Spermatogenesis: The Commitment to Meiosis

Running the gauntlet: challenges to genome integrity in spermiogenesis

Species' continuity depends on gametogenesis to produce the only cell types that can transmit genetic information across generations. Spermiogenesis, which encompasses post-meiotic, haploid stages of male gametogenesis, is a process that leads to the formation of sperm cells well-known for their motility. Spermiogenesis faces three major challenges. First, after two rounds of meiotic divisions, the genome lacks repair templates (no sister chromatids, no homologous chromosomes), making it incredibly vulnerable to any genomic insults over an extended time (typically days-weeks). Second, the sperm genome becomes transcriptionally silent, making it difficult to respond to new perturbations as spermiogenesis progresses. Third, the histone-to-protamine transition, which is essential to package the sperm genome, counterintuitively involves DNA break formation. How spermiogenesis handles these challenges remains poorly understood. In this review, we discuss each challenge and their intersection with the biology of protamines. Finally, we discuss the implication of protamines in the process of evolution.

Microenvironment of spermatogonial stem cells: a key factor in the regulation of spermatogenesis

Spermatogonial stem cells (SSCs) play a crucial role in the male reproductive system, responsible for maintaining continuous spermatogenesis. The microenvironment or niche of SSCs is a key factor in regulating their self-renewal, differentiation and spermatogenesis. This microenvironment consists of multiple cell types, extracellular matrix, growth factors, hormones and other molecular signals that interact to form a complex regulatory network. This review aims to provide an overview of the main components of the SSCs microenvironment, explore how they regulate the fate decisions of SSCs, and discuss the potential impact of microenvironmental abnormalities on male reproductive health.

TUBB4B is essential for the expansion of differentiating spermatogonia

Microtubules, polymers of αβ-tubulin heterodimers, are essential for various cellular processes. The incorporation of different tubulin isotypes, each encoded by distinct genes, is proposed to contribute to the functional diversity observed in microtubules. However, the functional roles of each tubulin isotype are not completely understood. In this study, we investigated the role of the β4B-tubulin isotype (Tubb4b) in spermatogenesis, utilizing a Tubb4b knockout mouse model. We showed that β4B-tubulin is expressed in the germ cells throughout spermatogenesis. β4B-tubulin was localized to cytoplasmic microtubules, mitotic spindles, manchette, and axonemes of sperm flagella. We found that the absence of β4B-tubulin resulted in male infertility and failure to produce sperm cells. Our findings demonstrate that a lack of β4B-tubulin leads to defects in the initial stages of spermatogenesis. Specifically, β4B-tubulin is needed for the expansion of differentiating spermatogonia, which is essential for the subsequent progression of spermatogenesis.

CALR3 defects disrupt sperm-zona pellucida binding in humans: new insights into male factor fertilization failure and relevant clinical therapeutic approaches

STUDY QUESTION

Do biallelic deleterious variants of Calreticulin 3 (CALR3) cause fertilization failure (FF), resulting in male infertility in humans?

SUMMARY ANSWER

Biallelic mutations in CALR3 were identified in two infertile men from unrelated families and were shown to cause FF associated with failed sperm-zona pellucida (ZP) binding.

WHAT IS KNOWN ALREADY

In male mice, the Calr3-knockout has been reported to cause male infertility and FF. However, the mechanism behind this remains unclear in humans.

STUDY DESIGN, SIZE, DURATION

Sequencing studies were conducted in a research hospital on samples from Han Chinese families with primary infertility and sperm head deformations to identify the underlying genetic causes.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Data from two infertile probands characterized by sperm head deformation were collected through in silico analysis. Sperm cells from the probands were characterized using light and electron microscopy and used to verify the pathogenicity of genetic factors through functional assays. Subzonal insemination (SUZI) and IVF assays were performed to determine the exact pathogenesis of FF. ICSI were administered to overcome CALR3-affected male infertility.

MAIN RESULTS AND THE ROLE OF CHANCE

Novel biallelic deleterious mutations in CALR3 were identified in two infertile men from unrelated families. We found one homozygous frameshift CALR3 mutation (M1: c.17_27del, p.V6Gfs*34) and one compound heterozygous CALR3 mutation (M2: c.943A>G, p.N315D; M3: c.544T>C, p.Y182H). These mutations are rare in the general population and cause acrosomal ultrastructural defects in affected sperm. Furthermore, spermatozoa from patients harbouring the CALR3 mutations were unable to bind to the sperm-ZP or they disrupted gamete fusion or prevented oocyte activation. Molecular assays have revealed that CALR3 is crucial for the maturation of the ZP binding protein in humans. Notably, the successful fertilization via SUZI and ICSI attempts for two patients, as well as the normal expression of PLCζ in the mutant sperm, suggests that ICSI is an optimal treatment for CALR3-deficient FF.

LIMITATIONS, REASONS FOR CAUTION

The results are based on sperm-related findings from two patients. Further studies are required to gain insight into the developmental stage and function of CALR3 in human testis.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings highlight the underlying risk of FF associated with sperm defects and provide a valuable reference for personalized genetic counselling and clinical treatment of these patients.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Key R&D Program of China (2021YFC2700901), Hefei Comprehensive National Science Center Medical-Industrial Integration Medical Equipment Innovation Research Platform Project (4801001202), the National Natural Science Foundation of China (82201803, 82371621, 82271639), Foundation of the Education Department of Anhui Province (gxgwfx2022007), Key Project of Natural Science Research of Anhui Educational Committee (2023AH053287), and the Clinical Medical Research Transformation Project of Anhui Province (202204295107020037). The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Effects of Leydig cell elimination on testicular interstitial cell populations: characterization by scRNA-seq and immunocytochemical techniques

Background

The mammalian testicular interstitial cells are not well-defined. The present study characterized the interstitial cell types and their turnover dynamics in adult rats. Additionally, the heterogeneity of the mesenchymal population and the effects of Leydig cell elimination on interstitial homeostasis were further analyzed by scRNA-seq datasets and immunocytochemical techniques.

Methods

Interstitial cells were defined at the transcriptomic level by scRNA-seq and then confirmed and quantified with protein markers. The dividing activity of the major cell types was determined by continuous EdU labeling of the animals for one week. Some of the rats were also treated with a dose of ethylenedimethylsulfonate (EDS) to examine how the loss of Leydig cells (LCs) could affect interstitial homeostasis for three weeks.

Results

Seven interstitial cell types were identified, including cell types (percentage of the whole interstitial population) as follows: Leydig (44.6%), macrophage and dendritic (19.1%), lymphoid (6.2%), vascular endothelial (7.9%), smooth muscle (10.7%), and mesenchymal (11.5%) cells. The EdU experiment indicated that most cell types were dividing at relatively low levels (<9%) except for the mesenchymal cells (MCs, 17.1%). Further analysis of the transcriptome of MCs revealed 4 subgroups with distinct functions, including 1) glutathione metabolism and xenobiotic detoxification, 2) ROS response and AP-1 signaling, 3) extracellular matrix synthesis and binding, and 4) immune response and regulation. Stem LCs (SLCs) are primarily associated with subgroup 3, expressing ARG1 and GAP43. EDS treatment not only eliminated LCs but also increased subgroup 3 and decreased subgroups 1 and 2 of the mesenchymal population. Moreover, EDS treatment increased the division of immune cells by more than tenfold in one week.

Conclusion

Seven interstitial cell types were identified and quantified for rat testis. Many may play more diversified roles than previously realized. The elimination of LCs led to significant changes in MCs and immune cells, indicating the importance of LCs in maintaining testicular interstitial homeostasis.

Histone demethylase KDM2A recruits HCFC1 and E2F1 to orchestrate male germ cell meiotic entry and progression

In mammals, the transition from mitosis to meiosis facilitates the successful production of gametes. However, the regulatory mechanisms that control meiotic initiation remain unclear, particularly in the context of complex histone modifications. Herein, we show that KDM2A, acting as a lysine demethylase targeting H3K36me3 in male germ cells, plays an essential role in modulating meiotic entry and progression. Conditional deletion of Kdm2a in mouse pre-meiotic germ cells results in complete male sterility, with spermatogenesis ultimately arrested at the zygotene stage of meiosis. KDM2A deficiency disrupts H3K36me2/3 deposition in c-KIT+ germ cells, characterized by a reduction in H3K36me2 but a dramatic increase in H3K36me3. Furthermore, KDM2A recruits the transcription factor E2F1 and its co-factor HCFC1 to the promoters of key genes required for meiosis entry and progression, such as Stra8, Meiosin, Spo11, and Sycp1. Collectively, our study unveils an essential role for KDM2A in mediating H3K36me2/3 deposition and controlling the programmed gene expression necessary for the transition from mitosis to meiosis during spermatogenesis.

