Spermatogenic cells of the prepuberal mouse. Isolation and morphological characterization

Ultrastructural changes in the spermatogenic cells of domestic chicken (Gallus gallus domesticus) observed at different reproductive stages

Spermatogenesis is a complex process. It is the modification of progenitor spermatogonia into mature spermatozoa. The stages are similar in all-male vertebrates, as well as avian species. However, studies on spermatogenesis in birds are fewer compared to mammals. The current study investigated the ultrastructural changes in the spermatogenic cells of domestic chickens in different reproductive stages. Thirty (30) male birds, ten (10) in each of the three reproductive stages: pre-pubertal, pubertal, and adult were used in the study. Testicular tissues from all age groups were processed for transmission electron microscopy (TEM). TEM results showed spermatogonia and primary spermatocytes in the pre-pubertal testis, and the seminiferous tubule lumen was wide and empty. Also, the nuclei of spermatogonia at this stage did not contain condensed chromatin material at the center nor scattered at the periphery of the nuclear membrane. There were slight differences between the spermatogenic cells in the pubertal and adult age groups. The spermatogonia, primary and secondary spermatocytes, and round spermatids with scanty chromatin material were observed in both age groups. In the adult age group, round and elongated spermatids with condensed chromatin materials were observed besides the other spermatogenic cells. Also, the seminiferous tubule lumen was filled with sperm cells and cellular debris, unlike in the pre-pubertal and pubertal age groups where they were wide and empty. The presence of numerous oval mitochondria were observed in all age groups. This signifies the active process of spermatogenesis in pre-pubertal, pubertal, and adult male domestic chickens.

Evolutionary innovations in germline biology of placental mammals identified by transcriptomics of first-wave spermatogenesis in opossum

Mammalian spermatogenesis is a highly stereotyped and conserved developmental process that is essential for fitness. At the same time, gene expression in spermatogenic cells is rapidly evolving. This combination of features has been suggested to drive rapid fixation of new gene expression patterns. Using a high-resolution dataset comprising bulk and single-cell data from juvenile and adult testes of the opossum Monodelphis domestica, a model marsupial, we define the developmental timing of the spermatogenic first wave in opossum and delineate conserved and divergent gene expression programs across the placental-marsupial split by comparison to equivalent data from mouse, a model placental mammal. Epigenomic data confirmed divergent regulation at the level of transcription, and comparison to data from four additional amniote species identified hundreds of genes with evidence of rapid fixation of expression. This gene set encompasses known and previously undescribed regulators of spermatogenic development.

RNA helicase D1PAS1 resolves R-loops and forms a complex for mouse pachytene piRNA biogenesis required for male fertility

During meiosis, RNA polymerase II transcribes pachytene piRNA precursors with unusually long and unspliced transcripts from discrete autosomal loci in the mouse genome. Despite the importance of piRNA for male fertility and a well-defined maturation process, the transcriptional machinery remains poorly understood. Here, we document that D1PAS1, an ATP-dependent RNA helicase, is critical for pachytene piRNA expression from multiple genomic loci and subsequent translocation into the cytoplasm to ensure mature piRNA biogenesis. Depletion of D1PAS1 in gene-edited mice results in the accumulation of R-loops in pachytene spermatocytes, leading to DNA-damage-induced apoptosis, disruption of piRNA biogenesis, spermatogenic arrest, and male infertility. Transcriptome, genome-wide R-loop profiling, and proteomic analyses document that D1PAS1 regulates pachytene piRNA transcript elongation and termination. D1PAS1 subsequently forms a complex with nuclear export components to ensure pachytene piRNA precursor translocation from the nucleus to the cytoplasm for processing into small non-coding RNAs. Thus, our study defines D1PAS1 as a specific transcription activator that promotes R-loop unwinding and is a critical factor in pachytene piRNA biogenesis.

Spermatogonial stem cell technologies: applications from human medicine to wildlife conservation†

Spermatogonial stem cell (SSC) technologies that are currently under clinical development to reverse human infertility hold the potential to be adapted and applied for the conservation of endangered and vulnerable wildlife species. The biobanking of testis tissue containing SSCs from wildlife species, aligned with that occurring in pediatric human patients, could facilitate strategies to improve the genetic diversity and fitness of endangered populations. Approaches to utilize these SSCs could include spermatogonial transplantation or testis tissue grafting into a donor animal of the same or a closely related species, or in vitro spermatogenesis paired with assisted reproduction approaches. The primary roadblock to progress in this field is a lack of fundamental knowledge of SSC biology in non-model species. Herein, we review the current understanding of molecular mechanisms controlling SSC function in laboratory rodents and humans, and given our particular interest in the conservation of Australian marsupials, use a subset of these species as a case-study to demonstrate gaps-in-knowledge that are common to wildlife. Additionally, we review progress in the development and application of SSC technologies in fertility clinics and consider the translation potential of these techniques for species conservation pipelines.

Temporal maturation of Sertoli cells during the establishment of the cycle of the seminiferous epithelium†

Sertoli cells, omnipresent, somatic cells within the seminiferous tubules of the mammalian testis are essential to male fertility. Sertoli cells maintain the integrity of the testicular microenvironment, regulate hormone synthesis, and of particular importance, synthesize the active derivative of vitamin A, all trans retinoic acid (atRA), which is required for germ cell differentiation and the commitment of male germ cells to meiosis. Stages VIII-IX, when atRA synthesis occurs in the testis, coincide with multiple germ cell development and testicular restructuring events that rely on Sertoli cell gene products to proceed normally. In this study, we have synchronized and captured the mouse testis at four recurrent points of atRA synthesis to observe transcriptomic changes within Sertoli cells as mice age and the Sertoli cells are exposed to increasingly developed germ cell subtypes. This work provides comprehensive, high-resolution characterization of the timing of induction of functional Sertoli cell genes across the first wave of spermatogenesis, and outlines in silico predictions of germ cell derived signaling mechanisms targeting Sertoli cells. We have found that Sertoli cells adapt to their environment, especially to the needs of the germ cell populations present and establish germ-Sertoli cell and Sertoli-Sertoli cell junctions early but gain many of their known immune-regulatory and protein secretory functions in preparation for spermiogenesis and spermiation. Additionally, we have found unique patterns of germ-Sertoli signaling present at each endogenous pulse of atRA, suggesting individual functions of the various germ cells in germ-Sertoli communication.

INO80 regulates chromatin accessibility to facilitate suppression of sex-linked gene expression during mouse spermatogenesis

The INO80 protein is the main catalytic subunit of the INO80-chromatin remodeling complex, which is critical for DNA repair and transcription regulation in murine spermatocytes. In this study, we explored the role of INO80 in silencing genes on meiotic sex chromosomes in male mice. INO80 immunolocalization at the XY body in pachytene spermatocytes suggested a role for INO80 in the meiotic sex body. Subsequent deletion of Ino80 resulted in high expression of sex-linked genes. Furthermore, the active form of RNA polymerase II at the sex chromosomes of Ino80-null pachytene spermatocytes indicates incomplete inactivation of sex-linked genes. A reduction in the recruitment of initiators of meiotic sex chromosome inhibition (MSCI) argues for INO80-facilitated recruitment of DNA repair factors required for silencing sex-linked genes. This role of INO80 is independent of a common INO80 target, H2A.Z. Instead, in the absence of INO80, a reduction in chromatin accessibility at DNA repair sites occurs on the sex chromosomes. These data suggest a role for INO80 in DNA repair factor localization, thereby facilitating the silencing of sex-linked genes during the onset of pachynema.

FBXO47 regulates centromere pairing as key component of centromeric SCF E3 ligase in mouse spermatocytes

Centromere pairing is crucial for synapsis in meiosis. This study delves into the Skp1-Cullin1-F-box protein (SCF) E3 ubiquitin ligase complex, specifically focusing on F-box protein 47 (FBXO47), in mouse meiosis. Here, we revealed that FBXO47 is localized at the centromere and it regulates centromere pairing cooperatively with SKP1 to ensure proper synapsis in pachynema. The absence of FBXO47 causes defective centromeres, resulting in incomplete centromere pairing, which leads to corruption of SC at centromeric ends and along chromosome axes, triggering premature dissociation of chromosomes and pachytene arrest. FBXO47 deficient pachytene spermatocytes exhibited drastically reduced SKP1 expression at centromeres and chromosomes. Additionally, FBXO47 stabilizes SKP1 by down-regulating its ubiquitination in HEK293T cells. In essence, we propose that FBXO47 collaborates with SKP1 to facilitate centromeric SCF formation in spermatocytes. In summary, we posit that the centromeric SCF E3 ligase complex regulates centromere pairing for pachynema progression in mice.

