ARMC12 regulates spatiotemporal mitochondrial dynamics during spermiogenesis and is required for male fertility

FBXO24 deletion causes abnormal accumulation of membraneless electron-dense granules in sperm flagella and male infertility

Ribonucleoprotein (RNP) granules are membraneless electron-dense structures rich in RNAs and proteins, and involved in various cellular processes. Two RNP granules in male germ cells, intermitochondrial cement and the chromatoid body (CB), are associated with PIWI-interacting RNAs (piRNAs) and are required for transposon silencing and spermatogenesis. Other RNP granules in male germ cells, the reticulated body and CB remnants, are also essential for spermiogenesis. In this study, we disrupted FBXO24, a testis-enriched F-box protein, in mice and found numerous membraneless electron-dense granules accumulated in sperm flagella. Fbxo24 knockout (KO) mice exhibited malformed flagellar structures, impaired sperm motility, and male infertility, likely due to the accumulation of abnormal granules. The amount and localization of known RNP granule-related proteins were not disrupted in Fbxo24 KO mice, suggesting that the accumulated granules were distinct from known RNP granules. Further studies revealed that RNAs and two importins, IPO5 and KPNB1, abnormally accumulated in Fbxo24 KO spermatozoa and that FBXO24 could ubiquitinate IPO5. In addition, IPO5 and KPNB1 were recruited to stress granules, RNP complexes, when cells were treated with oxidative stress or a proteasome inhibitor. These results suggest that FBXO24 is involved in the degradation of IPO5, disruption of which may lead to the accumulation of abnormal RNP granules in sperm flagella.

Update on the research on the antigens of anti-sperm antibodies over the last decade

This review summarizes the advancements over a decade of research on antigens of anti-sperm antibodies (ASAs), which are key to male immune infertility. Despite the progress in assisted reproductive technologies, understanding the roles and mechanisms of ASAs and their antigens remains vital for immune infertility management. We conducted a comprehensive literature search on PubMed from January 2013 to December 2023 using the following keywords: "anti-sperm antibody," "sperm antigen," and "immune infertility." In this review, we focus on the discoveries in sperm antigen identification and characterization through proteomics, gene disruption technology, and immunoinformatics, along with the development of fertility biomarkers. Here, we discuss the clinical applications of improved ASA detection methods and the progress in the development of immunocontraceptive vaccines. The intersection of advanced diagnostic techniques and vaccine development represents a promising frontier in reproductive health. The findings also highlight the need for standardized ASA detection methods and a comprehensive molecular-level approach to understanding ASA-related infertility. These insights underscore the significance of ongoing reproductive immunology research in enhancing clinical fertility outcomes and contraceptive vaccine development.

Voltage-dependent anion channels are involved in the maintenance of pig sperm quality during liquid preservation

Pigs are usually bred through artificial insemination with liquid semen preserved at 15-20 °C. While this method of preservation brings many benefits, including a greater reproductive performance compared to frozen-thawed sperm, the period of storage is a limiting factor. As the mitochondrion regulates many facets of sperm physiology, modulating its activity could have an impact on their lifespan. Aligned with this hypothesis, the present study sought to investigate whether inhibition of voltage-dependent anion channels (VDACs), which reside in the outer mitochondrial membrane and regulate the flux of ions between mitochondria and the cytosol in somatic cells, influences the resilience of pig sperm to liquid preservation at 17 °C. For this purpose, semen samples (N = 7) were treated with two different concentrations of TRO19622 (5 μM and 50 μM), an inhibitor of VDACs, and stored at 17 °C for 10 days. At days 0, 4 and 10, sperm quality and functionality parameters were evaluated by flow cytometry and computer-assisted sperm analysis (CASA). The effects of inhibiting VDACs depended on the concentration of the inhibitor. On the one hand, the greatest concentration of TRO19622 (50 μM) led to a decrease in sperm motility, viability and mitochondrial membrane potential, which could be related to the observed intracellular Ca2+ increase. In contrast, total sperm motility was higher in samples treated with 5 μM TRO19622 than in the control, suggesting that when VDACs channels are inhibited by the lowest concentration of the blocking agent the resilience of pig sperm to liquid storage increases. In conclusion, the current research indicates that mitochondrial function, as regulated by ion channels in the outer mitochondrial membrane like VDACs, is related to the sperm resilience to liquid preservation and may influence cell lifespan.

Methionine Improves Boar Sperm Quality by Promoting Mitochondrial Translation during Liquid Storage

Boar sperm quality serves as an important indicator of reproductive efficiency, playing a direct role in enhancing the output of livestock production. It has been demonstrated that mitochondrial protein translation is present in sperm and plays a crucial role in regulating sperm motility, capacitation and in vitro fertilization rate. The present study aimed to determine whether methionine supplementation enhances mitochondrial translation in boar sperm, thereby improving sperm quality. The results showed a significant elevation in the abundance of mitochondrial methionyl-tRNA formyltransferase (MTFMT), a crucial enzyme for mitochondrial protein translation, and mitochondrial DNA-encoded cytochrome c oxidase subunit 1 (COX1) in boar sperm exhibiting high motility. Both amino acids and methionine supplementation significantly enhanced boar sperm motility during storage. Moreover, methionine supplementation mitigates the loss of acrosomal integrity, enhances the expression of COX1, and boosts mitochondrial activity. Furthermore, the positive impact of methionine was negated in the presence of the mitochondrial translation inhibitor chloramphenicol. Together, these findings suggest that boar sperm may utilize methionine as a protein translation substrate to enhance sperm motility by stimulating mitochondrial protein translation. The supplementation of methionine may enhance the quality of boar sperm, thereby providing guidance for the optimization of diluent formulations for liquid storage and the identification of physiological regulators that regulate sperm motility.

Development of functional spermatozoa in mammalian spermiogenesis

Infertility is a global health problem affecting one in six couples, with 50% of cases attributed to male infertility. Spermatozoa are male gametes, specialized cells that can be divided into two parts: the head and the flagellum. The head contains a vesicle called the acrosome that undergoes exocytosis and the flagellum is a motility apparatus that propels the spermatozoa forward and can be divided into two components, axonemes and accessory structures. For spermatozoa to fertilize oocytes, the acrosome and flagellum must be formed correctly. In this Review, we describe comprehensively how functional spermatozoa develop in mammals during spermiogenesis, including the formation of acrosomes, axonemes and accessory structures by focusing on analyses of mouse models.

Homozygous ACTL9 mutations cause irregular mitochondrial sheath arrangement and abnormal flagellum assembly in spermatozoa and male infertility

PURPOSE

To identify novel variants in ACTL9 and new phenotypes responsible for male infertility.

