Sperm-borne microRNA-34c is required for the first cleavage division in mouse

Unraveling the role of sperm retained histones in bull fertility and daughter fertility

During spermatogenesis, a substantial proportion of histones are substituted by protamine to condense the genome within the sperm head. Studies indicate that a minority of histones, typically ranging from 1 to 15 %, persist in mammalian sperm post-substitution. The persistence of histones in the zygote facilitates chromatin accessibility to transcription factors in regions crucial for early embryonic development. Nevertheless, the potential causal relationship between retained histones and fertility phenotypes remains uncertain. This study seeks to investigate this relationship. The results indicate that in mature bovine sperm, regions of DNA associated with fertility that bind to histones are primarily concentrated in promoters and transcription start sites, potentially impacting bull fertility and offspring fertility through the regulation of relevant genes. Furthermore, microRNAs and estradiol/ESR are suggested to be the main regulators of the canonical pathways identified, highlighting the need for additional research to investigate their potential utility as biomarkers.

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.

High seminal BPA in IVF patients correlates with lower sperm count and up-regulated miR-21 and miR-130a

Bisphenol A (BPA) is a widespread industrial chemical, used as the key monomer of polycarbonate plastics and epoxy resins. BPA has been detected in human seminal fluid and has been correlated with changes in sperm parameters, crucial in determining male fertility. In this study, semen samples were collected from 100 patients aged 29-47 years undergoing fertility assessment between 2021 and 2023 and analyzed according to WHO guidelines. BPA levels in the seminal plasma were then measured through an enzyme-linked immunosorbent assay (ELISA) and compared to sperm quality metrics. The relative mRNA/miRNA expression of key genes associated to male reproduction, including androgen receptor, miR-34c, miR-21, miR-130a, was then quantified and compared between groups with high or low BPA content. Our results revealed that BPA levels were increased with age and were negatively correlated with sperm counts (p<0.05). The negative correlation remained significant when patients were age-matched. No other relationships between seminal BPA and motility, morphology or DNA fragmentation levels were observed. qPCR analysis showed that androgen receptor mRNA expression was significantly greater in sperm with high seminal BPA (p<0.05). Moreover, we found that the expression of miR-21 and miR-130a was also upregulated in the higher BPA group (p<0.05). These results display a relationship between BPA content in the semen and male fertility parameters, and provide insights into the molecular mechanisms through which BPA may be affecting male reproductive capability. Ultimately, this research can potentially drive changes to guidelines and exposure limits for BPA exposure.

Episodic ozone exposure in Long-Evans rats has limited effects on cauda sperm motility and non-coding RNA populations

Epidemiological evidence suggests the potential for air pollutants to induce male reproductive toxicity. In experimental studies, exposure to ozone during sensitive windows in the sperm lifecycle has been associated with impaired sperm motility. Subsequently, we sought to investigate the effects of episodic exposure to ozone during sperm maturation in the rat. Long-Evans rats were exposed to either filtered air or ozone (0.4 or 0.8 ppm) for five non-consecutive days over two weeks. Ozone exposure did not impact male reproductive organ weights or sperm motility ∼24 hours following the final exposure. Furthermore, circulating sex hormones remained unchanged despite increased T3 and T4 in the 0.8 ppm group. While there was indication of altered adrenergic signaling attributable to ozone exposure in the testis, there were minimal impacts on small non-coding RNAs detected in cauda sperm. Only two piwi-interacting RNAs (piRNAs) were altered in the mature sperm of ozone-exposed rats (piR-rno-346434 and piR-rno-227431). Data across all rats were next analyzed to identify any non-coding RNAs that may be correlated with reduced sperm motility. A total of 7 microRNAs (miRNAs), 8 RNA fragments, and 1682 piRNAs correlated well with sperm motility. Utilizing our exposure paradigm herein, we were unable to substantiate the relationship between ozone exposure during maturation with sperm motility. However, these approaches served to identify a suite of non-coding RNAs that were associated with sperm motility in rats. With additional investigation, these RNAs may prove to have functional roles in the acquisition of motility or be unique biomarkers for male reproductive toxicity.

From follicle to blastocyst: microRNA-34c from follicular fluid-derived extracellular vesicles modulates blastocyst quality

BACKGROUND

Within the follicular fluid, extracellular vesicles (EVs) guide oocyte growth through their cargo microRNAs (miRNAs). Here, we investigated the role of EVs and their cargo miRNAs by linking the miRNAs found in EVs, derived from the fluid of an individual follicle, to the ability of its oocyte to become a blastocyst (competent) or not (non-competent).

METHODS

Bovine antral follicles were dissected, categorized as small (2-4 mm) or large (5-8 mm) and the corresponding oocytes were subjected to individual maturation, fertilization and embryo culture to the blastocyst stage. Follicular fluid was pooled in 4 groups (4 replicates) based on follicle size and competence of the corresponding oocyte to produce a blastocyst. Follicular fluid-derived EVs were isolated, characterized, and subjected to miRNA-sequencing (Illumina Miseq) to assess differential expression (DE) in the 4 groups. Functional validation of the effect of miR-34c on embryo development was performed by supplementation of mimics and inhibitors during in vitro maturation (IVM).

RESULTS

We identified 16 DE miRNAs linked to oocyte competence when follicular size was not considered. Within the large and small follicles, 46 DE miRNAs were driving blastocyst formation in each group. Comparison of EVs from competent small and large follicles revealed 90 DE miRNAs. Cell regulation, cell differentiation, cell cycle, and metabolic process regulation were the most enriched pathways targeted by the DE miRNAs from competent oocytes. We identified bta-miR-34c as the most abundant in follicular fluid containing competent oocytes. Supplementation of miR-34c mimic and inhibitor during IVM did not affect embryo development. However, blastocyst quality, as evidenced by higher cell numbers, was significantly improved following oocyte IVM in the presence of miR-34c mimics, while miR-34c inhibitors resulted in the opposite effect.

CONCLUSION

This study demonstrates the regulatory effect of miRNAs from follicular fluid-derived EVs on oocyte competence acquisition, providing a further basis for understanding the significance of miRNAs in oocyte maturation and embryonic development. Up-regulation of miR-34c in EVs from follicular fluid containing competent oocytes and the positive impact of miR-34c mimics added during IVM on the resulting blastocysts indicate its pivotal role in oocyte competence.