Optimized methods for mapping DNA double-strand-break ends and resection tracts and application to meiotic recombination in mouse spermatocytes

DNA double-strand breaks (DSBs) made by SPO11 protein initiate homologous recombination during meiosis. Subsequent to DNA strand breakage, endo- and exo-nucleases process the DNA ends to resect the strands whose 5´ termini are at the DSB, generating long 3´-terminal single-stranded tails that serve as substrates for strand exchange proteins. DSB resection is essential for meiotic recombination, but a detailed understanding of its molecular mechanism is currently lacking. Genomic approaches to mapping DSBs and resection endpoints, e.g., S1-sequencing (S1-seq) and similar methods, play a critical role in studies of meiotic DSB processing. In these methods, nuclease S1 or other enzymes that specifically degrade ssDNA are used to trim resected DSBs, allowing capture and sequencing of the ends of resection tracts. Here, we present optimization of S1-seq that improves its signal:noise ratio and allows its application to analysis of spermatocyte meiosis in adult mice. Furthermore, quantitative features of meiotic resection are evaluated for reproducibility, and we suggest approaches for analysis and interpretation of S1-seq data. We also compare S1-seq to variants that use exonuclease T and/or exonuclease VII from Escherichia coli instead of nuclease S1. Detailed step-by-step protocols and suggestions for troubleshooting are provided.

Unraveling the Impact of the PROCA1 Mutation in Male Infertility: Incorporating Whole Exome Sequencing in Teratozoospermia Patients and Analyzing Proca1 Knockout Mice

In the world, about 15% of couples are infertile, and nearly half of all infertility was caused by men. A large number of genetic mutations are thought to affect spermatogenesis by regulating acrosome formation. Here, we identified three patients harbouring the protein interacting with cyclin A1 (PROCA1) mutation by whole exome sequencing (WES) and Sanger sequencing among patients with predominantly acrosome-deficient teratozoospermia. However, the expression and roles of PROCA1 in infertile men remain unclear. We found that PROCA1 is predominantly expressed in the testis, where it is specifically localized to the acrosome of normal human sperm. Proca1 knockout (KO) mice were subsequently generated using CRISPR-Cas9 technology. However, Proca1 KO adult male mice were fertile, with testis-to-body weight ratios comparable to those of wild-type (WT) mice. Testicular tissue or sperm morphology were not significantly different in Proca1 KO mice compared to WT mice. Expression of the acrosome markers PNA and SP56 in the acrosome was comparable between Proca1 KO and WT mice. In summary, these findings suggested that the PROCA1 mutation identified in humans does not affect acrosome biogenesis in mice.

Use of assisted reproductive technologies (ARTs) to shorten the generational interval in ruminants: current status and perspectives

The challenges posed by climate change and increasing world population are stimulating renewed efforts for improving the sustainability of animal production. To meet such challenges, the contribution of genomic selection approaches, in combination with assisted reproductive technologies (ARTs), to spreading and preserving animal genetics is essential. The largest increase in genetic gain can be achieved by shortening the generation interval. This review provides an overview of the current status and progress of advanced ARTs that could be applied to reduce the generation time in both female and male of domestic ruminants. In females, the use of juvenile in vitro embryo transfer (JIVET) enables to generate offspring after the transfer of in vitro produced embryos derived from oocytes of prepubertal genetically superior donors reducing the generational interval and acceleration genetic gain. The current challenge is increasing in vitro embryo production (IVEP) from prepubertal derived oocytes which is still low and variable. The two main factors limiting IVEP success are the intrinsic quality of prepubertal oocytes and the culture systems for in vitro maturation (IVM). In males, advancements in ARTs are providing new strategies to in vitro propagate spermatogonia and differentiate them into mature sperm or even to recapitulate the whole process of spermatogenesis from embryonic stem cells. Moreover, the successful use of immature cells, such as round spermatids, for intracytoplasmic injection (ROSI) and IVEP could allow to complete the entire process in few months. However, these approaches have been successfully applied to human and mouse whereas only a few studies have been published in ruminants and results are still controversial. This is also dependent on the efficiency of ROSI that is limited by the current isolation and selection protocols of round spermatids. In conclusion, the current efforts for improving these reproductive methodologies could lead toward a significant reduction of the generational interval in livestock animals that could have a considerable impact on agriculture sustainability.

In vitro proliferation and differentiation of mouse spermatogonial stem cells in decellularized human placenta matrix

Utilizing natural scaffold production derived from extracellular matrix components presents a promising strategy for advancing in vitro spermatogenesis. In this study, we employed decellularized human placental tissue as a scaffold, upon which neonatal mouse spermatogonial cells (SCs) were cultured three-dimensional (3D) configuration. To assess cellular proliferation, we examined the expression of key markers (Id4 and Gfrα1) at both 1 and 14 days into the culture. Our quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis revealed a notable increase in Gfrα1 gene expression, with the 3D culture group exhibiting the highest levels. Furthermore, the relative frequency of Gfrα1-positive cells significantly rose from 38.1% in isolated SCs to 46.13% and 76.93% in the two-dimensional (2D) and 3D culture systems, respectively. Moving forward to days 14 and 35 of the culture period, we evaluated the expression of differentiating markers (Sycp3, acrosin, and Protamine 1). Sycp3 and Prm1 gene expression levels were upregulated in both 2D and 3D cultures, with the 3D group displaying the highest expression. Additionally, acrosin gene expression increased notably within the 3D culture. Notably, at the 35-day mark, the percentage of Prm1-positive cells in the 3D group (36.4%) significantly surpassed that in the 2D group (10.96%). This study suggests that the utilization of placental scaffolds holds significant promise as a bio-scaffold for enhancing mouse in vitro spermatogenesis.

Intronless Pabpc6 encodes a testis-specific, cytoplasmic poly(A)-binding protein but is dispensable for spermatogenesis in the mouse†

Besides ubiquitous poly(A)-binding protein, cytoplasmic 1 (PABPC1), testis-specific PABPC2/PABPt (in humans, referred to as PABPC3), and female and male germline-specific PABPC1L/ePAB, have been reported in the mouse testis. Recent in silico analysis additionally identified testis-specific Pabpc6 in the mouse. In this study, we characterized PABPC6 and its mutant mice. PABPC6 was initially detectable in the cytoplasm of pachytene spermatocytes, increased in abundance in round spermatids, and decreased in elongating spermatids. PABPC6 was capable of binding to poly(A) tails of various mRNAs and interacting with translation-associated factors, including EIF4G, PAIP1, and PAIP2. Noteworthy was that PABPC6, unlike PABPC1, was barely associated with translationally active polysomes and enriched in chromatoid bodies of round spermatids. Despite these unique characteristics, neither synthesis of testicular proteins nor spermatogenesis was affected in the mutant mice lacking PABPC6, suggesting that PABPC6 is functionally redundant with other co-existing PABPC proteins during spermatogenesis.

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.

Profiling of testis-specific or testis-predominant genes expressed in mouse male germ cell lines GC-1 and GC-2

BACKGROUND

Spermatogenesis is a tightly organized process that utilizes an intrinsic genetic program composed of germ cell-specific genes. Although mouse germ cell-related cell lines are available, few germ cell-specific genes have been comprehensively identified in such cell lines.

OBJECTIVE

We aimed to profile gene expression in the male mouse germ cell-related cell lines, GC-1 and GC-2, characterize their transcriptomic nature, and identify potential testis- or germ cell-specific or -predominant genes expressed in these cell lines.

METHODS

We performed profiling analysis of genes transcribed in the mouse germ cell-related cell lines, GC-1 and GC-2, using our previous microarray data together with public transcriptome information. We analyzed the expression of a number of the cell line genes predicted to be preferentially expressed in testis by RT-PCR.

RESULTS

We found that most testis-specific or -predominant mRNAs are not expressed in GC-1 and GC-2 cells, implying that these cell lines have lost their testis- or germ cell-specific genetic characteristics. RT-PCR analysis of genes predicted to be expressed in the cell lines with preferential testicular expression showed the testis-specific or -predominant expression of nine genes and verified four of them as being expressed in the germ cell lines. Among them, only cyclin-dependent kinase inhibitor 3 genes (Cdkn3) showed testis and germ cell specificity.

CONCLUSION

Our study provides extensive transcriptomic information to shed light on the limited testicular characteristics of the mouse male germ cell-derived cell lines, GC-1 and GC-2, and offers a list of germ cell line genes with testicular preference.