Autophagy accompanying the developmental process of male germline stem cells

Germline stem cells are a crucial type of stem cell that can stably pass on genetic information to the next generation, providing the necessary foundation for the reproduction and survival of organisms. Male mammalian germline stem cells are unique cell types that include primordial germ cells and spermatogonial stem cells. They can differentiate into germ cells, such as sperm and eggs, thereby facilitating offspring reproduction. In addition, they continuously generate stem cells through self-renewal mechanisms to support the normal function of the reproductive system. Autophagy involves the use of lysosomes to degrade proteins and organelles that are regulated by relevant genes. This process plays an important role in maintaining the homeostasis of germline stem cells and the synthesis, degradation, and recycling of germline stem cell products. Recently, the developmental regulatory mechanism of germline stem cells has been further elucidated, and autophagy has been shown to be involved in the regulation of self-renewal and differentiation of germline stem cells. In this review, we introduce autophagy accompanying the development of germline stem cells, focusing on the autophagy process accompanying the development of male spermatogonial stem cells and the roles of related genes and proteins. We also briefly outline the effects of autophagy dysfunction on germline stem cells and reproduction.

Histone acetylation regulated by histone deacetylases during spermatogenesis

BACKGROUND

Physical, chemical, and biological factors in the environment constantly influence in vivo and in vitro biological processes, including diverse histone modifications involved in cancer and metabolism. However, the intricate mechanisms of acetylation regulation remain poorly elucidated. In mammalian spermatogenesis, acetylation plays a crucial role in repairing double-strand DNA breaks, regulating gene transcription, and modulating various signaling pathways.

RESULTS

This review summarizes the histone acetylation sites in the mouse testis and provides a comprehensive overview of how histone acetylation is involved in different stages of spermatogenesis under the regulation by histone deacetylases. The regulatory functions of various class histone deacetylases during spermatogenesis and the crossroad between histone acetylation and other histone modifications are highlighted. It is imperative to understand the mechanisms of histone acetylation regulated by histone deacetylases in spermatogenesis, which facilitates to prevent and treat infertility-related diseases.

The expression spectrum of yak epididymal epithelial cells reveals the functional diversity of caput, corpus and cauda regions

Sperm undergo a series of changes in the epididymis region before acquiring the ability to move and fertilize, and the identification of genes expressed in a region-specific manner in the epididymis provides a valuable insight into functional differences between regions. We collected epididymal tissue from three yaks and cultured epithelial cells from the caput, corpus and cauda regions of the yak epididymis using the tissue block method. RNA sequencing analysis (RNA-seq) technology was used to detect gene expression in yak epididymal caput, corpus and cauda epithelial cells. The results showed that the DEGs were highest in the caput vs. corpus comparison, and lowest in the corpus vs. cauda comparison. Six DEGs were verified by real-time fluorescence quantitative PCR (qRT-PCR), consistent with transcriptome sequencing results. The significantly enriched DNA replication pathway in the caput vs. corpus was coordinated with cell proliferation, while upregulated DEGs such as POLD1 and MCM4 were found in the DNA replication pathway. The AMPK signaling pathway was found significantly enriched in the caput vs cauda, suggesting its involvement in sperm maturation and capacitation. The TGF beta signaling pathway was screened in the corpus vs cauda and is crucial for mammalian reproductive regulation. Upregulated DEGs (TGFB3, INHBA, INHBB) are involved in the TGF beta signaling pathway. This study provides a reference for culturing yak epididymal epithelial cells in vitro, and elucidates the transcriptional profiles of epithelial cells in different segments of the epididymis, revealing the regulatory and functional differences between different segments, providing basic data for exploring the molecular mechanism of yak sperm maturation and improving the reproductive capacity of high-altitude mammals.

Roles of N6-methyladenosine writers, readers and erasers in the mammalian germline

N6-methyladenosine (m6A) is the most abundant internal modification of mRNAs in eukaryotes. Numerous studies have shown that m6A plays key roles in many biological and pathophysiological processes, including fertility. The factors involved in m6A-dependent mRNA regulation include writers, which deposit the m6A mark, erasers, which remove it, and readers, which bind to m6A-modified transcripts and mediate the regulation of mRNA fate. Many of these proteins are highly expressed in the germ cells of mammals, and some have been linked to fertility disorders in human patients. In this review, we summarise recent findings on the important roles played by proteins involved in m6A biology in mammalian gametogenesis and fertility. Continued study of the m6A pathway in the mammalian germline will shed further light on the importance of epitranscriptomics in reproduction and may lead to effective treatment of human fertility disorders.

CWF19L2 is Essential for Male Fertility and Spermatogenesis by Regulating Alternative Splicing

The progression of spermatogenesis along specific developmental trajectories depends on the coordinated regulation of pre-mRNA alternative splicing (AS) at the post-transcriptional level. However, the fundamental mechanism of AS in spermatogenesis remains to be investigated. Here, it is demonstrated that CWF19L2 plays a pivotal role in spermatogenesis and male fertility. In germline conditional Cwf19l2 knockout mice exhibiting male sterility, impaired spermatogenesis characterized by increased apoptosis and decreased differentiated spermatogonia and spermatocytes is observed. That CWF19L2 interacted with several spliceosome proteins to participate in the proper assembly and stability of the spliceosome is discovered. By integrating RNA-seq and LACE-seq data, it is further confirmed CWF19L2 directly bound and regulated the splicing of genes related to spermatogenesis (Znhit1, Btrc, and Fbxw7) and RNA splicing (Rbfox1, Celf1, and Rbm10). Additionally, CWF19L2 can indirectly amplify its effect on splicing regulation through modulating RBFOX1. Collectively, this research establishes that CWF19L2 orchestrates a splicing factor network to ensure accurate pre-mRNA splicing during the early steps of spermatogenesis.

Genome-wide analysis of two different regions of brain reveals the molecular changes of fertility related genes in rln3a-/- mutants in male Nile tilapia (Oreochromis niloticus)

Relaxin3 (rln3) has been associated with various emotional and cognitive processes, including stress, anxiety, learning, memory, motivational behavior, and circadian rhythm. Notably, previous report revealed that Rln3a played an indispensable role in testicular development and male fertility in Nile tilapia (Oreochromis niloticus). However, the underlying molecular mechanisms remain largely unknown. We found that Rln3a is expressed exclusively in the diencephalon* (Di*) of the brain. Deficiency of Rln3a resulted in a significant increase in serum dopamine level and an upregulation of gene expression of gnrh1 and kisspeptin2. To further elucidate the role of Rln3a in fish fertility, we collected two different regions of Di* and hypothalamus (Hyp) tissues for subsequent RNA-seq analysis of both wild-type (rln3a+/+) and rln3a-/- male tilapia. Upon the transcriptomic data, 1136 and 755 differentially expressed genes (DEGs) were identified in the Di* and Hyp tissues, respectively. In Di*, the up-regulated genes were enriched in circadian rhythm, chemical carcinogenesis, while the down-regulated genes were enriched in type II diabetes mellitus, dopaminergic synapse, and other pathways. In Hyp, the up-regulated genes were enriched in circadian rhythm, pyrimidine metabolism, while the down-regulated genes were enriched in type I diabetes mellitus, autoimmune thyroid disease, and other pathways. Subsequently, the results of both qRT-PCR and FISH assays highlighted a pronounced up-regulation of core circadian rhythm genes, cry1b and per3, whereas genes such as clocka, clockb, and arntl exhibited down-regulation. Furthermore, the genes associated with dopamine biosynthesis were significantly increased in the Hyp. In summary, the mutation of rln3a in male tilapia resulted in notable changes in circadian rhythm and disease-linked signaling pathways in the Di* and Hyp. These changes might account for the fertility defects observed in rln3a-/- male mutants in tilapia.

Single-cell RNA sequencing technology in human spermatogenesis: Progresses and perspectives

Spermatogenesis, a key part of the spermiation process, is regulated by a combination of key cells, such as primordial germ cells, spermatogonial stem cells, and somatic cells, such as Sertoli cells. Abnormal spermatogenesis can lead to azoospermia, testicular tumors, and other diseases related to male infertility. The application of single-cell RNA sequencing (scRNA-seq) technology in male reproduction is gradually increasing with its unique insight into deep mining and analysis. The data cover different periods of neonatal, prepubertal, pubertal, and adult stages. Different types of male infertility diseases including obstructive and non-obstructive azoospermia (NOA), Klinefelter Syndrome (KS), Sertoli Cell Only Syndrome (SCOS), and testicular tumors are also covered. We briefly review the principles and application of scRNA-seq and summarize the research results and application directions in spermatogenesis in different periods and pathological states. Moreover, we discuss the challenges of applying this technology in male reproduction and the prospects of combining it with other technologies.