Signatures of metabolic diseases on spermatogenesis and testicular metabolism

Diets leading to caloric overload are linked to metabolic disorders and reproductive function impairment. Metabolic and hormonal abnormalities stand out as defining features of metabolic disorders, and substantially affect the functionality of the testis. Metabolic disorders induce testicular metabolic dysfunction, chronic inflammation and oxidative stress. The disruption of gastrointestinal, pancreatic, adipose tissue and testicular hormonal regulation induced by metabolic disorders can also contribute to a state of compromised fertility. In this Review, we will delve into the effects of high-fat diets and metabolic disorders on testicular metabolism and spermatogenesis, which are crucial elements for male reproductive function. Moreover, metabolic disorders have been shown to influence the epigenome of male gametes and might have a potential role in transmitting phenotype traits across generations. However, the existing evidence strongly underscores the unmet need to understand the mechanisms responsible for transgenerational paternal inheritance of male reproductive function impairment related to metabolic disorders. This knowledge could be useful for developing targeted interventions to prevent, counteract, and most of all break the perpetuation chain of male reproductive dysfunction associated with metabolic disorders across generations.

Sperm-borne miR-34c-5p and miR-191-3p as markers for sperm motility and embryo developmental competence

BACKGROUND

Sperm-borne microRNAs play a pivotal role in influencing essential cellular processes during fertilization, impacting the quality of embryo development. Dysregulated microRNA profiles have been associated with compromised embryonic development and increased incidences of pregnancy loss.

OBJECTIVE

This study aimed to investigate the potential associations between the abundance of miR-34c-5p and miR-191-3p in human spermatozoa with sperm quality, as well as with embryo quality and metabolic performance during in vitro development.

MATERIALS AND METHODS

Thirteen couples who underwent a total of 13 cycles participated in this study. The sperm quality was assessed using conventional methods following World Health Organization guidelines. Quantitative polymerase chain reaction was employed to measure microRNA abundance in spermatozoa. Embryos were categorized as good, lagging, or bad based on morphokinetic evaluation. Evaluation of embryo metabolic performance involved tracking changes in specific metabolites within the cultured media using nuclear magnetic resonance spectroscopy. Statistical analysis was conducted to explore the correlation between microRNA abundance in human spermatozoa and all other collected data.

RESULTS

Our findings revealed a negative correlation between the abundance of miR-34c-5p (but not miR-191-3p) and total sperm motility, potentially mediated by the modulation of key signaling pathways. Additionally, higher levels of miR-34c-5p in spermatozoa were strongly associated with the consumption or release of key metabolites by developing embryos, particularly those linked with lipid and glucose metabolism, suggesting enhanced metabolic performance, while miR-191-3p was mostly associated with glucose consumption. Concurrently, only miR-34c-5p content in spermatozoa correlated with higher embryo quality.

DISCUSSION AND CONCLUSION

This study provides evidence suggesting that the abundance of miR-34c-5p in spermatozoa is correlated not only with total sperm motility but also with markers of embryo developmental competence, highlighting the potential significance of this sperm microRNA content as a biomarker in assisted reproduction.

Evaluation of microRNA expression profiles in human sperm frozen using permeable cryoprotectant-free droplet vitrification and conventional methods

For sperm cryopreservation, the conventional method, which requires glycerol, has been used for a long time. In addition, the permeable cryoprotectant-free vitrification method has been continuously studied. Although the differences of cryopreservation effects between the two methods have being studied, differences in microRNA (miRNA) profiles between them remain unclear. In this study, we investigated the differences in miRNA expression profiles among conventional freezing sperm, droplet vitrification freezing sperm and fresh human sperm. We also analyzed the differences between these methods in terms of differentially expressed miRNAs (DEmiRs) related to early embryonic development and paternal epigenetics. Our results showed no significant differences between the cryopreservation methods in terms of sperm motility ratio, plasma membrane integrity, DNA integrity, mitochondrial membrane potential, acrosome integrity, and ultrastructural damage. However, sperm miRNA-sequencing showed differences between the two methods in terms of the numbers of DEmiRs (28 and 19 with vitrification using a nonpermeable cryoprotectant and the conventional method, respectively) in postthaw and fresh sperm specimens. DEmiRs related to early embryonic development and paternal epigenetics mainly included common DEmiRs between the groups. Our results showed that the differences between conventional freezing and droplet vitrification were minimal in terms of miRNA expression related to embryonic development and epigenetics. Changes in sperm miRNA expression due to freezing are not always detrimental to embryonic development. This study compared differences in miRNA expression profiles before and after cryopreservation between cryopreservation by conventional and vitrification methods. It offers a new perspective to evaluate various methods of sperm cryopreservation.

Sperm long non-coding RNAs as markers for ram fertility

It is critical in sheep farming to accurately estimate ram fertility for maintaining reproductive effectiveness and for production profitability. However, there is currently a lack of reliable biomarkers to estimate semen quality and ram fertility, which is hindering advances in animal science and technology. The objective of this study was to uncover long non-coding RNAs (lncRNAs) in sperm from rams with distinct fertility phenotypes. Mature rams were allocated into two groups: high and low fertility (HF; n = 31; 94.5 ± 2.8%, LF; n = 25; 83.1 ± 5.73%; P = 0.028) according to the pregnancy rates sired by the rams (average pregnancy rate; 89.4 ± 7.2%). Total RNAs were isolated from sperm of the highest- and lowest-fertility rams (n = 4, pregnancy rate; 99.2 ± 1.6%, and 73.6 ± 4.4%, respectively) followed by next-generation sequencing of the transcripts. We uncovered 11,209 lncRNAs from the sperm of rams with HF and LF. In comparison to each other, there were 93 differentially expressed (DE) lncRNAs in sperm from the two distinct fertility phenotypes. Of these, 141 mRNAs were upregulated and 134 were downregulated between HF and LF, respectively. Genes commonly enriched for 9 + 2 motile cilium and sperm flagellum were ABHD2, AK1, CABS1, ROPN1, SEPTIN2, SLIRP, and TEKT3. Moreover, CABS1, CCDC39, CFAP97D1, ROPN1, SLIRP, TEKT3, and TTC12 were commonly enriched in flagellated sperm motility and sperm motility. Differentially expressed mRNAs were enriched in the top 16 KEGG pathways. Targets of the differentially expressed lncRNAs elucidate functions in cis and trans manner using the genetic context of the lncRNA locus, and lncRNA sequences revealed 471 mRNAs targets of 10 lncRNAs. This study illustrates the existence of potential lncRNA biomarkers that can be implemented in analyzing the quality of ram sperm and determining the sperm fertility and is used in breeding soundness exams for precision livestock farming to ensure food security on a global scale.

Could the sperm epigenome become a diagnostic tool for evaluation of the infertile man?

