miRNA and piRNA localization in the male mammalian meiotic nucleus

Role of miRNAs in assisted reproductive technology

Cellular proteins and the mRNAs that encode them are key factors in oocyte and sperm development, and the mechanisms that regulate their translation and degradation play an important role during early embryogenesis. There is abundant evidence that expression of microRNAs (miRNAs) is crucial for embryo development and are highly involved in regulating translation during oocyte and early embryo development. MiRNAs are a group of short (18-24 nucleotides) non-coding RNA molecules that regulate post-transcriptional gene silencing. The miRNAs are secreted outside the cell by embryos during preimplantation embryo development. Understanding regulatory mechanisms involving miRNAs during gametogenesis and embryogenesis will provide insights into molecular pathways active during gamete formation and early embryo development. This review summarizes recent findings regarding multiple roles of miRNAs in molecular signaling, plus their transport during gametogenesis and embryo preimplantation.

Downregulation of miR-211 expression in the blood plasma of infertile men compared to the fertile controls

OBJECTIVES

Infertility is inability to conceive after 12 months of regular unprotected sex. MiRNA expression changes can serve as potential biomarkers for infertility in males due to impaired spermatogenesis. This research was conducted to measure the expression level of miR-211 in plasma samples as a factor identifying infertility in comparison with the control group.

METHODS

In this study, blood plasma were taken from the infertile men (n = 103) nonobstructive azoospermia (NOA) or severe oligozoospermia (SO) and the control group (n = 121). The expression of circulating miR-211 in plasma was assessed by qRT-PCR. A relative quantification strategy was adopted using the 2-ΔΔCT method to calculate the target miR-211 expression level in both study groups.

RESULTS

Plasma miR-211 levels were significantly lower in infertile men compared to the control group (0.544 ± 0.028 and 1.203 ± 0.035, respectively, p < 0.001). Pearson's correlation analysis showed that miR-211 expression level has a positive and significant correlation with sperm parameters, including sperm concentration, sperm total motility, progressive motility, and normal morphology (p < 0.001).

CONCLUSIONS

Decreased expression of miR-211 in blood plasma seems to be associated with male infertility. This experiment showed that miR-211 can be considered as a biomarker for evaluation, diagnosis, and confirmation of the results of semen analysis in male infertility.

Mouse Pxt1 expression is regulated by Mir6996 miRNA

Mouse Pxt1 gene is expressed exclusively in male germ cells and encodes for a small, cell death inducing protein. However, upon PXT1 interaction with BAG6, cell death is prevented. In transiently transfected cell lines the PXT1 expression triggered massive cell death, thus we ask the question whether the interaction of PXT1 and BAG6 is the only mechanism preventing normal, developing male germ cells from being killed by PXT1. The Pxt1 gene contains a long 3'UTR thus we have hypothesized that Pxt1 can be regulated by miRNA. We have applied Pxt1 knockout and used Pxt1 transgenic mice that overexpressed this gene to shed more light on Pxt1 regulation. Using the ELISA assay we have demonstrated that PXT1 protein is expressed in adult mouse testis, though at low abundance. The application of dual-Glo luciferase assay and the 3'UTR cloned into p-MIR-Glo plasmid showed that Pxt1 is regulated by miRNA. Combining the use of mirDB and the site-directed mutagenesis further demonstrated that Pxt1 translation is suppressed by Mir6996-3p. Considering previous reports and our current results we propose a model for Pxt1 regulation in the mouse male germ cells.

Circulating microRNAs as promising testicular translatable safety biomarkers: current state and future perspectives

Drug-induced testicular injury (DITI) is one of the often-observed and challenging safety issues seen during drug development. Semen analysis and circulating hormones currently utilized have significant gaps in their ability to detect testicular damage accurately. In addition, no biomarkers enable a mechanistic understanding of the damage to the different regions of the testis, such as seminiferous tubules, Sertoli, and Leydig cells. MicroRNAs (miRNAs) are a class of non-coding RNAs that modulate gene expression post-transcriptionally and have been indicated to regulate a wide range of biological pathways. Circulating miRNAs can be measured in the body fluids due to tissue-specific cell injury/damage or toxicant exposure. Therefore, these circulating miRNAs have become attractive and promising non-invasive biomarkers for assessing drug-induced testicular injury, with several reports on their use as safety biomarkers for monitoring testicular damage in preclinical species. Leveraging emerging tools such as 'organs-on-chips' that can emulate the human organ's physiological environment and function is starting to enable biomarker discovery, validation, and clinical translation for regulatory qualification and implementation in drug development.

Gum Acacia attenuates cisplatin toxic effect spermatogenesis dysfunction and infertility in rats

This study aimed to investigate the potential benefits Gum Arabic/Acacia Senegal (GA) in mitigating the harmful effects of cisplatin (CP) on spermatogenesis and testicular health in male adult rats. A total of forty albino rats were used in the study and divided into four groups; control, GA, CP, and Co-treated group, which received both CP and GA concurrently. The results revealed that CP caused a significant increase in oxidative stress and a decrease in antioxidant levels (CAT, SOD, and GSH), which disturbed the testicular machinery. This caused significant histological and ultrastructural damage to the testicular structure, including atrophied seminiferous tubules with severely reduced germinal epithelium. Additionally, CP caused a decrease in reproductive hormones (testosterone and LH), a decline in nucleic proliferation PCNA immunoexpression, and an increase in cytoplasmic apoptotic Caspase-3 protein expression in testicular tissue, when compared to the control and GA groups. Moreover, The CP treatment impaired spermatogenesis and decreased sperm number and motility with abnormal morphology. However, co-administration of GA with CP mitigated the dysfunction in spermatogenesis and reversed testicular damage caused by CP through significantly (P < 0.01) reducing oxidative stress (MDA) and increasing the activities of CAT, SOD, and GSH. Additionally, co-administration of GA elevated the levels of testosterone and luteinizing hormone in blood sera, significantly (P < 0.01) improved the histometric measurements of seminiferous tubules diameter, their epithelial height, Johnsen's score of spermatogenesis, 4-level histological grading scale Cosentino's score, immunohistochemical expression of nucleic PCNA, and cytoplasmic Caspase-3 proteins. Furthermore, TEM examination confirmed the synergistic effect of GA in restoring the germinal epithelial cells ultrastructure, the elongated and transverse sections of spermatozoa in the lumen, and the interstitial tissue. All of these effects resulted in a significant improvement in sperm quality in the Co-treated animals compared with the CP group, as well as, a significant decline in the morphological abnormalities of sperm in Co-treated rats compared to those in the CP group. GA is a valuable agent for ameliorating chemotherapy-related infertility.

