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

Spatiotemporal single-cell architecture of gene expression in the Caenorhabditis elegans germ cells

Spermatogenesis is an intricate and tightly controlled process encompassing various layers of gene expression regulation. Despite the advance of our current understanding, the developmental trajectory and regulatory mechanisms dictating spermatogenesis remain elusive. In this study, we have generated single-cell gene expression profiles for Caenorhabditis elegans sperm cells and constructed gene regulatory networks alongside the developmental trajectories of these cells. Our findings indicate that each pre- and post-developmental stage is closely linked by co-expressed genes, while simultaneously being uniquely identified by the combined expression of specific gene families. To illustrate the applicability of this exhaustive gene expression catalog, we used gene regulatory networks to uncover potential transcription factors for (1) the expression of genes in the phosphorylation pathway, identifying NHR-23-to-phosphatase regulation for the meiotic cell division process; and (2) the expression of constituent components of small RNA pathways, identifying ELT-1-to-Argonaute protein regulation for siRNA maintenance and sperm activation. We expect that this sperm cell-specific gene expression directory will prompt investigations into the underlying mechanisms determining anatomy, differentiation, and function across the reproductive system. Finally, our expression data can be explored using the web application CelegansGermAtlas ( https://scgerm-atlas.sjtu.edu.cn/website/#/home ).

Paternal contributions to mammalian zygote - Beyond sperm-oocyte fusion

Contrary to a common misconception that the fertilizing spermatozoon acts solely as a vehicle for paternal genome delivery to the zygote, this chapter aims to illustrate how the male gamete makes other essential contributions , including the sperm borne-oocyte activation factors, centrosome components, and components of the sperm proteome and transcriptome that help to lay the foundation for pregnancy establishment and maintenance to term, and the newborn and adult health. Our inquiry starts immediately after sperm plasma membrane fusion with its oocyte counterpart, the oolemma. Parallel to and following sperm incorporation in the egg cytoplasm, some of the sperm structures (perinuclear theca) are dissolved and spent to induce development, others (nucleus, centriole) are transformed into zygotic structures enabling it, and yet others (mitochondrial and fibrous sheath, axonemal microtubules and outer dense fibers) are recycled as to not stand in its way. Noteworthy advances in this research include the identification of several sperm-borne oocyte activating factor candidates, the role of autophagy in the post-fertilization sperm mitochondrion degradation, new insight into zygotic centrosome origins and function, and the contributions of sperm-delivered RNA cargos to early embryo development. In concluding remarks, the unresolved issues, and clinical and biotechnological implications of sperm-vectored paternal inheritance are discussed.

The microRNA-mediated apoptotic signaling axis in male reproduction: a possible and targetable culprit in male infertility

Recently, infertility has emerged as a significant and prevalent public health concern warranting considerable attention. Apoptosis, recognized as programmed cell death, constitutes a crucial process essential for the maintenance of normal spermatogenesis. Multiple investigations have illustrated that the dysregulated apoptosis of reproductive cells, encompassing spermatogonial stem cells, Sertoli cells, and Leydig cells, serves as a causative factor in male infertility. MicroRNAs represent a class of small RNA molecules that exert negative regulatory control over gene expression using direct interaction with messenger RNA transcripts. Previous studies have established that aberrant expression of miRNAs induces apoptosis in reproductive tissues, correlating with reproductive dysfunctions and infertility. In this review, we offer a comprehensive overview of miRNAs and their respective target genes implicated in the apoptotic process. As well, miRNAs are involved in multiple apoptotic signaling pathways, namely the PI3K/AKT, NOTCH, Wnt/β-catenin, and mTOR signaling cascades, exerting both negative and positive effects. We additionally elucidate the significant functions played by lncRNAs and circular RNAs as competing endogenous RNAs in the process of apoptosis within reproductive cells. We further illustrate that external factors, including silica nanoparticles, Cyclosporine A, and smoking, induce dysregulation of miRNAs, resulting in apoptosis within reproductive cells and subsequent male reproductive toxicity. Further, we discuss the implication of heat stress, hypoxia, and diabetes in reproductive cell apoptosis induced by miRNA dysregulation in male infertility. Finally, we demonstrate that the modulation of miRNAs via traditional and novel medicine could protect reproductive cells from apoptosis and be implemented as a therapeutic approach in male infertility.