Although male infertility is currently diagnosed when abnormal sperm parameters are found, the poor predictive ability of sperm parameters on natural fecundity and medically assisted reproduction outcome poses the need for improved diagnostic techniques for male infertility. The accumulating evidence about the role played by the sperm epigenome in modulation of the early phases of embryonic development has led researchers to focus on the epigenetic mechanisms within the sperm epigenome to find new molecular markers of male infertility. Indeed, sperm epigenome abnormalities could explain some cases of unexplained male infertility in men showing normal sperm parameters and were found to be associated with poor embryo development in IVF cycles. The present mini-review summarizes the current knowledge about this interesting topic, starting from a description of the epigenetic mechanisms of gene expression regulation (i.e. DNA methylation, histone modifications, and non-coding RNAs' activity). We also discuss possible mechanisms by which environmental factors might cause epigenetic changes in the human germline and affect embryonic development, as well as subsequent generations' phenotypes. Studies demonstrating sperm epigenome abnormalities in men with male infertility are reviewed, with particular emphasis on those with the more severe form of spermatogenic dysfunction. Observations demonstrate that the diagnostic and prognostic efficacy of sperm epigenome evaluation will help facilitate the management of men with male factor infertility.

Impact of Sire on Embryo Development and Pregnancy

The use of in vitro embryo production (IVP) has increased globally, particularly in the United States. Although maternal factors influencing embryo development have been extensively studied, the influence of the sire is not well understood. Sperm plays a crucial role in embryo development providing DNA, triggering oocyte maturation, and aiding in mitosis. Current sire fertility measurements do not consistently align with embryo production outcomes. Low-fertility sires may perform well in IVP systems but produce fewer pregnancies. Testing sires in vitro could identify characteristics affecting embryo development and pregnancy loss risk in IVP and embryo transfer programs.

MicroRNAs in Male Fertility

Around 50% of all occurrences of infertility are attributable to the male factor, which is a significant global public health concern. There are numerous circumstances that might interfere with spermatogenesis and cause the body to produce abnormal sperm. While evaluating sperm, the count, the speed at which they migrate, and their appearance are the three primary characteristics that are analyzed. MicroRNAs, also known as miRNAs, are present in all physiological fluids and tissues. They participate in both physiological and pathological processes. Researches have demonstrated that the expression of microRNA genes differs in infertile men. These genes regulate spermatogenesis at various stages and in several male reproductive cells. Hence, microRNAs have the potential to act as useful indicators in the diagnosis and treatment of male infertility and other diseases affecting male reproduction. Despite this, additional research is necessary to determine the precise miRNA regulation mechanisms.

Small RNAs: an ideal choice as sperm quality biomarkers

Spermatozoa were classically known as vehicles for the delivery of the paternal genome to the oocyte. However, in 1962, spermatozoa were discovered to carry significant amounts of RNA in them, which raised questions about the significance of these molecules in such a highly specialized cell. Scientific research in the last six decades has investigated the biological significance of sperm RNAs by various means. Irrespective of what sperm RNAs do, their presence in spermatozoa has attracted attention for their exploitation as biomarkers of fertility. Research in this direction started in the year 2000 and is still underway. A major hurdle in this research is the definition of the standard human sperm RNAome. Only a few normozoospermic samples have been analyzed to define the normal sperm RNAome. In this article, we provide a perspective on the suitability of sperm RNAs as biomarkers of fertility and the importance of defining the normal sperm RNAome before we can succeed in identifying RNA-based biomarkers of sperm quality and fertility. The identification of sperm RNA biomarkers of fertility can be exploited for quality screening of donor sperm samples, explain infertility in idiopathic cases, and RNA therapeutics for the treatment of male infertility.

Insights into embryonic chromosomal instability: mechanisms of DNA elimination during mammalian preimplantation development

Mammalian preimplantation embryos often contend with aneuploidy that arose either by the inheritance of meiotic errors from the gametes, or from mitotic mis-segregation events that occurred following fertilization. Regardless of the origin, mis-segregated chromosomes become encapsulated in micronuclei (MN) that are spatially isolated from the main nucleus. Much of our knowledge of MN formation comes from dividing somatic cells during tumorigenesis, but the error-prone cleavage-stage of early embryogenesis is fundamentally different. One unique aspect is that cellular fragmentation (CF), whereby small subcellular bodies pinch off embryonic blastomeres, is frequently observed. CF has been detected in both in vitro and in vivo-derived embryos and likely represents a response to chromosome mis-segregation since it only appears after MN formation. There are multiple fates for MN, including sequestration into CFs, but the molecular mechanism(s) by which this occurs remains unclear. Due to nuclear envelope rupture, the chromosomal material contained within MN and CFs becomes susceptible to double stranded-DNA breaks. Despite this damage, embryos may still progress to the blastocyst stage and exclude chromosome-containing CFs, as well as non-dividing aneuploid blastomeres, from participating in further development. Whether these are attempts to rectify MN formation or eliminate embryos with poor implantation potential is unknown and this review will discuss the potential implications of DNA removal by CF/blastomere exclusion. We will also extrapolate what is known about the intracellular pathways mediating MN formation and rupture in somatic cells to preimplantation embryogenesis and how nuclear budding and DNA release into the cytoplasm may impact overall development.

Expression of sperm microRNAs related to bull fertility: A systematic review

In this study we proposed to address the following question: "Are there differentially expressed sperm microRNAs related to fertility in bulls?". A systematic review of scientific literature until November 2022 was performed, in accordance with PRISMA guidelines. The main outcome was differentially expressed sperm microRNA from bulls with low versus high fertility profiles identified by using different methods such as field fertility evaluation and sperm laboratory analysis. Were identified 786 documents, of which 13 were selected for qualitative analysis. A total of 182 unique differentially expressed miRNAs were identified, among these, 49 miRNAs were found in common between at least two studies. It is believed that from these 49 miRNAs, it is possible that miRNAs such as miR-10a, -10b, -103, -15b, -122, -125b, -126-5p, -151-5p, -193a-5p, -196a, -27a-5p and -99b could be potential universal biomarkers to assess the reproductive potential of males.

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.

Functions and mechanism of noncoding RNA in regulation and differentiation of male mammalian reproduction

Noncoding RNAs (ncRNAs) are active regulators of a wide range of biological and physiological processes, including the majority of mammalian reproductive events. Knowledge of the biological activities of ncRNAs in the context of mammalian reproduction will allow for a more comprehensive and comparative understanding of male sterility and fertility. In this review, we describe recent advances in ncRNA-mediated control of mammalian reproduction and emphasize the importance of ncRNAs in several aspects of mammalian reproduction, such as germ cell biogenesis and reproductive organ activity. Furthermore, we focus on gene expression regulatory feedback loops including hormones and ncRNA expression to better understand germ cell commitment and reproductive organ function. Finally, this study shows the role of ncRNAs in male reproductive failure and provides suggestions for further research.