METHODS

Genomic DNA was extracted from peripheral blood samples for whole-exome sequencing (WES). Computer-assisted sperm analysis (CASA) was used to test the motility of spermatozoa. The ultrastructure of flagella and the mitochondrial sheath were assessed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Immunostaining was used to validate the localization and expression of ACTL9 and ACTL7A. An Actl9-mutated mouse model was used to validate the phenotypes by CASA and TEM.

RESULTS

We identified novel homozygous variants in ACTL9 in two independent Chinese families. Spermatozoa with ACTL9 mutations showed decreased CASA parameters and a higher proportion of spermatozoa with abnormal morphology, exhibiting coiled flagella and a thickened midpiece. The spermatozoa were characterized by chaotic or irregular '9+2' structures and irregular mitochondrial sheath arrangements in the flagellum. Actl9 knock-in mice also showed abnormal CASA parameters and irregular '9+2' structures in flagella.

CONCLUSIONS

Our study expands the mutation spectrum and phenotypic spectrum of ACTL9.

Genetic mutation of Cep76 results in male infertility due to abnormal sperm tail composition

The transition zone is a specialised gate at the base of cilia/flagella, which separates the ciliary compartment from the cytoplasm and strictly regulates protein entry. We identified a potential new regulator of the male germ cell transition zone, CEP76. We demonstrated that CEP76 was involved in the selective entry and incorporation of key proteins required for sperm function and fertility into the ciliary compartment and ultimately the sperm tail. In the mutant, sperm tails were shorter and immotile as a consequence of deficits in essential sperm motility proteins including DNAH2 and AKAP4, which accumulated at the sperm neck in the mutant. Severe annulus, fibrous sheath, and outer dense fibre abnormalities were also detected in sperm lacking CEP76. Finally, we identified that CEP76 dictates annulus positioning and structure. This study suggests CEP76 as a male germ cell transition zone protein and adds further evidence to the hypothesis that the spermatid transition zone and annulus are part of the same functional structure.

Proteomic profiling of TBC1 domain family member 21-null sperms reveals the critical roles of TEKT 1 in their tail defects

BACKGROUND

Approximately 7% of the males exhibit reduced fertility; however, the regulatory genes and pathways involved remain largely unknown. TBC1 domain family member 21 (TBC1D21) contains a conserved RabGAP catalytic domain that induces GDP/GTP exchange to inactivate Rabs by interacting with microtubules. We previously reported that Tbc1d21-null mice exhibit severe sperm tail defects with a disrupted axoneme, and that TBC1D21 interacts with RAB10. However, the pathological mechanisms underlying the Tbc1d21 loss-induced sperm tail defects remain unknown.

RESULTS

Murine sperm from wild-type and Tbc1d21-null mice were comparatively analyzed using proteomic assays. Over 1600 proteins were identified, of which 15 were significantly up-regulated in Tbc1d21-null sperm. Notably, several tektin (TEKT) family proteins, belonging to a type of intermediate filament critical for stabilizing the microtubular structure of cilia and flagella, were significantly up-regulated in Tbc1d21-/- sperm. We also found that TBC1D21 interacts with TEKT1. In addition, TEKT1 co-localized with RAB10 during sperm tail formation. Finally, we found Tbc1d21-null sperm exhibited abnormal accumulation of TEKT1 in the midpiece region, accompanied by disrupted axonemal structures.

CONCLUSIONS

These results reveal that TBC1D21 modulates TEKTs protein localization in the axonemal transport system during sperm tail formation.

FBXO24 deletion causes abnormal accumulation of membraneless electron-dense granules in sperm flagella and male infertility

Ribonucleoprotein (RNP) granules are membraneless electron-dense structures rich in RNAs and proteins, and involved in various cellular processes. Two RNP granules in male germ cells, intermitochondrial cement and the chromatoid body (CB), are associated with PIWI-interacting RNAs (piRNAs) and are required for transposon silencing and spermatogenesis. Other RNP granules in male germ cells, the reticulated body and CB remnants, are also essential for spermiogenesis. In this study, we disrupted FBXO24, a testis-enriched F-box protein, in mice and found numerous membraneless electron-dense granules accumulated in sperm flagella. Fbxo24 knockout (KO) mice exhibited malformed flagellar structures, impaired sperm motility, and male infertility, likely due to the accumulation of abnormal granules. The amount and localization of known RNP granule-related proteins were not disrupted in Fbxo24 KO mice, suggesting that the accumulated granules were distinct from known RNP granules. Further studies revealed that RNAs and two importins, IPO5 and KPNB1, abnormally accumulated in Fbxo24 KO spermatozoa and that FBXO24 could ubiquitinate IPO5. In addition, IPO5 and KPNB1 were recruited to stress granules, RNP complexes, when cells were treated with oxidative stress or a proteasome inhibitor. These results suggest that FBXO24 is involved in the degradation of IPO5, disruption of which may lead to the accumulation of abnormal RNP granules in sperm flagella.

Affinity-tagged SMAD1 and SMAD5 mouse lines reveal transcriptional reprogramming mechanisms during early pregnancy

Endometrial decidualization, a prerequisite for successful pregnancies, relies on transcriptional reprogramming driven by progesterone receptor (PR) and bone morphogenetic protein (BMP)-SMAD1/SMAD5 signaling pathways. Despite their critical roles in early pregnancy, how these pathways intersect in reprogramming the endometrium into a receptive state remains unclear. To define how SMAD1 and/or SMAD5 integrate BMP signaling in the uterus during early pregnancy, we generated two novel transgenic mouse lines with affinity tags inserted into the endogenous SMAD1 and SMAD5 loci (Smad1HA/HA and Smad5PA/PA). By profiling the genome-wide distribution of SMAD1, SMAD5, and PR in the mouse uterus, we demonstrated the unique and shared roles of SMAD1 and SMAD5 during the window of implantation. We also showed the presence of a conserved SMAD1, SMAD5, and PR genomic binding signature in the uterus during early pregnancy. To functionally characterize the translational aspects of our findings, we demonstrated that SMAD1/5 knockdown in human endometrial stromal cells suppressed expressions of canonical decidual markers (IGFBP1, PRL, FOXO1) and PR-responsive genes (RORB, KLF15). Here, our studies provide novel tools to study BMP signaling pathways and highlight the fundamental roles of SMAD1/5 in mediating both BMP signaling pathways and the transcriptional response to progesterone (P4) during early pregnancy.

MORN2 regulates the morphology and energy metabolism of mitochondria and is required for male fertility in mice

BACKGROUND

Mitochondria produce adenosine triphosphate through respiratory activities to power sperm differentiation and motility, and decreased mitochondrial respiratory activity can result in poor sperm motility and asthenospermia. The mitochondrial sheath is a component of the mid-piece of the sperm flagellum, and dysfunction of the sheath can reduce sperm motility and cause male infertility. The membrane occupation and recognition nexus-motif protein 2 (MORN2) is testis enriched in mice, and the MORN motif was reported to play a role in the regulation of bioelectrical signal homeostasis in cardiomyocytes.