Novel Nuclear Roles for Testis-Specific ACTL7A and ACTL7B Supported by In Vivo Characterizations and AI Facilitated In Silico Mechanistic Modeling with Implications for Epigenetic Regulation in Spermiogenesis

A mechanistic role for nuclear function of testis-specific actin related proteins (ARPs) is proposed here through contributions of ARP subunit swapping in canonical chromatin regulatory complexes. This is significant to our understanding of both mechanisms controlling regulation of spermiogenesis, and the expanding functional roles of the ARPs in cell biology. Among these roles, actins and ARPs are pivotal not only in cytoskeletal regulation, but also in intranuclear chromatin organization, influencing gene regulation and nucleosome remodeling. This study focuses on two testis-specific ARPs, ACTL7A and ACTL7B, exploring their intranuclear activities and broader implications utilizing combined in vivo, in vitro, and in silico approaches. ACTL7A and ACTL7B, previously associated with structural roles, are hypothesized here to serve in chromatin regulation during germline development. This study confirms the intranuclear presence of ACTL7B in spermatocytes and round spermatids, revealing a potential role in intranuclear processes, and identifies a putative nuclear localization sequence conserved across mammalian ACTL7B, indicating a potentially unique mode of nuclear transport which differs from conventional actin. Ablation of ACTL7B leads to varied transcriptional changes reported here. Additionally, in the absence of ACTL7A or ACTL7B there is a loss of intranuclear localization of HDAC1 and HDAC3, which are known regulators of epigenetic associated acetylation changes that in turn regulate gene expression. Thus, these HDACs are implicated as contributors to the aberrant gene expression observed in the KO mouse testis transcriptomic analysis. Furthermore, this study employed and confirmed the accuracy of in silico models to predict ARP interactions with Helicase-SANT-associated (HSA) domains, uncovering putative roles for testis-specific ARPs in nucleosome remodeling complexes. In these models, ACTL7A and ACTL7B were found capable of binding to INO80 and SWI/SNF nucleosome remodeler family members in a manner akin to nuclear actin and ACTL6A. These models thus implicate germline-specific ARP subunit swapping within chromatin regulatory complexes as a potential regulatory mechanism for chromatin and associated molecular machinery adaptations in nuclear reorganizations required during spermiogenesis. These results hold implications for male fertility and epigenetic programing in the male-germline that warrant significant future investigation. In summary, this study reveals that ACTL7A and ACTL7B play intranuclear gene regulation roles in male gametogenesis, adding to the multifaceted roles identified also spanning structural, acrosomal, and flagellar stability. ACTL7A and ACTL7B unique nuclear transport, impact on HDAC nuclear associations, impact on transcriptional processes, and proposed mechanism for involvement in nucleosome remodeling complexes supported by AI facilitated in silico modeling contribute to a more comprehensive understanding of the indispensable functions of ARPs broadly in cell biology, and specifically in male fertility.

A loss-of-function variant in ZCWPW1 causes human male infertility with sperm head defect and high DNA fragmentation

BACKGROUND

Male infertility is a global health issue. The more causative genes related to human male infertility should be further explored. The essential role of Zcwpw1 in male mouse fertility has been established and the role of ZCWPW1 in human reproduction needs further investigation to verify.

METHODS

An infertile man with oligoasthenoteratozoospermia phenotype and his parents were recruited from West China Second University Hospital, Sichuan University. A total of 200 healthy Han Chinese volunteers without any evidence of infertility were recruited as normal controls, while an additional 150 infertile individuals were included to assess the prevalence of ZCWPW1 variants in a sporadic male sterile population. The causative gene variant was identified by Whole-exome sequencing and Sanger sequencing. The phenotype of the oligoasthenoteratozoospermia was determined by Papanicolaou staining, immunofluorescence staining and electron microscope. In-vitro experiments, western blot and in-silicon analysis were applied to assess the pathogenicity of the identified variant. Additionally, we examined the influence of the variant on the DNA fragmentation and DNA repair capability by Sperm Chromatin Dispersion and Neutral Comet Assay.

RESULTS

The proband exhibits a phenotype of oligoasthenoteratozoospermia, his spermatozoa show head defects by semen examination, Papanicolaou staining and electron microscope assays. Whole-exome sequencing and Sanger sequencing found the proband carries a homozygous ZCWPW1 variant (c.1064C > T, p. P355L). Immunofluorescence analysis shows a significant decrease in ZCWPW1 expression in the proband's sperm. By exogenous expression with ZCWPW1 mutant plasmid in vitro, the obvious declined expression of ZCWPW1 with the mutation is validated in HEK293T. After being treated by hydroxyurea, MUT-ZCWPW1 transfected cells and empty vector transfected cells have a higher level of γ-H2AX, increased tail DNA and reduced H3K9ac level than WT-ZCWPW1 transfected cells. Furthermore, the Sperm Chromatin Dispersion assay revealed the proband's spermatozoa have high DNA fragmentation.

CONCLUSIONS

It is the first report that a novel homozygous missense mutation in ZCWPW1 caused human male infertility with sperm head defects and high DNA fragmentation. This finding enriches the gene variant spectrum and etiology of oligoasthenoteratozoospermia.

Ultrastructural study: in vitro and in vivo differentiation of mice spermatogonial stem cells

Mouse testicular tissue is composed of seminiferous tubules and interstitial tissue. Mammalian spermatogenesis is divided into three stages: spermatocytogenesis (mitotic divisions) in which spermatogonial stem cells (SSCs) turn into spermatocytes, followed by two consecutive meiotic divisions in which spermatocytes form spermatids. Spermatids differentiate into spermatozoa during spermiogenesis. Various factors affect the process of spermatogenesis and the organization of cells in the testis. Any disorder in different stages of spermatogenesis will have negative effects on male fertility. The aim of the current study was to compare the in vitro and in vivo spermatogenesis processes before and after transplantation to azoospermic mice using ultrastructural techniques. In this study, mice were irradiated with single doses of 14 Gy 60Co radiation. SSCs isolated from neonatal mice were cultured in vitro for 1 week and were injected into the seminiferous tubule recipient's mice. Testicular cells of neonatal mice were cultured in the four groups on extracellular matrix-based 3D printing scaffolds. The transplanted testes (8 weeks after transplantation) and cultured testicular cells in vitro (after 3 weeks) were then processed for transmission electron microscopy studies. Our study's findings revealed that the morphology and ultrastructure of testicular cells after transplantation and in vitro culture are similar to those of in vivo spermatogenesis, indicating that spermatogenic cell nature is unaltered in vitro.

RNA polymerase II pausing is essential during spermatogenesis for appropriate gene expression and completion of meiosis

Male germ cell development requires precise regulation of gene activity in a cell-type and stage-specific manner, with perturbations in gene expression during spermatogenesis associated with infertility. Here, we use steady-state, nascent and single-cell RNA sequencing strategies to comprehensively characterize gene expression across male germ cell populations, to dissect the mechanisms of gene control and provide new insights towards therapy. We discover a requirement for pausing of RNA Polymerase II (Pol II) at the earliest stages of sperm differentiation to establish the landscape of gene activity across development. Accordingly, genetic knockout of the Pol II pause-inducing factor NELF in immature germ cells blocks differentiation to spermatids. Further, we uncover unanticipated roles for Pol II pausing in the regulation of meiosis during spermatogenesis, with the presence of paused Pol II associated with double-strand break (DSB) formation, and disruption of meiotic gene expression and DSB repair in germ cells lacking NELF.

Inositol hexakisphosphate kinase 1 is essential for cell junction integrity in the mouse seminiferous epithelium

Inositol hexakisphosphate kinases (IP6Ks) are enzymes that catalyse the synthesis of the inositol pyrophosphate 5-IP7 which is involved in the regulation of many physiological processes in mammals. The IP6K paralog IP6K1 is expressed at high levels in the mammalian testis, and its deletion leads to sterility in male mice. Here, we show that the loss of IP6K1 in mice causes a delay in the first wave of spermatogenesis. Testes from juvenile Ip6k1 knockout mice show downregulation of transcripts that are involved in cell adhesion and formation of the testis-specific inter-Sertoli cell impermeable junction complex known as the blood-testis barrier (BTB). We demonstrate that loss of IP6K1 in the mouse testis causes BTB disruption associated with transcriptional misregulation of the tight junction protein claudin 3, and subcellular mislocalization of the gap junction protein connexin 43. In addition to BTB disruption, we also observe a loss of germ cell adhesion in the seminiferous epithelium of Ip6k1 knockout mice, ultimately resulting in premature sloughing of round spermatids into the epididymis. Mechanistically, we show that loss of IP6K1 in the testis enhances cofilin dephosphorylation in conjunction with increased AKT/ERK and integrin signalling, resulting in destabilization of the actin-based cytoskeleton in Sertoli cells and germ cell loss.

