicative of a defective histone-to-protamine transition. These results demonstrate that TSSK6 is required for γH2AX formation during spermiogenesis, and also link γH2AX to the histone-to-protamine transition and male fertility.

Complementary Critical Functions of Zfy1 and Zfy2 in Mouse Spermatogenesis and Reproduction

The mammalian Y chromosome plays a critical role in spermatogenesis. However, the exact functions of each gene in the Y chromosome have not been completely elucidated, partly owing to difficulties in gene targeting analysis of the Y chromosome. Zfy was first proposed to be a sex determination factor, but its function in spermatogenesis has been recently elucidated. Nevertheless, Zfy gene targeting analysis has not been performed thus far. Here, we adopted the highly efficient CRISPR/Cas9 system to generate individual Zfy1 or Zfy2 knockout (KO) mice and Zfy1 and Zfy2 double knockout (Zfy1/2-DKO) mice. While individual Zfy1 or Zfy2-KO mice did not show any significant phenotypic alterations in fertility, Zfy1/2-DKO mice were infertile and displayed abnormal sperm morphology, fertilization failure, and early embryonic development failure. Mass spectrometric screening, followed by confirmation with western blot analysis, showed that PLCZ1, PLCD4, PRSS21, and HTT protein expression were significantly deceased in spermatozoa of Zfy1/2-DKO mice compared with those of wild-type mice. These results are consistent with the phenotypic changes seen in the double-mutant mice. Collectively, our strategy and findings revealed that Zfy1 and Zfy2 have redundant functions in spermatogenesis, facilitating a better understanding of fertilization failure and early embryonic development failure.