METHODS

We generated Morn2-/- mice using CRISPR/Cas9 and evaluated the potential functions of MORN2 in spermiogenesis through histological analysis, fertility examination, RT-PCR, CASA, immunofluorescence, TUNEL, electron microscopy analysis, mitochondrial energy metabolism analysis, etc. RESULTS: The Morn2-/- mice were infertile, and their sperm showed severe motility defects. Morn2-/- sperm also had abnormal morphology characterized by bent heads, aberrant mitochondrial sheath formation, lower mitochondrial membrane potential, higher levels of reactive oxygen species, and decreased mitochondrial respiratory activity.

CONCLUSIONS

Our study demonstrates that MORN2 is essential for male fertility and indicates that MORN2 functions in mitochondrial sheath formation and regulates mitochondrial respiratory activity.

Disruption of testis-enriched cytochrome c oxidase subunit COX6B2 but not COX8C leads to subfertility

Mammalian sperm flagellum contains the midpiece characterized by a mitochondrial sheath that packs tightly around the axoneme and outer dense fibers. Mitochondria are known as the "powerhouse" of the cell, and produce ATP through the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS). However, the contribution of the TCA cycle and OXPHOS to sperm motility and male fertility is less clear. Cytochrome c oxidase (COX) is an oligomeric complex localized within the mitochondrial inner membrane, and the terminal enzyme of the mitochondrial electron transport chain in eukaryotes. Both COX6B2 and COX8C are testis-enriched COX subunits whose functions in vivo are poorly studied. Here, we generated Cox6b2 and Cox8c knockout (KO) mice using the CRISPR/Cas9 system. We examined their fertility and sperm mitochondrial function to determine the significance of testis-enriched COX subunits in male fertility. The mating test revealed that disrupting COX6B2 induces male subfertility, while disrupting COX8C does not affect male fertility. Cox6b2 KO spermatozoa showed low sperm motility, but mitochondrial function was normal according to oxygen consumption rates. Therefore, low sperm motility seems to cause subfertility in Cox6b2 KO male mice. These results also indicate that testis-enriched COX, COX6B2 and COX8C, are not essential for OXPHOS in mouse spermatozoa.

Affinity-tagged SMAD1 and SMAD5 mouse lines reveal transcriptional reprogramming mechanisms during early pregnancy

Endometrial decidualization, a prerequisite for successful pregnancies, relies on transcriptional reprogramming driven by progesterone receptor (PR) and bone morphogenetic protein (BMP)-SMAD1/SMAD5 signaling pathways. Despite their critical roles in early pregnancy, how these pathways intersect in reprogramming the endometrium into a receptive state remains unclear. To define how SMAD1 and/or SMAD5 integrate BMP signaling in the uterus during early pregnancy, we generated two novel transgenic mouse lines with affinity tags inserted into the endogenous SMAD1 and SMAD5 loci (Smad1HA/HA and Smad5PA/PA). By profiling the genome-wide distribution of SMAD1, SMAD5, and PR in the mouse uterus, we demonstrated the unique and shared roles of SMAD1 and SMAD5 during the window of implantation. We also showed the presence of a conserved SMAD1, SMAD5, and PR genomic binding signature in the uterus during early pregnancy. To functionally characterize the translational aspects of our findings, we demonstrated that SMAD1/5 knockdown in human endometrial stromal cells suppressed expressions of canonical decidual markers (IGFBP1, PRL, FOXO1) and PR-responsive genes (RORB, KLF15). Here, our studies provide novel tools to study BMP signaling pathways and highlight the fundamental roles of SMAD1/5 in mediating both BMP signaling pathways and the transcriptional response to progesterone (P4) during early pregnancy.

TMEM225 Is Essential for Sperm Maturation and Male Fertility by Modifying Protein Distribution of Sperm in Mice

Nonobstructive azoospermia is the leading cause of male infertility. Abnormal levels of transmembrane protein 225 (TMEM225), a testis-specific protein, have been found in patients with nonobstructive azoospermia, suggesting that TMEM225 plays an essential role in male fertility. Here, we generated a Tmem225 KO mouse model to explore the function and mechanism of TMEM225 in male reproduction. Male Tmem225 KO mice were infertile. Surprisingly, Tmem225 deletion did not affect spermatogenesis, but TMEM225-null sperm exhibited abnormalities during epididymal maturation, resulting in reduced sperm motility and an abnormal hairpin-loop configuration. Furthermore, proteomics analyses of cauda sperm revealed that signaling pathways related to mitochondrial function, the glycolytic pathway, and sperm flagellar morphology were abnormal in Tmem225 KO sperm, and spermatozoa lacking TMEM225 exhibited high reactive oxygen species levels, reduced motility, and flagellar folding, leading to typical asthenospermia. These findings suggest that testicular TMEM225 may control the sperm maturation process by regulating the expression of proteins related to mitochondrial function, glycolysis, and sperm flagellar morphology in epididymal spermatozoa.

Multiple ageing effects on testicular/epididymal germ cells lead to decreased male fertility in mice

In mammals, females undergo reproductive cessation with age, whereas male fertility gradually declines but persists almost throughout life. However, the detailed effects of ageing on germ cells during and after spermatogenesis, in the testis and epididymis, respectively, remain unclear. Here we comprehensively examined the in vivo male fertility and the overall organization of the testis and epididymis with age, focusing on spermatogenesis, and sperm function and fertility, in mice. We first found that in vivo male fertility decreased with age, which is independent of mating behaviors and testosterone levels. Second, overall sperm production in aged testes was decreased; about 20% of seminiferous tubules showed abnormalities such as germ cell depletion, sperm release failure, and perturbed germ cell associations, and the remaining 80% of tubules contained lower number of germ cells because of decreased proliferation of spermatogonia. Further, the spermatozoa in aged epididymides exhibited decreased total cell numbers, abnormal morphology/structure, decreased motility, and DNA damage, resulting in low fertilizing and developmental rates. We conclude that these multiple ageing effects on germ cells lead to decreased in vivo male fertility. Our present findings are useful to better understand the basic mechanism behind the ageing effect on male fertility in mammals including humans.

CCDC183 is essential for cytoplasmic invagination around the flagellum during spermiogenesis and male fertility

Sperm flagellum plays a crucial role in male fertility. Here, we generated Ccdc183 knockout mice using the CRISPR/Cas9 system to reveal the protein function of the testis-specific protein CCDC183 in spermiogenesis. We demonstrated that the absence of CCDC183 causes male infertility with morphological and motility defects in spermatozoa. Owing to the lack of CCDC183, centrioles after elongation of axonemal microtubules do not connect the cell surface and nucleus during spermiogenesis, which causes subsequent loss of cytoplasmic invagination around the flagellum. As a result, the flagellar compartment does not form properly and cytosol-exposed axonemal microtubules collapse during spermiogenesis. In addition, ectopic localization of accessory structures, such as the fibrous sheath and outer dense fibers, and abnormal head shape as a result of abnormal sculpting by the manchette are observed in Ccdc183 knockout spermatids. Our results indicate that CCDC183 plays an essential role in cytoplasmic invagination around the flagellum to form functional spermatozoa during spermiogenesis.