Line graph attention networks for predicting disease-associated Piwi-interacting RNAs

PIWI proteins and Piwi-Interacting RNAs (piRNAs) are commonly detected in human cancers, especially in germline and somatic tissues, and correlate with poorer clinical outcomes, suggesting that they play a functional role in cancer. As the problem of combinatorial explosions between ncRNA and disease exposes gradually, new bioinformatics methods for large-scale identification and prioritization of potential associations are therefore of interest. However, in the real world, the network of interactions between molecules is enormously intricate and noisy, which poses a problem for efficient graph mining. Line graphs can extend many heterogeneous networks to replace dichotomous networks. In this study, we present a new graph neural network framework, line graph attention networks (LGAT). And we apply it to predict PiRNA disease association (GAPDA). In the experiment, GAPDA performs excellently in 5-fold cross-validation with an AUC of 0.9038. Not only that, it still has superior performance compared with methods based on collaborative filtering and attribute features. The experimental results show that GAPDA ensures the prospect of the graph neural network on such problems and can be an excellent supplement for future biomedical research.

miR-188-3p-targeted regulation of ATG7 affects cell autophagy in patients with nonobstructive azoospermia

BACKGROUND

Nonobstructive azoospermia (NOA) is one of the most difficult forms of male infertility to treat, and its pathogenesis is still unclear. miRNAs can regulate autophagy by affecting their target gene expression. Our previous study found that miR-188-3p expression in NOA patients was low. There are potential binding sites between the autophagy gene ATG7 and miR-188-3p. This study aimed to verify the binding site between miR-188-3p and ATG7 and whether miR-188-3p affects autophagy and participates in NOA by regulating ATG7 to influence the autophagy marker genes LC3 and Beclin-1.

METHODS

Testicular tissue from 16 NOA patients and 16 patients with normal spermatogenesis and 5 cases in each group of pathological sections were collected. High-throughput sequencing was performed to detect mRNA expression differences. Quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting, immunohistochemical staining and immunofluorescence were used to detect protein localization and expression. Autophagosome changes were detected by electron microscopy. The targeting relationship between miR-188-3p and ATG7 was confirmed by a luciferase assay.

RESULTS

ATG7 protein was localized in the cytoplasm of spermatogenic cells at all levels, and the ATG7 gene (p = 0.019) and protein (p = 0.000) were more highly expressed in the NOA group. ATG7 expression after overexpression/inhibition of miR-188-3p was significantly lower (p = 0.029)/higher (p = 0.021) than in the control group. After overexpression of miR-188-3p, the ATG7 3'UTR-WT luciferase activity was impeded (p = 0.004), while the ATG7 3'UTR-MUT luciferase activity showed no significant difference (p = 0.46). LC3 (p = 0.023) and Beclin-1 (p = 0.041) expression in the NOA group was significantly higher. LC3 and Beclin-1 gene expression after miR-188-3p overexpression/inhibition was significantly lower (p = 0.010 and 0.024, respectively) and higher (p = 0.024 and 0.049, respectively). LC3 punctate aggregation in the cytoplasm decreased after overexpression of miR-188-3p, while the LC3 punctate aggregation in the miR-188-3p inhibitor group was higher. The number of autophagosomes in the miR-188-3p mimic group was lower than the number of autophagosomes in the mimic NC group.

CONCLUSIONS

LC3 and Beclin-1 were more highly expressed in NOA testes and negatively correlated with the expression of miR-188-3p, suggesting that miR-188-3p may be involved in the process of autophagy in NOA. miR-188-3p may regulate its target gene ATG7 to participate in autophagy anDual luciferase experiment d affect the development of NOA.

Comparison of miRNA and mRNA Expression in Sika Deer Testes With Age

To elucidate the complex physiological process of testis development and spermatogenesis in Sika deer, this study evaluated the changes of miRNA and mRNA profiles in the four developmental stages of testis in the juvenile (1-year-old), adolescence (3-year-old), adult (5-year-old), and aged (10-year-old) stages. The results showed that a total of 198 mature, 66 novel miRNAs, and 23,558 differentially expressed (DE) unigenes were obtained; 14,918 (8,413 up and 6,505 down), 4,988 (2,453 up and 2,535 down), and 5,681 (2,929 up and 2,752 down) DE unigenes, as well as 88 (43 up and 45 down), 102 (44 up and 58 down), and 54 (18 up and 36 down) DE miRNAs were identified in 3- vs. 1-, 5- vs. 3-, and 10- vs. 5-year-old testes, respectively. By integrating miRNA and mRNA expression profiles, we predicted 10,790 mRNA-mRNA and 69,883 miRNA-mRNA interaction sites. The target genes were enriched by GO and KEGG pathways to obtain DE mRNA (IGF1R, ALKBH5, Piwil, HIF1A, BRDT, etc.) and DE miRNA (miR-140, miR-145, miR-7, miR-26a, etc.), which play an important role in testis development and spermatogenesis. The data show that DE miRNAs could regulate testis developmental and spermatogenesis through signaling pathways, including the MAPK signaling pathway, p53 signaling pathway, PI3K-Akt signaling pathway, Hippo signaling pathway, etc. miR-140 was confirmed to directly target mutant IGF1R-3'UTR by the Luciferase reporter assays. This study provides a useful resource for future studies on the role of miRNA regulation in testis development and spermatogenesis.

Phosphoproteomics of ATR signaling in mouse testes

The phosphatidylinositol 3' kinase (PI3K)-related kinase ATR is crucial for mammalian meiosis. ATR promotes meiotic progression by coordinating key events in DNA repair, meiotic sex chromosome inactivation (MSCI), and checkpoint-dependent quality control during meiotic prophase I. Despite its central roles in meiosis, the ATR-dependent meiotic signaling network remains largely unknown. Here, we used phosphoproteomics to define ATR signaling events in testes from mice following chemical and genetic ablation of ATR signaling. Quantitative analysis of phosphoproteomes obtained after germ cell-specific genetic ablation of the ATR activating 9-1-1 complex or treatment with ATR inhibitor identified over 14,000 phosphorylation sites from testes samples, of which 401 phosphorylation sites were found to be dependent on both the 9-1-1 complex and ATR. Our analyses identified ATR-dependent phosphorylation events in crucial DNA damage signaling and DNA repair proteins including TOPBP1, SMC3, MDC1, RAD50, and SLX4. Importantly, we identified ATR and RAD1-dependent phosphorylation events in proteins involved in mRNA regulatory processes, including SETX and RANBP3, whose localization to the sex body was lost upon ATR inhibition. In addition to identifying the expected ATR-targeted S/T-Q motif, we identified enrichment of an S/T-P-X-K motif in the set of ATR-dependent events, suggesting that ATR promotes signaling via proline-directed kinase(s) during meiosis. Indeed, we found that ATR signaling is important for the proper localization of CDK2 in spermatocytes. Overall, our analysis establishes a map of ATR signaling in mouse testes and highlights potential meiotic-specific actions of ATR during prophase I progression.

