Testis-specific miRNA-469 up-regulated in gonadotropin-regulated testicular RNA helicase (GRTH/DDX25)-null mice silences transition protein 2 and protamine 2 messages at sites within coding region: implications of its role in germ cell development

Fluoride-induced testicular and ovarian toxicity: evidence from animal studies

Fluoride (F), as a natural element found in a wide range of sources such as water and certain foods, has been proven to be beneficial in preventing dental caries, but concerns have been raised regarding its potential deleterious effects on overall health. Sodium fluoride (NaF), another form of F, has the ability to accumulate in reproductive organs and interfere with hormonal regulation and oxidative stress pathways, contributing to reproductive toxicity. While the exact mechanisms of F-induced reproductive toxicity are not fully understood, this review aims to elucidate the mechanisms involved in testicular and ovarian injury. In males, F exposure at different doses has been associated with reduced testis weight, reduced sperm quality in terms of count, motility, and viability, as well as abnormal sperm morphology and disruption of seminiferous tubules by altering hormone levels (especially testosterone), impairing spermatogenesis, and inducing oxidative stress and zinc deficiency. Similarly, administration of F can impact female reproductive health by affecting ovarian function, hormone levels, oocyte quality, and the regularity of the estrous cycle. However, the impact of F exposure on LH, FSH, and GnRH levels is controversial between males and females. In both males and females, F exerts its adverse effects by triggering apoptosis, autophagy, inflammation, mitochondrial dysfunction, reduction in ATP synthesis, and modulation of important genes involved in steroidogenesis. Furthermore, genetic susceptibility and individual variations in F metabolism may contribute to different responses to fluoride exposure.

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.

MicroRNAs in spermatogenesis dysfunction and male infertility: clinical phenotypes, mechanisms and potential diagnostic biomarkers

Infertility affects approximately 10-15% of couples worldwide who are attempting to conceive, with male infertility accounting for 50% of infertility cases. Male infertility is related to various factors such as hormone imbalance, urogenital diseases, environmental factors, and genetic factors. Owing to its relationship with genetic factors, male infertility cannot be diagnosed through routine examination in most cases, and is clinically called 'idiopathic male infertility.' Recent studies have provided evidence that microRNAs (miRNAs) are expressed in a cell-or stage-specific manner during spermatogenesis. This review focuses on the role of miRNAs in male infertility and spermatogenesis. Data were collected from published studies that investigated the effects of miRNAs on spermatogenesis, sperm quality and quantity, fertilization, embryo development, and assisted reproductive technology (ART) outcomes. Based on the findings of these studies, we summarize the targets of miRNAs and the resulting functional effects that occur due to changes in miRNA expression at various stages of spermatogenesis, including undifferentiated and differentiating spermatogonia, spermatocytes, spermatids, and Sertoli cells (SCs). In addition, we discuss potential markers for diagnosing male infertility and predicting the varicocele grade, surgical outcomes, ART outcomes, and sperm retrieval rates in patients with non-obstructive azoospermia (NOA).

miR-1202 acts as anti-oncomiR in myeloid leukaemia by down-modulating GATA-1S expression

Transient abnormal myelopoiesis (TAM) is a Down syndrome-related pre-leukaemic condition characterized by somatic mutations in the haematopoietic transcription factor GATA-1 that result in exclusive production of its shorter isoform (GATA-1S). Given the common hallmark of altered miRNA expression profiles in haematological malignancies and the pro-leukaemic role of GATA-1S, we aimed to search for miRNAs potentially able to modulate the expression of GATA-1 isoforms. Starting from an in silico prediction of miRNA binding sites in the GATA-1 transcript, miR-1202 came into our sight as potential regulator of GATA-1 expression. Expression studies in K562 cells revealed that miR-1202 directly targets GATA-1, negatively regulates its expression, impairs GATA-1S production, reduces cell proliferation, and increases apoptosis sensitivity. Furthermore, data from TAM and myeloid leukaemia patients provided substantial support to our study by showing that miR-1202 down-modulation is accompanied by increased GATA-1 levels, with more marked effects on GATA-1S. These findings indicate that miR-1202 acts as an anti-oncomiR in myeloid cells and may impact leukaemogenesis at least in part by down-modulating GATA-1S levels.

The Role of microRNA in Spermatogenesis: Is There a Place for Fertility Preservation Innovation?

Oncological treatments have dramatically improved over the last decade, and as a result, survival rates for cancer patients have also improved. Quality of life, including concerns about fertility, has become a major focus for both oncologists and patients. While oncologic treatments are often highly effective at suppressing neoplastic growth, they are frequently associated with severe gonadotoxicity, leading to infertility. For male patients, the therapeutic option to preserve fertility is semen cryopreservation. In prepubertal patients, immature testicular tissue can be sampled and stored to allow post-cure transplantation of the tissue, immature germ cells, or in vitro spermatogenesis. However, experimental techniques have not yet been proven effective for restoring sperm production for these patients. MicroRNAs (miRNAs) have emerged as promising molecular markers and therapeutic tools in various diseases. These small regulatory RNAs possess the unique characteristic of having multiple gene targets. MiRNA-based therapeutics can, therefore, be used to modulate the expression of different genes involved in signaling pathways dysregulated by changes in the physiological environment (disease, temperature, ex vivo culture, pharmacological agents). This review discusses the possible role of miRNA as an innovative treatment option in male fertility preservation-restoration strategies and describes the diverse applications where these new therapeutic tools could serve as fertility protection agents.

Small RNAs, spermatogenesis, and male infertility: a decade of retrospect

Small non-coding RNAs (sncRNAs), being the top regulators of gene expression, have been thoroughly studied in various biological systems, including the testis. Research over the last decade has generated significant evidence in support of the crucial roles of sncRNAs in male reproduction, particularly in the maintenance of primordial germ cells, meiosis, spermiogenesis, sperm fertility, and early post-fertilization development. The most commonly studied small RNAs in spermatogenesis are microRNAs (miRNAs), PIWI-interacting RNA (piRNA), small interfering RNA (siRNA), and transfer RNA-derived small RNAs (ts-RNAs). Small non-coding RNAs are crucial in regulating the dynamic, spatial, and temporal gene expression profiles in developing germ cells. A number of small RNAs, particularly miRNAs and tsRNAs, are loaded on spermatozoa during their epididymal maturation. With regard to their roles in fertility, miRNAs have been studied most often, followed by piRNAs and tsRNAs. Dysregulation of more than 100 miRNAs has been shown to correlate with infertility. piRNA and tsRNA dysregulations in infertility have been studied in only 3-5 studies. Sperm-borne small RNAs hold great potential to act as biomarkers of sperm quality and fertility. In this article, we review the role of small RNAs in spermatogenesis, their association with infertility, and their potential as biomarkers of sperm quality and fertility.