Efficient Enrichment of Synchronized Mouse Spermatocytes Suitable for Genome-Wide Analysis

Chromatin undergoes extensive remodeling during meiosis, leading to specific patterns of gene expression and chromosome organization, which ultimately controls fundamental meiotic processes such as recombination and homologous chromosome associations. Recent game-changing advances have been made by analysis of chromatin binding sites of meiotic specific proteins genome-wide in mouse spermatocytes. However, further progress is still highly dependent on the reliable isolation of sufficient quantities of spermatocytes at specific stages of prophase I. Here, we describe a combination of methodologies we adapted for rapid and reliable isolation of synchronized fixed mouse spermatocytes. We show that chromatin isolated from these cells can be used to study chromatin-binding sites by ChIP-seq. High-quality data we obtained from INO80 ChIP-seq in zygotene cells was used for functional analysis of chromatin-binding sites.

Efficient isolation and purification of spermatogonia, spermatocytes, and spermatids from mice, piglets, and adult boars using an optimized STA-PUT method

Spermatogenesis is a delicate and complex biological process in which spermatogonial stem cells continue to proliferate and differentiate into mature spermatozoa, maintaining sperm production in male mammals throughout the lifetime. To study the molecular mechanism of spermatogenesis, researchers had to isolate different germ cell subpopulations for in vitro culture and characterization. However, due to the existence of several stages of germ cells and a variety of populations of somatic cells in the testis of male mammals, it is a challenge for us to obtain high-purity germ cell subpopulations for further research. Here, we optimized the STA-PUT device and successfully applied it to isolate and purify spermatogonia populations in piglets, and multiple germ cell populations at different developmental stages in testes of adult mice and boars. This work provides a simple platform for germ cell fractionation to facilitate the molecular mechanistic study of animal spermatogenesis in vitro.

De novo transcriptome assembly of mouse male germ cells reveals novel genes, stage-specific bidirectional promoter activity, and noncoding RNA expression

In mammals, the adult testis is the tissue with the highest diversity in gene expression. Much of that diversity is attributed to germ cells, primarily meiotic spermatocytes and postmeiotic haploid spermatids. Exploiting a newly developed cell purification method, we profiled the transcriptomes of such postmitotic germ cells of mice. We used a de novo transcriptome assembly approach and identified thousands of novel expressed transcripts characterized by features distinct from those of known genes. Novel loci tend to be short in length, monoexonic, and lowly expressed. Most novel genes have arisen recently in evolutionary time and possess low coding potential. Nonetheless, we identify several novel protein-coding genes harboring open reading frames that encode proteins containing matches to conserved protein domains. Analysis of mass-spectrometry data from adult mouse testes confirms protein production from several of these novel genes. We also examine overlap between transcripts and repetitive elements. We find that although distinct families of repeats are expressed with differing temporal dynamics during spermatogenesis, we do not observe a general mode of regulation wherein repeats drive expression of nonrepetitive sequences in a cell type-specific manner. Finally, we observe many fairly long antisense transcripts originating from canonical gene promoters, pointing to pervasive bidirectional promoter activity during spermatogenesis that is distinct and more frequent compared with somatic cells.

Core binding factor subunit β plays diverse and essential roles in the male germline

Much of the foundation for lifelong spermatogenesis is established prior to puberty, and disruptions during this developmental window negatively impact fertility long into adulthood. However, the factors that coordinate prepubertal germline development are incompletely understood. Here, we report that core-binding factor subunit-β (CBFβ) plays critical roles in prepubertal development and the onset of spermatogenesis. Using a mouse conditional knockout (cKO) approach, inactivation of Cbfb in the male germline resulted in rapid degeneration of the germline during the onset of spermatogenesis, impaired overall sperm production, and adult infertility. Utilizing a different Cre driver to generate another Cbfb cKO model, we determined that the function of CBFβ in the male germline is likely limited to undifferentiated spermatogonia despite expression in other germ cell types. Within undifferentiated spermatogonia, CBFβ regulates proliferation, survival, and overall maintenance of the undifferentiated spermatogonia population. Paradoxically, we discovered that CBFβ also distally regulates meiotic progression and spermatid formation but only with Cbfb cKO within undifferentiated spermatogonia. Spatial transcriptomics revealed that CBFβ modulates cell cycle checkpoint control genes associated with both proliferation and meiosis. Taken together, our findings demonstrate that core programs established within the prepubertal undifferentiated spermatogonia population are necessary for both germline maintenance and sperm production.

Effects of a Sertoli cell-specific knockout of Connexin43 on maturation and proliferation of postnatal Sertoli cells

Adult male Sertoli cell-specific Connexin43 knockout mice (SCCx43KO) exhibit higher Sertoli cell (SC) numbers per seminiferous tubule compared to their wild type (WT) littermates. Thus, deletion of this testicular gap junction protein seems to affect the proliferative potential and differentiation of "younger" SC. Although SC have so far mostly been characterised as postmitotic cells that cease to divide and become an adult, terminally differentiated cell population at around puberty, there is rising evidence that there exist exceptions from this for a very long time accepted paradigm. Aim of this study was to investigate postnatal SC development and to figure out underlying causes for observed higher SC numbers in adult KO mice. Therefore, the amount of SC mitotic figures was compared, resulting in slightly more and prolonged detection of SC mitotic figures in KO mice compared to WT. SC counting per tubular cross section revealed significantly different time curves, and comparing proliferation rates using Bromodesoxyuridine and Sox9 showed higher proliferation rates in 8-day old KO mice. SC proliferation was further investigated by Ki67 immunohistochemistry. SC in KO mice displayed a delayed initiation of cell-cycle-inhibitor p27Kip1 synthesis and prolonged synthesis of the phosphorylated tumour suppressor pRb and proliferation marker Ki67. Thus, the higher SC numbers in adult male SCCx43KO mice may arise due to two different reasons: Firstly, in prepubertal KO mice, the proliferation rate of SC was higher. Secondly, there were differences in their ability to cease proliferation as shown by the delayed initiation of p27Kip1 synthesis and the prolonged production of phosphorylated pRb and Ki67. Immunohistochemical results indicating a prolonged period of SC proliferation in SCCx43KO were confirmed by detection of proliferating SC in 17-days-old KO mice. In conclusion, deletion of the testicular gap junction protein Cx43 might prevent normal SC maturation and might even alter also the proliferation potential of adult SC.

Mouse Pramel1 regulates spermatogonial development by inhibiting retinoic acid signaling during spermatogenesis

Spermatogenesis begins when cell fate-committed prospermatogonia migrate to the basement membrane and initiate spermatogenesis in response to retinoic acid (RA) in the neonatal testis. The underlying cellular and molecular mechanisms in this process are not fully understood. Here, we report findings on the involvement of a cancer/testis antigen, PRAMEL1, in the initiation and maintenance of spermatogenesis. By analyzing mouse models with either global or conditional Pramel1 inactivation, we found that PRAMEL1 regulates the RA responsiveness of the subtypes of prospermatogonia in the neonatal testis, and affects their homing process during the initiation of spermatogenesis. Pramel1 deficiency led to increased fecundity in juvenile males and decreased fecundity in mature males. In addition, Pramel1 deficiency resulted in a regional Sertoli cell-only phenotype during the first round of spermatogenesis, which was rescued by administration of the RA inhibitor WIN18,446, suggesting that PRAMEL1 functions as an inhibitor of RA signaling in germ cells. Overall, our findings suggest that PRAMEL1 fine-tunes RA signaling, playing a crucial role in the proper establishment of the first and subsequent rounds of spermatogenesis.

Rhox8 homeobox gene ablation leads to rete testis abnormality and male subfertility in mice†

The reproductive homeobox X-linked (Rhox) genes encode transcription factors that are expressed selectively in reproductive tissues including the testis, epididymis, ovary, and placenta. While many Rhox genes are expressed in germ cells in the mouse testis, only Rhox8 is expressed exclusively in the Sertoli cells during embryonic and postnatal development, suggesting a possible role of Rhox8 in embryonic gonad development. Previously, Sertoli cell-specific knockdown of RHOX8 resulted in male subfertility due to germ cell defects. However, this knockdown model was limited in examining the functions of Rhox8 as RHOX8 knockdown occurred only postnatally, and there was still residual RHOX8 in the testis. In this study, we generated new Rhox8 knockout (KO) mice using the CRISPR/Cas9 system. Sex determination and fetal testis development were apparently normal in mutant mice. Fertility analysis showed a low fecundity in Rhox8 KO adult males, with disrupted spermatogenic cycles, increased germ cell apoptosis, and reduced sperm count and motility. Interestingly, Rhox8 KO testes showed an increase in testis size with dilated seminiferous tubules and rete testis, which might be affected by efferent duct (ED) Rhox8 ablation dysregulating the expression of metabolism and transport genes in the EDs. Taken together, the data presented in this study suggest that Rhox8 in the Sertoli cells is not essential for sex determination and embryonic testis differentiation but has an important role in complete spermatogenesis and optimal male fertility.