Non-coding RNAs and chromatin: key epigenetic factors from spermatogenesis to transgenerational inheritance

Cellular fate and gene expression patterns are modulated by different epigenetic factors including non-coding RNAs (ncRNAs) and chromatin organization. Both factors are dynamic throughout male germ cell differentiation on the seminiferous tubule, despite the transcriptional inactivation in the last stages of spermatogenesis. Sperm maturation during the caput-to-cauda transit on the epididymis involves changes in chromatin organization and the soma-to-germ line transference of ncRNAs that are essential to obtain a functional sperm for fertilization and embryo development. Here, the male environment (diseases, drugs, mental stress) is crucial to modulate these epigenetic factors throughout sperm maturation, affecting the corresponding offspring. Paternal transgenerational inheritance has been directly related to sperm epigenetic changes, most of them associated with variations in the ncRNA content and chromatin marks. Our aim is to give an overview about how epigenetics, focused on ncRNAs and chromatin, is pivotal to understand spermatogenesis and sperm maturation, and how the male environment impacts the sperm epigenome modulating the offspring gene expression pattern.

Novel localizations and interactions of intercellular bridge proteins revealed by proteomic profiling†

Intercellular bridges (ICBs) connecting germ cells are essential for spermatogenesis, and their deletion causes male infertility. However, the functions and component factors of ICBs are still unknown. We previously identified novel ICB-associated proteins by proteomics analysis using ICB enrichment. Here, we performed immunoprecipitation-proteomics analyses using antibodies specific to known ICB proteins MKLP1, RBM44, and ectoplasmic specialization-associated protein KIAA1210 and predicted protein complexes in the ICB cores. KIAA1210, its binding protein topoisomerase2B (TOP2B), and tight junction protein ZO1 were identified as novel ICB proteins. On the other hand, as well as KIAA1210 and TOP2B, MKLP1 and RBM44, but not TEX14, were localized at the XY body of spermatocytes, suggesting that there is a relationship between ICB proteins and meiotic chromosomes. Moreover, small RNAs interacted with an ICB protein complex that included KIAA1210, RBM44, and MKLP1. These results indicate dynamic movements of ICB proteins and suggest that ICB proteins could be involved not only in the communication between germ cells but also in their epigenetic regulation. Our results provide a novel perspective on the function of ICBs and could be helpful in revealing the biological function of the ICB.

Using miRNAs as diagnostic biomarkers for male infertility: opportunities and challenges

The non-coding genome has been extensively studied for its role in human development and diseases. MicroRNAs (miRNAs) are small non-coding RNAs, which can regulate the expression of hundreds of genes at the post-transcriptional level. Therefore, any defects in miRNA biogenesis or processing can affect the genes and have been linked to several diseases. Male infertility is a clinical disorder with a significant number of cases being idiopathic. Problems in spermatogenesis and epididymal maturation, testicular development, sperm maturation or migration contribute to male infertility, and many of these idiopathic cases are related to issues with the miRNAs which tightly regulate these processes. This review summarizes the recent research on various such miRNAs and puts together the candidate miRNAs that may be used as biomarkers for diagnosis. The development of strategies for male infertility treatment using anti-miRs or miRNA mimics is also discussed. Although promising, the development of miRNA diagnostics and therapeutics is challenging, and ways to overcome some of these challenges are also reviewed.

The mechanisms and functions of microRNAs in mediating the fate determinations of human spermatogonial stem cells and Sertoli cells

Human spermatogonial stem cells (SSCs) and Sertoli cells might have the applications in reproduction and regenerative medicine. Abnormal spermatogenesis results in male infertility, which seriously affects human reproduction and health. Spermatogenesis depends on the epigenetic and genetic regulation of male germ cells and somatic cells. A number of microRNAs (miRNAs) have been identified in human testicular tissues, and they are closely related to male fertility. Significantly, we and peers have recently demonstrated that numerous miRNAs are essential for regulating the self-renewal and apoptosis of human SSCs and Sertoli cells through controlling their mRNA and lncRNA targets. In this review, we critically discuss these findings regarding the important functions and mechanisms of miRNAs in mediating the fate determinations of human SSCs and Sertoli cells. Meanwhile, we illustrate the regulatory networks for miRNAs by forming the upstream and downstream regulators of mRNAs and lncRNAs in human SSCs, and we address that miRNAs regulate the decisions of Sertoli cells by targeting genes and via N6-methyladenosine (m6A). We also point out the future directions for further studies on this field. This review could offer an update on novel molecular targets for treating male infertility and new insights into epigenetic regulation of human spermatogenesis.

Histone Post-Translational Modifications and CircRNAs in Mouse and Human Spermatozoa: Potential Epigenetic Marks to Assess Human Sperm Quality

Spermatozoa (SPZ) are motile cells, characterized by a cargo of epigenetic information including histone post-translational modifications (histone PTMs) and non-coding RNAs. Specific histone PTMs are present in developing germ cells, with a key role in spermatogenic events such as self-renewal and commitment of spermatogonia (SPG), meiotic recombination, nuclear condensation in spermatids (SPT). Nuclear condensation is related to chromatin remodeling events and requires a massive histone-to-protamine exchange. After this event a small percentage of chromatin is condensed by histones and SPZ contain nucleoprotamines and a small fraction of nucleohistone chromatin carrying a landascape of histone PTMs. Circular RNAs (circRNAs), a new class of non-coding RNAs, characterized by a nonlinear back-spliced junction, able to play as microRNA (miRNA) sponges, protein scaffolds and translation templates, have been recently characterized in both human and mouse SPZ. Since their abundance in eukaryote tissues, it is challenging to deepen their biological function, especially in the field of reproduction. Here we review the critical role of histone PTMs in male germ cells and the profile of circRNAs in mouse and human SPZ. Furthermore, we discuss their suggested role as novel epigenetic biomarkers to assess sperm quality and improve artificial insemination procedure.