The Small Non-Coding RNA Profile of Human and Mouse Sperm

Small non-coding RNAs constitute a dynamic epigenetic layer in mature spermatozoa that can exert transgenerational regulatory functions. Here, we review recent advances in the field of small RNAs in spermatozoa, how their profiles change in response to lifestyle or environmental factors, and their impact on offsprings' physiology. The profile of these RNAs changes dramatically during spermatozoa maturation. The majority of intracellular small RNAs during early spermatogenesis are miRNAs and piRNAs, but, in mature spermatozoa, tRNA- and rRNA-derived fragments (tRFs and rRFs, respectively) are the predominant forms, primarily delivered from the epididymis via extracellular vesicles. Diet, exercise, and environmental exposures have a direct effect on small RNA levels in spermatozoa, and this differential abundance can reprogram the development of the embryo. Offsprings of fathers with different lifestyles can have different phenotypes, including altered metabolism or behavior. Therefore, small RNAs in spermatozoa are emerging as an important epigenetic layer in development and transgenerational inheritance.

Exploring the Characters of Non-Coding RNAs in Spermatogenesis and Male Infertility

Infertility is a widespread clinical problem that affects human reproduction and species persistence worldwide. Around 40-70% of cases are due to male reproductive defects. Functional spermatogenesis (sperm production through several coordinated events) is at the heart of male fertility. Non-coding RNAs (ncRNAs) are the primary regulators of gene expression, controlling extensive critical cellular processes, for example proliferation, differentiation, apoptosis, and reproduction. Due to advancements in high-throughput sequencing tools, many studies have revealed that ncRNAs are widely expressed in germ cells, meiosis, spermatogenesis, sperm fertility, early post-fertilization development, and male infertility. The present review examines the biology and function of ncRNAs, including microRNAs, circular RNAs, and long ncRNAs, in spermatogenesis, their correlation with infertility, and their potential as biomarkers for sperm quality and fertility. The function of ncRNA in Sertoli cells (SCs) and Leydig cells (LCs) is also outlined throughout this study, because spermatogenesis requires testicular somatic cells to be involved in testicular development and male fertility. Meanwhile, the future development of ncRNAs for the clinical treatment of male infertility is also anticipated and discussed.

Do Delta-9-tetrahydrocannabinol and Cannabidiol have opposed effects on male fertility?

Cannabis sativa is a complex plant, renowned for its diverse array of bioactive compounds, the most prominent of which are delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). These compounds exhibit markedly opposing pharmacological effects, with THC being primarily psychoactive and CBD known for its non-psychoactive properties. In recent years, there has been growing interest in the potential health implications of these compounds, particularly concerning male reproductive health. Accumulating evidence over the past decade has alluded to the potential negative effects of THC, including its association with reduced sperm quality, altered hormone levels, changes in genetic and epigenetic profiles, and potential impacts on fertility. Conversely, emerging studies suggest that CBD may exert protective and beneficial effects on male reproductive health, possibly through its anti-inflammatory and antioxidant properties. This review aims to provide a comprehensive analysis of the current scientific literature, delineating the mechanisms by which THC and CBD influence male reproductive health, highlighting the disparities in their effects, and discussing the clinical and therapeutic implications of these findings.

RNA profiles differ between small and large extracellular vesicle subsets isolated from porcine seminal plasma

BACKGROUND

Extracellular vesicles (EVs) are essential for cell-to-cell communication because they transport functionally active molecules, including proteins, RNA, and lipids, from secretory cells to nearby or distant target cells. Seminal plasma contains a large number of EVs (sEVs) that are phenotypically heterogeneous. The aim of the present study was to identify the RNA species contained in two subsets of porcine sEVs of different sizes, namely small sEVs (S-sEVs) and large sEVs (L-sEVs). The two subsets of sEVs were isolated from 54 seminal plasma samples by a method combining serial centrifugations, size exclusion chromatography, and ultrafiltration. The sEVs were characterized using an orthogonal approach. Analysis of RNA content and quantification were performed using RNA-seq analysis.