Chronic oral administration of L-carnitine induces testicular injury: in vivo evidence

PURPOSE

While L-carnitine is commonly used to treat oligoasthenozoospermia, concerns have been raised regarding its potential harm to spermatogenesis. This study aims to investigate the potential testicular toxicity of long-term oral administration of L-carnitine.

METHODS

In this study, we refer to the clinical adult dosage and mode of L-carnitine administration, and after converting to mouse doses, mice were daily intragastrical administered L-carnitine to investigate whether it was harmful to the testis. The investigation involved assessing its potential testicular toxicity through histopathological staining, sperm motility analysis, and quantitative real-time PCR.

RESULTS

Our results showed that L-carnitine increased sperm motility after 14 days of continuous administration, but increased luminal exfoliated spermatogenic cells occurred in the testis, and TUNEL results showed increased apoptotic cells. Compared with the control group, the mRNA expression of the spermatogenic cell marker at each stage was decreased in mice treated for 14 consecutive days of L-carnitine. After 50 days of continuous administration followed by 14 days of drug withdrawal, the total sperm motility of mice was almost 0, and a large number of abnormal eosinophilic spermatogenic cells appeared in the testis. These indicate that oral L-carnitine for more than 14 days impairs spermatogenesis in mice, and sudden discontinuation of administration results in substantial death of established spermatogenic cell populations.

CONCLUSION

Our findings suggest that chronic oral administration of L-carnitine impairs spermatogenic function in the testis. The oral administration of L-carnitine to enhance sperm motility should not exceed the 2/5 point of the spermatogenic cycle.

Contraceptive efficacy: Determining the threshold for effective suppression based on sperm concentration, motility, and morphology

INTRODCTION

Human spermatogenesis is a complex process that transforms spermatogonial stem cells through mitosis and meiosis to spermatozoa. Testosterone is the key regulator of the terminal stages of meiosis, adherence of spermatids to Sertoli cells, and spermiation. Follicle-stimulating hormone (FSH) may be required for early spermatogenesis and is important for maintaining normal spermatogenesis in men. Hormonal contraception suppresses FSH, luteinizing hormone, and intratesticular testosterone concentration, resulting in marked suppression of sperm output.

RESULTS

Clinical trials using testosterone alone or testosterone plus progestin demonstrate that sustained suppression of sperm concentration to ≤1 million/mL is sufficient to prevent pregnancy in the female partner. New agents that target spermatogenesis could use this as a target for contraceptive efficacy while others that block sperm function or transport may require a lower threshold. When sperm concentrations are suppressed to such low levels, measurement of sperm motility and morphology is technically difficult and unnecessary. With current data from fertile and infertile men, it is not possible to establish a lower limit of sperm motility or percent normal morphology that equates to the prevention of conception. New compounds that decrease sperm motility or alter sperm morphology may need to demonstrate a complete absence of sperm motility or altered morphology in all spermatozoa in the ejaculate. Sperm function tests may be useful depending on the mechanism of action of each new compound.

CONCLUSION

Monitoring of sperm surrogate markers to ensure effective contraception relies on laboratories experienced in semen analyses. The development of at-home tests to assess sperm parameters has progressed rapidly. Some tests have been assessed in clinical trials and approved by regulatory agencies for at-home use for fertility assessment. However, caution must be exercised in using these tests as many have not been rigorously validated against semen parameters measured in laboratories by trained technologists using standardized tests defined in the World Health Organization Semen Manual.

Sertoli cells require hnRNPC to support normal spermatogenesis and male fertility in mice†

Sertoli cells act as highly polarized testicular cells that nutritionally support multiple stages of germ cell development. However, the gene regulation network in Sertoli cells for modulating germ cell development has yet to be fully understood. In this study, we report that heterogeneous nuclear ribonucleoproteins C in Sertoli cells are essential for germ cell development and male fertility. Conditional knockout of heterogeneous nuclear ribonucleoprotein C in mouse Sertoli cells leads to aberrant Sertoli cells proliferation, disrupted cytoskeleton of Sertoli cells, and compromised blood-testis barrier function, resulting in loss of supportive cell function and, ultimately, defective spermiogenesis in mice. Further ribonucleic acid-sequencing analyses revealed these phenotypes are likely caused by the dysregulated genes in heterogeneous nuclear ribonucleoprotein C-deficient Sertoli cells related to cell adhesion, cell proliferation, and apoptotic process. In conclusion, this study demonstrates that heterogeneous nuclear ribonucleoprotein C plays a critical role in Sertoli cells for maintaining the function of Sertoli cells and sustaining steady-state spermatogenesis in mice.

Understanding testicular single cell transcriptional atlas: from developmental complications to male infertility

Spermatogenesis is a multi-step biological process where mitotically active diploid (2n) spermatogonia differentiate into haploid (n) spermatozoa via regulated meiotic programming. The alarming rise in male infertility has become a global concern during the past decade thereby demanding an extensive profiling of testicular gene expression. Advancements in Next-Generation Sequencing (NGS) technologies have revolutionized our empathy towards complex biological events including spermatogenesis. However, despite multiple attempts made in the past to reveal the testicular transcriptional signature(s) either with bulk tissues or at the single-cell, level, comprehensive reviews on testicular transcriptomics and associated disorders are limited. Notably, technologies explicating the genome-wide gene expression patterns during various stages of spermatogenic progression provide the dynamic molecular landscape of testicular transcription. Our review discusses the advantages of single-cell RNA-sequencing (Sc-RNA-seq) over bulk RNA-seq concerning testicular tissues. Additionally, we highlight the cellular heterogeneity, spatial transcriptomics, dynamic gene expression and cell-to-cell interactions with distinct cell populations within the testes including germ cells (Gc), Sertoli cells (Sc), Peritubular cells (PTc), Leydig cells (Lc), etc. Furthermore, we provide a summary of key finding of single-cell transcriptomic studies that have shed light on developmental mechanisms implicated in testicular disorders and male infertility. These insights emphasize the pivotal roles of Sc-RNA-seq in advancing our knowledge regarding testicular transcriptional landscape and may serve as a potential resource to formulate future clinical interventions for male reproductive health.

HSF5 Deficiency Causes Male Infertility Involving Spermatogenic Arrest at Meiotic Prophase I in Humans and Mice

Meiosis is a specialized cell division process that generates gametes for sexual reproduction. However, the factors and underlying mechanisms involving meiotic progression remain largely unknown, especially in humans. Here, it is first showed that HSF5 is associated with human spermatogenesis. Patients with a pathogenic variant of HSF5 are completely infertile. Testicular histologic findings in the patients reveal rare postmeiotic germ cells resulting from meiotic prophase I arrest. Hsf5 knockout (KO) mice confirms that the loss of HSF5 causes defects in meiotic recombination, crossover formation, sex chromosome synapsis, and sex chromosome inactivation (MSCI), which may contribute to spermatocyte arrest at the late pachytene stage. Importantly, spermatogenic arrest can be rescued by compensatory HSF5 adeno-associated virus injection into KO mouse testes. Mechanistically, integrated analysis of RNA sequencing and chromatin immunoprecipitation sequencing data revealed that HSF5 predominantly binds to promoters of key genes involved in crossover formation (e.g., HFM1, MSH5 and MLH3), synapsis (e.g., SYCP1, SYCP2 and SYCE3), recombination (TEX15), and MSCI (MDC1) and further regulates their transcription during meiotic progression. Taken together, the study demonstrates that HSF5 modulates the transcriptome to ensure meiotic progression in humans and mice. These findings will aid in genetic diagnosis of and potential treatments for male infertility.

The therapeutic effect and metabolic mechanism analysis of Guilingji on idiopathic oligo-asthenoteratozoospermia

Introduction

Guilingji, a famous traditional Chinese medicine (TCM) formula, has been used to combat aging and male sexual dysfunction in China for centuries. To date, there has been little evidence-based clinical research on the use of Guilingji to treat idiopathic oligo-asthenoteratozoospermia (OAT), and the therapeutic mechanism from a metabolic perspective needs to be investigated further.