Synaptonemal Complex-Deficient Drosophila melanogaster Females Exhibit Rare DSB Repair Events, Recurrent Copy-Number Variation, and an Increased Rate of de Novo Transposable Element Movement

Genetic stability depends on the maintenance of a variety of chromosome structures and the precise repair of DNA breaks. During meiosis, programmed double-strand breaks (DSBs) made in prophase I are normally repaired as gene conversions or crossovers. DSBs can also be made by other mechanisms, such as the movement of transposable elements (TEs), which must also be resolved. Incorrect repair of these DNA lesions can lead to mutations, copy-number changes, translocations, and/or aneuploid gametes. In Drosophila melanogaster, as in most organisms, meiotic DSB repair occurs in the presence of a rapidly evolving multiprotein structure called the synaptonemal complex (SC). Here, whole-genome sequencing is used to investigate the fate of meiotic DSBs in D. melanogaster mutant females lacking functional SC, to assay for de novo CNV formation, and to examine the role of the SC in transposable element movement in flies. The data indicate that, in the absence of SC, copy-number variation still occurs and meiotic DSB repair by gene conversion occurs infrequently. Remarkably, an 856-kilobase de novo CNV was observed in two unrelated individuals of different genetic backgrounds and was identical to a CNV recovered in a previous wild-type study, suggesting that recurrent formation of large CNVs occurs in Drosophila. In addition, the rate of novel TE insertion was markedly higher than wild type in one of two SC mutants tested, suggesting that SC proteins may contribute to the regulation of TE movement and insertion in the genome. Overall, this study provides novel insight into the role that the SC plays in genome stability and provides clues as to why the sequence, but not structure, of SC proteins is rapidly evolving.

Computational Resources for Prediction and Analysis of Functional miRNA and Their Targetome

microRNAs are evolutionarily conserved, endogenously produced, noncoding RNAs (ncRNAs) of approximately 19-24 nucleotides (nts) in length known to exhibit gene silencing of complementary target sequence. Their deregulated expression is reported in various disease conditions and thus has therapeutic implications. In the last decade, various computational resources are published in this field. In this chapter, we have reviewed bioinformatics resources, i.e., miRNA-centered databases, algorithms, and tools to predict miRNA targets. First section has enlisted more than 75 databases, which mainly covers information regarding miRNA registries, targets, disease associations, differential expression, interactions with other noncoding RNAs, and all-in-one resources. In the algorithms section, we have compiled about 140 algorithms from eight subcategories, viz. for the prediction of precursor (pre-) and mature miRNAs. These algorithms are developed on various sequence, structure, and thermodynamic based features incorporated into different machine learning techniques (MLTs). In addition, computational identification of miRNAs from high-throughput next generation sequencing (NGS) data and their variants, viz. isomiRs, differential expression, miR-SNPs, and functional annotation, are discussed. Prediction and analysis of miRNAs and their associated targets are also evaluated under miR-targets section providing knowledge regarding novel miRNA targets and complex host-pathogen interactions. In conclusion, we have provided comprehensive review of in silico resources published in miRNA research to help scientific community be updated and choose the appropriate tool according to their needs.

Evolution and meiotic organization of heteromorphic sex chromosomes

The evolution of heteromorphic sex chromosomes has occurred independently many times in different lineages. The differentiation of sex chromosomes leads to dramatic changes in sequence composition and function and guides the evolutionary trajectory and utilization of genes in pivotal sex determination and reproduction roles. In addition, meiotic recombination and pairing mechanisms are key in orchestrating the resultant impact, retention and maintenance of heteromorphic sex chromosomes, as the resulting exposure of unpaired DNA at meiosis triggers ancient repair and checkpoint pathways. In this review, we summarize the different ways in which sex chromosome systems are organized at meiosis, how pairing is affected, and differences in unpaired DNA responses. We hypothesize that lineage specific differences in meiotic organization is not only a consequence of sex chromosome evolution, but that the establishment of epigenetic changes on sex chromosomes contributes toward their evolutionary conservation.

Roles of microRNAs in mammalian reproduction: from the commitment of germ cells to peri-implantation embryos

MicroRNAs (miRNAs) are active regulators of numerous biological and physiological processes including most of the events of mammalian reproduction. Understanding the biological functions of miRNAs in the context of mammalian reproduction will allow a better and comparative understanding of fertility and sterility in male and female mammals. Herein, we summarize recent progress in miRNA‐mediated regulation of mammalian reproduction and highlight the significance of miRNAs in different aspects of mammalian reproduction including the biogenesis of germ cells, the functionality of reproductive organs, and the development of early embryos. Furthermore, we focus on the gene expression regulatory feedback loops involving hormones and miRNA expression to increase our understanding of germ cell commitment and the functioning of reproductive organs. Finally, we discuss the influence of miRNAs on male and female reproductive failure, and provide perspectives for future studies on this topic.

miR‐31 Regulates Spermatogonial Stem Cells Meiosis via Targeting Stra8

Stra8 (stimulated by retinoic acid gene 8) is a specific gene that is expressed in mammalian germ cells during transition from mitosis to meiosis and plays a key role in the initiation of meiosis in mammals and birds. So, the evaluation of the Stra8 pathway in cSSCs may provide a deeper insight into mammalian spermatogenesis. miRNA was also an important regulating factor for meiosis of SSCs. However, there is currently no data indicating that miRNA regulate the meiosis of SSCs via Stra8. Here, we predicted the prospective miRNA targeting to Stra8 using the online Bioinformatics database‐Targetscan, and performed an analysis of the dual‐luciferase recombinant vector, pGL3‐CMV‐LUC‐MCS‐Stra8‐3′UTR. miR‐31 mimics (miR‐31m), miR‐31 inhibitors (miR‐31i), Control (NC, scrambled oligonucleotides transfection) were transfected into cSSCs; Stra8 and miRNA were analyzed by RT‐qPCR, immunofluorescence, and Western blot. The detection of haploid was conducted by flow cytometry. The results showed that miR‐31 regulates meiosis of cSSCs via targeting Stra8 in vitro and in vivo. Our study identifies a new regulatory pathway that miR‐31 targets Stra8 and inhibits spermatogenesis. J. Cell. Biochem. 118: 4844–4853, 2017. © 2017 Wiley Periodicals, Inc.

miRNAs, Melanoma and Microenvironment: An Intricate Network

miRNAs are central players in cancer biology and they play a pivotal role in mediating the network communication between tumor cells and their microenvironment. In melanoma, miRNAs can impair or facilitate a wide array of processes, and here we will focus on: the epithelial to mesenchymal transition (EMT), the immune milieu, and metabolism. Multiple miRNAs can affect the EMT process, even at a distance, for example through exosome-mediated mechanisms. miRNAs also strongly act on some components of the immune system, regulating the activity of key elements such as antigen presenting cells, and can facilitate an immune evasive/suppressive phenotype. miRNAs are also involved in the regulation of metabolic processes, specifically in response to hypoxic stimuli where they can mediate the metabolic switch from an oxidative to a glycolytic metabolism. Overall, this review discusses and summarizes recent findings on miRNA regulation in the melanoma tumor microenvironment, analyzing their potential diagnostic and therapeutic applications.