Expression of miR-138 in cryopreserved bovine sperm is related to their fertility potential

BACKGROUND

MicroRNAs (miRNAs) are small, single-stranded, non-coding RNA molecules of 22-24 nucleotides that regulate gene expression. In the last decade, miRNAs have been described in sperm of several mammals, including cattle. It is known that miRNAs can act as key gene regulators of early embryogenesis in mice and humans; however, little is known about the content, expression, and function of sperm-borne miRNAs in early bovine embryo. In this study, total sperm RNA was isolated from 29 cryopreserved sperm samples (each coming from a separate bull) using a RNeasy kit and treatment with DNase I. RNA concentration and purity were determined through an Epoch spectrophotometer and an Agilent Bioanalyzer. The expression of 10 candidate miRNAs in bovine sperm (bta-miR-10a, bta-miR-10b, bta-miR-138, bta-miR-146b, bta-miR-19b, bta-miR-26a, bta-miR-34a, bta-miR-449a, bta-miR-495 and bta-miR-7), previously identified in testis and/or epididymis, was evaluated with RT-qPCR. The cel-miR-39-3p was used as a spike-in exogenous control. Nonparametric Mann-Whitney tests were run to evaluate which miRNAs were differentially expressed between bulls with high fertility [HF; non-return rates (NRR) ranging from 39.5 to 43.5] and those with subfertility (SF; NRR ranging from 33.3 to 39.3). Several sperm functionality parameters (e.g., viability, membrane stability or oxygen consumption, among others) were measured by multiplexing flow cytometry and oxygen sensing technologies.

RESULTS

RNA concentration and purity (260/280 nm ratio) (mean ± SD) from the 29 samples were 99.3 ± 84.6 ng/µL and 1.97 ± 0.72, respectively. Bioanalyzer results confirmed the lack of RNA from somatic cells. In terms of the presence or absence of miRNAs, and after applying the Livak method, 8 out of 10 miRNAs (bta-miR-10b, -138, -146b, -19b, -26a, -449a, -495, -7) were consistently detected in bovine sperm, whereas the other two (bta-miR-10a, and -34a) were absent. Interestingly, the relative expression of one miRNA (bta-miR-138) in sperm was significantly lower in the SF than in the HF group (P = 0.038). In addition to being associated to fertility potential, the presence of this miRNA was found to be negatively correlated with sperm oxygen consumption. The expression of three other miRNAs (bta-miR-19b, bta-miR-26a and bta-miR-7) was also correlated with sperm function variables.

CONCLUSIONS

In conclusion, although functional validation studies are required to confirm these results, this study suggests that sperm bta-miR-138 is involved in fertilization events and beyond, and supports its use as a fertility biomarker in cattle.

Pluripotency-Associated microRNAs in Early Vertebrate Embryos and Stem Cells

MicroRNAs (miRNAs), small non-coding RNA molecules, regulate a wide range of critical biological processes, such as proliferation, cell cycle progression, differentiation, survival, and apoptosis, in many cell types. The regulatory functions of miRNAs in embryogenesis and stem cell properties have been extensively investigated since the early years of miRNA discovery. In this review, we will compare and discuss the impact of stem-cell-specific miRNA clusters on the maintenance and regulation of early embryonic development, pluripotency, and self-renewal of embryonic stem cells, particularly in vertebrates.

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.

Comparative analysis of microRNA and messengerRNA expression profiles in plateau zokor testicular cells under reproductive suppression

Introduction

Reproductive suppression is an adaptive strategy that affects the success rate and reproductive efficiency in animals, which in turn affects population continuation and evolution. However, no studies on the miRNAs in testicular development and spermatogenesis regulatory mechanisms under reproductive suppression have been reported.

Methods

In this study, the differentially expressed (DE) miRNAs, miRNA-mRNA interaction network and function of the plateau zokor testicular cells of non-breeders and breeders during the breeding season were comprehensively analyzed by transcriptomics.

Results

In total, 381 known and 94 novel miRNAs were determined. Compared with that in the breeders, 70 downregulated and 68 upregulated DE miRNAs were identified in the non-breeders. We predicted 1670 significant target mRNAs by analyzing the miRNA and mRNA expression profiles. According to the miRNA-mRNA interaction network, the target mRNAs of the DE miRNAs were related to testicular development and spermatogenesis. GO indicate that the target mRNAs were related to testicular development and spermatogenesis. KEGG indicate that pathways of target mRNAs enrichment related to testicular development, spermatogenesis, and energy metabolism. PROK2 was determined as the target mRNA of rno-miR-143-3p.

Discussion

Our study offers a basis for the regulatory mechanisms of miRNAs in testicular development and spermatogenesis in plateau zokor under reproductive suppression and offers a reference for reproductive regulation.

In vivo functions of miRNAs in mammalian spermatogenesis

MicroRNAs (miRNAs) are believed to play important roles in mammalian spermatogenesis mainly because spermatogenesis is more or less disrupted when genes encoding key enzymes for miRNA biogenesis are mutated. However, it is challenging to study the functions of individual miRNAs due to their family-wise high sequence similarities and the clustered genomic distributions of their genes, both of which expose difficulties in using genetic methods. Accumulating evidence shows that a number of miRNAs indeed play important roles in mammalian spermatogenesis and the underlying mechanisms start to be understood. In this mini review, we focus on highlighting the roles of miRNAs in mammalian spermatogenesis elucidated mainly by using in vivo genetic methods and on discussing the underlying mechanisms. We propose that studies on the roles of miRNAs in spermatogenesis should and can be conducted in a more fruitful way given the progress in traditional methods and the birth of new technologies.

Sperm-borne microRNA-34c regulates maternal mRNA degradation and preimplantation embryonic development in mice

BACKGROUND

Studies have shown that sperm-borne microRNAs (miRNAs) are involved in mammalian preimplantation embryonic development. In humans, spermatozoan miR-34c levels are correlated with in vitro fertilization outcomes, such as embryo quality and the clinical pregnancy and live birth rates. In rabbits and cows, miR-34c improves the developmental competence of embryos generated by somatic cell nuclear transfer. However, the mechanisms underlying the regulation of embryonic development by miR-34c remain unknown.

METHODS

Female C57BL/6 mice (6-8 weeks old) were superovulated, and pronucleated zygotes were collected and microinjected with an miR-34c inhibitor or a negative-control RNA. The embryonic development of the microinjected zygotes was evaluated, and the messenger RNA (mRNA) expression profiles of the embryos at the two-cell, four-cell and blastocyst stages (five embryos per group) were determined by RNA sequencing analysis. Gene expression levels were verified by reverse transcription-quantitative polymerase chain reaction. Cluster analysis and heat map visualization were performed to detect differentially expressed mRNAs. Pathway and process enrichment analyses were performed using ontology resources. Differentially expressed mRNAs were systematically analyzed using the Search Tool for the Retrieval of Interacting Genes/Proteins database to determine their biological functions.