Small Non-Coding RNAs in Male Reproduction

Male reproductive functions are strictly regulated in order to maintain sperm production and fertility. All processes are controlled by precise regulation of gene expression, which creates specific gene expression programs for different developmental stages and cell types, and forms the functional basis for the reproductive system. Small non-coding RNAs (sncRNAs) are involved in gene regulation by targeting mRNAs for translational repression and degradation through complementary base pairing to recognize their targets. This review article summarizes the current knowledge on the function of different classes of sncRNAs, in particular microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs), during male germ cell differentiation, with the focus on sncRNAs expressed in the germline. Although transcriptionally inactive, mature spermatozoa contain a complex population of sncRNAs, and we also discuss the recently identified role of sperm sncRNAs in the intergenerational transmission of epigenetic information on father's environmental and lifestyle exposures to offspring. Finally, we summarize the current information on the utility of sncRNAs as potential biomarkers of infertility that may aid in the diagnosis and prediction of outcomes of medically assisted reproduction.

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.

Sperm epigenetics landscape: correlation with embryo quality, reproductive outcomes and offspring's health

Epigenetics refers to how gene expression and function are modulated without modifying the DNA sequence but through subtle molecular changes or interactions with it. As spermatogenesis progresses, male germ cells suffer plenty of epigenetic modifications, resulting in the definitive epigenome of spermatozoa conditioning its functionality, and this process can be altered by several internal and external factors. The paternal epigenome is crucial for sperm function, fertilization, embryo development, and offspring's health, and altered epigenetic states are associated with male infertility with or without altered semen parameters, embryo quality impairment, and worse ART outcomes together with the future offspring's health risks mainly through intergenerational transmission of epigenetic marks. Identifying epigenetic biomarkers may improve male factor diagnosis and the development of targeted therapies, not only to improve fertility but also to allow an early detection of risk and disease prevention in the progeny. While still there is much research to be done, hopefully in the near future, improvements in high-throughput technologies applied to epigenomes will permit our understanding of the underlying epigenetic mechanisms and the development of diagnostics and therapies leading to improved reproductive outcomes. In this review, we discuss the mechanisms of epigenetics in sperm and how epigenetics behave during spermatogenesis. Additionally, we elaborate on the relationship of sperm epigenetics with sperm parameters and male infertility, and highlight the impact of sperm epigenetic alterations on sperm parameters, embryo quality, ART outcomes, miscarriage rates and offspring's health. Furthermore, we provide insights into the future research of epigenetic alterations in male infertility.

miRNA Expression Profiles of Mouse Round Spermatids in GRTH/DDX25-Mediated Spermiogenesis: mRNA-miRNA Network Analysis

GRTH/DDX25 is a testis-specific DEAD-box family of RNA helicase, which plays an essential role in spermatogenesis and male fertility. There are two forms of GRTH, a 56 kDa non-phosphorylated form and a 61 kDa phosphorylated form (pGRTH). GRTH-KO and GRTH Knock-In (KI) mice with R242H mutation (lack pGRTH) are sterile with a spermatogenic arrest at step 8 of spermiogenesis due to failure of round spermatids (RS) to elongate. We performed mRNA-seq and miRNA-seq analysis on RS of WT, KI, and KO to identify crucial microRNAs (miRNAs) and mRNAs during RS development by establishing a miRNA-mRNA network. We identified increased levels of miRNAs such as miR146, miR122a, miR26a, miR27a, miR150, miR196a, and miR328 that are relevant to spermatogenesis. mRNA-miRNA target analysis on these DE-miRNAs and DE-mRNAs revealed miRNA target genes involved in ubiquitination process (Ube2k, Rnf138, Spata3), RS differentiation, and chromatin remodeling/compaction (Tnp1/2, Prm1/2/3, Tssk3/6), reversible protein phosphorylation (Pim1, Hipk1, Csnk1g2, Prkcq, Ppp2r5a), and acrosome stability (Pdzd8). Post-transcriptional and translational regulation of some of these germ-cell-specific mRNAs by miRNA-regulated translation arrest and/or decay may lead to spermatogenic arrest in KO and KI mice. Our studies demonstrate the importance of pGRTH in the chromatin compaction and remodeling process, which mediates the differentiation of RS into elongated spermatids through miRNA-mRNA interactions.

Ssc-MiR-21-5p and Ssc-MiR-615 Regulates the Proliferation and Apoptosis of Leydig Cells by Targeting SOX5

Leydig cells (LCs) are the predominant cells of androgen production, which plays key roles in spermatogenesis and maintaining male secondary sexual characteristics. Abnormal development of LCs affects androgen levels in vivo, affects fertility and may even lead to infertility. Little is known about the regulation mechanism on LCs’ development and maturation in domestic animals, especially the regulation of non-coding RNAs. In this study, we continued to dig deeper in the previous RNA-seq data of porcine LCs from our group, combined with detecting the expression profiles in different tissues and different types of cells in the testis, to screen out candidate microRNAs (miRNAs) that may affect the regulation of LCs. A total of two miRNAs, ssc-miR-21-5p and ssc-miR-615 (“ssc” is omitted below), were finally determined. After overexpression and interference of miRNAs in vitro, the effects of candidate miRNAs on the proliferation and apoptosis of TM3 (mouse Leydig cell line) were explored. The results showed that miR-21-5p led to a decrease in TM3 cell density and p53 (apoptosis related protein) expression. Meanwhile, miR-21-5p decreased EdU positive cell numbers, but increased TUNEL positive cell numbers, suggesting miR-21-5p could inhibit proliferation and promote apoptosis. Conversely, miR-615 could increase TM3 cell density. Western blot and TUNEL assay indicated miR-615 inhibited apoptosis, but had no effect on proliferation. In addition, Sox5 was identified a potential target gene of these two miRNAs by Dual-Luciferase reporter system assay. Our findings about functions of miRNAs in TM3 and the mapping of miRNAs-target gene regulatory network would provide an important basis for the further elucidation of miRNAs in regulating pig LCs.