The roles of microRNAs and siRNAs in mammalian spermatogenesis

MicroRNAs and siRNAs, both of which are AGO-bound small RNAs, are essential for mammalian spermatogenesis. Although their precise germline roles remain largely uncharacterized, recent discoveries suggest that they function in mechanisms beyond microRNA-mediated post-transcriptional control, playing roles in DNA repair and transcriptional regulation within the nucleus. Here, we discuss the latest findings regarding roles for AGO proteins and their associated small RNAs in the male germline. We integrate genetic, clinical and genomics data, and draw upon findings from non-mammalian models, to examine potential roles for AGO-bound small RNAs during spermatogenesis. Finally, we evaluate the emerging and differing roles for AGOs and AGO-bound small RNAs in the male and female germlines, suggesting potential reasons for these sexual dimorphisms.

Summary: This Review article summarizes the latest findings regarding roles for AGO proteins and their associated small RNAs in the male germline, with a particular focus on spermatogenesis.

MicroRNA-202 maintains spermatogonial stem cells by inhibiting cell cycle regulators and RNA binding proteins

miRNAs play important roles during mammalian spermatogenesis. However, the function of most miRNAs in spermatogenesis and the underlying mechanisms remain unknown. Here, we report that miR-202 is highly expressed in mouse spermatogonial stem cells (SSCs), and is oppositely regulated by Glial cell-Derived Neurotrophic Factor (GDNF) and retinoic acid (RA), two key factors for SSC self-renewal and differentiation. We used inducible CRISPR-Cas9 to knockout miR-202 in cultured SSCs, and found that the knockout SSCs initiated premature differentiation accompanied by reduced stem cell activity and increased mitosis and apoptosis. Target genes were identified with iTRAQ-based proteomic analysis and RNA sequencing, and are enriched with cell cycle regulators and RNA-binding proteins. Rbfox2 and Cpeb1 were found to be direct targets of miR-202 and Rbfox2 but not Cpeb1, is essential for the differentiation of SSCs into meiotic cells. Accordingly, an SSC fate-regulatory network composed of signaling molecules of GDNF and RA, miR-202 and diverse downstream effectors has been identified.

Expression of microRNA in male reproductive tissues and their role in male fertility

MicroRNA (miRNA) are small non-coding RNA, approximately 22 nucleotides in length, that regulate gene expression through their ability to bind to mRNA. The role of miRNA in cellular and tissue development is well documented and their importance in male reproductive tissue development is actively being evaluated. They are present in spermatogonia, Sertoli and Leydig cells within the testis and are present in mature spermatozoa, indicating roles in normal testicular development, function and spermatogenesis. Their presence in spermatozoa has led to postulations about the roles of male miRNA during early embryonic development after fertilisation, including chromatin restructuring and possible epigenetic effects on embryo development. MiRNAs are also present in body fluids, such as blood serum, milk, ovarian follicular fluid and seminal fluid. Circulating miRNAs are stable, and aberrant expression of cellular or extracellular miRNA has been associated with multiple pathophysiological conditions, the most studied being numerous forms of cancer. Considering that miRNAs are present in spermatozoa and in seminal fluid, their stability and the relatively non-invasive procedures required to obtain these samples make miRNAs excellent candidates for use as biomarkers of male reproduction and fertility. Biomarkers, such as miRNAs, identifying fertile males would be of financial interest to the animal production industry.

Reduced microRNA-188-3p expression contributes to apoptosis of spermatogenic cells in patients with azoospermia

BACKGROUND AND AIMS

Human mutL homologl (MLH1) works coordinately in sequential steps to initiate repair of DNA mismatches, and aberrant MLH1 expression is related to spermatogenetic malfunction. In the present study, MLH1 expression in patients with azoospermia was investigated, and moderating effects of miR-188-3p on MLH1 expression and spermatogenesis were identified.

METHODS

Testicular tissues from 16 patients with obstructive azoospermia (OA) and non-obstructive azoospermia (NOA), and tissues of eight healthy patients were collected. Real-time PCR, Western blotting and immunohistochemical staining were used to detect MLH1 expression. Chromatin immunoprecipitation assay and luciferase reporter assay were performed to evaluate histone acetylation level of miR-188-3p and relationships between miR-188-3p and MLH1.

RESULTS

Testicular MLH1 expression at mRNA and protein levels was significantly increased, while miR-188-3p expression was lower in patients with OA and NOA than that in controls. Reduced histone acetylation level of miR-188-3p promoter was observed in patients with azoospermia. Overexpression/inhibition of HDAC1, but not HDAC2, contributed to the significant reduction/increase of miR-188-3p expression. miR-188-3p targeted 3' UTR of MLH1 and regulated MLH1 expression. miR-188-3p inhibitor led to elevation of apoptotic level of spermatogenic cells in mice, while this effect was reversed by si-MLH1.

CONCLUSION

Down-regulation of miR-188-3p by reducing histone acetylation up-regulated MLH1 expression and contributed to promotion of apoptosis in spermatogenic cells, in patients with azoospermia.

Clinical potential of oligonucleotide-based therapeutics in the respiratory system

The discovery of an ever-expanding plethora of coding and non-coding RNAs with nodal and causal roles in the regulation of lung physiology and disease is reinvigorating interest in the clinical utility of the oligonucleotide therapeutic class. This is strongly supported through recent advances in nucleic acids chemistry, synthetic oligonucleotide delivery and viral gene therapy that have succeeded in bringing to market at least three nucleic acid-based drugs. As a consequence, multiple new candidates such as RNA interference modulators, antisense, and splice switching compounds are now progressing through clinical evaluation. Here, manipulation of RNA for the treatment of lung disease is explored, with emphasis on robust pharmacological evidence aligned to the five pillars of drug development: exposure to the appropriate tissue, binding to the desired molecular target, evidence of the expected mode of action, activity in the relevant patient population and commercially viable value proposition.