RNase H1 facilitates recombinase recruitment by degrading DNA-RNA hybrids during meiosis

DNA-RNA hybrids play various roles in many physiological progresses, but how this chromatin structure is dynamically regulated during spermatogenesis remains largely unknown. Here, we show that germ cell-specific knockout of Rnaseh1, a specialized enzyme that degrades the RNA within DNA-RNA hybrids, impairs spermatogenesis and causes male infertility. Notably, Rnaseh1 knockout results in incomplete DNA repair and meiotic prophase I arrest. These defects arise from the altered RAD51 and DMC1 recruitment in zygotene spermatocytes. Furthermore, single-molecule experiments show that RNase H1 promotes recombinase recruitment to DNA by degrading RNA within DNA-RNA hybrids and allows nucleoprotein filaments formation. Overall, we uncover a function of RNase H1 in meiotic recombination, during which it processes DNA-RNA hybrids and facilitates recombinase recruitment.

Understanding the age-related alterations in the testis-specific proteome

INTRODUCTION

Fertility rates in developing countries have declined over the past decades, and the trend of delayed fatherhood is rising as societies develop. The reasons behind the decline in male fertility with advancing age remain mysterious, making it a compelling and crucial area for further research. However, the limited number of studies dedicated to unraveling this enigma poses a challenge. Thus, our objective is to illuminate some of the upregulated and downregulated mechanisms in the male testis during the aging process.

AREAS COVERED

Herein, we present a critical overview of the studies addressing the alterations of testicular proteome through the aging process, starting from sexually matured young males to end-of-life-expectancy aged males. The comparative studies of the proteomic testicular profile of men with and without spermatogenic impairment are also discussed and key proteins and pathways involved are highlighted.

EXPERT OPINION

The difficulty of making age-comparative studies, especially of advanced-age study subjects, makes this topic of study quite challenging. Another topic worth mentioning is the heterogeneous nature and vast cellular composition of testicular tissue, which makes proteome data interpretation tricky. The cell type sorting and comorbidities testing in the testicular tissue of the studied subjects would help mitigate these problems.

Testis-specific serine kinase 3 is required for sperm morphogenesis and male fertility

BACKGROUND

The importance of phosphorylation in sperm during spermatogenesis has not been pursued extensively. Testis-specific serine kinase 3 (Tssk3) is a conserved gene, but TSSK3 kinase functions and phosphorylation substrates of TSSK3 are not known.

OBJECTIVE

The goals of our studies were to understand the mechanism of action of TSSK3.

MATERIALS AND METHODS

We analyzed the localization of TSSK3 in sperm, used CRISPR/Cas9 to generate Tssk3 knockout (KO) mice in which nearly all of the Tssk3 open reading frame was deleted (ensuring it is a null mutation), analyzed the fertility of Tssk3 KO mice by breeding mice for 4 months, and conducted phosphoproteomics analysis of male testicular germ cells.

RESULTS

TSSK3 is expressed in elongating sperm and localizes to the sperm tail. To define the essential roles of TSSK3 in vivo, heterozygous (HET) or homozygous KO male mice were mated with wild-type females, and fertility was assessed over 4 months; Tssk3 KO males are sterile, whereas HET males produced normal litter sizes. The absence of TSSK3 results in disorganization of all stages of testicular seminiferous epithelium and significantly increased vacuolization of germ cells, leading to dramatically reduced sperm counts and abnormal sperm morphology; despite these histologic changes, Tssk3 null mice have normal testis size. To elucidate the mechanisms causing the KO phenotype, we conducted phosphoproteomics using purified germ cells from Tssk3 HET and KO testes. We found that proteins implicated in male infertility, such as GAPDHS, ACTL7A, ACTL9, and REEP6, showed significantly reduced phosphorylation in KO testes compared to HET testes, despite unaltered total protein levels.

CONCLUSIONS

We demonstrated that TSSK3 is essential for male fertility and crucial for phosphorylation of multiple infertility-related proteins. These studies and the pathways in which TSSK3 functions have implications for human male infertility and nonhormonal contraception.

RNA polymerase II pausing is essential during spermatogenesis for appropriate gene expression and completion of meiosis

Male germ cell development requires precise regulation of gene activity in a cell-type and stage-specific manner, with perturbations in gene expression during spermatogenesis associated with infertility. Here, we use steady-state, nascent and single-cell RNA sequencing strategies to comprehensively characterize gene expression across male germ cell populations, to dissect the mechanisms of gene control and provide new insights towards therapy. We discover a requirement for pausing of RNA Polymerase II (Pol II) at the earliest stages of sperm differentiation to establish the landscape of gene activity across development. Accordingly, genetic knockout of the Pol II pause-inducing factor NELF in immature germ cells blocks differentiation to mature spermatids. Further, we uncover unanticipated roles for Pol II pausing in the regulation of meiosis during spermatogenesis, with the presence of paused Pol II associated with double strand break formation by SPO11, and disruption of SPO11 expression in germ cells lacking NELF.

Sequencing of the ZMYND15 gene in a cohort of infertile Chinese men reveals novel mutations in patients with teratozoospermia

BACKGROUND

The information of ZMYND15 in human reproduction is very limited, resulting in the unclear link between ZMYND15 variants and male infertility.

METHODS

Whole exome sequencing and Sanger sequencing to identify the potential pathogenic variation of ZMYND15 in infertile men, Papanicolaou staining and electron microscopy to investigate the spermatozoa morphology, western blotting and immunofluorescence staining to confirm the pathogenicity of the identified variants, and proteomic analysis and coimmunoprecipitation to clarify the potential molecular mechanism.

RESULTS

A total of 31 ZMYND15 variants were identified in 227 infertile patients. Three deleterious biallelic variants, including a novel compound heterozygous variant of c.1105delG (p.A369Qfs*15) and c.1853T>C (p.F618S), a new homozygous splicing mutation of c.1297+5G>A and a reported homozygous nonsense mutation of c.1209T>A (p.Y403*), were detected in three affected individuals with oligoasthenoteratozoospermia, showing a biallelic pathogenic mutation frequency of 1.3% (3/227). No biallelic pathogenic mutation was found in 692 fertile men. Morphology analysis showed abnormalities in sperm morphology in the patients harbouring ZMYND15 mutations. Western blotting and immunofluorescence staining confirmed the nearly absent ZMYND15 expression in the sperm of the patients. Mechanistically, ZMYND15 might regulate spermatogenesis by interacting with key molecules involved in sperm development, such as DPY19L2, AKAP4 and FSIP2, and might also mediate the expression of the autophagy-associated protein SPATA33 to maintain sperm individualisation and unnecessary cytoplasm removal.

CONCLUSION

Our findings broaden the variant and phenotype spectrum of ZMYND15 in male infertility, and reveal the potential signalling pathway of ZMYND15 regulating spermatogenesis, finally confirming the essential role of ZMYND15 in human fertility.

Proteasome-Associated Proteins, PA200 and ECPAS, Are Essential for Murine Spermatogenesis

Proteasomes are highly sophisticated protease complexes that degrade non-lysosomal proteins, and their proper regulation ensures various biological functions such as spermatogenesis. The proteasome-associated proteins, PA200 and ECPAS, are predicted to function during spermatogenesis; however, male mice lacking each of these genes sustain fertility, raising the possibility that these proteins complement each other. To address this issue, we explored these possible roles during spermatogenesis by producing mice lacking these genes (double-knockout mice; dKO mice). Expression patterns and quantities were similar throughout spermatogenesis in the testes. In epididymal sperm, PA200 and ECPAS were expressed but were differentially localized to the midpiece and acrosome, respectively. Proteasome activity was considerably reduced in both the testes and epididymides of dKO male mice, resulting in infertility. Mass spectrometric analysis revealed LPIN1 as a target protein for PA200 and ECPAS, which was confirmed via immunoblotting and immunostaining. Furthermore, ultrastructural and microscopic analyses demonstrated that the dKO sperm displayed disorganization of the mitochondrial sheath. Our results indicate that PA200 and ECPAS work cooperatively during spermatogenesis and are essential for male fertility.