Application of Induced Pluripotent Stem Cell-Derived Models for Investigating microRNA Regulation in Developmental Processes

Advances in induced pluripotent stem cell (iPSC) techniques have opened up new perspectives in research on developmental biology. Compared with other sources of human cellular models, iPSCs present a great advantage in hosting the unique genotype background of donors without ethical concerns. A wide spectrum of cellular and organoid models can be generated from iPSCs under appropriate in vitro conditions. The pluripotency of iPSCs is orchestrated by external signalling and regulated at the epigenetic, transcriptional and posttranscriptional levels. Recent decades have witnessed the progress of studying tissue-specific expressions and functions of microRNAs (miRNAs) using iPSC-derived models. MiRNAs are a class of short non-coding RNAs with regulatory functions in various biological processes during development, including cell migration, proliferation and apoptosis. MiRNAs are key modulators of gene expression and promising candidates for biomarker in development; hence, research on the regulation of human development by miRNAs is expanding. In this review, we summarize the current progress in the application of iPSC-derived models to studies of the regulatory roles of miRNAs in developmental processes.

Spatiotemporal Small Non-coding RNAs Expressed in the Germline as an Early Biomarker of Testicular Toxicity and Transgenerational Effects Caused by Prenatal Exposure to Nanosized Particles

In recent years, an apparent decline in human sperm quality has been observed worldwide. One in every 5.5 couples suffers from infertility, with male reproductive problems contributing to nearly 40% of all infertility cases. Although the reasons for the increasing number of infertility cases are largely unknown, both genetic and environmental factors can be contributing factors. In particular, exposure to chemical substances during mammalian male germ cell development has been linked to an increased risk of infertility in later life owing to defective sperm production, reproductive tract obstruction, inflammation, and sexual disorders. Prenatal exposure to nanomaterials (NMs) is no exception. In animal experiments, maternal exposure to NMs has been reported to affect the reproductive health of male offspring. Male germ cells require multiple epigenetic reprogramming events during their lifespan to acquire reproductive capacity. Given that spermatozoa deliver the paternal genome to oocytes upon fertilization, we hypothesized that maternal exposure to NMs negatively affects male germ cells by altering epigenetic regulation, which may in turn affect embryo development. Small non-coding RNAs (including microRNAs, PIWI-interacting RNAs, tRNA-derived small RNAs, and rRNA-derived small RNAs), which are differentially expressed in mammalian male germ cells in a spatiotemporal manner, could play important regulatory roles in spermatogenesis and embryogenesis. Thus, the evaluation of RNAs responsible for sperm fertility is of great interest in reproductive toxicology and medicine. However, whether the effect of maternal exposure to NMs on spermatogenesis in the offspring (intergenerational effects) really triggers multigenerational effects remains unclear, and infertility biomarkers for evaluating paternal inheritance have not been identified to date. In this review, existing lines of evidence on the effects of prenatal exposure to NMs on male reproduction are summarized. A working hypothesis of the transgenerational effects of sperm-derived epigenomic changes in the F1 generation is presented, in that such maternal exposure could affect early embryonic development followed by deficits in neurodevelopment and male reproduction in the F2 generation.

Chromatoid Bodies in the Regulation of Spermatogenesis: Novel Role of GRTH

Post-transcriptional and translational control of specialized genes play a critical role in the progression of spermatogenesis. During the early stages, mRNAs are actively transcribed and stored, temporarily bound to RNA binding proteins in chromatoid bodies (CBs). CBs are membrane-less dynamic organelles which serve as storehouses and processing centers of mRNAs awaiting translation during later stages of spermatogenesis. These CBs can also regulate the stability of mRNAs to secure the correct timing of protein expression at different stages of sperm formation. Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) is an essential regulator of spermatogenesis. GRTH transports mRNAs from the nucleus to the cytoplasm and phospho-GRTH transports mRNAs from the cytoplasm to the CBs. During spermiogenesis, there is precise control of mRNAs transported by GRTH from and to the CBs, directing the timing of translation of critical proteins which are involved in spermatid elongation and acrosomal development, resulting in functional sperm formation. This chapter presents our current knowledge on the role of GRTH, phospho-GRTH and CBs in the control of spermiogenesis. In addition, it covers the components of CBs compared to those of stress granules and P-bodies.

Alternative splicing and MicroRNA: epigenetic mystique in male reproduction

Infertility is rarely life threatening, however, it poses a serious global health issue posing far-reaching socio-economic impacts affecting 12–15% of couples worldwide where male factor accounts for 70%. Functional spermatogenesis which is the result of several concerted coordinated events to produce sperms is at the core of male fertility, Alternative splicing and microRNA (miRNA) mediated RNA silencing (RNAi) constitute two conserved post-transcriptional gene (re)programming machinery across species. The former by diversifying transcriptome signature and the latter by repressing target mRNA activity orchestrate a spectrum of testicular events, and their dysfunctions has several implications in male infertility. This review recapitulates the knowledge of these mechanistic events in regulation of spermatogenesis and testicular homoeostasis. In addition, miRNA payload in sperm, vulnerable to paternal inputs, including unhealthy diet, infection and trauma, creates epigenetic memory to initiate intergenerational phenotype. Naive zygote injection of sperm miRNAs from stressed father recapitulates phenotypes of offspring of stressed father. The epigenetic inheritance of paternal pathologies through miRNA could be a tantalizing avenue to better appreciate ‘Paternal Origins of Health and Disease’ and the power of tiny sperm.

Regulation of mammalian spermatogenesis by miRNAs

Male fertility requires the continual production of sperm by the process of spermatogenesis. This process requires the correct timing of regulatory signals to germ cells during each phase of their development. MicroRNAs (miRNAs) in germ cells and supporting Sertoli cells respond to regulatory signals and cause down- or upregulation of mRNAs and proteins required to produce proteins that act in various pathways to support spermatogenesis. The targets and functional consequences of altered miRNA expression in undifferentiated and differentiating spermatogonia, spermatocytes, spermatids and Sertoli cells are discussed. Mechanisms are reviewed by which miRNAs contribute to decisions that promote spermatogonia stem cell self-renewal versus differentiation, entry into and progression through meiosis, differentiation of spermatids, as well as the regulation of Sertoli cell proliferation and differentiation. Also discussed are miRNA actions providing the very first signals for the differentiation of spermatogonia stem cells in a non-human primate model of puberty initiation.