Integrated molecular-network analysis reveals infertility-associated key genes and transcription factors in the non-obstructive azoospermia

BACKGROUND

Male infertility is a multifactorial reproductive health problem with complex causes. Non-obstructive azoospermia (NOA) is characterized by failure of spermatogenesis, leading to the absence of spermatozoa in ejaculates. The molecular mechanism underlying the NOA is still not well understood.

OBJECTIVES

This study aims to identify the key genes involved in male infertility that could be a potential biomarker in the diagnosis and prognosis of azoospermia.

STUDY DESIGN

The microarray expression profiles dataset GSE45885 and GSE45887 were downloaded from the NCBI's Gene Expression Omnibus (GEO) database and analyzed for male infertility-associated differentially expressed genes (DEGs) using the GEO2R tool. The common DEGs between the two datasets were combined and their protein-protein interaction (PPI) network was constructed using Cytoscape to reveal the hub genes by topology and module analysis. In addition, transcription factors (TFs) and protein kinases regulating the hub genes were identified using the X2K tool. Then, the expression of the hub genes was validated by analyzing the GSE190752 microarray dataset. Further, the PPI network was screened for biological roles and enriched pathways using DAVID software.

RESULTS

About 256 DEGs associated with NOA were identified and constructed the PPI network to find the infertility-associated proteins. The biological processes linked with these proteins were spermatogenesis, cell differentiation, flagellated sperm motility, and spermatid development. The topology and module analysis of the infertility-associated protein network identified the hub genes TEX38, FAM71F, PRR30, FAM166A, LYZL6, TPPP2, ARMC12, SPACA4, and FAM205A, which were found to be upregulated in the non-obstructive azoospermia. In addition, a total of 23 transcription factors and 3 protein kinases that are regulating these key hub genes were identified. Further these hub genes expression was validated using the microarray data and found that their expression was increased in the testicular biopsies obtained from NOA subjects, compared to healthy individuals.

CONCLUSION

The identified key genes and its associated transcription factors are known to regulate the infertility-related processes in the non-obstructive azoospermia. Also, the clinical sample-based microarray data validation for the expression of these key hub genes indicates their potentiality to develop them as diagnostic or prognostic biomarkers for NOA.

Human VDAC pseudogenes: an emerging role for VDAC1P8 pseudogene in acute myeloid leukemia

BACKGROUND

Voltage-dependent anion selective channels (VDACs) are the most abundant mitochondrial outer membrane proteins, encoded in mammals by three genes, VDAC1, 2 and 3, mostly ubiquitously expressed. As 'mitochondrial gatekeepers', VDACs control organelle and cell metabolism and are involved in many diseases. Despite the presence of numerous VDAC pseudogenes in the human genome, their significance and possible role in VDAC protein expression has not yet been considered.

RESULTS

We investigated the relevance of processed pseudogenes of human VDAC genes, both in physiological and in pathological contexts. Using high-throughput tools and querying many genomic and transcriptomic databases, we show that some VDAC pseudogenes are transcribed in specific tissues and pathological contexts. The obtained experimental data confirm an association of the VDAC1P8 pseudogene with acute myeloid leukemia (AML).

CONCLUSIONS

Our in-silico comparative analysis between the VDAC1 gene and its VDAC1P8 pseudogene, together with experimental data produced in AML cellular models, indicate a specific over-expression of the VDAC1P8 pseudogene in AML, correlated with a downregulation of the parental VDAC1 gene.

FKBP5 genetic variants are associated with respiratory- and sleep-related parameters in Chinese patients with obstructive sleep apnea

Introduction

Obstructive sleep apnea (OSA) has been associated with psychiatric disorders, especially depression and posttraumatic stress disorder (PTSD). FKBP5 genetic variants have been previously reported to confer the risk of depression and PTSD. This study aimed to investigate the association of single nucleotide polymorphisms (SNPs) in the FKBP5 gene with OSA and OSA-related quantitative traits.

Methods

Four SNPs within the FKBP5 gene (rs1360780, rs3800373, rs9296158, rs9470080) were genotyped in 5773 participants with anthropometric and polysomnography data. Linear regression and logistic regression analyses were performed to evaluate the relationship between FKBP5 SNPs and OSA-related traits. Binary logistic regression was used to assess the effect of SNPs on OSA susceptibility. Interacting genes of SNPs were assessed based on the 3DSNP database, and expression quantitative trait loci (eQTL) analysis for SNPs was adopted to examine the correlation of SNPs with gene expression. Gene expression analyses in human brains were performed with the aid of Brain Atlas.

Results

In moderate-to-severe OSA patients, all four SNPs were positively associated with AHI_REM, and rs9296158 showed the strongest association (ß = 1.724, p = 0.001). Further stratified analyses showed that in men with moderate OSA, rs1360780, rs3800373 and rs9470080 were positively associated with wake time (p = 0.0267, p = 0.0254 and p = 0.0043, respectively). Rs1360780 and rs3800373 were 28 and 29.4%more likely to rate a higher ordered MAI category (OR (95% CI) = 1.280 (1.042 - 1.575), p = 0.019; OR (95% CI) = 1.294 (1.052 - 1.592), p = 0.015, respectively). Rs9296158 and rs9470080 increased the risk of low sleep efficiency by 25.7 and 28.1% (OR (95% CI) = 1.257 (1.003 - 1.575), p = 0.047; OR (95% CI) = 1.281 (1.026-1.6), p = 0.029, respectively). Integrated analysis of eQTL and gene expression patterns revealed that four SNPs may exert their effects by regulating FKBP5, TULP1, and ARMC12.

Conclusion

Single nucleotide polymorphisms in the FKBP5 gene were associated with sleep respiratory events in moderate-to-severe OSA patients during REM sleep and associated with sleep architecture variables in men with moderate OSA. FKBP5 variants may be a potential predisposing factor for sleep disorders, especially in REM sleep.

ADAD2 functions in spermiogenesis and piRNA biogenesis in mice

BACKGROUND

Adenosine deaminase domain containing 2 (ADAD2) is a testis-specific protein composed of a double-stranded RNA binding domain and a non-catalytic adenosine deaminase domain. A recent study showed that ADAD2 is indispensable for the male reproduction in mice. However, the detailed functions of ADAD2 remain elusive.

OBJECTIVES

This study aimed to investigate the cause of male sterility in Adad2 mutant mice and to understand the molecular functions of ADAD2.