Time-resolved ICP-MS analysis of mineral element contents and distribution patterns in spermatogenic cells of different types

Mineral elements play an important role in the spermatogenesis, maturation, and fertilization of sperm. It is of great scientific significance to study the role of mineral elements in spermatogenesis by accurately measuring the content of elements in different spermatogenic cells and analyzing the distribution pattern of elements in spermatogenesis. Here, time-resolved inductively coupled plasma mass spectrometry (ICP-MS) was used to analyze the content and distribution patterns of mineral elements in spermatogenic cells of different types at the single cell level. Firstly, spermatogonia, spermatocytes, round spermatids and elongating spermatids were successfully isolated from testis of mice of different weeks of age by differential adherent method and discontinuous bovine serum albumin (BSA) density gradient method. Then, signal profiles and elemental distributions of ²⁴Mg, ³¹P, ⁵²Cr, ⁵⁵Mn, ⁵⁶Fe and ⁶⁶Zn in spermatogenic cells were obtained with dwell time at 0.1 ms. Based on the results of acid digestion, we derived a formula to calculate element content in single cell from peak area for each element, and the feasibility and universality of the formula in the quantitative detection of single cell elements were verified by sperm samples to a certain extent. The detection results of element content in single cell showed that the content of ³¹P in elongating spermatids was significantly higher than that in spermatogonia, spermatocytes and round spermatids (P < 0.01), and the distribution range was wider. However, the ⁵²Cr and ⁵⁶Fe content of elongating spermatids was lower than that of spermatogonia, spermatocytes and round spermatids (P < 0.05). When spermatogonia developed into round spermatids, the contents of ⁵⁵Mn and ⁶⁶Zn in single cell increased significantly (P < 0.05), then decreased to the lowest in elongating spermatids. In addition, the significant decrease of ⁵²Cr, ⁵⁵Mn, ⁵⁶Fe and ⁶⁶Zn content in elongating spermatids also be visually observed from the center of the fitting curve of the element signal intensity distribution moving to the left. This study provides an elemental view of the changes in elemental content at various stages of spermatogenesis at the single-cell level. Time-resolved ICP-MS is used to detect mineral elements content and distribution patterns in spermatogenic cells of testis, which is helpful to better explore the stages and modes of action of various elements in spermatogenesis, and provide direct evidence for revealing the effects of element content changes on spermatogenesis and semen quality regulation.

FSIP2 plays a role in the acrosome development during spermiogenesis

BACKGROUND

Loss-of-function mutations in FSIP2 result in multiple morphological abnormalities of the flagella in humans and mice. Intriguingly, a recent study found that FSIP2 might regulate the expression of acrosomal proteins, indicating that Fsip2 might be involved in acrosome development in mice. However, whether FSIP2 also function in acrosome biogenesis in humans is largely unknown, and the underlying mechanism of which is unexplored.

OBJECTIVE

Our objective was to reveal potential function of FSIP2 in regulating sperm acrosome formation.

METHODS

We performed whole exome sequencing on four asthenoteratozoospermic patients. Western blot analysis and immunofluorescence staining were conducted to assess the protein expression of FSIP2. Proteomics approach, liquid chromatography-tandem mass spectrometry and co-immunoprecipitation were implemented to clarify the molecules in acrosome biogenesis regulated by FSIP2.

RESULTS

Biallelic FSIP2 variants were identified in four asthenoteratozoospermic individuals. The protein expression of MUT-FSIP2 was sharply decreased or absent in vitro or in vivo. Interestingly, aside from the sperm flagellar defects, the acrosomal hypoplasia was detected in numerous sperm from the four patients. FSIP2 co-localised with peanut agglutinin in the acrosome during spermatogenesis. Moreover, FSIP2 interacted with proteins (DPY19L2, SPACA1, HSP90B1, KIAA1210, HSPA2 and CLTC) involved in acrosome biogenesis. In addition, spermatozoa from patients carrying FSIP2 mutations showed downregulated expression of DPY19L2, ZPBP, SPACA1, CCDC62, CCIN, SPINK2 and CSNK2A2.

CONCLUSION

Our findings unveil that FSIP2 might involve in sperm acrosome development, and consequently, its mutations might contribute to globozoospermia or acrosomal aplasia. We meanwhile first uncover the potential molecular mechanism of FSIP2 regulating acrosome biogenesis.

Multi-Omics Approaches for Revealing the Epigenetic Regulation of Histone H3.1 during Spermatogonial Stem Cell Differentiation In Vitro

Epigenetic regulation, particularly post-translational modifications (PTMs) of histones, participates in spermatogonial stem cell (SSCs) differentiation. However, there is a lack of systemic studies of histone PTM regulation during the differentiation of SSCs due to its low number in vivo. Herein, we quantified dynamic changes of 46 different PTMs on histone H3.1 by targeted quantitative proteomics using mass spectrometry during SSCs differentiation in vitro, in combination with our RNA-seq data. We identified seven histone H3.1 modifications to be differentially regulated. In addition, we selected H3K9me2 and H3S10ph for subsequent biotinylated peptide pull-down experiments and identified 38 H3K9me2-binding proteins and 42 H3S10ph-binding proteins, which contain several transcription factors, such as GTF2E2 and SUPT5H, which appear to be crucial for epigenetic regulation of SSC differentiation.

Genetic control of meiosis surveillance mechanisms in mammals

Meiosis is a specialized cell division that generates haploid gametes and is critical for successful sexual reproduction. During the extended meiotic prophase I, homologous chromosomes progressively pair, synapse and desynapse. These chromosomal dynamics are tightly integrated with meiotic recombination (MR), during which programmed DNA double-strand breaks (DSBs) are formed and subsequently repaired. Consequently, parental chromosome arms reciprocally exchange, ultimately ensuring accurate homolog segregation and genetic diversity in the offspring. Surveillance mechanisms carefully monitor the MR and homologous chromosome synapsis during meiotic prophase I to avoid producing aberrant chromosomes and defective gametes. Errors in these critical processes would lead to aneuploidy and/or genetic instability. Studies of mutation in mouse models, coupled with advances in genomic technologies, lead us to more clearly understand how meiosis is controlled and how meiotic errors are linked to mammalian infertility. Here, we review the genetic regulations of these major meiotic events in mice and highlight our current understanding of their surveillance mechanisms. Furthermore, we summarize meiotic prophase genes, the mutations that activate the surveillance system leading to meiotic prophase arrest in mouse models, and their corresponding genetic variants identified in human infertile patients. Finally, we discuss their value for the diagnosis of causes of meiosis-based infertility in humans.

CLPP Depletion Causes Diplotene Arrest; Underlying Testis Mitochondrial Dysfunction Occurs with Accumulation of Perrault Proteins ERAL1, PEO1, and HARS2

Human Perrault syndrome (PRLTS) is autosomal, recessively inherited, and characterized by ovarian insufficiency with hearing loss. Among the genetic causes are mutations of matrix peptidase CLPP, which trigger additional azoospermia. Here, we analyzed the impact of CLPP deficiency on male mouse meiosis stages. Histology, immunocytology, different OMICS and biochemical approaches, and RT-qPCR were employed in CLPP-null mouse testis. Meiotic chromosome pairing and synapsis proceeded normally. However, the foci number of the crossover marker MLH1 was slightly reduced, and foci persisted in diplotene, most likely due to premature desynapsis, associated with an accumulation of the DNA damage marker γH2AX. No meiotic M-phase cells were detected. Proteome profiles identified strong deficits of proteins involved in male meiotic prophase (HSPA2, SHCBP1L, DMRT7, and HSF5), versus an accumulation of AURKAIP1. Histone H3 cleavage, mtDNA extrusion, and cGAMP increase suggested innate immunity activation. However, the deletion of downstream STING/IFNAR failed to alleviate pathology. As markers of underlying mitochondrial pathology, we observed an accumulation of PRLTS proteins ERAL1, PEO1, and HARS2. We propose that the loss of CLPP leads to the extrusion of mitochondrial nucleotide-binding proteins to cytosol and nucleus, affecting late meiotic prophase progression, and causing cell death prior to M-phase entry. This phenotype is more severe than in mito-mice or mutator-mice.

SOX17-positive rete testis epithelium is required for Sertoli valve formation and normal spermiogenesis in the male mouse

Seminiferous tubules (STs) in the mammalian testes are connected to the rete testis (RT) via a Sertoli valve (SV). Spermatozoa produced in the STs are released into the tubular luminal fluid and passively transported through the SV into the RT. However, the physiological functions of the RT and SV remain unclear. Here, we identified the expression of Sox17 in RT epithelia. The SV valve was disrupted before puberty in RT-specific Sox17 conditional knockout (Sox17-cKO) male mice. This induced a backflow of RT fluid into the STs, which caused aberrant detachment of immature spermatids. RT of Sox17-cKO mice had reduced expression levels of various growth factor genes, which presumably support SV formation. When transplanted next to the Sox17⁺ RT, Sertoli cells of Sox17-cKO mice reconstructed the SV and supported proper spermiogenesis in the STs. This study highlights the novel and unexpected modulatory roles of the RT in SV valve formation and spermatogenesis in mouse testes, as a downstream action of Sox17.