Methods

This was a multicenter, double-blind, randomized controlled clinical study of 240 patients with idiopathic OAT recruited from four hospitals between January 2020 and January 2022. Patients were randomly assigned in a 1꞉1 ratio to receive oral Guilingji capsules or placebo for 12 weeks. The total progressive motile sperm count (TPMSC) was considered the primary outcome, and the other sperm parameters, seminal plasma parameters and serum hormones were considered the secondary outcome. A nontargeted metabolomics analysis of serum from OAT patients before and after Guilingji administration was performed by HPLC-MS to identify key metabolites. Furthermore, we used a rat model to show spermatogenesis phenotypes to validate the effect of the key metabolites screened from the patients.

Results

At weeks 4, 8 and 12, TPMSC and other sperm parameters were significantly improved in the Guilingji group compared with the placebo group (P < 0.05 for all comparisons). At week 4, superoxide dismutase (SOD) and acrosomal enzyme activity of seminal plasma were significantly elevated in the Guilingji group compared with the placebo group, while reactive oxygen species (ROS) levels were significantly reduced (P < 0.05). Lactate dehydrogenase-X (LDHX) levels appeared to be significantly increased after 12 weeks continuous medication compared with Placebo group (P = 0.032). The metabolomics analysis of serum from OAT patients before and after Guilingji administration showed that the glucose-6-phosphate (G6P) concentration in patients' serum was significantly elevated after Guilingji treatment. Compared to the control, when Kidney-Yang deficiency model rats were treated with Guilingji or its key intermediate metabolite G6P, their sperm concentration and spermatozoic activity were improved similarly, and their structural damage of rat's testicular and epididymal tissues were recovered.

Conclusion

This study provided valuable clinical evidence for the utility of Guilingji as a treatment for OAT. These findings thus demonstrate that G6P is involved in the therapeutic mechanism of Guilingji in OAT treatment based on clinical and rat intervention studies.

Transplantation of spermatogonial stem cells in stallions

Spermatogonial stem cells originate from gonocytes and undergo self-renewal and differentiation to generate mature spermatozoa via spermatogenesis in the seminiferous tubules of the testis in male mammals. Owing to the unique capacity of these cells, the spermatogonial stem cell transplantation technique, which enables the restoration of male fertility by transfer of germlines between donor and recipient males, has been developed. Thus, spermatogonial stem cell transplantation can be used as an important next-generation reproductive and breeding tool in livestock production. However, in large animals, this approach is associated with many technical limitations and inefficiency. Furthermore, research regrading spermatogonial stem cell transplantation in stallions is limited. Therefore, this review article describes the history and current knowledge regarding spermatogonial stem cell transplantation in animals and challenges in establishing an experimental protocol for successful spermatogonial stem cell transplantation in stallions, which have been presented under the following heads: spermatogonial stem cell isolation, recipient preparation, and spermatogonial stem cell transplantation. Additionally, we suggest that further investigation based on previous unequivocal evidence regarding donor-derived spermatogenesis in large animals must be conducted. A detailed and better understanding of the physical and physiological aspects is required to discuss the current status of this technique field and develop future directions for the establishment of spermatogonial stem cell transplantation in stallions.

Paternal Use of Metformin During the Sperm Development Period Preceding Conception and Risk for Major Congenital Malformations in Newborns

BACKGROUND

Metformin is the most used oral antidiabetic medication. Despite its established safety profile, it has known antiandrogenic and epigenetic modifying effects. This raised concerns about possible adverse developmental effects caused by genomic alterations related to paternal use of metformin during the spermatogenesis period preceding conception.

OBJECTIVE

To assess the potential adverse intergenerational effect of metformin by examining the association between paternal metformin use during spermatogenesis and major congenital malformations (MCMs) in newborns.

DESIGN

Nationally representative cohort study.

SETTING

A large Israeli health fund.

PARTICIPANTS

383 851 live births linked to fathers and mothers that occurred in 1999 to 2020.

MEASUREMENTS

MCMs and parental cardiometabolic conditions were ascertained using clinical diagnoses, medication dispensing information, and laboratory test results. The effect of metformin use on MCMs was estimated using general estimating equations, accounting for concurrent use of other antidiabetic medications and parental cardiometabolic morbidity.

RESULTS

Compared with unexposed fathers, the prevalence of cardiometabolic morbidity was substantially higher among fathers who used metformin during spermatogenesis, and their spouses. Whereas the crude odds ratio (OR) for paternal metformin exposure in all formulations and MCMs was 1.28 (95% CI, 1.01 to 1.64), the adjusted OR was 1.00 (CI, 0.76 to 1.31). Within specific treatment regimens, the adjusted OR was 0.86 (CI, 0.60 to 1.23) for metformin in monotherapy and 1.36 (CI, 1.00 to 1.85) for metformin in polytherapy, a treatment that was more common in patients with more poorly controlled diabetes.

LIMITATION

Laboratory test results for hemoglobin A1c to assess underlying diabetes severity were available only for a subset of the cohort.

CONCLUSION

Paternal use of metformin in monotherapy does not increase the risk for MCMs. Association for metformin in polytherapy could potentially be explained by worse underlying parental cardiometabolic risk profile.

PRIMARY FUNDING SOURCE

None.

The emerging and diverse roles of F-box proteins in spermatogenesis and male infertility

F-box proteins play essential roles in various cellular processes of spermatogenesis by means of ubiquitylation and subsequent target protein degradation. They are the substrate-recognition subunits of SKP1-cullin 1-F-box protein (SCF) E3 ligase complexes. Dysregulation of F‑box protein‑mediated proteolysis could lead to male infertility in humans and mice. The emerging studies revealed the physiological function, pathological evidence, and biochemical substrates of F-box proteins in the development of male germ cells, which urging us to review the current understanding of how F‑box proteins contribute to spermatogenesis. More functional and mechanistic study will be helpful to define the roles of F-box protein in spermatogenesis, which will pave the way for the logical design of F-box protein-targeted diagnosis and therapies for male infertility, as the spermatogenic role of many F-box proteins remains elusive.

Protein disulfide isomerase is essential for spermatogenesis in mice

Spermatogenesis requires precise posttranslational control in the endoplasmic reticulum (ER), but the mechanism remains largely unknown. The protein disulfide isomerase (PDI) family is a group of thiol oxidoreductases responsible for catalyzing the disulfide bond formation of nascent proteins. In this study, we generated 14 strains of KO mice lacking the PDI family enzymes and found that only PDI deficiency caused spermatogenesis defects. Both inducible whole-body PDI-KO (UBC-Cre/Pdifl/fl) mice and premeiotic PDI-KO (Stra8-Cre/Pdifl/fl) mice experienced a significant decrease in germ cells, testicular atrophy, oligospermia, and complete male infertility. Stra8-Cre/Pdifl/fl spermatocytes had significantly upregulated ER stress-related proteins (GRP78 and XBP1) and apoptosis-related proteins (Cleaved caspase-3 and BAX), together with cell apoptosis. PDI deletion led to delayed DNA double-strand break repair and improper crossover at the pachytene spermatocytes. Quantitative mass spectrometry indicated that PDI deficiency downregulated vital proteins in spermatogenesis such as HSPA4L, SHCBP1L, and DDX4, consistent with the proteins' physical association with PDI in normal testes tissue. Furthermore, PDI served as a thiol oxidase for disulfide bond formation of SHCBP1L. Thus, PDI plays an essential role in protein quality control for spermatogenesis in mice.

The Role of Retinoic Acid in Spermatogenesis and Its Application in Male Reproduction

Spermatogenesis in mammalian testes is essential for male fertility, ensuring a continuous supply of mature sperm. The testicular microenvironment finely tunes this process, with retinoic acid, an active metabolite of vitamin A, serving a pivotal role. Retinoic acid is critical for various stages, including the differentiation of spermatogonia, meiosis in spermatogenic cells, and the production of mature spermatozoa. Vitamin A deficiency halts spermatogenesis, leading to the degeneration of numerous germ cells, a condition reversible with retinoic acid supplementation. Although retinoic acid can restore fertility in some males with reproductive disorders, it does not work universally. Furthermore, high doses may adversely affect reproduction. The inconsistent outcomes of retinoid treatments in addressing infertility are linked to the incomplete understanding of the molecular mechanisms through which retinoid signaling governs spermatogenesis. In addition to the treatment of male reproductive disorders, the role of retinoic acid in spermatogenesis also provides new ideas for the development of male non-hormone contraceptives. This paper will explore three facets: the synthesis and breakdown of retinoic acid in the testes, its role in spermatogenesis, and its application in male reproduction. Our discussion aims to provide a comprehensive reference for studying the regulatory effects of retinoic acid signaling on spermatogenesis and offer insights into its use in treating male reproductive issues.