RNA Helicases in Microsatellite Repeat Expansion Disorders and Neurodegeneration

Short repeated sequences of 3-6 nucleotides are causing a growing number of over 50 microsatellite expansion disorders, which mainly present with neurodegenerative features. Although considered rare diseases in relation to the relatively low number of cases, these primarily adult-onset conditions, often debilitating and fatal in absence of a cure, collectively pose a large burden on healthcare systems in an ageing world population. The pathological mechanisms driving disease onset are complex implicating several non-exclusive mechanisms of neuronal injury linked to RNA and protein toxic gain- and loss- of functions. Adding to the complexity of pathogenesis, microsatellite repeat expansions are polymorphic and found in coding as well as in non-coding regions of genes. They form secondary and tertiary structures involving G-quadruplexes and atypical helices in repeated GC-rich sequences. Unwinding of these structures by RNA helicases plays multiple roles in the expression of genes including repeat-associated non-AUG (RAN) translation of polymeric-repeat proteins with aggregating and cytotoxic properties. Here, we will briefly review the pathogenic mechanisms mediated by microsatellite repeat expansions prior to focus on the RNA helicases eIF4A, DDX3X and DHX36 which act as modifiers of RAN translation in C9ORF72-linked amyotrophic lateral sclerosis/frontotemporal dementia (C9ORF72-ALS/FTD) and Fragile X-associated tremor/ataxia syndrome (FXTAS). We will further review the RNA helicases DDX5/17, DHX9, Dicer and UPF1 which play additional roles in the dysregulation of RNA metabolism in repeat expansion disorders. In addition, we will contrast these with the roles of other RNA helicases such as DDX19/20, senataxin and others which have been associated with neurodegeneration independently of microsatellite repeat expansions. Finally, we will discuss the challenges and potential opportunities that are associated with the targeting of RNA helicases for the development of future therapeutic approaches.

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

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

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.

Exploring dysregulated miRNAs in cryptorchidism: a systematic review

Objective

To identify dysregulated miRNAs in testicular tissues from animal models and patients with cryptorchidism.

Methods

Databases were systematically searched for studies published before 10 May 2020 that had investigated miRNAs in cryptorchidism. Predicted targets of the identified miRNA biomarkers were obtained by searching TargetScan and Starbase. Gene ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analyses were subsequently conducted.

Results

Five publications met the eligibility criteria for the review. 21 differentially expressed miRNAs were the most abundantly reported in 185 animal and human tissue samples. Three miRNAs (miR-210, miR-449a and miR-34c) were dysregulated in both animal and human testicular tissues. The top five relevant lncRNAs associated with the miRNAs were NEAT1, KCNQ1OT1, XIST, AC005154.1, and TUG1.

Conclusions

Further research is warranted to explore the potential of these dysregulated miRNAs as biomarkers or therapeutic targets for male infertility associated with cryptorchidism.

Linking Phospho-Gonadotropin Regulated Testicular RNA Helicase (GRTH/DDX25) to Histone Ubiquitination and Acetylation Essential for Spermatid Development During Spermiogenesis

GRTH/DDX25 is a testicular RNA helicase expressed in germ cells that plays a crucial role in completion of spermatogenesis. Previously, we demonstrated a missense mutation (R242H) of GRTH gene in Japanese infertile patients (5.8%) with non-obstructive azoospermia. This mutation upon expression in COS-1 cells revealed absence of the 61 kDa phosphorylated GRTH in cytoplasm and the presence of the 56 kDa non-phosphorylated GRTH in the nucleus. GRTH knock-in (KI) mice carrying the human GRTH (R242H) mutation, lack phosphorylated GRTH, and sperm due to failure of round spermatid elongation during spermiogenesis. To determine the impact of phosphorylated GRTH on molecular events/pathways participating in spermatid development during spermiogenesis, we analyzed transcriptome profiles obtained from RNA-Seq of germ cells from KI and WT mice. RNA-Seq analysis of 2624 differentially expressed genes revealed 1404 down-regulated and 1220 up-regulated genes in KI mice. Genes relevant to spermatogenesis, spermatid development and spermatid differentiation were significantly down-regulated. KEGG enrichment analysis showed genes related to ubiquitin-mediated proteolysis and protein processing in endoplasmic reticulum pathway genes were significantly down-regulated while the up-regulated genes were found to be involved in Focal adhesion and ECM-receptor interaction pathways. Real-Time PCR analysis confirmed considerable reduction in transcripts of ubiquitination related genes Ube2j1, Ube2k, Ube2w, Rnf8, Rnf133, Rnf138, Cul3 and increased expression of Ccnd2, Col1a, Lamb1, Cav1, Igf1, Itga9 mRNA's in KI mice compared to WT. Also, marked reduction in protein expression of UBE2J1, RNF8, RNF138 (ubiquitination network), MOF (histone acetyltransferase), their modified Histone substrates (H2AUb, H2BUb) and H4Ac, H4K16Ac were observed in KI mice. GRTH-IP mRNA binding studies revealed that Rnf8 and Ube2J1 mRNAs from WT mice associated with GRTH protein and the binding is greatly impaired in the KI mice. Immunohistochemistry analysis showed significantly reduced expression of RNF8, MOF, H4Ac and H4K16Ac in round spermatids of KI mice. Absence of phosphorylated GRTH impairs UBE2J1, RNF8 and MOF-dependent histone ubiquitination and acetylation essential for histone replacement, chromatin condensation and spermatid elongation during spermiogenesis.

Comparative Transcriptomics Analysis of Testicular miRNA from Cryptorchid and Normal Horses

Simple Summary

The testis is an important organ for mammals, and testicular microRNA expression is associated with male fertility to a certain extent. Cryptorchidism is the failure of one or both testes to descend into the scrotal sac. It is a common congenital malformation in horses. The major clinical consequence of this abnormality is impaired fertility. The expression of testicular microRNAs is influenced by many factors, including high temperature and disease, in cryptorchid horses. Here, we investigated the microRNA expression levels of normal and retained testes. Their expression patterns showed significant differences. In addition, we obtained comprehensive expression data for equine testicular microRNA, which is fundamental information for further analysis.