MATERIALS AND METHODS

Adad2 homozygous mutant mouse lines, Adad2-/- and Adad2Δ/Δ , were generated by CRISPR/Cas9. Western blotting and immunohistochemistry were used to reveal the expression and subcellular localization of ADAD2. Co-immunoprecipitation tandem mass spectrometry was employed to determine the ADAD2-interacting proteins in mouse testes. RNA-sequencing analyses were carried out to analyze the transcriptome and PIWI-interacting RNA (piRNA) populations in wildtype and Adad2 mutant testes.

RESULTS

Adad2-/- and Adad2Δ/Δ mice exhibit male-specific sterility because of abnormal spermiogenesis. ADAD2 interacts with multiple RNA-binding proteins involved in piRNA biogenesis, including MILI, MIWI, RNF17, and YTHDC2. ADAD2 co-localizes and forms novel granules with RNF17 in spermatocytes. Ablation of ADAD2 impairs the formation of RNF17 granules, decreases the number of cluster-derived pachytene piRNAs, and increases expression of ping-pong-derived piRNAs.

DISCUSSION AND CONCLUSION

In collaboration with RNF17 and other RNA-binding proteins in spermatocytes, ADAD2 directly or indirectly functions in piRNA biogenesis.

Biochemical Features of X or Y Chromosome-Bearing Spermatozoa for Sperm Sexing

This review presents information on biochemical features of spermatozoa bearing X or Y chromosome, enabling production of a sperm fraction with pre-defined sex chromosome. The almost only technology currently used for such separation (called sexing) is based on the fluorescence-activated cell sorting of sperm depending on DNA content. In addition to the applied aspects, this technology made it possible to analyze properties of the isolated populations of spermatozoa bearing X or Y chromosome. In recent years, existence of the differences between these populations at the transcriptome and proteome level have been reported in a number of studies. It is noteworthy that these differences are primarily related to the energy metabolism and flagellar structural proteins. New methods of sperm enrichment with X or Y chromosome cells are based on the differences in motility between the spermatozoa with different sex chromosomes. Sperm sexing is a part of the widespread protocol of artificial insemination of cows with cryopreserved semen, it allows to increase proportion of the offspring with the required sex. In addition, advances in the separation of X and Y spermatozoa may allow this approach to be applied in clinical practice to avoid sex-linked diseases.

Actin-related protein ACTL7B ablation leads to OAT with multiple morphological abnormalities of the flagellum and male infertility in mice†

The formation of fertilisation-competent sperm requires spermatid morphogenesis (spermiogenesis), a poorly understood program that involves complex coordinated restructuring and specialised cytoskeletal structures. A major class of cytoskeletal regulators are the actin-related proteins (ARPs), which include conventional actin variants, and related proteins that play essential roles in complexes regulating actin dynamics, intracellular transport, and chromatin remodeling. Multiple testis-specific ARPs are well conserved among mammals, but their functional roles are unknown. One of these is actin-like 7b (Actl7b) that encodes an orphan ARP highly similar to the ubiquitously expressed beta actin (ACTB). Here we report ACTL7B is expressed in human and mouse spermatids through the elongation phase of spermatid development. In mice, ACTL7B specifically localises to the developing acrosome, within the nucleus of early spermatids, and to the flagellum connecting region. Based on this localisation pattern and high level of sequence conservation in mice, humans, and other mammals, we examined the requirement for ACTL7B in spermiogenesis by generating and characterising the reproductive phenotype of male Actl7b KO mice. KO mice were infertile, with severe and variable oligoteratozoospermia (OAT) and multiple morphological abnormalities of the flagellum (MMAF) and sperm head. These defects phenocopy human OAT and MMAF, which are leading causes of idiopathic male infertility. In conclusion, this work identifies ACTL7B as a key regulator of spermiogenesis that is required for male fertility.

Biallelic mutations in ARMC12 cause asthenozoospermia and multiple midpiece defects in humans and mice

BACKGROUND

Asthenozoospermia is a major factor contributing to male infertility. The mitochondrial sheath (MS), an important organelle in the midpiece of spermatozoa, is crucial to sperm motility. ARMC12 is a mitochondrial peripheral membrane protein. Deletion of Armc12 impairs the arrangement of MS and causes infertility in mice. However, the role of ARMC12 in human asthenozoospermia remains unknown.

OBJECTIVE

To study the genetic defects in patients with asthenozoospermia.

METHODS

A total of 125 patients with asthenozoospermia and 120 men with proven fertility were recruited. Whole-exome sequencing and Sanger sequencing were performed for genetic analysis. Papanicolaou staining, HE staining, immunofluorescent staining, transmission electron microscopy and field emission scanning electron microscopy were employed to observe the morphological and structural defects of the spermatozoa and testes. Armc12-knockout mice were generated using the CRISPR-Cas9 system. Intracytoplasmic sperm injection was used to treat the patients.

RESULTS

Biallelic ARMC12 mutations were identified in three patients, including homozygous mutations in two siblings from a consanguineous family and compound heterozygous mutations in one sporadic patient. ARMC12 is mainly expressed in the midpiece of elongated and late spermatids in the human testis. The patients' spermatozoa displayed multiple midpiece defects, including absent MS and central pair, scattered or forked axoneme and incomplete plasma membrane. Spermatozoa from Armc12^-/- mice showed parallel defects in the midpiece. Moreover, two patients were treated with intracytoplasmic sperm injection and achieved good outcomes.

CONCLUSION

Our findings prove for the first time that defects in ARMC12 cause asthenozoospermia and multiple midpiece defects in humans.

Lnc956-TRIM28-HSP90B1 complex on replication forks promotes CMG helicase retention to ensure stem cell genomic stability and embryogenesis

Replication stress is a major source of endogenous DNA damage. Despite the identification of numerous proteins on replication forks to modulate fork or replication machinery activities, it remains unexplored whether noncoding RNAs can localize on stalled forks and play critical regulatory roles. Here, we identify an uncharacterized long noncoding RNA NONMMUT028956 (Lnc956 for short) predominantly expressed in mouse embryonic stem cells. Lnc956 is accumulated on replication forks to prevent fork collapse and preserve genomic stability and is essential for mouse embryogenesis. Mechanistically, it drives assembly of the Lnc956-TRIM28-HSP90B1 complex on stalled forks in an interdependent manner downstream of ataxia telangiectasia and Rad3-related (ATR) signaling. Lnc956-TRIM28-HSP90B1 complex physically associates with minichromosome maintenance proteins 2 (MCM2) to minichromosome maintenance proteins 7 (MCM7) hexamer via TRIM28 and directly regulates the CDC45-MCM-GINS (CMG) helicase retention on chromatin. The regulation of Lnc956-TRIM28-HSP90B1 on CMG retention is mediated by HSP90B1's chaperoning function. These findings reveal a player that actively regulates replisome retention to prevent fork collapse.