Intracellular and extracellular microRNA: An update on localization and biological role

MicroRNA (miRNA) is a class of small non-coding RNAs which mediate post-transcriptional gene silencing (PTGS) by sequence-specific inhibition of target mRNAs translation and/or lowering their half-lives in the cytoplasm. Together with their binding partners, Argonaute (AGO) proteins, miRNAs form cores of RNA-induced silencing complexes (RISC). Despite a substantial progress in understanding RISC structure, until recently little was known about its localization in the cell. This review is aimed to provide an overview of the emerging picture of miRNA and RISC localization and function both in the intracellular space and outside of the cell. In contrast to the common assumption that PTGS occurs in the cytoplasm, it was found to operate mainly on the membranes of the endoplasmic reticulum (ER). Besides ER membranes miRNAs were found in all main cellular compartments including nucleus, nucleolus and mitochondria where they regulate various processes including transcription, translation, alternative splicing and DNA repair. Moreover, a certain pool of miRNAs may not be associated with RISC and carry completely different functions. Finally, the discovery of cell-free miRNAs in all biological fluids suggests that miRNAs might also act as signaling molecules outside the cell, and may be utilized as biomarkers for a variety of diseases. In this review we discuss miRNA secretion mechanisms and possible pathways of cell-cell communication via miRNA-containing exosomes in vivo.

The Whereabouts of microRNA Actions: Cytoplasm and Beyond

MicroRNAs (miRNAs) are a conserved class of approximately 22 nucleotide (nt) short noncoding RNAs that normally silence gene expression via translational repression and/or degradation of targeted mRNAs in plants and animals. Identifying the whereabouts of miRNAs potentially informs miRNA functions, some of which are perhaps specialized to specific cellular compartments. In this review, the significance of miRNA localizations in the cytoplasm, including those at RNA granules and endomembranes, and the export of miRNAs to extracellular space will be discussed. How miRNA localizations and functions are regulated by protein modifications on the core miRNA-binding protein Argonaute (AGO) during normal and stress conditions will be explored, and in conclusion new AGO partners, non-AGO miRNA-binding proteins, and the emergent understanding of miRNAs found in the nucleoplasm, nucleoli, and mitochondria will be discussed.

Genome-wide differential expression of genes and small RNAs in testis of two different porcine breeds and at two different ages

Some documented evidences proved small RNAs (sRNA) and targeted genes are involved in mammalian testicular development and spermatogenesis. However, the detailed molecular regulation mechanisms of them remain largely unknown so far. In this study, we obtained a total of 10,716 mRNAs, 67 miRNAs and 16,953 piRNAs which were differentially expressed between LC and LW pig breeds or between the two sexual maturity stages. Of which, we identified 16 miRNAs and 28 targeted genes possibly related to spermatogenesis; 14 miRNA and 18 targeted genes probably associated with cell adhesion related testis development. We also annotated 579 piRNAs which could potentially regulate cell death, nucleosome organization and other basic biology process, which implied that those piRNAs might be involved in sexual maturation difference. The integrated network analysis results suggested that some differentially expressed genes were involved in spermatogenesis through the ECM-receptor interaction, focal adhesion, Wnt and PI3K-Akt signaling pathways, some particular miRNAs have the negative regulation roles and some special piRNAs have the positive and negative regulation roles in testicular development. Our data provide novel insights into the molecular expression and regulation similarities and diversities of spermatogenesis and testicular development in different pig breeds at different stages of sexual maturity.

The enigmatic meiotic dense body and its newly discovered component, SCML1, are dispensable for fertility and gametogenesis in mice

Meiosis is a critical phase in the life cycle of sexually reproducing organisms. Chromosome numbers are halved during meiosis, which requires meiosis-specific modification of chromosome behaviour. Furthermore, suppression of transposons is particularly important during meiosis to allow the transmission of undamaged genomic information between generations. Correspondingly, specialized genome defence mechanisms and nuclear structures characterize the germ line during meiosis. Survival of mammalian spermatocytes requires that the sex chromosomes form a distinct silenced chromatin domain, called the sex body. An enigmatic spherical DNA-negative structure, called the meiotic dense body, forms in association with the sex body. The dense body contains small non-coding RNAs including microRNAs and PIWI-associated RNAs. These observations gave rise to speculations that the dense body may be involved in sex body formation and or small non-coding RNA functions, e.g. the silencing of transposons. Nevertheless, the function of the dense body has remained mysterious because no protein essential for dense body formation has been reported yet. We discovered that the polycomb-related sex comb on midleg-like 1 (SCML1) is a meiosis-specific protein and is an essential component of the meiotic dense body. Despite abolished dense body formation, Scml1-deficient mice are fertile and proficient in sex body formation, transposon silencing and in timely progression through meiosis and gametogenesis. Thus, we conclude that dense body formation is not an essential component of the gametogenetic program in the mammalian germ line.

Non-coding RNA in Spermatogenesis and Epididymal Maturation

Testicular germ and somatic cells express many classes of small ncRNAs, including Dicer-independent PIWI-interacting RNAs, Dicer-dependent miRNAs, and endogenous small interfering RNA. Several studies have identified ncRNAs that are highly, exclusively, or preferentially expressed in the testis and epididymis in specific germ and somatic cell types. Temporal and spatial expression of proteins is a key requirement of successful spermatogenesis and large-scale gene transcription occurs in two key stages, just prior to transcriptional quiescence in meiosis and then during spermiogenesis just prior to nuclear silencing in elongating spermatids. More than 60 % of these transcripts are then stockpiled for subsequent translation. In this capacity ncRNAs may act to interpret and transduce cellular signals to either maintain the undifferentiated stem cell population and/or drive cell differentiation during spermatogenesis and epididymal maturation. The assignation of specific roles to the majority of ncRNA species implicated as having a role in spermatogenesis and epididymal function will underpin fundamental understanding of normal and disease states in humans such as infertility and the development of germ cell tumours.