Abstract

In the biological process of testicular spermatogenesis, the expression and interaction of many genes are regulated by microRNAs (miRNAs). However, comparisons of miRNA expression between descended testes (DTs) and undescended testes (UDTs) are rarely done in horses. In this study, we selected two UDTs (CKY2b and GU4b) from Chakouyi (CKY) and Guanzhong (GU) horses and eight DTs (GU1–3, CKY1, CKY3, CKY2a, GU4a, and GU5). Three groups were compared to evaluate expression patterns of testicular miRNA in stallion testes. Group 1 compared normal CKY horses and GU horses (CKY1 and CKY3 vs. GU1–3). Group 2 (CKY2a and GU4a (DTs) vs. CKY2b and GU4b (UDTs)) and group 3 (GU1–3, CKY1, CKY3 (DTs) vs. CKY2b and GU4b (UDTs)) compared the expression levels in unilateral retained testes to normal testes. The results show that 42 miRNAs (7 upregulated and 35 downregulated) had significantly different expression levels in both comparisons. The expression levels of eca-miR-545, eca-miR-9084, eca-miR-449a, eca-miR-9024, eca-miR-9121, eca-miR-8908e, eca-miR-136, eca-miR-329b, eca-miR-370, and eca-miR-181b were further confirmed by quantitative real-time PCR assay. The target genes of differentially expressed miRNAs in three comparisons were predicted, and the functions were annotated. The putative target genes of the 42 co-differentially expressed miRNAs were annotated to 15 functional terms, including metal ion binding, GTPase activator activity, zinc ion binding, intracellular, cytoplasm, and cancer pathways, and osteoclast differentiation. Our data indicate that the differentially expressed miRNAs in undescended testis suggests a potential role in male fertility and a relationship with cryptorchidism in horses. The discovery of miRNAs in stallion testes might contribute to a new direction in the search for biomarkers of stallion fertility.

Bovid microRNAs involved in the process of spermatogonia differentiation into spermatocytes

The male infertility of cattleyak resulted from spermatogenic arrest has greatly restricted the effective utilization of the heterosis from crossbreeding of cattle and yak. Based on our previous studies, the significant divergences of the transcriptomic and proteomic sequencing between yak and cattleyak prompt us to investigate the critical roles of microRNAs in post-transcriptional regulation of gene expression during spermatogenesis. TUNEL-POD analysis presented sharply decreased spermatogenic cell types and the increased apoptotic spermatogonia in cattleyak. The STA-PUT velocity sedimentation was employed to obtain spermatogonia and spermatocytes from cattle, yak and cattleyak and these spermatogenic cells were verified by the morphological and phenotypic identification. MicroRNA microarray showed that 27 differentially expressed miRNAs were simultaneously identified both in cattleyak vs cattle and in cattleyak vs yak comparisons. Further analysis revealed that the down-regulation of bta-let-7 families, bta-miR-125 and bta-miR-23a might impair the RA-induced differentiation of spermatogonia. Target gene analysis for differentially expressed miRNAs revealed that miRNAs targeted major players involved in vesicle-mediated transport, regulation of protein kinase activity and Pathways in cancer. In addition, spermatogonia transfection analysis revealed that the down-regulation of bta-miR-449a in the cattleyak might block the transition of male germ cells from the mitotic cycle to the meiotic program. The present study provided valuable information for future elucidating the regulatory roles of miRNAs involved in spermatogenic arrest of cattleyak.

Fluoride-induced unrestored arrest during haploid period of spermatogenesis via the regulation of DDX25 in rats

The effect of fluoride as an ongoing topic has attracted much attentions due to the decline in overall human fertility worldwide. However, whether fluorine causes a temporary stimulus or permanent damage to the male reproductive system, as well as the mechanism of fluoride influencing spermatogenesis remained unclear. 48 adult male rats were randomly divided into four groups (twelve each). Control group received the distilled water, while the other three groups were treated with 25, 50, 100 mg/L NaF via drinking water for 8 weeks. Six rats from each group were selected randomly to detect the levels of various indices related to spermatogenesis. The remaining rats were given only distilled water and left for recovery of a period of 2 weeks. Results showed that the levels of serum CK, ALP, CHE, BUN, UA, and Cr, testis morphology and the ultrastructure of sperm acrosome and chromatoid body (CB) were significantly changed by fluoride. Interestingly, the elongated spermatid counts, spermatids elongation ratio, and mRNA expressions of Prm1/2 and MIWI, TDRD1, TDRD 6, TDRD7, PABP, and Hsp72 related to CB decreased markedly in fluoride treatment groups compared to the control. Furthermore, the expression levels of DDX25 and associated regulatory proteins like CRM1, HMG2, H4, TP2, and PGK2 were down-regulated by fluoride. After 2-weeks withdrawal period, out of the 19 altered spermatogenesis indicators, 15 indicators in 100 mg/L group and 3 indicators in 50 mg/L group still exhibited a significant change, while none showed change in 25 mg/L group. These results proved that the reversibility of fluoride toxicity is dose-dependent on the male reproductive system. Meanwhile, fluoride caused unrestored arrest during the haploid period of spermatogenesis, where reduced DDX25 and associated regulatory proteins play a crucial role in this process, which could provide the underlying insights to the toxic mechanism of fluoride induced male reproductive toxicity.

Characterization of the Phosphorylation Site of GRTH/DDX25 and Protein Kinase A Binding Interface Provides Structural Basis for the Design of a Non-Hormonal Male Contraceptive

Gonadotropin Regulated Testicular Helicase (GRTH/DDX25), expressed in the male gonad, is essential for the completion of spermatogenesis. Our early studies revealed a missense mutation (R242H) of GRTH in 5.8% of Japanese patient population with azoospermia. Transfection of the mutant GRTH construct in COS-1 cells leads to loss of the 61 kDa cytoplasmic phospho-species. Mice with knock-in of the human GRTH mutation are sterile and lack sperm with normal androgen and mating behavior. These findings provide an avenue for the development of a non-hormonal male contraceptive. Using site directed mutagenesis and a site-specific phospho-antibody, we have identified T239, structurally adjacent to the patient’s mutant site as the GRTH phospho-site. Molecular modelling provided structural basis for the role of R242 and other critical solvent-exposed residues at the GRTH/PKA interface (E165/K240/D237), on the control of GRTH phosphorylation at T239. Single or double mutations of these residues caused marked reduction or abolition of the phospho-form. These effects can be ascribed to critical disruptions of intramolecular H-bonds at the GRTH/PKA interface, which leads to modest but consequential structural changes that can affect PKA catalytic efficiency. Inhibition of phosphorylation may be achieved by small, drug-like molecules that bind to GRTH and reconfigure the GRTH/PKA interface.