Testis-enriched ferlin, FER1L5, is required for Ca2+-activated acrosome reaction and male fertility

Spermatozoa need to undergo an exocytotic event called the acrosome reaction before fusing with eggs. Although calcium ion (Ca2+) is essential for the acrosome reaction, its molecular mechanism remains unknown. Ferlin is a single transmembrane protein with multiple Ca2+-binding C2 domains, and there are six ferlins, dysferlin (DYSF), otoferlin (OTOF), myoferlin (MYOF), fer-1-like 4 (FER1L4), FER1L5, and FER1L6, in mammals. Dysf, Otof, and Myof knockout mice have been generated, and each knockout mouse line exhibited membrane fusion disorders such as muscular dystrophy in Dysf, deafness in Otof, and abnormal myogenesis in Myof. Here, by generating mutant mice of Fer1l4, Fer1l5, and Fer1l6, we found that only Fer1l5 is required for male fertility. Fer1l5 mutant spermatozoa could migrate in the female reproductive tract and reach eggs, but no acrosome reaction took place. Even a Ca2+ ionophore cannot induce the acrosome reaction in Fer1l5 mutant spermatozoa. These results suggest that FER1L5 is the missing link between Ca2+ and the acrosome reaction.

Evaluation of the efficacy of creatine chemical exchange saturation transfer imaging in assessing testicular maturity

Purpose

Microscopic testicular sperm extraction is the most effective treatment for NOA, but the sperm retrieval rate is low and depends on testicular maturity. However, there are limited useful tests to assess testicular maturity. Chemical exchange saturation transfer (CEST) imaging is a new magnetic resonance imaging (MRI) technique that can image the distribution of trace substances in vivo. We focused on the potential role of creatine (Cr) in testes and hypothesized that Cr-CEST could indicate intratesticular spermatogenesis.

Methods

We performed Cr-CEST by using 7T MRI on wild-type C57B6/J mice and several types of male infertility models such as Sertoli-cell only (SCO) (Kitw/Kitwv), maturation arrest (MA) (Zfp541 knockout mouse and Kctd19 knockout mouse), and teratozoospermia (Tbc1d21 knockout mouse). After performing Cr-CEST, histological analysis was performed.

Results

The SCO and MA models showed decreased CEST signal intensity (p < 0.05), while no reduction was observed in the teratozoospermia model (p = 1.0). CEST signal intensity increased as the spermatogenesis stage progressed from the SCO model to the MA and teratozoospermia models. Furthermore, CEST signal intensity was reduced in 4-week-old wild-type mice with immature testes (p < 0.05).

Conclusions

This study suggests that Cr-CEST evaluates intratesticular spermatogenesis noninvasively and provides a new therapeutic strategy for treating male infertility.

The Expansion of the Spectrum in Stuttering Disorders to a Novel ARMC Gene Family (ARMC3)

Stuttering is a common neurodevelopment speech disorder that negatively affects the socio-psychological dimensions of people with disability. It displays many attributes of a complex genetic trait, and a few genetic loci have been identified through linkage studies. Stuttering is highly variable regarding its phenotypes and molecular etiology. However, all stutters have some common features, including blocks in speech, prolongation, and repetition of sounds, syllables, and words. The involuntary actions associated with stuttering often involve increased eye blinking, tremors of the lips or jaws, head jerks, clenched fists, perspiration, and cardiovascular changes. In the present study, we recruited a consanguineous Pakistani family showing an autosomal recessive mode of inheritance. The exome sequencing identified a homozygous splice site variant in ARMC3 (Armadillo Repeat Containing 3) in a consanguineous Pashtun family of Pakistani origin as the underlying genetic cause of non-syndromic stuttering. The homozygous splice site variant (NM_173081.5:c.916 + 1G > A) segregated with the stuttering phenotype in this family. The splice change leading to the skipping of exon-8 is a loss of function (LoF) variant, which is predicted to undergo NMD (Nonsense mediated decay). Here, we report ARMC3 as a novel candidate gene causing the stuttering phenotype. ARMC3 may lead to neurodevelopmental disorders, including stuttering in humans.

TBC1D21 is an essential factor for sperm mitochondrial sheath assembly and male fertility‡

During spermiogenesis, the formation of the mitochondrial sheath is critical for male fertility. The molecular processes that govern the development of the mitochondrial sheath remain unknown. Whether TBC1D21 serves as a GTPase-activating protein (GAP) for GTP hydrolysis in the testis is unclear, despite recent findings indicating that it collaborates with numerous proteins to regulate the formation of the mitochondrial sheath. To thoroughly examine the property of TBC1D21 in spermiogenesis, we applied the CRISPR/Cas9 technology to generate the Tbc1d21-/- mice, Tbc1d21D125A R128K mice with mutation in the GAP catalytic residues (IxxDxxR), and Tbc1d21-3xFlag mice. Male Tbc1d21-/- mice were infertile due to the curved spermatozoa flagella. In vitro fertilization is ineffective for Tbc1d21-/- sperm, although healthy offspring were obtained by intracytoplasmic sperm injection. Electron microscopy revealed aberrant ultrastructural changes in the mitochondrial sheath. Thirty-four Rab vectors were constructed followed by co-immunoprecipitation, which identified RAB13 as a novel TBC1D21 binding protein. Interestingly, infertility was not observed in Tbc1d21D125A R128K mice harboring the catalytic residue, suggesting that TBC1D21 is not a typical GAP for Rab-GTP hydrolysis. Moreover, TBC1D21 was expressed in the sperm mitochondrial sheath in Tbc1d21-3xFlag mice. Immunoprecipitation-mass spectrometry demonstrated the interactions of TBC1D21 with ACTB, TPM3, SPATA19, and VDAC3 to regulate the architecture of the sperm midpiece. The collective findings suggest that TBC1D21 is a scaffold protein required for the organization and stabilization of the mitochondrial sheath morphology.

TULP2 deletion mice exhibit abnormal outer dense fiber structure and male infertility

Purpose

Tulp2 (tubby-like protein 2) is a member of the tubby protein family and expressed predominantly in mouse testis. Recently, it was reported that Tulp2 knockout (KO) mice exhibited disrupted sperm tail morphology; however, it remains to be determined how TULP2 deletion causes abnormal tail formation.

Methods

The authors analyzed male fertility, sperm morphology, and motility of two Tulp2 KO mouse lines that were generated using the conventional method that utilizes homologous recombination in embryonic stem (ES) cells as well as the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) system. Furthermore, the authors observed the spermatogenesis of Tulp2 KO mice in more detail using scanning and transmission electron microscopy (SEM and TEM).

Results

Both mouse lines of Tulp2 KO exhibited male infertility, abnormal tail morphology, and impaired sperm motility. No overt abnormalities were found in the formation of the mitochondrial sheath in Tulp2 KO mice using the freeze-fracture method with SEM. In contrast, abnormal outer dense fiber (ODF) structure was observed in Tulp2 KO testis with TEM.