Retracted article: In vitro derivation of mammalian germ cells from stem cells and their potential therapeutic application

Pluripotent stem cells (PSCs) are a unique type of cells because they exhibit the characteristics of self-renewal and pluripotency. PSCs may be induced to differentiate into any cell type, even male and female germ cells, suggesting their potential as novel cell-based therapeutic treatment for infertility problems. Spermatogenesis is an intricate biological process that starts from self-renewal of spermatogonial stem cells (SSCs) and leads to differentiated haploid spermatozoa. Errors at any stage in spermatogenesis may result in male infertility. During the past decade, much progress has been made in the derivation of male germ cells from various types of progenitor stem cells. Currently, there are two main approaches for the derivation of functional germ cells from PSCs, either the induction of in vitro differentiation to produce haploid cell products, or combination of in vitro differentiation and in vivo transplantation. The production of mature and fertile spermatozoa from stem cells might provide an unlimited source of autologous gametes for treatment of male infertility. Here, we discuss the current state of the art regarding the differentiation potential of SSCs, embryonic stem cells, and induced pluripotent stem cells to produce functional male germ cells. We also discuss the possible use of livestock-derived PSCs as a novel option for animal reproduction and infertility treatment.

Escape of X-linked miRNA genes from meiotic sex chromosome inactivation

Past studies have indicated that transcription of all X-linked genes is repressed by meiotic sex chromosome inactivation (MSCI) during the meiotic phase of spermatogenesis in mammals. However, more recent studies have shown an increase in steady-state levels of certain X-linked miRNAs in pachytene spermatocytes, suggesting that either synthesis of these miRNAs increases or that degradation of these miRNAs decreases dramatically in these cells. To distinguish between these possibilities, we performed RNA-FISH to detect nascent transcripts from multiple miRNA genes in various spermatogenic cell types. Our results show definitively that Type I X-linked miRNA genes are subject to MSCI, as are all or most X-linked mRNA genes, whereas Type II and III X-linked miRNA genes escape MSCI by continuing ongoing, active transcription in primary spermatocytes. We corroborated these results by co-localization of RNA-FISH signals with both a corresponding DNA-FISH signal and an immunofluorescence signal for RNA polymerase II. We also found that X-linked miRNA genes that escape MSCI locate non-randomly to the periphery of the XY body, whereas genes that are subject to MSCI remain located within the XY body in pachytene spermatocytes, suggesting that the mechanism of escape of X-linked miRNA genes from MSCI involves their relocation to a position outside of the repressive chromatin domain associated with the XY body. The fact that Type II and III X-linked miRNA genes escape MSCI suggests an immediacy of function of the encoded miRNAs specifically required during the meiotic stages of spermatogenesis.

Small RNA Detection by in Situ Hybridization Methods

Small noncoding RNAs perform multiple regulatory functions in cells, and their exogenous mimics are widely used in research and experimental therapies to interfere with target gene expression. MicroRNAs (miRNAs) are the most thoroughly investigated representatives of the small RNA family, which includes short interfering RNAs (siRNAs), PIWI-associated RNA (piRNAs), and others. Numerous methods have been adopted for the detection and characterization of small RNAs, which is challenging due to their short length and low level of expression. These include molecular biology methods such as real-time RT-PCR, northern blotting, hybridization to microarrays, cloning and sequencing, as well as single cell miRNA detection by microscopy with in situ hybridization (ISH). In this review, we focus on the ISH method, including its fluorescent version (FISH), and we present recent methodological advances that facilitated its successful adaptation for small RNA detection. We discuss relevant technical aspects as well as the advantages and limitations of ISH. We also refer to numerous applications of small RNA ISH in basic research and molecular diagnostics.

Role of microRNAs in mammalian spermatogenesis and testicular germ cell tumors

microRNAs (miRNAs) are a class of small endogenous RNAs, 19–25 nucleotides in size, which play a role in the regulation of gene expression at transcriptional and post-transcriptional levels. Spermatogenesis is a complex process through which spermatogonial stem cells (SSCs) proliferate and differentiate into mature spermatozoa. A large number of miRNAs are abundantly expressed in spermatogenic cells. Growing evidence supports the essential role of miRNA regulation in normal spermatogenesis and male fertility and cumulative research has shown that this form of regulation contributes to the etiology of testicular germ cell tumors (TGCTs). In this review, we addressed recent advancements of miRNA expression profiles in testis and focused on the regulatory functions of miRNA in the process of SSC renewal, spermatogonial mitosis, spermatocyte meiosis, spermiogenesis, and the occurrence of TGCTs.

microRNA in Human Reproduction

microRNAs constitute a large family of approximately 21-nucleotide-long, noncoding RNAs. They emerged more than 20 years ago as key posttranscriptional regulators of gene expression. The regulatory role of these small RNA molecules has recently begun to be explored in the human reproductive system. microRNAs have been shown to play an important role in control of reproductive functions, especially in the processes of oocyte maturation, folliculogenesis, corpus luteum function, implantation, and early embryonic development. Knockout of Dicer, the cytoplasmic enzyme that cleaves the pre-miRNA to its mature form, results in postimplantation embryonic lethality in several animal models, attributing to these small RNA vital functions in reproduction and development. Another intriguing characteristic of microRNAs is their presence in body fluids in a remarkably stable form that is protected from endogenous RNase activity. In this chapter we will describe the current knowledge on microRNAs, specifically relating to human gonadal cells. We will focus on their role in the ovarian physiologic process and ovulation dysfunction, regulation of spermatogenesis and male fertility, and putative involvement in human normal and aberrant trophoblast differentiation and invasion through the process of placentation.

Small RNAs: Their Possible Roles in Reproductive Failure

Posttranscriptional gene regulation is a regulatory mechanism which occurs "above the genome" and confers different phenotypes and functions within a cell. Transcript and protein abundance above the level of transcription can be regulated via noncoding ribonucleic acid (ncRNA) molecules, which potentially play substantial roles in the regulation of reproductive function. MicroRNA (miRNA), endogenous small interfering RNA (endo-siRNA), and PIWI-interacting RNA (piRNA) are three primary classes of small ncRNA. Similarities and distinctions between their biogenesis and in the interacting protein machinery that facilitate their function distinguish these three classes. Characterization of the expression and importance of the critical components for the biogenesis of each class in different tissues contributes a clearer understanding of their contributions in specific reproductive tissues and their ability to influence fertility in both males and females. This chapter discusses the expression and potential roles of miRNA, endo-siRNA, and piRNA in the regulation of reproductive function. Additionally, this chapter elaborates on investigations aimed to address and characterize specific mechanisms through which miRNA may influence infertility and the use of miRNA as biomarkers associated with several reproductive calamities such as defective spermatogenesis in males, polycystic ovarian failure, endometriosis and obesity, and chemical-induced subfertility.