Modeling mammalian spermatogonial differentiation and meiotic initiation in vitro

In mammalian testes, premeiotic spermatogonia respond to retinoic acid by completing an essential lengthy differentiation program before initiating meiosis. The molecular and cellular changes directing these developmental processes remain largely undefined. This wide gap in knowledge is due to two unresolved technical challenges: (1) lack of robust and reliable in vitro models to study differentiation and meiotic initiation; and (2) lack of methods to isolate large and pure populations of male germ cells at each stage of differentiation and at meiotic initiation. Here, we report a facile in vitro differentiation and meiotic initiation system that can be readily manipulated, including the use of chemical agents that cannot be safely administered to live animals. In addition, we present a transgenic mouse model enabling fluorescence-activated cell sorting-based isolation of millions of spermatogonia at specific developmental stages as well as meiotic spermatocytes.

Novel biallelic mutations in TTC29 cause asthenoteratospermia and male infertility

BACKGROUND

Multiple morphological abnormalities of the sperm flagella (MMAF), which is characterized as asthenoteratospermia involving absent, short, bent, coiled, and/or irregular-caliber flagella, is a rare recessive inherited disorder associated with male infertility. To date, genetic causes of MMAF cases are not fully explored.

METHODS

Whole-exome sequencing was conducted to identify pathogenic variants in a patient with MMAF. The functional effect of the identified mutations was investigated by immunofluorescence staining and western blotting. Intracytoplasmic sperm injection was used to assist fertilization for the patient with MMAF.

RESULTS

We identified novel biallelic mutations, a splicing variant NC_000004.12:g.146937593C>T (c.254+1G>A), and a nonsense mutation NM_001300761.4:c.1185C>G (NP_001287690.1:p.Tyr395*), in TTC29 from an infertile patient. In addition to the typical MMAF phenotype, the patient also presented aberrant morphology of sperm heads. Further functional experiments confirmed the absence of TTC29 expression in the spermatozoa. We also explored the specific expression pattern of TTC29 in human and mouse spermatogenesis. The outcome of intracytoplasmic sperm injection in the patient was unsuccessful, while additional female risk factors should not be excluded.

CONCLUSIONS

Our study revealed the novel biallelic mutations in TTC29 in a MMAF patient, which findings expand the mutational spectrum of TTC29 and further contribute to the diagnosis, genetic counseling, and prognosis of male infertility.

The ZFP541-KCTD19 complex is essential for pachytene progression by activating meiotic genes during mouse spermatogenesis

Meiosis is essential for fertility in sexually reproducing species and this sophisticated process has been extensively studied. Notwithstanding these efforts, key factors involved in meiosis have not been fully characterized. In this study, we investigate the regulatory roles of zinc finger protein 541 (ZFP541) and its interacting protein potassium channel tetramerization domain containing 19 (KCTD19) in spermatogenesis. ZFP541 is expressed from leptotene to the round spermatid stage, while the expression of KCTD19 is initiated in pachytene. Depletion of Zfp541 or Kctd19 leads to infertility in male mice and delays progression from early to mid/late pachynema. In addition, Zfp541^-/- spermatocytes show abnormal programmed DNA double-strand break repair, impaired crossover formation and resolution, and asynapsis of the XY chromosomes. ZFP541 interacts with KCTD19, histone deacetylase 1/2 (HDAC1/2), and deoxynucleotidyl transferase terminal-interacting protein 1 (DNTTIP1). Moreover, ZFP541 binds to and activates the expression of genes involved in meiosis and post-meiosis including Kctd19; in turn, KCTD19 promotes the transcriptional activation activity of ZFP541. Taken together, our studies reveal that the ZFP541/KCTD19 signaling complex, acting as a key transcription regulator, plays an indispensable role in male fertility by regulating pachytene progression.

DNA methylome of primary spermatocyte reveals epigenetic dysregulation associated with male sterility of cattleyak

DNA cytosine methylation modification in the germline is of particular importance since it is a highly heritable epigenetic mark. Although cytosine methylation has been analyzed at the genome-scale for several mammalian species, our knowledge of DNA methylation patterns and the mechanisms underlying male hybrid sterility is still limited in domestic animals such as cattleyak. Here we for the first time show the genome-wide and single-base resolution landscape of methylcytosines (mC) in the primary spermatocyte (PSC) genome of yak with normal spermatogenesis and the inter-specific hybrid cattleyak with male infertility. A comparative investigation revealed that widespread differences are observed in the composition and patterning of DNA cytosine methylation between the two methylomes. Global CG or non-CG DNA methylation levels, as well as the number of mC sites, are increased in cattleyak compared to yak. Notably, the DNA methylome in cattleyak PSC exhibits promoter hypermethylation of meiosis-specific genes and piRNA pathway genes with respect to yak. Furthermore, major retrotransposonson classes are predominantly hypermethylated in cattleyak while those are fully hypomethylated in yak. KEGG pathway enrichment indicates Rap1 signaling and MAPK pathways may play potential roles in the spermatogenic arrest of cattleyak. Our present study not only provides valuable insights into distinct features of the cattleyak PSC methylome but also paves the way toward elucidating the complex, yet highly coordinated epigenetic modification during male germline development for inter-specific hybrid animals.

RBM46 is essential for gametogenesis and functions in post-transcriptional roles affecting meiotic cohesin subunits

RBM46 is a germ cell-specific RNA-binding protein required for gametogenesis, but the targets and molecular functions of RBM46 remain unknown. Here, we demonstrate that RBM46 binds at specific motifs in the 3'UTRs of mRNAs encoding multiple meiotic cohesin subunits and show that RBM46 is required for normal synaptonemal complex formation during meiosis initiation. Using a recently reported, high-resolution technique known as LACE-seq and working with low-input cells, we profiled the targets of RBM46 at single-nucleotide resolution in leptotene and zygotene stage gametes. We found that RBM46 preferentially binds target mRNAs containing GCCUAU/GUUCGA motifs in their 3'UTRs regions. In Rbm46 knockout mice, the RBM46-target cohesin subunits displayed unaltered mRNA levels but had reduced translation, resulting in the failed assembly of axial elements, synapsis disruption, and meiotic arrest. Our study thus provides mechanistic insights into the molecular functions of RBM46 in gametogenesis and illustrates the power of LACE-seq for investigations of RNA-binding protein functions when working with low-abundance input materials.

Two complementary approaches for efficient isolation of Sertoli cells for transcriptomic analysis

Sertoli cells (SCs) are the only somatic cells that reside in seminiferous tubules of testis. They directly interact with and support the development of germ cells, thus have an indispensable role in the process of spermatogenesis. SCs first appear in a proliferative state and then, with the initiation of the first wave of spermatogenesis, progress to a mature “nurturing” state which supports lifelong continuous sperm production. During this development, the SC transcriptome must adapt rapidly as obstacles in SC maturation often result in deficiencies in male fertility. Due to its importance in spermatogenesis, a reliable, rapid, and precise method for the isolation of high purity, viable and unadulterated SC has been largely missing. We have developed an improved method for the preparation of a testicular single cell suspension comprised of two alternative protocols to separate SCs from the rest of the testicular cells by FACS. The first sorting scheme is based on their co-expression of surface specific markers, FSHr and Occludin-1, while the second focuses on the co-staining of SCs with FSHr-specific antibody and Hoechst 33342, which discriminates DNA content of testicular cells. The entire procedure can be completed in less than 3 h which permits the analysis of the development-related transcriptional profile of these cells. Notably, our comparative study showed that this method resulted in a SC transcriptome that is largely comparable to SCs which were briskly isolated due to their cell-specific expression of fluorescent protein. Interestingly, we also show that SCs sorted as FSHr⁺Occludin⁺ cells contained a tangible portion of transcripts from all types of testicular germ cells. Sorting of SCs according to their 2C DNA content significantly reduced the presence of these transcripts, thus seems to be the most suitable approach for accurate determination of the SC transcriptome. We believe that these novel approaches for the isolation of SCs will assist researchers in the elucidation of their function as well as their role in spermatogenesis and disorders related to male infertility.

The germ cell-specific RNA binding protein RBM46 is essential for spermatogonial differentiation in mice

Control over gene expression is exerted, in multiple stages of spermatogenesis, at the post-transcriptional level by RNA binding proteins (RBPs). We identify here an essential role in mammalian spermatogenesis and male fertility for 'RNA binding protein 46' (RBM46). A highly evolutionarily conserved gene, Rbm46 is also essential for fertility in both flies and fish. We found Rbm46 expression was restricted to the mouse germline, detectable in males in the cytoplasm of premeiotic spermatogonia and meiotic spermatocytes. To define its requirement for spermatogenesis, we generated Rbm46 knockout (KO, Rbm46-/-) mice; although male Rbm46-/- mice were viable and appeared grossly normal, they were infertile. Testes from adult Rbm46-/- mice were small, with seminiferous tubules containing only Sertoli cells and few undifferentiated spermatogonia. Using genome-wide unbiased high throughput assays RNA-seq and 'enhanced crosslinking immunoprecipitation' coupled with RNA-seq (eCLIP-seq), we discovered RBM46 could bind, via a U-rich conserved consensus sequence, to a cohort of mRNAs encoding proteins required for completion of differentiation and subsequent meiotic initiation. In summary, our studies support an essential role for RBM46 in regulating target mRNAs during spermatogonia differentiation prior to the commitment to meiosis in mice.