RESULTS

Embryonic developmental potential was significantly reduced in zygotes microinjected with the miR-34c inhibitor compared with those microinjected with a negative-control RNA. Two-cell stage embryos microinjected with an miR-34c inhibitor presented altered transcriptomic profiles, with upregulated expression of maternal miR-34c target mRNAs and classical maternal mRNAs. Differentially expressed transcripts were mainly of genes associated with lipid metabolism and cellular membrane function at the two-cell stage, with cell-cycle phase transition and energy metabolism at the four-cell stage; and with vesicle organization, lipid biosynthetic process and endomembrane system organization at the blastocyst stage. We also showed that genes related to preimplantation embryonic development, including Alkbh4, Sp1, Mapk14, Sin3a, Sdc1 and Laptm4b, were significantly downregulated after microinjection of an miR-34c inhibitor.

CONCLUSIONS

Sperm-borne miR-34c may regulate preimplantation embryonic development by affecting multiple biological processes, such as maternal mRNA degradation, cellular metabolism, cell proliferation and blastocyst implantation. Our data demonstrate the importance of sperm-derived miRNAs in the development of preimplantation embryos.

Selecting Normalizers for MicroRNA RT-qPCR Expression Analysis in Murine Preimplantation Embryos and the Associated Conditioned Culture Media

Normalizing RT-qPCR miRNA datasets that encompass numerous preimplantation embryo stages requires the identification of miRNAs that may be used as stable reference genes. A need has also arisen for the normalization of the accompanying conditioned culture media as extracellular miRNAs may serve as biomarkers of embryo developmental competence. Here, we evaluate the stability of six commonly used miRNA normalization candidates, as well as small nuclear U6, using five different means of evaluation (BestKeeper, NormFinder, geNorm, the comparative Delta Ct method and RefFinder comprehensive analysis) to assess their stability throughout murine preimplantation embryo development from the oocyte to the late blastocyst stages, both in whole embryos and the associated conditioned culture media. In descending order of effectiveness, miR-16, miR-191 and miR-106 were identified as the most stable individual reference miRNAs for developing whole CD1 murine preimplantation embryos, while miR-16, miR-106 and miR-103 were ideal for the conditioned culture media. Notably, the widely used U6 reference was among the least appropriate for normalizing both whole embryo and conditioned media miRNA datasets. Incorporating multiple reference miRNAs into the normalization basis via a geometric mean was deemed beneficial, and combinations of each set of stable miRNAs are further recommended, pending validation on a per experiment basis.

Immunosenescence, Inflammaging, and Frailty: Role of Myeloid Cells in Age-Related Diseases

The immune system is the central regulator of tissue homeostasis, ensuring tissue regeneration and protection against both pathogens and the neoformation of cancer cells. Its proper functioning requires homeostatic properties, which are maintained by an adequate balance of myeloid and lymphoid responses. Aging progressively undermines this ability and compromises the correct activation of immune responses, as well as the resolution of the inflammatory response. A subclinical syndrome of "homeostatic frailty" appears as a distinctive trait of the elderly, which predisposes to immune debilitation and chronic low-grade inflammation (inflammaging), causing the uncontrolled development of chronic and degenerative diseases. The innate immune compartment, in particular, undergoes to a sequela of age-dependent functional alterations, encompassing steps of myeloid progenitor differentiation and altered responses to endogenous and exogenous threats. Here, we will review the age-dependent evolution of myeloid populations, as well as their impact on frailty and diseases of the elderly.

Differentially expressed microRNAs in biochemically characterized FrieswalTM crossbred bull semen

In addition to the transmission of paternal genome, spermatozoa also carry coding as well as noncoding microRNAs (miRNAs) into the female oocyte during the process of biological fertilization. Based on RNA deep sequencing, a total 28 number of differentially expressed miRNAs were cataloged in categorized Frieswal^TM crossbred (Holstein Friesian X Sahiwal) bull semen on the basis of conception rate (CR) in field progeny testing program. Validation of selected miRNAs viz. bta-mir-182, bta-let-7b, bta-mir-34c and bta-mir-20a revealed that, superior bull semen having comparatively (p < .05) lower level of all the miRNAs in contrast to inferior bull semen. Additionally, it was illustrated that, bta-mir-20a and bta-mir-34c miRNAs are negatively (p < .01) correlated with seminal plasma catalase (CAT) activity and glutathione peroxidase (GPx) level. Interactome studies identified that bta-mir-140, bta-mir-342, bta-mir-1306 and bta-mir-217 can target few of the important solute carrier (SLC) proteins viz. SLC30A3, SLC39A9, SLC31A1 and SLC38A2, respectively. Interestingly, it was noticed that all the SLCs were significantly (p < .05) expressed at higher level in superior quality bull semen and they are negatively correlated (p < .01) with their corresponding miRNAs as mentioned. This study may reflect the role of miRNAs in regulating few of the candidate genes and thus may influence the bull semen quality traits.

Sperm DNA Fragmentation and Sperm-Borne miRNAs: Molecular Biomarkers of Embryo Development?

The evaluation of morpho-functional sperm characteristics alone is not enough to explain infertility or to predict the outcome of Assisted Reproductive Technologies (ART): more sensitive diagnostic tools are needed in clinical practice. The aim of the present study was to analyze Sperm DNA Fragmentation (SDF) and sperm-borne miR-34c-5p and miR-449b-5p levels in men of couples undergoing ART, in order to investigate any correlations with fertilization rate, embryo quality and development. Male partners (n = 106) were recruited. Semen analysis, SDF evaluation and molecular profiling analysis of miR-34c-5p and miR-449b-5p (in 38 subjects) were performed. Sperm DNA Fragmentation evaluation- a positive correlation between SDF post sperm selection and the percentage of low-quality embryos and a negative correlation with viable embryo were found. SDF > 2.9% increased the risk of obtaining a non-viable embryo by almost 4-fold. Sperm miRNAs profile—we found an association with both miRNAs and sperm concentration, while miR-449b-5p is positively associated with SDF. Moreover, the two miRNAs are positively correlated. Higher levels of miR-34c-5p compared to miR-449b-5p increases by 14-fold the probability of obtaining viable embryos. This study shows that SDF, sperm miR-34c-5p, and miR-449b-5p have a promising role as biomarkers of semen quality and ART outcome.