MicroRNAs: Recent insights towards their role in male infertility and reproductive cancers

Spermatogenesis is a tightly controlled, multi-step process in which mature spermatozoa are produced. Disruption of regulatory mechanisms in spermatogenesis can lead to male infertility, various diseases of male reproductive system, or even cancer. The spermatogenic impairment in infertile men can be associated with different etiologies, and the exact molecular mechanisms are yet to be determined. MicroRNAs (miRNAs) are a type of non-protein coding RNAs, about 22 nucleotides long, with an essential role in post-transcriptional regulation. miRNAs have been recognized as important regulators of various biological processes, including spermatogenesis. The aim of this review is to summarize the recent literature on the role of miRNAs in spermatogenesis, male infertility and reproductive cancers, and to evaluate their potential in diagnosis, prognosis and therapy of disease. Experimental evidence shows that aberrant expression of miRNAs affects spermatogenesis at multiple stages and in different cell types, most often resulting in infertility. In more severe cases, dysregulation of miRNAs leads to cancer. miRNAs have enormous potential to be used as diagnostic and prognostic markers as well as therapeutic targets in male infertility and reproductive system diseases. However, to exploit this potential fully, we need a better understanding of miRNA-mediated regulation of spermatogenesis, including the characterization of yet unidentified miRNAs and related regulatory mechanisms.

Gonadotropin Regulation Testicular RNA Helicase, Two Decades of Studies on Its Structure Function and Regulation From Its Discovery Opens a Window for Development of a Non-hormonal Oral Male Contraceptive

Gonadotropin Regulated Testicular Helicase (GRTH/DDX25) is member of the DEAD-box family of RNA helicases present in Leydig and germ cells. GRTH is the only family member regulated by hormones, luteinizing hormone, through androgen action. Male mice with knock-out of the GRTH gene are sterile, lack sperm with arrest at round spermatids. GRTH participates on the nuclear export and transport of specific mRNAs, the structural integrity of Chromatoid Bodies of round spermatids, where mRNAs are processed and stored, and in their transit to polyribosomes, where it may regulate translation of relevant genes. GRTH has a central role in the control of germ cell apoptosis and acts as negative regulator of miRNAs which regulate expression of genes involved in the progress of spermatogenesis. In Leydig cells, GRTH gene transcription is regulated by LH via autocrine actions of androgen/androgen receptor and has regulatory effects in steroidogenesis. In germ cells, androgen actions are indirect via receptors in Sertoli cells. Transgenic mice carrying GRTH 5' flanking region-GFP permitted to discern regions in the gene which directs its expression upstream, in germ cells, and downstream in Leydig cells, and the androgen-regulated transcription at interstitial (autocrine), and germ cell (paracrine) compartments. Further evidence for paracrine actions of androgen/androgen receptor is their transcriptional induction of Germ Cell Nuclear Factor as requisite up-regulator of GRTH gene transcription in round spermatids, linking androgen action to two relevant germ cell genes essential for the progress of spermatogenesis. A missense mutation of R to H at amino acid 242 of GRTH found in 5.8% of a patient population with azoospermia causes loss of the cytoplasmic phospho-GRTH species with preservation of the non-phospho form in transfected cells. Mice with knock-in of the human mutation, lack sperm due to arrest at round spermatids. This model permits to discern the function of phospho-GRTH. The GRTH phospho-site resides at a Threonine structurally adjacent to the mutant site found in patients. Molecular modeling of this site elucidated the amino acids that form the GRTH/PKA interphase and provide the basis for drug design for use as male contraceptive.

The role of microRNAs in embryonic stem cell and induced pluripotent stem cell differentiation in male germ cells

New perspectives have been opened by advances in stem cell research for reproductive and regenerative medicine. Several different cell types can be differentiated from stem cells (SCs) under suitable in vitro and in vivo conditions. The differentiation of SCs into male germ cells has been reported by many groups. Due to their unlimited pluripotency and self-renewal, embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can be used as valuable tools for drug delivery, disease modeling, developmental studies, and cell-based therapies in regenerative medicine. The unique features of SCs are controlled by a dynamic interplay between extrinsic signaling pathways, and regulations at epigenetic, transcriptional and posttranscriptional levels. In recent years, significant progress has been made toward better understanding of the functions and expression of specific microRNAs (miRNAs) in the maintenance of SC pluripotency. miRNAs are short noncoding molecules, which play a functional role in the regulation of gene expression. In addition, the important regulatory role of miRNAs in differentiation and dedifferentiation has been recently demonstrated. A balance between differentiation and pluripotency is maintained by miRNAs in the embryo and stem cells. This review summarizes the recent findings about the role of miRNAs in the regulation of self-renewal and pluripotency of iPSCs and ESCs, as well as their impact on cellular reprogramming and stem cell differentiation into male germ cells.

Differentially expressed microRNAs between cattleyak and yak testis

Cattleyak are interspecific hybrids between cattle and yak, exhibiting the same prominent adaptability as yak and much higher performances than yak. However, male infertility of cattleyak resulted from spermatogenic arrest has greatly restricted their effective utilization in yak breeding. In past decades, much work has been done to investigate the mechanisms of spermatogenic arrest, but little is known about the differences of the post-transcriptional regulators between cattleyak and yak, which may contribute to the impaired spermatogenesis. MiRNAs, a class of endogenous non-coding small RNA, were revealed to play crucial roles in regulating gene expression at post-transcriptional level. In the present study, we identified 50 differentially expressed (DE) known miRNAs and 11 novel miRNAs by using Illumina HISeq and bioinformatic analysis. A total of 50 putative target sites for the 13 DE known miRNAs and 30 for the 6 DE novel miRNAs were identified, respectively. GO and KEGG analyses were performed to reveal the functions of target genes for DE miRNAs. In addition, RT-qPCR was performed to validate the expression of the DE miRNAs and its targets. The identification of these miRNAs may provide valuable information for a better understanding of spermatogenic arrest in cattleyak.

Identification and expression analysis of microRNAs in medaka gonads

Gonad development is a highly regulated, coordinated biological process and increasing evidences have indicated that microRNA (miRNA) may be involved in this dynamic program. Medaka (Oryzias latipes) is a good model for reproductive research as it has distinct sex determining genes, however, research in gonadal miRNAs is lacked. In this study, two small RNA libraries from the ovaries and testes were constructed and sequenced. A total of 285 conserved and 388 novel miRNAs were obtained, among which 142 mature miRNAs were significantly (> two-fold change) up or down regulated in the testis compared to the ovary. Quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR) analysis showed that miR-430c, miR-26a and miR-202-5p were expressed in a gonad-specific or sex-biased pattern. Fluorescence in situ hybridization (FISH) indicated that miR-202-5p was present throughout spermatogenesis and was only detected at the early stages of oogenesis, this sex biased expression pattern suggested that miR-202-5p might be a crucial candidate in male differentiation and development. Our study provides the repertoire, a comprehensive annotation of miRNAs from gonads and a reference for functional studies of miRNAs in medaka.