Conclusions

TULP2 may play roles in the correct formation and/or maintenance of ODF, which may lead to abnormal tail morphology, impaired sperm motility, and male infertility.

Kastor and Polluks polypeptides encoded by a single gene locus cooperatively regulate VDAC and spermatogenesis

Although several long noncoding RNAs (lncRNAs) have recently been shown to encode small polypeptides, those in testis remain largely uncharacterized. Here we identify two sperm-specific polypeptides, Kastor and Polluks, encoded by a single mouse locus (Gm9999) previously annotated as encoding a lncRNA. Both Kastor and Polluks are inserted in the outer mitochondrial membrane and directly interact with voltage-dependent anion channel (VDAC), despite their different amino acid sequences. Male VDAC3-deficient mice are infertile as a result of reduced sperm motility due to an abnormal mitochondrial sheath in spermatozoa, and deficiency of both Kastor and Polluks also severely impaired male fertility in association with formation of a similarly abnormal mitochondrial sheath. Spermatozoa lacking either Kastor or Polluks partially recapitulate the phenotype of those lacking both. Cooperative function of Kastor and Polluks in regulation of VDAC3 may thus be essential for mitochondrial sheath formation in spermatozoa and for male fertility.

A number of testes-specific lncRNAs have been annotated but their roles remain largely unexplored. Here the authors identify two small peptides encoded by the lncRNA Gm9999, Kastor and Polluks, both of which are required for male fertility in mice.

Mitochondrial regulation during male germ cell development

Mitochondria tailor their morphology to execute their specialized functions in different cell types and/or different environments. During spermatogenesis, mitochondria undergo continuous morphological and distributional changes with germ cell development. Deficiencies in these processes lead to mitochondrial dysfunction and abnormal spermatogenesis, thereby causing male infertility. In recent years, mitochondria have attracted considerable attention because of their unique role in the regulation of piRNA biogenesis in male germ cells. In this review, we describe the varied characters of mitochondria and focus on key mitochondrial factors that play pivotal roles in the regulation of spermatogenesis, from primordial germ cells to spermatozoa, especially concerning metabolic shift, stemness and reprogramming, mitochondrial transformation and rearrangement, and mitochondrial defects in human sperm. Further, we discuss the molecular mechanisms underlying these processes.

Molecular basis of the morphogenesis of sperm head and tail in mice

Background

The spermatozoon has a complex molecular apparatus necessary for fertilization in its head and flagellum. Recently, numerous genes that are needed to construct the molecular apparatus of spermatozoa have been identified through the analysis of genetically modified mice.

Methods

Based on the literature information, the molecular basis of the morphogenesis of sperm heads and flagella in mice was summarized.

Main findings (Results)

The molecular mechanisms of vesicular trafficking and intraflagellar transport in acrosome and flagellum formation were listed. With the development of cryo‐electron tomography and mass spectrometry techniques, the details of the axonemal structure are becoming clearer. The fine structure and the proteins needed to form the central apparatus, outer and inner dynein arms, nexin‐dynein regulatory complex, and radial spokes were described. The important components of the formation of the mitochondrial sheath, fibrous sheath, outer dense fiber, and the annulus were also described. The similarities and differences between sperm flagella and Chlamydomonas flagella/somatic cell cilia were also discussed.

Conclusion

The molecular mechanism of formation of the sperm head and flagellum has been clarified using the mouse as a model. These studies will help to better understand the diversity of sperm morphology and the causes of male infertility.

In-cell structures of conserved supramolecular protein arrays at the mitochondria-cytoskeleton interface in mammalian sperm

Spatial organization of mitochondria is vital for cellular function. In many specialized cell types, mitochondria are immobilized at specific subcellular loci through interactions with the cytoskeleton. One of the most striking mitochondrial configurations occurs in mammalian sperm, where mitochondria wrap around the flagellum. Malformation of the mitochondrial sheath causes infertility, but the molecular structures underlying this intricate arrangement are unknown. Here, we analyzed the mitochondrial sheath in sperm from three mammalian species. We find that although mitochondrial dimensions and cristae architecture vary across species, molecular assemblies mediating intermitochondria and mitochondria–cytoskeleton interactions are conserved. These findings yield important insight into sperm physiology and evolution and are relevant for other polarized cell types, such as muscles, neurons, photoreceptors, and hair cells.

Mitochondria–cytoskeleton interactions modulate cellular physiology by regulating mitochondrial transport, positioning, and immobilization. However, there is very little structural information defining mitochondria–cytoskeleton interfaces in any cell type. Here, we use cryofocused ion beam milling-enabled cryoelectron tomography to image mammalian sperm, where mitochondria wrap around the flagellar cytoskeleton. We find that mitochondria are tethered to their neighbors through intermitochondrial linkers and are anchored to the cytoskeleton through ordered arrays on the outer mitochondrial membrane. We use subtomogram averaging to resolve in-cell structures of these arrays from three mammalian species, revealing they are conserved across species despite variations in mitochondrial dimensions and cristae organization. We find that the arrays consist of boat-shaped particles anchored on a network of membrane pores whose arrangement and dimensions are consistent with voltage-dependent anion channels. Proteomics and in-cell cross-linking mass spectrometry suggest that the conserved arrays are composed of glycerol kinase-like proteins. Ordered supramolecular assemblies may serve to stabilize similar contact sites in other cell types in which mitochondria need to be immobilized in specific subcellular environments, such as in muscles and neurons.

FAM209 associates with DPY19L2, and is required for sperm acrosome biogenesis and fertility in mice

Infertility afflicts up to 15% of couples globally each year with men a contributing factor in 50% of these cases. Globozoospermia is a rare condition found in infertile men, which is characterized by defective acrosome biogenesis leading to the production of round-headed sperm. Here, we report that family with sequence similarity 209 (Fam209) is required for acrosome biogenesis in mouse sperm. FAM209 is a small transmembrane protein conserved among mammals. Loss of Fam209 results in fertility defects that are secondary to abnormalities in acrosome biogenesis during spermiogenesis, reminiscent of globozoospermia. Analysis of the FAM209 proteome identified DPY19L2, whose human orthologue is involved in the majority of globozoospermia cases. Although mutations in human and mouse Dpy19l2 have been shown to cause globozoospermia, no in vivo interacting partners of DPY19L2 have been identified until now. FAM209 colocalizes with DPY19L2 at the inner nuclear membrane to maintain the developing acrosome. Here, we identified FAM209 as the first interacting partner of DPY19L2, and the second protein that is essential for acrosome biogenesis that localizes to the inner nuclear membrane.