Promising novel biomarkers and therapy targets: The application of cell-free seminal nucleotides in male reproduction research

Liquid biopsy has the advantage of diagnosing diseases in a non-invasive manner. Seminal plasma contains secretions from the bilateral testes, epididymides, seminal vesicles, bulbourethral glands, and the prostate. These organs are relatively small and contain delicate tubes that are prone to damage by invasive diagnosis. Cell-free seminal nucleic acids test is a newly emerged item in liquid biopsy. Here, we present a comprehensive overview of all known cell-free DNA and cell-free RNAs (mRNA, miRNA, lncRNA, circRNA, piRNA, YRNA, tsRNA, etc.) and discuss their roles as biomarker candidates in liquid biopsy. With great advantages, including high stability, sensitivity, representability, and non-invasiveness, cell-free DNA/RNAs may be developed as promising biomarkers for the screening, diagnosis, prognosis, and follow-up of diseases in semen-secreting organs. Moreover, RNAs in semen may participate in important processes, including sperm maturation, early embryo development, and transgenerational disease inheritance, which may be developed as potential treatment targets for future clinical use.

The Sperm Small RNA Transcriptome: Implications beyond Reproductive Disorder

Apart from the paternal half of the genetic material, the male gamete carries assorted epigenetic marks for optimal fertilization and the developmental trajectory for the early embryo. Recent works showed dynamic changes in small noncoding RNA (sncRNA) in spermatozoa as they transit through the testicular environment to the epididymal segments. Studies demonstrated the changes to be mediated by epididymosomes during the transit through the adluminal duct in the epididymis, and the changes in sperm sncRNA content stemmed from environmental insults significantly altering the early embryo development and predisposing the offspring to metabolic disorders. Here, we review the current knowledge on the establishment of the sperm sncRNA transcriptome and their role in male-factor infertility, evidence of altered offspring health in response to the paternal life experiences through sperm sncRNA species and, finally, their implications in assisted reproductive technology in terms of epigenetic inheritance.

Expression of microRNA let-7 in cleavage embryos modulates cell fate determination and formation of mouse blastocysts†

After fertilization, the zygote undergoes cell division. Up to the 8-cell stage, the blastomeres of mouse preimplantation embryos are morphologically identical. The first cell differentiation starts in the morula leading to the formation of trophectoderm cells and inner cell mass cells of the blastocyst. The regulation of the differentiation event and the formation of blastocysts are not fully known. Lethal-7 (let-7) is a family of evolutionarily conserved microRNAs. Here, we showed that the expression of let-7a and let-7g decreased drastically from the 1-cell stage to the 2-cell stage, remained low up to the 8-cell stage and slightly increased after the morula stage of mouse embryos. The expression of let-7 in the inner cell mass was higher than that in the trophectoderm. Forced expression of let-7a in embryos at the 1-cell and 4-cell stage inhibited blastocyst formation and downregulated the expression of CDX2 but maintained that of OCT4 in the trophectoderm. Forced expression of other let-7 isoforms exhibited similar inhibitory action on blastulation. On the other hand, inhibition of let-7a at the 4-cell stage and the 8-cell stage enhanced blastocyst formation. Co-injection of green fluorescent protein (GFP) mRNA (lineage tracer) with either precursor of let-7a (pre-let-7a) or scramble control into one blastomere of 2-cell embryos showed that ~75% of the resulting blastocysts possessed GFP+ cells in their inner cell mass only. The biased development towards the inner cell mass with forced expression of let-7 was reproduced in 2-cell chimeric embryos consisting of one wildtype blastomere and one GFP mRNA-injected blastomere from another 2-cell embryo carrying a doxycycline-inducible let-7g gene. Bioinformatics analysis indicated that Tead4 was a potential target of let-7. Let-7 bound to the 3'UTR of Tead4 and let-7 forced expression downregulated the expression of Tead4 in mouse blastocysts. Co-injection of Tead4 mRNA partially nullified the modulatory roles of let-7a in the inner cell mass cell fate. In conclusion, a high level of let-7 at the 2-cell stage favored the formation of the inner cell mass, whereas a low level of let-7 at the 4-cell to 8-cell stage enhanced blastocyst formation. Tead4 mediated the action of let-7 on the inner cell mass cell-fate determination.

miRNA Profiling of Major Testicular Germ Cells Identifies Stage-Specific Regulators of Spermatogenesis

Spermatogenesis is tightly controlled at transcriptional, post-transcriptional, and epigenetic levels by various regulators, including miRNAs. This study deals with the identification of miRNAs critical to the three important stages of germ cell development (spermatocytes, round spermatids, and mature sperm) during spermatogenesis. We used high-throughput transcriptome sequencing to identify the differentially expressed miRNAs in the pachytene spermatocytes, round spermatids, and mature sperm of rat. We identified 1843 miRNAs that were differentially expressed across the three stages of germ cell development. These miRNAs were further categorized into three classes according to their pattern of expression during spermatogenesis: class 1 - miRNAs found exclusively in one stage and absent in the other two stages; class 2 - miRNAs found in any two stages but absent in the third stage; class 3 - miRNAs expressed in all the three stages. Six hundred forty-six miRNAs were found to be specific to one developmental stage, 443 miRNAs were found to be common across any two stages, and 754 miRNAs were common to all the three stages. Target prediction for ten most abundant miRNAs specific to each category identified miRNA regulators of mitosis, meiosis, and cell differentiation. The expression of each miRNA is specific to a particular developmental stage, which is required to maintain a significant repertoire of target mRNAs in the respective stage. Thus, this study provided valuable data that can be used in the future to identify the miRNAs involved in spermatogenic arrest at a particular stage of the germ cell development.

The developmental miR-17-92 cluster and the Sfmbt2 miRNA cluster cannot rescue the abnormal embryonic development generated using obstructive epididymal environment-producing sperm in C57BL/6 J mice

BACKGROUND

Sperm, during epididymal transit, acquires microRNAs(miRNAs), which are crucial for embryonic development. However, whether sperm miRNAs influenced by an obstructive epididymal environment affect embryonic development remains unknown.

METHOD

The sham operation and vasectomy were performed in C57BL/6 J mice to create the control group (CON) and the obstructive epididymal environment group(OEE) group, respectively. The morphology of the testis and epididymis was observed using hematoxylin and eosin staining (HE staining) to establish the OEE mice model. The sperm quality test, intracytoplasmic sperm injection (ICSI), and epididymosomes fusion were employed to observe the effect of the obstructive epididymal environment on sperm and resultant embryonic development. The alteration of the sperm small RNA (sRNA) profile was analyzed by sRNA sequencing. RT-qPCR and DNA methylation were applied to observe the effect of obstructive epididymis on the expression of sperm miRNAs. The miRNAs microinjection was used to explore the impacts of sperm miRNAs on embryonic development.