The Odad3 Gene Is Necessary for Spermatozoa Development and Male Fertility in Mice

Odad3 gene loss-of-function mutation leads to Primary Ciliary Dyskinesia (PCD), a disease caused by motile cilia dysfunction. Previously, we demonstrated that knockout of the Odad3 gene in mice replicates several features of PCD, such as hydrocephalus, defects in left-right body symmetry, and male infertility, with a complete absence of sperm in the reproductive tract. The majority of Odad3 knockout animals die before sexual maturation due to severe hydrocephalus and failure to thrive, which precludes fertility studies. Here, we performed the expression analysis of the Odad3 gene during gonad development and in adult testes. We showed that Odad3 starts its expression during the first wave of spermatogenesis, specifically at the meiotic stage, and that its expression is restricted to the germ cells in the adult testes, suggesting that Odad3 plays a role in spermatozoa formation. Subsequently, we conditionally deleted the Odad3 gene in adult males and demonstrated that even partial ablation of the Odad3 gene leads to asthenoteratozoospermia with multiple morphological abnormalities of sperm flagella (MMAF) in mice. The analysis of the seminiferous tubules in Odad3-deficient mice revealed defects in spermatogenesis with accumulation of seminiferous tubules at the spermiogenesis and spermiation phases. Furthermore, analysis of fertility in heterozygous Odad3+/- knockout mice revealed a reduction in sperm count and motility as well as abnormal sperm morphology. Additionally, Odad3+/- males exhibited a shorter fertile lifespan. Overall, these results suggest the important role of Odad3 and Odad3 gene dosage in male fertility. These findings may have an impact on the genetic and fertility counseling practice of PCD patients carrying Odad3 loss-of-function mutations.

pH Homeodynamics and Male Fertility: A Coordinated Regulation of Acid-Based Balance during Sperm Journey to Fertilization

pH homeostasis is crucial for spermatogenesis, sperm maturation, sperm physiological function, and fertilization in mammals. HCO3- and H+ are the most significant factors involved in regulating pH homeostasis in the male reproductive system. Multiple pH-regulating transporters and ion channels localize in the testis, epididymis, and spermatozoa, such as HCO3- transporters (solute carrier family 4 and solute carrier family 26 transporters), carbonic anhydrases, and H+-transport channels and enzymes (e.g., Na+-H+ exchangers, monocarboxylate transporters, H+-ATPases, and voltage-gated proton channels). Hormone-mediated signals impose an influence on the production of some HCO3- or H+ transporters, such as NBCe1, SLC4A2, MCT4, etc. Additionally, ion channels including sperm-specific cationic channels for Ca2+ (CatSper) and K+ (SLO3) are directly or indirectly regulated by pH, exerting specific actions on spermatozoa. The slightly alkaline testicular pH is conducive to spermatogenesis, whereas the epididymis's low HCO3- concentration and acidic lumen are favorable for sperm maturation and storage. Spermatozoa pH increases substantially after being fused with seminal fluid to enhance motility. In the female reproductive tract, sperm are subjected to increasing concentrations of HCO3- in the uterine and fallopian tube, causing a rise in the intracellular pH (pHi) of spermatozoa, leading to hyperpolarization of sperm plasma membranes, capacitation, hyperactivation, acrosome reaction, and ultimately fertilization. The physiological regulation initiated by SLC26A3, SLC26A8, NHA1, sNHE, and CFTR localized in sperm is proven for certain to be involved in male fertility. This review intends to present the key factors and characteristics of pHi regulation in the testes, efferent duct, epididymis, seminal fluid, and female reproductive tract, as well as the associated mechanisms during the sperm journey to fertilization, proposing insights into outstanding subjects and future research trends.

Tissue clearing and imaging approaches for in toto analysis of the reproductive system†

New microscopy techniques in combination with tissue clearing protocols and emerging analytical approaches have presented researchers with the tools to understand dynamic biological processes in a three-dimensional context. This paves the road for the exploration of new research questions in reproductive biology, for which previous techniques have provided only approximate resolution. These new methodologies now allow for contextualized analysis of far-larger volumes than was previously possible. Tissue optical clearing and three-dimensional imaging techniques posit the bridging of molecular mechanisms, macroscopic morphogenic development, and maintenance of reproductive function into one cohesive and comprehensive understanding of the biology of the reproductive system. In this review, we present a survey of the various tissue clearing techniques and imaging systems, as they have been applied to the developing and adult reproductive system. We provide an overview of tools available for analysis of experimental data, giving particular attention to the emergence of artificial intelligence-assisted methods and their applicability to image analysis. We conclude with an evaluation of how novel image analysis approaches that have been applied to other organ systems could be incorporated into future experimental evaluation of reproductive biology.

Exploration of tissue fixation methods suitable for digital pathological studies of the testis

BACKGROUND

The way of testicular tissue fixation directly affects the correlation and structural integrity between connective tissue and seminiferous tubules, which is essential for the study of male reproductive development. This study aimed to find the optimal fixative and fixation time to produce high-quality testicular histopathological sections, and provided a suitable foundation for in-depth study of male reproductive development with digital pathology technology.

METHODS

Testes were removed from both sides of 25 male C57BL/6 mice. Samples were fixed in three different fixatives, 10% neutral buffered formalin (10% NBF), modified Davidson's fluid (mDF), and Bouin's Fluid (BF), for 8, 12, and 24 h, respectively. Hematoxylin and eosin (H&E) staining, periodic acid Schiff-hematoxylin (PAS-h) staining, and immunohistochemistry (IHC) were used to evaluate the testicle morphology, staging of mouse seminiferous tubules, and protein preservation. Aperio ScanScope CS2 panoramic scanning was used to perform quantitative analyses.

RESULTS

H&E staining showed 10% NBF resulted in an approximately 15-17% reduction in the thickness of seminiferous epithelium. BF and mDF provided excellent results when staining acrosomes with PAS-h. IHC staining of synaptonemal complexes 3 (Sycp3) was superior in mDF compared to BF-fixed samples. Fixation in mDF and BF improved testis tissue morphology compared to 10% NBF.

CONCLUSIONS

Quantitative analysis showed that BF exhibited a very low IHC staining efficiency and revealed that mouse testes fixed for 12 h with mDF, exhibited morphological details, excellent efficiency of PAS-h staining for seminiferous tubule staging, and IHC results. In addition, the morphological damage of testis was prolonged with the duration of fixation time.

Inter- and trans-generational impacts of environmental exposures on the germline resolved at the single-cell level

Reproduction is a remarkably intricate process involving the interaction of multiple cell types and organ systems unfolding over long periods of time and that culminates with the production of gametes. The initiation of germ cell development takes place during embryogenesis but only completes decades later in humans. The complexity inherent to reproduction and its study has long hampered our ability to decipher how environmental agents disrupt this process. Single-cell approaches provide an opportunity for a deeper understanding of the action of toxicants on germline function and analyze how the response to their exposure is differentially distributed across tissues and cell types. In addition to single-cell RNA sequencing, other single-cell or nucleus level approaches such as ATAC-sequencing and multi-omics have expanded the strategies that can be implemented in reproductive toxicological studies to include epigenomic and the nuclear transcriptomic data. Here we will discuss the current state of single-cell technologies and how they can best be utilized to advance reproductive toxicological studies. We will then discuss case studies in two model organisms (Caenorhabditis elegans and mouse) studying different environmental exposures (alcohol and e-cigarettes respectively) to highlight the value of single-cell and single-nucleus approaches for reproductive biology and reproductive toxicology.

Testicular dysfunction and "its recovery effect" after cadmium exposure

In recent years, with the acceleration of industrialization, the decline of male fertility caused by heavy metal pollution has attracted much attention. However, whether the inhibition of testicular function after cadmium exposure is reversible remains to be studied. In this study, we constructed rat models of cadmium exposure and dis-exposure, and collected relative samples to observe the changes of related indicators. The results showed that cadmium exposure could reduce the fertility, inhibit the hypothalamic-pituitary-testis axis and activate hypothalamic-pituitary-adrenal axis function, the testicular GR/PI3K-AKT/AMPK signal was abnormal, cell proliferation was inhibited and apoptosis was enhanced. Four weeks after the exposure was stopped, the fertility was still decreased, testicular testosterone synthesis and spermatogenesis were inhibited, cell proliferation was inhibited and apoptosis was enhanced, but all of them were reversed. After eight weeks of cadmium exposure, the above indicators were observed to return to normal. At the same time, by giving different concentrations of corticosterone to spermatogonium, we confirmed that corticosterone may regulate the proliferation and apoptosis of spermatogonium through GR/PI3K-AKT/AMPK signal. In this study, the reproductive toxicity of cadmium, a metal environmental pollutant, was analyzed in depth to provide a new theoretical and experimental basis for ensuring male reproductive health.