FAM71F1 binds to RAB2A and RAB2B and is essential for acrosome formation and male fertility in mice

The acrosome is a cap-shaped, Golgi-derived membranous organelle that is located over the anterior of the sperm nucleus and highly conserved throughout evolution. Although morphological changes during acrosome biogenesis in spermatogenesis have been well described, the molecular mechanism underlying this process is still largely unknown. Family with sequence similarity 71, member F1 and F2 (FAM71F1 and FAM71F2) are testis-enriched proteins that contain a RAB2B-binding domain, a small GTPase involved in vesicle transport and membrane trafficking. Here, by generating mutant mice for each gene, we found that Fam71f1 is essential for male fertility. In Fam71f1-mutant mice, the acrosome was abnormally expanded at the round spermatid stage, likely because of enhanced vesicle trafficking. Mass spectrometry analysis after immunoprecipitation indicated that, in testes, FAM71F1 binds not only RAB2B, but also RAB2A. Further study suggested that FAM71F1 binds to the GTP-bound active form of RAB2A/B, but not the inactive form. These results indicate that a complex of FAM71F1 and active RAB2A/B suppresses excessive vesicle trafficking during acrosome formation.

LRRC23 is a conserved component of the radial spoke that is necessary for sperm motility and male fertility in mice

Cilia and flagella are ancient structures that achieve controlled motor functions through the coordinated interaction based on microtubules and some attached projections. Radial spokes (RSs) facilitate the beating motion of these organelles by mediating signal transduction between dyneins and a central pair (CP) of singlet microtubules. RS complex isolation from Chlamydomonas axonemes enabled the detection of 23 radial spoke proteins (RSP1-RSP23), although the roles of some radial spoke proteins remain unknown. Recently, RSP15 has been reported to be bound to the stalk of RS2, but its homolog in mammals has not been identified. Herein, we show that Lrrc23 is an evolutionarily conserved testis-enriched gene encoding an RSP15 homolog in mice. We found that LRRC23 localizes to the RS complex within murine sperm flagella and interacts with RSPH3A and RSPH3B. The knockout of Lrrc23 resulted in male infertility due to RS disorganization and impaired motility in murine spermatozoa, whereas the ciliary beating was not significantly affected. These data indicate that LRRC23 is a key regulator that underpins the integrity of the RS complex within the flagella of mammalian spermatozoa, whereas it is dispensable in cilia. This article has an associated First Person interview with the first author of the paper.

SPATA33 localizes calcineurin to the mitochondria and regulates sperm motility in mice

Calcineurin is a target of immunosuppressive drugs such as cyclosporine A and tacrolimus. In the immune system, calcineurin interacts with NFAT via the PxIxIT motif to activate T cells. In contrast, little is known about the proteins that interact with a testis-enriched calcineurin that is essential for sperm motility and male fertility. Here, we discovered that calcineurin interacts with SPATA33 via a PQIIIT sequence in the testis. Further analyses reveal that SPATA33 plays critical roles in sperm motility and male fertility. Our finding sheds new light on the molecular mechanisms of sperm motility regulation and the etiology of human male fertility. Furthermore, it may help us not only understand reproductive toxicities but also develop nonhormonal male contraceptives.

Calcineurin is a calcium-dependent phosphatase that plays roles in a variety of biological processes including immune responses. In spermatozoa, there is a testis-enriched calcineurin composed of PPP3CC and PPP3R2 (sperm calcineurin) that is essential for sperm motility and male fertility. Because sperm calcineurin has been proposed as a target for reversible male contraceptives, identifying proteins that interact with sperm calcineurin widens the choice for developing specific inhibitors. Here, by screening the calcineurin-interacting PxIxIT consensus motif in silico and analyzing the function of candidate proteins through the generation of gene-modified mice, we discovered that SPATA33 interacts with sperm calcineurin via a PQIIIT sequence. Spata33 knockout mice exhibit reduced sperm motility because of an inflexible midpiece, leading to impaired male fertility, which phenocopies Ppp3cc and Ppp3r2 knockout mice. Further analysis reveals that sperm calcineurin disappears from the mitochondria in the Spata33 knockout testis. In addition, immunoprecipitation analysis indicates that sperm calcineurin interacts with not only SPATA33 but also the mitochondrial protein VDAC2. These results indicate that SPATA33 localizes calcineurin to the mitochondria and regulates sperm motility.

CRISPR/Cas9-based genetic screen of SCNT-reprogramming resistant genes identifies critical genes for male germ cell development in mice

Male germ cells undergo complex developmental processes eventually producing spermatozoa through spermatogenesis, although the molecular mechanisms remain largely elusive. We have previously identified somatic cell nuclear transfer-reprogramming resistant genes (SRRGs) that are highly enriched for genes essential for spermatogenesis, although many of them remain uncharacterized in knockout (KO) mice. Here, we performed a CRISPR-based genetic screen using C57BL/6N mice for five uncharacterized SRRGs (Cox8c, Cox7b2, Tuba3a/3b, Faiml, and Gm773), together with meiosis essential gene Majin as a control. RT-qPCR analysis of mouse adult tissues revealed that the five selected SRRGs were exclusively expressed in testis. Analysis of single-cell RNA-seq datasets of adult testis revealed stage-specific expression (pre-, mid-, or post-meiotic expression) in testicular germ cells. Examination of testis morphology, histology, and sperm functions in CRISPR-injected KO adult males revealed that Cox7b2, Gm773, and Tuba3a/3b are required for the production of normal spermatozoa. Specifically, Cox7b2 KO mice produced poorly motile infertile spermatozoa, Gm773 KO mice produced motile spermatozoa with limited zona penetration abilities, and Tuba3a/3b KO mice completely lost germ cells at the early postnatal stages. Our genetic screen focusing on SRRGs efficiently identified critical genes for male germ cell development in mice, which also provides insights into human reproductive medicine.

CRISPR/Cas9-mediated genome editing reveals 12 testis-enriched genes dispensable for male fertility in mice

Gene expression analyses suggest that more than 1000–2000 genes are expressed predominantly in mouse and human testes. Although functional analyses of hundreds of these genes have been performed, there are still many testis-enriched genes whose functions remain unexplored. Analyzing gene function using knockout (KO) mice is a powerful tool to discern if the gene of interest is essential for sperm formation, function, and male fertility in vivo. In this study, we generated KO mice for 12 testis-enriched genes, 1700057G04Rik, 4921539E11Rik, 4930558C23Rik, Cby2, Ldhal6b, Rasef, Slc25a2, Slc25a41, Smim8, Smim9, Tmem210, and Tomm20l, using the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) system. We designed two gRNAs for each gene to excise almost all the protein-coding regions to ensure that the deletions in these genes result in a null mutation. Mating tests of KO mice reveal that these 12 genes are not essential for male fertility, at least when individually ablated, and not together with other potentially compensatory paralogous genes. Our results could prevent other laboratories from expending duplicative effort generating KO mice, for which no apparent phenotype exists.