RESULTS

We confirmed postoperative 8-week mice as the OEE mice model by examining the morphology of the testis and epididymis. In the OEE group, we observed that sperm quality degraded and the development potential of embryos was reduced, which can be saved by the normal epididymal environment. The sperm sRNA sequencing revealed that the expression of the developmental miR-17-92 cluster and the Sfmbt2 miRNA cluster was downregulated in the OEE group. The expression of these two miRNA clusters in epididymis was also downregulated and regulated by DNA methylation. However, the downregulation of either the miR-17-92 cluster or the Sfmbt2 miRNA cluster in normal zygotes did not impair embryonic development.

CONCLUSION

The obstructive epididymal environment influences sperm quality and resultant embryonic development, as well as the abundance of the developmental miR-17-92 cluster and the Sfmbt2 miRNA cluster in sperm, but these miRNA clusters are not the cause of abnormal embryonic development. It implies that epididymis is important in early embryonic development and may play a potential role in sperm epigenome.

Identification and Characterization of Sex-Biased miRNAs in the Golden Pompano (Trachinotus blochii)

The golden pompano (Trachinotus blochii) is a marine fish of considerable commercial importance in China. It shows notable sexual size dimorphism; the growth rate of females is faster than that of males. Therefore, sex-biased research is of great importance in T. blochii breeding. However, there have been few studies on sex differentiation and mechanisms underlying sex determination in T. blochii. MicroRNAs (miRNAs) play crucial roles in sex differentiation and determination in animals. However, limited miRNA data are available on fish. In this study, two small RNA libraries prepared from the gonads of T. blochii were constructed and sequenced. The RNA-seq analysis yielded 1366 known and 69 novel miRNAs with 289 significantly differentially expressed miRNAs (p < 0.05). Gene ontology (GO) analysis confirmed that the TFIIA transcription factor complex (GO: 0005672) was the most significantly enriched GO term. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the differentially expressed miRNAs and target genes were mainly related to sex determination and gonadal developmental signaling pathways, specifically the Wnt signaling pathway, MAPK signaling pathway, and steroid biosynthetic pathway. MiRNA-mRNA co-expression network analysis strongly suggested a role for sex-biased miRNAs in sex determination/differentiation and gonadal development. For example, gata4, foxo3, wt1, and sf1 genes were found to be regulated by bta-miR-2898; esr2 and foxo3 by novel_176, and ar by oar-let-7b. Quantitative real-time polymerase chain reaction analysis of selected mRNAs and miRNAs validated the integrated analysis. This study established a set of sex-biased miRNAs that are potential regulatory factors in gonadal development in T. blochii. These results provide new insight into the function of miRNAs in sex differentiation and determination in T. blochii and highlight some key miRNAs for future studies.

The physiological and pathological mechanisms of early embryonic development

Early embryonic development is a complex process. The zygote undergoes several rounds of division to form a blastocyst, and during this process, the zygote undergoes the maternal-to-zygotic transition to gain control of embryonic development and makes two cell fate decisions to differentiate into an embryonic and two extra-embryonic lineages. With the use of new molecular biotechnologies and animal models, we can now further study the molecular mechanisms of early embryonic development and the pathological causes of early embryonic arrest. Here, we first summarize the known molecular regulatory mechanisms of early embryonic development in mice. Then we discuss the pathological factors leading to the early embryonic arrest. We hope that this review will give researchers a relatively complete view of the physiology and pathology of early embryonic development.

Correlation between Sperm Micro Ribonucleic Acid-34b and -34c Levels and Clinical Outcomes of Intracytoplasmic Sperm Injection in Men with Male Factor Infertility

Few studies have examined the correlation between sperm miRNA levels and clinical outcomes of intracytoplasmic sperm injection (ICSI). In this study, we aimed to assess the correlation of sperm miR-34b, miR-34c, miR-122, and miR-429 levels with ICSI outcomes in men with teratozoospermia and asthenozoospermia. TaqMan microRNA quantitative polymerase chain reaction was used to evaluate the relative expression of miRNAs in sperm. The relative miRNA levels quantified using a comparative method found that the four miRNAs were not associated with fertilization rate and early embryo development. However, revels of miR-34b and miR-34c in teratozoospermia sperm of the live birth group were significantly higher than those in the non-live birth group. Receiver operating characteristic curve analysis revealed that the optimal cut-off delta cycle threshold values of miR-34b and miR-34c were 8.630 and 7.883, respectively. Statistical analysis found that the levels of miR-34b and the miR-34c in teratozoospermic and asthenozoospermic sperm above the thresholds were not associated with the fertilization rate and the high-quality embryo rate above 50%; however, they were more likely to exhibit higher implantation, pregnancy, and live birth rates. miR-34b and miR-34c were significantly associated with ICSI clinical outcomes in male factor infertility, especially teratozoospermia. Further validation is required before it becomes a clinically valid reference indicator.

The Improvement of Porcine In Vitro Embryo Development through Regulating Autophagy by miRNA-143 Inhibition

In vitro embryo research is an important stage for the advancement of many reproductive technologies in research and agriculture. For this reason, the improvement of in vitro embryo development is a strategic field worthy of investigation. Relatively little is known about miR-143 and its effects on autophagy associated with embryo development and in vitro embryo culture. In this study, we examined the effect of miR-143 (via mimics and inhibitors) on embryonic development threatened by microinjection after parthenogenetic activation. We evaluated rates of cleavage, blastocyst, and total cell number of blastocyst; additionally, we performed LC3 immunofluorescence analysis and mRNA expression analyses of genes associated with autophagy, endoplasmic reticulum (ER)-phagy, ER stress, embryo quality, and apoptosis. The inhibition of miR-143 positively influenced embryo development by increasing the activity of autophagy and ER-phagy and the expression of embryo quality-related genes, while reducing apoptosis. In contrast, treatment with miR-143 mimics increased ER stress-related gene expression and apoptosis, and reduced embryo development. Together, our findings indicate that miR-143 plays a role in the interplay between autophagy, ER-phagy, and embryo quality during early porcine embryo development.

Investigation of Sperm and Seminal Plasma Candidate MicroRNAs of Bulls with Differing Fertility and In Silico Prediction of miRNA-mRNA Interaction Network of Reproductive Function

Simple Summary

The objective of this study was to identify differentially expressed (DE) sperm and seminal plasma microRNAs (miRNAs) in high- and low-fertile Holstein bulls (four bulls per group), integrate miRNAs to their target genes, and categorize target genes based on predicted biological processes. Out of 84 bovine-specific, prioritized miRNAs analyzed by RT-PCR, 30 were differentially expressed in high-fertile sperm and seminal plasma compared to low-fertile sperm and seminal plasma, respectively (p ≤ 0.05, fold regulation ≥5 magnitudes). Interestingly, expression levels of DE-miRNAs in sperm and seminal plasma followed a similar pattern. Highly scored integrated genes of DE-miRNAs predicted various biological and molecular functions, cellular process, and pathways. Further in silico analysis revealed categorized genes may have a plausible association with pathways regulating sperm structure and function, fertilization, and embryo and placental development. In conclusion, highly DE-miRNAs in bovine sperm and seminal plasma could be used as a tool for predicting reproductive functions. Since the identified miRNA-mRNA interactions were mostly based on predictions from public databases, the causal regulations of miRNA-mRNA and the underlying mechanisms require further functional characterization in future studies.