Germline FOXJ2 overexpression causes male infertility via aberrant autophagy activation by LAMP2A upregulation

Spermatogenesis is a complex biological process that produces haploid spermatozoa and requires precise regulation by many tissue-specific factors. In this study, we explored the role and mechanism of Fork head box J2 (FOXJ2, which is highly expressed in spermatocytes) in the regulation of spermatogenesis using a germline-specific conditional Foxj2 knock-in mouse model (Stra8-Cre; Foxj2 ^tg/tg mouse). Foxj2 overexpression in mouse testes led to spermatogenesis failure, which started at the initiation of meiosis, and resulted in male infertility. Lysosomes and autophagy-related genes were upregulated in Stra8-cre; Foxj2 ^tg/tg mouse testes and the number of autolysosomes in the spermatocytes in Stra8-cre; Foxj2 ^tg/tg mice was increased. Chromatin immunoprecipitation-PCR and Dual-luciferase reporter assays showed that Lamp2 (encoding lysosome-associated membrane protein-2) was a target of FOXJ2. Foxj2 overexpression increased the expression levels of Lamp2a and Hsc70 (70-kDa cytoplasmic heat shock protein) in the Stra8-cre; Foxj2 ^tg/tg mouse testes. Our results suggested that Foxj2 overexpression in the germ cells of mouse testes affects chaperone-mediated autophagy by upregulating LAMP2A, leading to spermatogenesis failure at the initiation of meiosis, thus resulting in male infertility. Our findings provide a new insight into the function of FOXJ2 in spermatogenesis and the significance of autophagy regulation in spermatogenesis.

Connexin43 represents an important regulator for Sertoli cell morphology, Sertoli cell nuclear ultrastructure, and Sertoli cell maturation

The Sertoli cell (SC)-specific knockout (KO) of connexin43 (Cx43) was shown to be an effector of multiple histological changes in tubular morphology, resulting in germ cell loss through to a Sertoli-cell-only (SCO) phenotype and vacuolated seminiferous tubules containing SC-clusters. Our present study focused on the effects of Cx43 loss on SC ultrastructure. Using serial block-face scanning electron microscopy (SBF-SEM), we could confirm previous results. Ultrastructural analysis of Sertoli cell nuclei (SCN) revealed that these appear in clusters with a phenotype resembling immature/proliferating SCs in KO mice. Surprisingly, SCs of fertile wild type (WT) mice contained SCN with a predominantly smooth surface instead of deep indentations of the nuclear envelope, suggesting that these indentations do not correlate with germ cell support or spermatogenesis. SBF-SEM facilitated the precise examination of clustered SCs. Even if the exact maturation state of mutant SCs remained unclear, our study could detect indications of cellular senescence as well as immaturity, emphasising that Cx43 affects SC maturation. Moreover, Sudan III staining and transmission electron microscopy (TEM) demonstrated an altered lipid metabolism in SCs of Cx43 deficient mice.

A loss-of-function variant in SSFA2 causes male infertility with globozoospermia and failed oocyte activation

Globozoospermia (OMIM: 102530) is a rare type of teratozoospermia (< 0.1%). The etiology of globozoospermia is complicated and has not been fully revealed. Here, we report an infertile patient with globozoospermia. Variational analysis revealed a homozygous missense variant in the SSFA2 gene (NM_001130445.3: c.3671G > A; p.R1224Q) in the patient. This variant significantly reduced the protein expression of SSFA2. Immunofluorescence staining showed positive SSFA2 expression in the acrosome of human sperm. Liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) and Coimmunoprecipitation (Co-IP) analyses identified that GSTM3 and Actin interact with SSFA2. Further investigation revealed that for the patient, regular intracytoplasmic sperm injection (ICSI) treatment had a poor prognosis. However, Artificial oocyte activation (AOA) by a calcium ionophore (A23187) after ICSI successfully rescued the oocyte activation failure for the patient with the SSFA2 variant, and the couple achieved a live birth. This study revealed that SSFA2 plays an important role in acrosome formation, and the homozygous c.3671G > A loss-of-function variant in SSFA2 caused globozoospermia. SSFA2 may represent a new gene in the genetic diagnosis of globozoospermia, especially the successful outcome of AOA-ICSI treatment for couples, which has potential value for clinicians in their treatment regimen selections.

The testis-specific E3 ubiquitin ligase RNF133 is required for fecundity in mice

BACKGROUND

Ubiquitination is a post-translational modification required for a number of physiological functions regulating protein homeostasis, such as protein degradation. The endoplasmic reticulum (ER) quality control system recognizes and degrades proteins no longer needed in the ER through the ubiquitin-proteasome pathway. E2 and E3 enzymes containing a transmembrane domain have been shown to function in ER quality control. The ER transmembrane protein UBE2J1 is a E2 ubiquitin-conjugating enzyme reported to be essential for spermiogenesis at the elongating spermatid stage. Spermatids from Ube2j1 KO male mice are believed to have defects in the dislocation step of ER quality control. However, associated E3 ubiquitin-protein ligases that function during spermatogenesis remain unknown.

RESULTS

We identified four evolutionarily conserved testis-specific E3 ubiquitin-protein ligases [RING finger protein 133 (Rnf133); RING finger protein 148 (Rnf148); RING finger protein 151 (Rnf151); and Zinc finger SWIM-type containing 2 (Zswim2)]. Using the CRISPR/Cas9 system, we generated and analyzed the fertility of mutant mice with null alleles for each of these E3-encoding genes, as well as double and triple knockout (KO) mice. Male fertility, male reproductive organ, and sperm-associated parameters were analyzed in detail. Fecundity remained largely unaffected in Rnf148, Rnf151, and Zswim2 KO males; however, Rnf133 KO males displayed severe subfertility. Additionally, Rnf133 KO sperm exhibited abnormal morphology and reduced motility. Ultrastructural analysis demonstrated that cytoplasmic droplets were retained in Rnf133 KO spermatozoa. Although Rnf133 and Rnf148 encode paralogous genes that are chromosomally linked and encode putative ER transmembrane E3 ubiquitin-protein ligases based on their protein structures, there was limited functional redundancy of these proteins. In addition, we identified UBE2J1 as an E2 ubiquitin-conjugating protein that interacts with RNF133.

CONCLUSIONS

Our studies reveal that RNF133 is a testis-expressed E3 ubiquitin-protein ligase that plays a critical role for sperm function during spermiogenesis. Based on the presence of a transmembrane domain in RNF133 and its interaction with the ER containing E2 protein UBE2J1, we hypothesize that these ubiquitin-regulatory proteins function together in ER quality control during spermatogenesis.

BET bromodomain inhibitor JQ1 regulates spermatid development by changing chromatin conformation in mouse spermatogenesis

As a BET bromodomain inhibitor, JQ1 has been proven have efficacy against a number of different cancers. In terms of male reproduction, JQ1 may be used as a new type of contraceptive, since JQ1 treatment in male mice could lead to germ cell defects and a decrease of sperm motility, moreover, this effect is reversible. However, the mechanism of JQ1 acting on gene regulation in spermatogenesis remains unclear. Here, we performed single-cell RNA sequencing (scRNA-seq) on mouse testes treated with JQ1 or vehicle control to determine the transcriptional regulatory function of JQ1 in spermatogenesis at the single cell resolution. We confirmed that JQ1 treatment could increase the numbers of somatic cells and spermatocytes and decrease the numbers of spermatid cells. Gene Ontology (GO) analysis demonstrated that differentially expressed genes which were down-regulated after JQ1 injection were mainly enriched in "DNA conformation change" biological process in early developmental germ cells and "spermatid development" biological process in spermatid cells. ATAC-seq data further confirmed that JQ1 injection could change the open state of chromatin. In addition, JQ1 could change the numbers of accessible meiotic DNA double-stranded break sites and the types of transcription factor motif that functioned in pachytene spermatocytes and round spermatids. The multi-omics analysis revealed that JQ1 had the ability to regulate gene transcription by changing chromatin conformation in mouse spermatogenesis, which would potentiate the availability of JQ1 in male contraceptive.