Sperm RNA as a Mediator of Genomic Plasticity

Sperm RNA has been linked recently to trans-generational, non-Mendelian patterns of inheritance. Originally dismissed as “residual” to spermatogenesis, some sperm RNA may have postfertilization functions including the transmission of acquired characteristics. Sperm RNA may help explain how trans-generational effects are transmitted and it may also have implications for assisted reproductive technologies (ART) where sperm are subjected to considerable, ex vivo manual handling. The presence of sperm RNA was originally a controversial topic because nuclear gene expression is switched off in the mature mammalian spermatozoon. With the recent application of next generation sequencing (NGS), an unexpectedly rich and complex repertoire of RNAs has been revealed in the sperm of several species that makes its residual presence counterintuitive. What follows is a personal survey of the science behind our understanding of sperm RNA and its functional significance based on experimental observations from my laboratory as well as many others who have contributed to the field over the years and are continuing to contribute today. The narrative begins with a historical perspective and ends with some educated speculation on where research into sperm RNA is likely to lead us in the next 10 years or so.

A non-canonical landscape of the microRNA system

Microribonucleic acids, best known as microRNAs or miRNAs, are small, non-coding RNAs with important regulatory roles in eukaryotic cells. Here, I present a broad review on highly relevant but generally non-depicted features of miRNAs, among which stand out the non-conventional miRNA seed sites, the unusual messenger RNA (mRNA) target regions, the non-canonical miRNA-guided mechanisms of gene expression regulation, and the recently identified new class of miRNA ligands. Furthermore, I address the miRNA uncommon genomic location, transcription, and subcellular localization. Altogether, these unusual features and roles place the miRNA system as a very diverse, complex, and intriguing biological mechanism.

MicroRNAs and spermatogenesis

In mammals, male gametes are produced inside the testis by spermatogenesis, which has three phases: mitotic proliferation of spermatogonia, meiosis of spermatocytes, and haploid differentiation of spermatids. The genome of male germ cells is actively transcribed to produce phase-specific gene expression patterns. Male germ cells have a complex transcriptome. In addition to protein-coding messenger RNAs, many noncoding RNAs, including microRNAs (miRNAs), are produced. The miRNAs are important regulators of gene expression. They function mainly post-transcriptionally to control the stability or translation of their target messenger RNAs. The miRNAs are expressed in a cell-specific manner during spermatogenesis to participate in the control of each step of male germ cell differentiation. Genetically modified mouse models have demonstrated the importance of miRNA pathways for normal spermatogenesis, and functional studies have been designed to dissect the roles of specific miRNAs in distinct cell types. Clinical studies have exploited the well-defined expression profiles of miRNAs, and human spermatozoal or seminal plasma miRNAs have been explored as potential biomarkers for male factor infertility. This review article discusses the current findings that support the central role of miRNAs in the regulation of spermatogenesis and male fertility.

Phosphorylation of CDK2 at threonine 160 regulates meiotic pachytene and diplotene progression in mice

Telomere clustering is a widespread phenomenon among eukaryotes. However, the molecular mechanisms that regulate formation of telomere clustering in mammalian meiotic prophase I, are still largely unknown. Here, we show that CDK2, especially p39(cdk2), as a potential meiosis-specific connector interaction with SUN1 mediates formation of telomere clustering during mouse meiosis. The transition from CDK2 to p-CDK2 also regulates the progression from homologous recombination to desynapsis by interacting with MLH1. In addition, disappearance of CDK2 on the telomeres and of p-CDK2 on recombination sites, were observed in Sun1(-/-) mice and in pachytene-arrested hybrid sterile mice (pwk×C57BL/6 F1), respectively. These results suggest that transition from CDK2 to p-CDK2 plays a critical role for regulating meiosis progression.

Small RNA expression and deep sequencing analyses of the nucleolus reveal the presence of nucleolus-associated microRNAs

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miRNA expression arrays and RNA Seq were employed for unbiased spatial analyses of miRNAs.

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Small RNomics of subcellular compartments revealed the presence of miRNAs in the nucleolus.

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Several miRNAs were detected at low abundance in cancer cell nucleoli.

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The nucleolar abundance of miR-31 was dependent on CRM1 export factor.

Micro RNAs (miRNA) are non-coding RNAs expressed in the cytoplasm as their mature, 21–22-nucleotide short forms. More recently, mature miRNAs have also been detected in the nucleus, raising the possibility that their spatial distribution may be more complex than anticipated. Here we undertook comprehensive systematic analyses of miRNA distribution in several subcellular compartments of human cancer cells. In particular, we focused on the potential presence of miRNAs in the nucleolus, which contains an abundance of small non-coding RNAs. We employed two miRNA expression array platforms and small RNA deep sequencing of small RNAs isolated from cells, nuclei, cytoplasm and the nucleoli. We developed an assay to compare RNAs of isolated nucleoli before and after denaturation and used Northern hybridization to verify the presence of miRNAs in the subcellular compartments. Consistently, we found more than 10 miRNAs associated with the nucleolar preparations. Several miRNAs had greater relative abundance in the nucleolus compared to the other compartments. The nucleolar presence of miRNAs was independent of Dicer and the main activity of the nucleolus, RNA polymerase I transcription, but was dependent on CRM1 previously associated with nucleolar trafficking of small nucleolar RNAs. These results highlight the complexity of miRNA spatial arrangement and regulation.

Phosphorylation of CDK2 on threonine 160 influences silencing of sex chromosome during male meiosis

In mammalian meiosis, the X and Y chromosomes are largely unsynapsed and transcriptionally silenced during the pachytene stage of meiotic prophase (meiotic sex chromosome inactivation), forming a specialized nuclear territory called sex or XY body. An increasing number of proteins and noncoding RNAs were found to localize to the sex body and take part in influencing expression of sex chromosome genes. Cyclin-dependent kinase 2 (Cdk2 (-/-)) spermatocytes show incomplete sex chromosome pairing. Here, we further showed that phosphorylation of CDK2 isoform 1 (p-CDK2(39) [39 kDa]) on threonine 160 localizes to the sites of asynapsis and the sex body, interacting with phosphorylated gamma-H2AX. Meanwhile, p-CDK2(39) is frequently mislocalized throughout the sex body, and meiotic sex chromosome inactivation is disrupted in PWK×C57BL/6J hybrid mice. Furthermore, pachytene spermatocytes treated with mevastatin (an inhibitor of p-CDK2) showed overexpression of sex chromosome-linked genes. Our results highlight an important role for p-CDK2(39) in influencing silencing of the sex chromosomes during male meiosis by interacting with gamma-H2AX.