Regulatory Functions of MicroRNAs in Male Reproductive Health: A New Approach to Understanding Male Infertility

MicroRNAs (miRNAs) are a novel class of small noncoding RNAs (ncRNAs) that play critical roles in regulation of gene expression, especially at posttranscriptional level. Over the past decade, the degree to which miRNAs are involved in male infertility has become clear. They are expressed in a cell- or phase-specific manner during spermatogenesis and play crucial role in male reproductive health. Therefore, dysregulation of miRNAs in testicular cells can be considered as a molecular basis for reproductive failure and male infertility. The abnormal expression pattern of miRNAs can be transmitted to the offspring via assisted reproductive techniques (ART) and results in the birth of children with a higher risk of infertility, congenital abnormalities, and morbidity. This review expounds on the miRNAs reported to play essential roles in somatic cells development, germ cells differentiation, steroidogenesis, normal spermatogenesis, sperm maturation, and male infertility, as well as emphasizes their importance as minimally invasive biomarkers of male infertility.

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.

The roles of microRNAs in regulation of mammalian spermatogenesis

Mammalian spermatogenesis contains three continuous and organized processes, by which spermatogonia undergo mitosis and differentiate to spermatocytes, follow on meiosis to form haploid spermatids and ultimately transform into spermatozoa. These processes require an accurately, spatially and temporally regulated gene expression patterns. The microRNAs are a novel class of post-transcriptional regulators. Cumulating evidences have demonstrated that microRNAs are expressed in a cell-specific or stage-specific manner during spermatogenesis. In this review, we focus on the roles of microRNAs in spermatogenesis. We highlight that N6-methyladenosine (m6A) is involved in the biogenesis of microRNAs and miRNA regulates the m6A modification on mRNA, and that specific miRNAs have been exploited as potential biomarkers for the male factor infertility, which will provide insightful understanding of microRNA roles in spermatogenesis.

Epigenetic dynamics and interplay during spermatogenesis and embryogenesis: implications for male fertility and offspring health

Mapping epigenetic modifications and identifying their roles in the regulation of spermatogenesis and embryogenesis are essential for gaining fundamental medical understandings and for clinical applications. More and more evidence has shown that specific epigenetic modifications are established during spermatogenesis, which will be transferred into oocyte via fertilisation, and play an important role in the early embryo development. Defects in epigenetic patterns may increase the risk of abnormal spermatogenesis, fertilisation failure, early embryogenesis abnormality and several other complications during pregnancy. This review mainly discusses the relationship between altered epigenetic profiles and reproductive diseases, highlighting how epigenetic defects affect the quality of sperm and embryo.

MicroRNAs: New Insight in Modulating Follicular Atresia: A Review

Our understanding of the post-transcriptional mechanisms involved in follicular atresia is limited; however, an important development has been made in understanding the biological regulatory networks responsible for mediating follicular atresia. MicroRNAs have come to be seen as a key regulatory actor in determining cell fate in a wide range of tissues in normal and pathological processes. Profiling studies of miRNAs during follicular atresia and development have identified several putative miRNAs enriched in apoptosis signaling pathways. Subsequent in vitro and/or in vivo studies of granulosa cells have elucidated the functional role of some miRNAs along with their molecular pathways. In particular, the regulatory roles of some miRNAs have been consistently observed during studies of follicular cellular apoptosis. Continued work should gradually lead to better understanding of the role of miRNAs in this field. Ultimately, we expect this understanding will have substantial benefits for fertility management at both the in vivo or/and in vitro levels. The stable nature of miRNA holds remarkable promise in clinical use as a diagnostic tool and in reproductive medicine to solve the ever-increasing fertility problem. In this review, we summarize current knowledge of the involvement of miRNAs in follicular atresia, discuss the challenges for further work and pinpoint areas for future research.

The multiple functions of RNA helicases as drivers and regulators of gene expression

RNA helicases comprise the largest family of enzymes involved in the metabolism of mRNAs, the processing and fate of which rely on their packaging into messenger ribonucleoprotein particles (mRNPs). In this Review, we describe how the capacity of some RNA helicases to either remodel or lock the composition of mRNP complexes underlies their pleiotropic functions at different steps of the gene expression process. We illustrate the roles of RNA helicases in coordinating gene expression steps and programmes, and propose that RNA helicases function as molecular drivers and guides of the progression of their mRNA substrates from one RNA-processing factory to another, to a productive mRNA pool that leads to protein synthesis or to unproductive mRNA pools that are stored or degraded.

A Role of MicroRNAs in Cell Differentiation During Gonad Development

MicroRNAs (miRNAs) are a group of small noncoding RNA molecules that play a major role in posttranscriptional regulation of gene expression and are expressed in an organ-specific manner. One miRNA can potentially regulate the expression of several genes, depending on cell type and differentiation stage. miRNAs are differentially expressed in the male and female gonads and have an organ-specific reproductive function. Exerting their affect through germ cells and gonadal somatic cells, miRNAs regulate key proteins necessary for gonad development. The role of miRNAs in the testes is only starting to emerge though they have been shown to be required for adequate spermatogenesis. Widely explored in the ovary, miRNAs were suggested to play a fundamental role in follicles' assembly, growth, differentiation, and ovulation. In this chapter, we focus on data obtained from mice in which distinct proteins that participate in the biosynthesis of miRNAs were conditionally knocked out from germ cells (spermatogonial cells or oocytes) or gonadal somatic cells (Sertoli or granulosa cells). We detail recent advances in identification of particular miRNAs and their significance in the development and function of male and female gonads. miRNAs can serve as biomarkers and therapeutic agents of pathological conditions; thus, elucidating the branched and complex network of reproduction-related miRNAs will aid understanding of gonads' physiology and managing reproduction disorders.