The uniqueness of on-demand male contraception

Because nearly half of pregnancies worldwide are unintended, available contraceptive methods are inadequate. Moreover, due to the striking imbalance between contraceptive options available for men compared to the myriad of options available to women, there is an urgent need for new methods of contraception for men. This review summarizes ongoing efforts to develop male contraceptives highlighting the unique aspects particular to on-demand male contraception, where a man takes a contraceptive only when and as often as needed.

Epigenetic priming in the male germline

Epigenetic priming presets chromatin states that allow the rapid induction of gene expression programs in response to differentiation cues. In the germline, it provides the blueprint for sexually dimorphic unidirectional differentiation. In this review, we focus on epigenetic priming in the mammalian male germline and discuss how cellular memories are regulated and inherited to the next generation. During spermatogenesis, epigenetic priming predetermines cellular memories that ensure the lifelong maintenance of spermatogonial stem cells and their subsequent commitment to meiosis and to the production of haploid sperm. The paternal chromatin state is also essential for the recovery of totipotency after fertilization and contributes to paternal epigenetic inheritance. Thus, epigenetic priming establishes stable but reversible chromatin states during spermatogenesis and enables epigenetic inheritance and reprogramming in the next generation.

Single-Nucleus RNA-Seq Reveals Spermatogonial Stem Cell Developmental Pattern in Shaziling Pigs

Normal testicular development ensures the process of spermatogenesis, which is a complex biological process. The sustained high productivity of spermatogenesis throughout life is predominantly attributable to the constant proliferation and differentiation of spermatogonial stem cells (SSCs). The self-renewal and differentiation processes of SSCs are strictly regulated by the SSC niche. Therefore, understanding the developmental pattern of SSCs is crucial for spermatogenesis. The Shaziling pig is a medium-sized indigenous pig breed originating from central China. It is renowned for its superior meat quality and early male sexual maturity. The spermatogenic ability of the boars is of great economic importance to the pig industry. To investigate testicular development, particularly the pattern of SSC development in Shaziling pigs, we used single-cell transcriptomics to identify gene expression patterns in 82,027 individual cells from nine Shaziling pig testes at three key postnatal developmental stages. We generated an unbiased cell developmental atlas of Shaziling pig testicular tissues. We elucidated the complex processes involved in the development of SSCs within their niche in the Shaziling pig. Specifically, we identified potential marker genes and cellular signaling pathways that regulate SSC self-renewal and maintenance. Additionally, we proposed potential novel marker genes for SSCs that could be used for SSC isolation and sorting in Shaziling pigs. Furthermore, by immunofluorescence staining of testicular tissues of different developmental ages using marker proteins (UCHL1 and KIT), the developmental pattern of the spermatogonia of Shaziling pigs was intensively studied. Our research enhances the comprehension of the development of SSCs and provides a valuable reference for breeding Shaziling pigs.

Deletion of ACTRT1 is associated with male infertility as sperm acrosomal ultrastructural defects and fertilization failure in human

STUDY QUESTION

Could actin-related protein T1 (ACTRT1) deficiency be a potential pathogenic factor of human male infertility?

SUMMARY ANSWER

A 110-kb microdeletion of the X chromosome, only including the ACTRT1 gene, was identified as responsible for infertility in two Chinese males with sperm showing acrosomal ultrastructural defects and fertilization failure.

WHAT IS KNOWN ALREADY

The actin-related proteins (e.g. ACTRT1, ACTRT2, ACTL7A, and ACTL9) interact with each other to form a multimeric complex in the subacrosomal region of spermatids, which is crucial for the acrosome-nucleus junction. Actrt1-knockout (KO) mice are severely subfertile owing to malformed sperm heads with detached acrosomes and partial fertilization failure. There are currently no reports on the association between ACTRT1 deletion and male infertility in humans.

STUDY DESIGN, SIZE, DURATION

We recruited a cohort of 120 infertile males with sperm head deformations at a large tertiary hospital from August 2019 to August 2023. Genomic DNA extracted from the affected individuals underwent whole exome sequencing (WES), and in silico analyses were performed to identify genetic variants. Morphological analysis, functional assays, and ART were performed in 2022 and 2023.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The ACTRT1 deficiency was identified by WES and confirmed by whole genome sequencing, PCR, and quantitative PCR. Genomic DNA of all family members was collected to define the hereditary mode. Papanicolaou staining and electronic microscopy were performed to reveal sperm morphological changes. Western blotting and immunostaining were performed to explore the pathological mechanism of ACTRT1 deficiency. ICSI combined with artificial oocyte activation (AOA) was applied for one proband.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified a whole-gene deletion variant of ACTRT1 in two infertile males, which was inherited from their mothers, respectively. The probands exhibited sperm head deformations owing to acrosomal detachment, which is consistent with our previous observations on Actrt1-KO mice. Decreased expression and ectopic distribution of ACTL7A and phospholipase C zeta were observed in sperm samples from the probands. ICSI combined with AOA effectively solved the fertilization problem in Actrt1-KO mice and in one of the two probands.

LIMITATIONS, REASONS FOR CAUTION

Additional cases are needed to further confirm the genetic contribution of ACTRT1 variants to male infertility.

WIDER IMPLICATIONS OF THE FINDINGS

Our results reveal a gene-disease relation between the ACTRT1 deletion described here and human male infertility owing to acrosomal detachment and fertilization failure. This report also describes a good reproductive outcome of ART with ICSI-AOA for a proband.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Chongqing medical scientific research project (Joint project of Chongqing Health Commission and Science and Technology Bureau, 2023MSXM008 and 2023MSXM054). There are no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Retinoic acid mitigates the NSC319726-induced spermatogenesis dysfunction through cuproptosis-independent mechanisms

Copper ionophore NSC319726 has attracted researchers' attention in treating diseases, particularly cancers. However, its potential effects on male reproduction during medication are unclear. This study aimed to determine whether NSC319726 exposure affected the male reproductive system. The reproductive toxicity of NSC319726 was evaluated in male mice following a continuous exposure period of 5 weeks. The result showed that NSC319726 exposure caused testis index reduction, spermatogenesis dysfunction, and architectural damage in the testis and epididymis. The exposure interfered with spermatogonia proliferation, meiosis initiation, sperm count, and sperm morphology. The exposure also disturbed androgen synthesis and blood testis barrier integrity. NSC319726 treatment could elevate the copper ions in the testis to induce cuproptosis in the testis. Copper chelator rescued the elevated copper ions in the testis and partly restored the spermatogenesis dysfunction caused by NSC319726. NSC319726 treatment also decreased the level of retinol dehydrogenase 10 (RDH10), thereby inhibiting the conversion of retinol to retinoic acid, causing the inability to initiate meiosis. Retinoic acid treatment could rescue the meiotic initiation and spermatogenesis while not affecting the intracellular copper ion levels. The study provided an insight into the bio-safety of NSC319726. Retinoic acid could be a potential therapy for spermatogenesis impairment in patients undergoing treatment with NSC319726.

Exploring the biological roles of DHX36, a DNA/RNA G-quadruplex helicase, highlights functions in male infertility: A comprehensive review

It is estimated that 15 % of couples at reproductive age worldwide suffer from infertility, approximately 50 % of cases are caused by male factors. Significant progress has been made in the diagnosis and treatment of male infertility through assisted reproductive technology and molecular genetics methods. However, there is still inadequate research on the underlying mechanisms of gene regulation in the process of spermatogenesis. Guanine-quadruplexes (G4s) are a class of non-canonical secondary structures of nucleic acid commonly found in genomes and RNAs that play important roles in various biological processes. Interestingly, the DEAH-box helicase 36 (DHX36) displays high specificity for the G4s which can unwind both DNA G4s and RNA G4s enzymatically and is highly expressed in testis, thereby regulating multiple cellular functions including transcription, pre-mRNA splicing, translation, telomere maintenance, genomic stability, and RNA metabolism in development and male infertility. This review provides an overview of the roles of G4s and DHX36 in reproduction and development. We mainly focus on the potential role of DHX36 in male infertility. We also discuss possible future research directions regarding the mechanism of spermatogenesis mediated by DHX36 through G4s in spermatogenesis-related genes and provide new targets for gene therapy of male infertility.