RESULTS

The two subsets of sEVs had different size distributions (P < 0.001). They also showed differences in concentration, morphology, and specific protein markers (P < 0.05). A total of 735 RNAs were identified and quantified, which included: (1) mRNAs, rRNAs, snoRNAs, snRNAs, tRNAs, other ncRNAs (termed as "all RNAs"), (2) miRNAs and (3) piRNAs. The distribution pattern of these RNA classes differed between S-sEVs and L-sEVs (P < 0.05). More than half of "all RNAs", miRNAs and piRNAs were found to be differentially abundant between S- and L-sEVs (FDR < 0.1%). Among the differentially abundant RNAs, "all RNAs" were more abundant in L- than in S-sEVs, whereas the most of the miRNAs were more abundant in S- than in L-sEVs. Differentially abundant piRNAs were equally distributed between S- and L-sEVs. Some of the all RNAs and miRNAs found to be differentially abundant between S- and L-sEVs were associated with sperm quality and functionality and male fertility success.

CONCLUSIONS

Small and large sEVs isolated from porcine seminal plasma show quantitative differences in RNA content. These differences would suggest that each sEV subtype exerts different functional activities in the targeted cells, namely spermatozoa and functional cells of the female reproductive tract.

microRNA as an Important Mediator in the Regulation of Male Gallus gallus domesticus Reproduction: Current State of the Problem

During all periods of male ontogenesis, physiological processes responsible for the correct functioning of reproductive organs and spermatogenesis are under the influence of various factors (neuro-humoral, genetic, and paratypical). Recently, the attention of researchers has increasingly turned to the study of epigenetic factors. In scientific publications, one can increasingly find references to the direct role of microRNAs, small non-coding RNAs involved in post-transcriptional regulation of gene expression, in the processes of development and functioning of reproductive organs. Although the role of microRNAs in the reproduction of mammals, including humans, has been intensively studied, this area of knowledge in birds remains under-researched and limited to single experiments. This is likely due to the unique features of embryogenesis and the structure of the avian reproductive system. This review summarizes the current state of knowledge on the role of microRNAs in avian reproduction. Insight into the molecular basis of spermatogenesis in Gallus gallus domesticus is provided. Data on the functions and mechanisms by which microRNAs influence the processes of growth, development, and formation of rooster germ cells that determine the necessary morphofunctional qualitative characteristics of mature spermatozoa are summarized. Particular attention is paid to miRNA biogenesis as an important step affecting the success of spermatogenesis, as well as the role of miRNAs in avian sex differentiation during early embryogenesis. The modern literature sources systematized in this review, revealing the questions about the role of miRNAs in the reproductive function of birds, create a theoretical basis and define new perspectives and directions for further research in this field.

Developmental epigenetics: Understanding genetic and sexually dimorphic responses to parental diet and outcomes following assisted reproduction

The developmental integrity and wellbeing of offspring are influenced by events that occur in utero, particularly around the time of conception. While extraneous factors such as environmental temperature and exposure to environmental chemicals can each have a bearing on these events, the epigenetic mechanisms that direct cellular differentiation during early development in ruminants are best described for studies which have investigated the effects of parental nutrition or pregnancy outcomes following assisted reproduction. In this article the case is made that the genetic constitution of an individual directs epigenetic responses to environmental stimuli, and consideration in this regard is also given to the origins of sexual dimorphism and mechanisms of germline intergenerational inheritance. These aspects are considered in the context of epigenetic modifications that take place during the normal course of gametogenesis and embryogenesis, and again following either dietary or procedural interventions such as embryo culture. A recurring feature of such interventions, irrespective of species, is that one carbon metabolic pathways are invariably disrupted, and this affects the provision of methyl groups for chromatin and RNA methylation. Inter-specific variation in how these pathways operate, both within the liver and in germ cells, indicates that ruminants may be particularly sensitive in this regard. Recent advances in genomic technologies should enable rapid progress in these areas. Knowledge gained can be integrated into breed improvement programs and used to tailor management practices to specific breeds and strains (including sexes) within breeds. Ultimately, consideration should be given to integrating metagenomics into analyses of genetic-directed epigenetic programming of animal development.