Comprehensive analysis of human small RNA sequencing data provides insights into expression profiles and miRNA editing

MicroRNAs (miRNAs) play key regulatory roles in various biological processes and diseases. A comprehensive analysis of large scale small RNA sequencing data (smRNA-seq) will be very helpful to explore tissue or disease specific miRNA markers and uncover miRNA variants. Here, we systematically analyzed 410 human smRNA-seq datasets, which samples are from 24 tissue/disease/cell lines. We tested the mapping strategies and found that it was necessary to make multiple-round mappings with different mismatch parameters. miRNA expression profiles revealed that on average ∼70% of known miRNAs were expressed at low level or not expressed (RPM < 1) in a sample and only ∼9% of known miRNAs were relatively highly expressed (RPM > 100). About 30% known miRNAs were not expressed in all of our used samples. The miRNA expression profiles were compiled into an online database (HMED, http://bioinfo.life.hust.edu.cn/smallRNA/). Dozens of tissue/disease specific miRNAs, disease/control dysregulated miRNAs and miRNAs with arm switching events were discovered. Further, we identified some highly confident editing sites including 24 A-to-I sites and 23 C-to-U sites. About half of them were widespread miRNA editing sites in different tissues. We characterized that the 2 types of editing sites have different features with regard to location, editing level and frequency. Our analyses for expression profiles, specific miRNA markers, arm switching, and editing sites, may provide valuable information for further studies of miRNA function and biomarker finding.

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.

Identification of MicroRNAs in Zebrafish Spermatozoa

MicroRNAs (miRNAs) participate in almost all biological processes. Plenty of evidences show that some testis- or spermatozoa-specific miRNAs play crucial roles in the process of gonad and germ cell development. In this study, the spermatozoa miRNA profiles were investigated through a combination of illumina deep sequencing and bioinformatics analysis in zebrafish. Deep sequencing of small RNAs yielded 11,820,680 clean reads. By mapping to the zebrafish genome, we identified 400 novel and 204 known miRNAs that could be grouped into 104 families. Furthermore, we selected the six highest expressions of known miRNAs to detect their expression patterns in different tissues by stem-loop quantitative real-time polymerase chain reaction. We found that among the six miRNAs, dre-miR-202-5p displayed specific and high expression in zebrafish spermatozoa and testis. Fluorescence in situ hybridization analysis indicated that dre-miR-202-5p was predominantly expressed in all kind of germ cells at different spermatogenetic stages, including spermatogonia and spermatozoa, but barely expressed in the germ cells in the ovary. This sex-biased expression pattern suggests that dre-miR-202-5p might be related to spermatogenesis and the functioning of spermatozoa. The identification of miRNAs in zebrafish spermatozoa and germ cells offers new insights into the spermatogenesis and spermatozoa in the teleost and other vertebrates.

MicroRNAs and DNA methylation as epigenetic regulators of mitosis, meiosis and spermiogenesis

Spermatogenesis is composed of three distinctive phases, which include self-renewal of spermatogonia via mitosis, spermatocytes undergoing meiosis I/II and post-meiotic development of haploid spermatids via spermiogenesis. Spermatogenesis also involves condensation of chromatin in the spermatid head before transformation of spermatids to spermatozoa. Epigenetic regulation refers to changes of heritably cellular and physiological traits not caused by modifications in the DNA sequences of the chromatin such as mutations. Major advances have been made in the epigenetic regulation of spermatogenesis. In this review, we address the roles and mechanisms of epigenetic regulators, with a focus on the role of microRNAs and DNA methylation during mitosis, meiosis and spermiogenesis. We also highlight issues that deserve attention for further investigation on the epigenetic regulation of spermatogenesis. More importantly, a thorough understanding of the epigenetic regulation in spermatogenesis will provide insightful information into the etiology of some unexplained infertility, offering new approaches for the treatment of male infertility.

Expression and preliminary functional profiling of the let-7 family during porcine ovary follicle atresia

Most follicles in the mammalian ovary undergo atresia. Granulosa cell apoptosis is a hallmark of follicle atresia. Our previous study using a microRNA (miRNA) microarray showed that the let-7 microRNA family was differentially expressed during follicular atresia. However, whether the let-7 miRNA family members are related to porcine (Sus scrofa) ovary follicular apoptosis is unclear. In the current study, real-time quantitative polymerase chain reaction showed that the expression levels of let-7 family members in follicles and granulosa cells were similar to our microarray data, in which miRNAs let-7a, let-7b, let-7c, and let-7i were significantly decreased in early atretic and progressively atretic porcine ovary follicles compared with healthy follicles, while let-7g was highly expressed during follicle atresia. Furthermore, flow cytometric analysis and Hoechst33342 staining demonstrated that let-7g increased the apoptotic rate of cultured granulosa cells. In addition, let-7 target genes were predicted and annotated by TargetScan, PicTar, gene ontology and Kyoto encyclopedia of genes and genomes pathways. Our data provide new insight into the association between the let-7 miRNA family in granulosa cell programmed death.

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.

miR-1182 attenuates gastric cancer proliferation and metastasis by targeting the open reading frame of hTERT

In humans, telomerase reverse transcriptase (hTERT) determines the activity of telomerase. hTERT is an ideal anticancer target because it is universally expressed in cancer cells and plays a crucial role in carcinogenesis. In this study, we report the miR-1182-mediated post-transcriptional regulation of hTERT. Over-expression of miR-1182 in different gastric cancer cells decreased hTERT protein levels. Bioinformation and dual-luciferase assays revealed that miR-1182 modulated hTERT by binding to its open reading frame (ORF), and this miRNA recognizes elements in the nucleotide region between 2695 and 2719 of hTERT mRNA. Over-expression of hTERT by transfecting pIRES2-hTERT into U2OS cells was abolished by miR-1182, while pIRES2-hTERT-MT, in which miR-1182 target site was synonymously mutated, failed to respond to miR-1182. Further investigation revealed that miR-1182 inhibited gastric cancer proliferation and migration by targeting the ORF1 of hTERT. We also found that miR-1182 could attenuate the proliferative and metastatic potential of SGC-7901 cell in vivo. Moreover, we found a statistically significant inverse correlation between miR-1182 and hTERT protein levels in tissues from 42 gastric cancer patients. These data indicate that miR-1182 suppresses TERT, and thus it could be an effective target for the treatment of gastric cancer.

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.

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.

Small noncoding RNAs and male infertility

Small noncoding RNAs (ncRNAs) are a novel class of gene regulators that modulate gene expression at transcriptional, post-transcriptional, and epigenetic levels, and they play crucial roles in almost all cellular processes in eukaryotes. Recent studies have indicated that several types of small noncoding RNAs, including microRNAs (miRNAs), endo-small interference RNAs (endo-siRNAs), and Piwi-interacting RNAs (piRNAs), are expressed in the male germline and are required for spermatogenesis in animals. In this review, we summarize the recent knowledge of these small noncoding RNAs in male germ cells and their biological functions and mechanisms of action in animal spermatogenesis.