Ca2+ homeostasis and male fertility: a target for a new male contraceptive system

Ca2+ is a key secondary messenger that determines sperm motility patterns. Mammalian sperm undergo capacitation, a process to acquire fertilizing ability, in the female reproductive tract. Capacitated sperm change their flagellar waveform to develop hyperactivated motility, which is crucial for successful sperm navigation to the eggs and fertilization. The sperm-specific channel, CATSPER, and an ATPase transporter, PMCA4, serve as major paths for Ca2+ influx and efflux, respectively, in sperm. The ionic paths coordinate Ca2+ homeostasis in the sperm, and their loss-of-function impairs sperm motility, to cause male infertility. In this review, we summarize the physiological significance of these two Ca2+ gates and suggest their potential applications in novel male contraceptives.

LanCL2 Implicates in Testicular Redox Homeostasis and Acrosomal Maturation

Redox balance plays an important role in testicular homeostasis. While lots of antioxidant molecules have been identified as widely expressed, the understanding of the critical mechanisms for redox management in male germ cells is inadequate. This study identified LanCL2 as a major male germ cell-specific antioxidant gene that is important for testicular homeostasis. Highly expressed in the brain and testis, LanCL2 expression correlates with testicular maturation and brain development. LanCL2 is enriched in spermatocytes and round spermatids of the testis. By examining LanCL2 knockout mice, we found that LanCL2 deletion did not affect postnatal brain development but injured the sperm parameters of adult mice. With histopathological analysis, we noticed that LanCL2 KO caused a pre-maturation and accelerated the self-renewal of spermatogonial stem cells in the early stage of spermatogenesis. In contrast, at the adult stage, LanCL2 KO damaged the acrosomal maturation in spermiogenesis, resulting in spermatogenic defects with a reduced number and motility of spermatozoa. Furthermore, we show that this disruption of testicular homeostasis in the LanCL2 KO testis was due to dysbalanced testicular redox homeostasis. This study demonstrates the critical role of LanCL2 in testicular homeostasis and redox balance.

The deubiquitinase cofactor UAF1 interacts with USP1 and plays an essential role in spermiogenesis

Spermiogenesis defines the final phase of male germ cell differentiation. While multiple deubiquitinating enzymes have been linked to spermiogenesis, the impacts of deubiquitination on spermiogenesis remain poorly characterized. Here, we investigated the function of UAF1 in mouse spermiogenesis. We selectively deleted Uaf1 in premeiotic germ cells using the Stra8-Cre knock-in mouse strain (Uaf1 sKO), and found that Uaf1 is essential for spermiogenesis and male fertility. Further, UAF1 interacts and colocalizes with USP1 in the testes. Conditional knockout of Uaf1 in testes results in disturbed protein levels and localization of USP1, suggesting that UAF1 regulates spermiogenesis through the function of the deubiquitinating enzyme USP1. Using tandem mass tag-based proteomics, we identified that conditional knockout of Uaf1 in the testes results in reduced levels of proteins that are essential for spermiogenesis. Thus, we conclude that the UAF1/USP1 deubiquitinase complex is essential for normal spermiogenesis by regulating the levels of spermiogenesis-related proteins.

Chromatin remodeler CHD8 is required for spermatogonial proliferation and early meiotic progression

Meiosis is a key step during germ cell differentiation, accompanied by the activation of thousands of genes through germline-specific chromatin reorganization. The chromatin remodeling mechanisms underpinning early meiotic stages remain poorly understood. Here we focus on the function of one of the major autism genes, CHD8, in spermatogenesis, based on the epidemiological association between autism and low fertility rates. Specific ablation of Chd8 in germ cells results in gradual depletion of undifferentiated spermatogonia and the failure of meiotic double-strand break (DSB) formation, leading to meiotic prophase I arrest and cell death. Transcriptional analyses demonstrate that CHD8 is required for extensive activation of spermatogenic genes in spermatogonia, necessary for spermatogonial proliferation and meiosis. CHD8 directly binds and regulates genes crucial for meiosis, including H3K4me3 histone methyltransferase genes, meiotic cohesin genes, HORMA domain-containing genes, synaptonemal complex genes, and DNA damage response genes. We infer that CHD8 contributes to meiotic DSB formation and subsequent meiotic progression through combined regulation of these meiosis-related genes. Our study uncovers an essential role of CHD8 in the proliferation of undifferentiated spermatogonia and the successful progression of meiotic prophase I.

Molecular functional characterization of the setdb1 and its potential target gene sox5 illuminate the histone modification-mediated orchestration of gonadal development in Chinese tongue sole (Cynoglossus semilaevis)

SET (SuVar3-9, Enhancer of Zeste, Trithorax) domain bifurcated histone lysine methyltransferase 1, setdb1, is the predominant histone lysine methyltransferase catalyzing H3K9me3. Prior studies have illustrated that setdb1 and H3K9me3 critically regulate sex differentiation and gametogenesis. However, the molecular details by which setdb1 is involved in these processes in fish have been poorly reported. Here, we cloned and characterized the setdb1 ORF (open reading frame) sequence from Chinese tongue sole (Cynoglossus semilaevis). The setdb1 ORF sequence was 3,669 bp, encoding a 1,222-amino-acid protein. Phylogenetic analysis showed that setdb1 was structurally conserved. qRT-PCR revealed that setdb1 had a high expression level in the testes at 12 mpf (months post fertilization). Single-cell RNA-seq data at 24 mpf indicated that setdb1 was generally expressed in spermatogenic cells at each stage except for sperm and was centrally expressed in oogonia. H3K9me3 modification was observed in gonads with the immunofluorescence technique. Furthermore, the overexpression experiment suggested that sox5 was a candidate target of setdb1. sox5 was abundantly expressed in male and pseudomale gonads at 24 mpf. Single-cell RNA-seq data showed that sox5 was mainly expressed in spermatogonia and its expression gradually declined with differentiation. Taken together, our findings imply that setdb1 regulates sox5 transcription in gonads, which provides molecular clues into histone modification-mediated orchestration of sex differentiation and gametogenesis.

Gene regulation during meiosis

Meiosis is essential for gamete production in all sexually reproducing organisms. It entails two successive cell divisions without DNA replication, producing haploid cells from diploid ones. This process involves complex morphological and molecular differentiation that varies across species and between sexes. Specialized genomic events like meiotic recombination and chromosome segregation are tightly regulated, including preparation for post-meiotic development. Research in model organisms, notably yeast, has shed light on the genetic and molecular aspects of meiosis and its regulation. Although mammalian meiosis research faces challenges, particularly in replicating gametogenesis in vitro, advances in genetic and genomic technologies are providing mechanistic insights. Here we review the genetics and molecular biology of meiotic gene expression control, focusing on mammals.

Updates on the management of inflammatory bowel disease from periconception to pregnancy and lactation

Inflammatory bowel disease (IBD) affects reproductive planning due to psychological effects and mechanical problems related to surgery. Children of people with IBD have an increased risk of about 10% if one parent has IBD and up to 33% if both parents have IBD. The fertility of people with IBD is similar to the general population, but fertility might be reduced in individuals with active IBD, ileal pouch-anal anastomosis, or perianal Crohn's disease. Flaring disease during pregnancy increases complications, such as preterm birth. Thus, disease management with appropriate medications can optimise outcomes. As most medications have minimal fetal risks, people with IBD should be informed about the risks of stopping medications and the importance of maintaining remission. A period of disease remission is advisable before pregnancy and could reduce the risks for both the pregnant person and the fetus. Flexible endoscopy, intestinal ultrasound, and gadolinium-free magnetic resonance enterography are safe during pregnancy. We provide state-of-the-art knowledge on the basis of the latest evidence to ensure successful pregnancy outcomes in controlled IBD.