Sperm RNA code in spermatogenesis and male infertility

Spermatozoa are traditionally thought to be transcriptionally inert, but recent studies have revealed the presence of sperm RNA, some of which is derived from the residues of spermatocyte transcription and some from epididymosomes. Paternal sperm RNA can be affected by external factors and further modified at the post-transcriptional level, for example N6-methyladenosine (m6A), thus shaping spermatogenesis and reproductive outcome. This review briefly introduces the origin of sperm RNA and, on this basis, summarizes the current knowledge on RNA modifications and their functional role in spermatogenesis and male infertility. The bottlenecks and knowledge gaps in the current research on RNA modification in male reproduction have also been indicated. Further investigations are needed to elucidate the functional consequences of these modifications, providing new therapeutic and preventive strategies for reproductive health and genetic inheritance.

MicroRNA Analysis of In Vitro Differentiation of Spermatogonial Stem Cells Using a 3D Human Testis Organoid System

Spermatogenesis produces male gametes from spermatogonial stem cells (SSC), beginning at puberty. Modern-day laboratory techniques allow for the long-term culture of SSC and in vitro spermatogenesis. The specific biochemical processes that occur during spermatogenesis remain poorly understood. One particular element of spermatogenesis that has yet to be characterized is the role of microRNAs (miRNA), short, non-transcribed RNAs that act as post-translational regulators of gene activity. In this study, we seek to describe the presence of miRNA in a two-dimensional (2D) SSC culture and a 3D human testis organoid (HTO) system. Testicular cells were isolated from the frozen tissue of three brain-dead subjects, propagated in cultures for four to five weeks, and used to form 3D HTOs. Following organoid formation, differentiation of testicular cells was induced. RNA was isolated from the whole testis tissue (WT) showing in vivo conditions, HTO Day Zero (2D SSC culture), Day 2 HTOs, and Day 23 differentiated HTOs, then analyzed for changes in miRNA expression using the Nanostring nCounter miRNA panel. One hundred ninety-five miRNAs met the criteria for expression in WT, 186 in 2D culture, 190 in Day 2 HTOs, and 187 in differentiated HTOs. One hundred thirty-three miRNAs were common across all conditions, and 41, 17, 6, and 11 miRNAs were unique for WT, 2D culture, Day 2 HTOs, and differentiated HTOs, respectively. Twenty-two miRNAs were similar between WT and differentiated HTOS. We evaluated the miRNA expression profiles of progressively complex stages of testicular cell culture, culminating in a 3D organoid model capable of meiotic differentiation, and compared these to WT. We identified a great variance between the native tissue and the culture system; however, some miRNAs are preserved. These data may provide avenues for deeper understanding of spermatogenesis and the ability to improve this process in the laboratory. Research on miRNA continues to be an essential avenue for understanding human spermatogenesis.

From TgO/GABA-AT, GABA, and T-263 Mutant to Conception of Toxoplasma

Toxoplasma gondii causes morbidity, mortality, and disseminates widely via cat sexual stages. Here, we find T. gondii ornithine aminotransferase (OAT) is conserved across phyla. We solve TgO/GABA-AT structures with bound inactivators at 1.55 Å and identify an inactivator selective for TgO/GABA-AT over human OAT and GABA-AT. However, abrogating TgO/GABA-AT genetically does not diminish replication, virulence, cyst-formation, or eliminate cat's oocyst shedding. Increased sporozoite/merozoite TgO/GABA-AT expression led to our study of a mutagenized clone with oocyst formation blocked, arresting after forming male and female gametes, with "Rosetta stone"-like mutations in genes expressed in merozoites. Mutations are similar to those in organisms from plants to mammals, causing defects in conception and zygote formation, affecting merozoite capacitation, pH/ionicity/sodium-GABA concentrations, drawing attention to cyclic AMP/PKA, and genes enhancing energy or substrate formation in TgO/GABA-AT-related-pathways. These candidates potentially influence merozoite's capacity to make gametes that fuse to become zygotes, thereby contaminating environments and causing disease.