Consequences of Exposure to Hypobaric Hypoxia Associated with High Altitude on Spermatogenesis and Seminal Parameters: A Literature Review

Preclinical research has provided compelling evidence indicating that exposure to hypobaric hypoxia (HH) results in a deterioration of spermatogenesis. This adverse effect extends to the underlying molecular mechanisms, progressively leading to impairments in the seminiferous epithelium and germ cells and alterations in semen parameters. Indeed, several studies have demonstrated that animals exposed to HH, whether in natural high-altitude environments or under simulated hypoxic conditions, exhibit damage to the self-renewal and differentiation of spermatogenesis, an increase in germline cell apoptosis, and structural alterations in the seminiferous tubules. One of the primary mechanisms associated with the inhibition of differentiation and an increase in apoptosis among germ cells is an elevated level of oxidative stress, which has been closely associated with HH exposure. Human studies have shown that individuals exposed to HH, such as mountaineers and alpinists, exhibit decreased sperm count, reduced motility, diminished viability, and increased sperm with abnormal morphology in their semen. This evidence strongly suggests that exposure to HH may be considered a significant risk factor that could elevate the prevalence of male infertility. This literature review aims to provide a comprehensive description and propose potential mechanisms that could elucidate the infertility processes induced by HH. By doing so, it contributes to expanding our understanding of the challenges posed by extreme environments on human physiology, opening new avenues for research in this field.

PRC1 directs PRC2-H3K27me3 deposition to shield adult spermatogonial stem cells from differentiation

Spermatogonial stem cells functionality reside in the slow-cycling and heterogeneous undifferentiated spermatogonia cell population. This pool of cells supports lifelong fertility in adult males by balancing self-renewal and differentiation to produce haploid gametes. However, the molecular mechanisms underpinning long-term stemness of undifferentiated spermatogonia during adulthood remain unclear. Here, we discover that an epigenetic regulator, Polycomb repressive complex 1 (PRC1), shields adult undifferentiated spermatogonia from differentiation, maintains slow cycling, and directs commitment to differentiation during steady-state spermatogenesis in adults. We show that PRC2-mediated H3K27me3 is an epigenetic hallmark of adult undifferentiated spermatogonia. Indeed, spermatogonial differentiation is accompanied by a global loss of H3K27me3. Disruption of PRC1 impairs global H3K27me3 deposition, leading to precocious spermatogonial differentiation. Therefore, PRC1 directs PRC2-H3K27me3 deposition to maintain the self-renewing state of undifferentiated spermatogonia. Importantly, in contrast to its role in other tissue stem cells, PRC1 negatively regulates the cell cycle to maintain slow cycling of undifferentiated spermatogonia. Our findings have implications for how epigenetic regulators can be tuned to regulate the stem cell potential, cell cycle and differentiation to ensure lifelong fertility in adult males.

An organism-wide atlas of hormonal signaling based on the mouse lemur single-cell transcriptome

Hormones mediate long-range cell communication and play vital roles in physiology, metabolism, and health. Traditionally, endocrinologists have focused on one hormone or organ system at a time. Yet, hormone signaling by its very nature connects cells of different organs and involves crosstalk of different hormones. Here, we leverage the organism-wide single cell transcriptional atlas of a non-human primate, the mouse lemur (Microcebus murinus), to systematically map source and target cells for 84 classes of hormones. This work uncovers previously-uncharacterized sites of hormone regulation, and shows that the hormonal signaling network is densely connected, decentralized, and rich in feedback loops. Evolutionary comparisons of hormonal genes and their expression patterns show that mouse lemur better models human hormonal signaling than mouse, at both the genomic and transcriptomic levels, and reveal primate-specific rewiring of hormone-producing/target cells. This work complements the scale and resolution of classical endocrine studies and sheds light on primate hormone regulation.

Spaghetti Connections: Synaptonemal Complexes as a Tool to Explore Chromosome Structure, Evolution, and Meiotic Behavior in Fish

BACKGROUND

The synaptonemal complex (SC) is a protein axis formed along chromosomes during meiotic prophase to ensure proper pairing and crossing over. SC analysis has been widely used to study the chromosomes of mammals and less frequently of birds, reptiles, and fish. It is a promising method to investigate the evolution of fish genomes and chromosomes as a part of complex approach.

SUMMARY

Compared with conventional metaphase chromosomes, pachytene chromosomes are less condensed and exhibit pairing between homologous chromosomes. These features of SCs facilitate the study of the small chromosomes that are typical in fish. Moreover, it allows the study of heteromorphisms in sex chromosomes and supernumerary chromosomes. In addition, it enables the investigation of the pairing between orthologous chromosomes in hybrids, which is crucial for uncovering the causes of hybrid sterility and asexual reproduction, such as gynogenesis or hybridogenesis. However, the application of SC analysis to fish chromosomes is limited by the associated complications. First, in most fish, meiosis does not occur during every season and life stage. Second, different SC preparation methods are optimal for different fish species. Third, commercial antibodies targeting meiotic proteins have been primarily developed against mammalian antigens, and not all of them are suitable for fish chromosomes.

KEY MESSAGES

In the present review, we provide an overview of the methods for preparing fish SCs and highlight important studies using SC analysis in fish. This study will be valuable for planning and designing research that applies SC analysis to fish cytogenetics and genomics.

The Cby3/ciBAR1 complex positions the annulus along the sperm flagellum during spermiogenesis

Proper compartmentalization of the sperm flagellum is essential for fertility. The annulus is a septin-based ring that demarcates the midpiece (MP) and the principal piece (PP). It is assembled at the flagellar base, migrates caudally, and halts upon arriving at the PP. However, the mechanisms governing annulus positioning remain unknown. We report that a Chibby3 (Cby3)/Cby1-interacting BAR domain-containing 1 (ciBAR1) complex is required for this process. Ablation of either gene in mice results in male fertility defects, caused by kinked sperm flagella with the annulus mispositioned in the PP. Cby3 and ciBAR1 interact and colocalize to the annulus near the curved membrane invagination at the flagellar pocket. In the absence of Cby3, periannular membranes appear to be deformed, allowing the annulus to migrate over the fibrous sheath into the PP. Collectively, our results suggest that the Cby3/ciBAR1 complex regulates local membrane properties to position the annulus at the MP/PP junction.

Integrated analysis of lncRNA, miRNA and mRNA expression profiles reveals regulatory pathways associated with pig testis function

Long noncoding RNA (lncRNA) and microRNA (miRNA) are known to play pivotal roles in mammalian testicular function and spermatogenesis. However, their impact on porcine male reproduction has yet to be well unraveled. Here, we sequenced and identified lncRNA and miRNA expressed in the testes of Chinese indigenous Banna mini-pig inbred line (BMI) and introduced Western Duroc (DU) and Large White (LW) pigs. By pairwise comparison (BMI vs DU, BMI vs LW, and DU vs LW), we found the gene expression differences in the testes between Chinese local pigs and introduced Western commercial breeds were more striking than those between introduced commercial breeds. Furthermore, we found 1622 co-differentially expressed genes (co-DEGs), 122 co-differentially expressed lncRNAs (co-DELs), 39 co-differentially expressed miRNAs (co-DEMs) in BMI vs introduced commercial breeds (DU and LW). Functional analysis revealed that these co-DEGs and co-DELs/co-DEMs target genes were enriched in male sexual function pathways, including MAPK, AMPK, TGF-β/Smad, Hippo, NF-kappa B, and PI3K/Akt signaling pathways. Additionally, we established 10,536 lncRNA-mRNA, 11,248 miRNA-mRNA pairs, and 62 ceRNA (lncRNA-miRNA-mRNA) networks. The ssc-miR-1343 had the most interactive factors in the ceRNA network, including 20 mRNAs and 3 lncRNAs, consisting of 56 ceRNA pairs. These factors played extremely important roles in the regulation of testis function as key nodes in the interactive regulatory network. Our results provide insight into the functional roles of lncRNAs and miRNAs in porcine testis and offer a valuable resource for understanding the differences between Chinese indigenous and introduced Western pigs.

Pyruvate kinase M in germ cells is essential for sperm motility and male fertility but not spermatogenesis

Male germ cells employ specific metabolic pathways throughout their developmental stages. In a previous study, we discovered heightened expression of pyruvate kinase M (PKM), a pivotal glycolytic enzyme, in spermatogonia and spermatids. To gain deeper insights into PKM's roles in spermatogenesis, sperm function, and male fertility, we engineered a conditional-knockout mouse model ( Pkm -vKO mice) to selectively disrupt the Pkm gene within germ cells. Despite maintaining regular testicular histology and sperm morphology, the male Pkm -vKO mice were infertility, characterized by significant impairments in sperm motility and adenosine triphosphate (ATP) generation. In addition, Pkm -null spermatozoa exhibited similar deficits in protein tyrosine phosphorylation linked to capacitation, as well as compromised performance in in vitro fertilization experiments. To conclude, PKM's presence is not obligatory for the entirety of spermatogenesis in male germ cells; however, it emerges as a critical factor influencing sperm motility and overall male fertility.