Abstract

Recent advances in high-throughput in silico techniques portray experimental data as exemplified biological networks and help us understand the role of individual proteins, interactions, and their biological functions. The objective of this study was to identify differentially expressed (DE) sperm and seminal plasma microRNAs (miRNAs) in high- and low-fertile Holstein bulls (four bulls per group), integrate miRNAs to their target genes, and categorize the target genes based on biological process predictions. Out of 84 bovine-specific, prioritized miRNAs analyzed by RT-PCR, 30 were differentially expressed in high-fertile sperm and seminal plasma compared to low-fertile sperm and seminal plasma, respectively (p ≤ 0.05, fold regulation ≥ 5 magnitudes). The expression levels of DE-miRNAs in sperm and seminal plasma followed a similar pattern. Highly scored integrated genes of DE-miRNAs predicted various biological and molecular functions, cellular process, and pathways. Further, analysis of the categorized genes showed association with pathways regulating sperm structure and function, fertilization, and embryo and placental development. In conclusion, highly DE-miRNAs in bovine sperm and seminal plasma could be used as a tool for predicting reproductive functions. Since the identified miRNA-mRNA interactions were mostly based on predictions from public databases, the causal regulations of miRNA-mRNA and the underlying mechanisms require further functional characterization in future studies.

Qualitative and quantitative assessment of sperm miRNAs identifies hsa-miR-9-3p, hsa-miR-30b-5p and hsa-miR-122-5p as potential biomarkers of male infertility and sperm quality

BACKGROUND

In contrast with the preceding stages of the germ cells, spermatozoa are unusually rich in small non-coding RNAs in comparison to the coding RNAs. These small RNAs may have had an essential role in the process of spermatogenesis or may have critical roles in the post-fertilization development. Sporadic efforts have identified a few differentially expressed miRNAs in infertile individuals, which do not replicate in other studies.

METHODS

In order to identify miRNAs signatures of infertility or poor sperm quality, we compared miRNA differential expression data across nine datasets, followed by their analysis by real-time PCR in a case-control study. This was followed by the validation of potential biomarkers in yet another set of cases and controls. For this, total RNA was isolated from 161 sperm samples. miRNA expression levels in infertile cases and fertile controls were measured using TaqMan real-time PCR. Meta-analyses of two miRNAs (hsa-miR-9-3p and hsa-miR-122-5p) were performed using Comprehensive Meta-Analysis Software (version 2). All statistical analyses were performed with the help of GraphPad Prism Software (version 8).

RESULTS

Literature search identified seven miRNAs (hsa-let-7a-5p, hsa-miR-9-3p, hsa-miR-22-5p, has-miR-30b-5p, hsa-miR-103-3p, hsa-miR-122-5p and hsa-miR-335-5p) showing consistent dysregulation in infertility across a minimum of four studies. In the discovery phase, six miRNAs showed strong association with infertility with four (hsa-miR-9-3p, hsa-miR-30b-5p, hsa-miR-103-3p and hsa-miR-122-5p) showing consistent differential regulation across all sub-groups. Receiver operating characteristic (ROC) curve analysis showed that the area under curve of > 0.75 was achieved by three (hsa-mir-9-3p, hsa-miR-30b-5p and hsa-miR-122-5p) miRNAs. In the validation phase, these three miRNAs showed consistent association with infertility (hsa-mir-9-3p, hsa-miR-30b-5p, and hsa-miR-122-5p). Meta-analysis on hsa-miR-122-5p showed its significant quantitative association with infertility [Hedge's g = -2.428, p = 0.001 (Random effects)].

CONCLUSIONS

Three miRNAs (hsa-miR-9-3p, hsa-miR-30b-5p and hsa-miR-122-5p) have strong linkage with infertility and a high potential as sperm quality biomarkers.

Cinnamaldehyde prevents intergenerational effect of paternal depression in mice via regulating GR/miR-190b/BDNF pathway

Paternal stress exposure-induced high corticosterone (CORT) levels may contribute to depression in offspring. Clinical studies disclose the association of depressive symptoms in fathers with their adolescent offspring. However, there is limited information regarding the intervention for intergenerational inheritance of depression. In this study we evaluated the intervention of cinnamaldehyde, a major constituent of Chinese herb cinnamon bark, for intergenerational inheritance of depression in CORT- and CMS-induced mouse models of depression. Depressive-like behaviors were induced in male mice by injection of CORT (20 mg·kg^-1·d^-1, sc) for 6 weeks or by chronic mild stress (CMS) for 6 weeks. We showed that co-administration of cinnamaldehyde (10, 20, or 40 mg·kg^-1·d^-1, ig) for 6 weeks in F0 males prevented the depressive-like phenotypes of F1 male offspring. In addition, co-administration of cinnamaldehyde (20 mg·kg^-1·d^-1, ig) for 4 weeks significantly ameliorated depressive-like behaviors of chronic variable stress (CVS)-stimulated F1 offspring born to CMS mice. Notably, cinnamaldehyde had no reproductive toxicity, while positive drug fluoxetine showed remarkable reproductive toxicity. We revealed that CMS and CORT significantly reduced testis glucocorticoid receptor (GR) expression, and increased testis and sperm miR-190b expression in F0 depressive-like models. Moreover, pre-miR-190b expression was upregulated in testis of F0 males. The amount of GR on miR-190b promoter regions was decreased in testis of CORT-stimulated F0 males. Cinnamaldehyde administration reversed CORT-induced GR reduction in testis, miR-190b upregulation in testis and sperm, pre-miR-190b upregulation in testis, and the amount of GR on miR-190b promoter regions of F0 males. In miR-190b-transfected Neuro 2a (N2a) cells, we demonstrated that miR-190b might directly bind to the 3'-UTR of brain-derived neurotrophic factor (BDNF). In the hippocampus of F1 males of CORT- or CMS-induced depressive-like models, increased miR-190b expression was accompanied by reduced BDNF and GR, which were ameliorated by cinnamaldehyde. In conclusion, cinnamaldehyde is a potential intervening agent for intergenerational inheritance of depression, probably by regulating GR/miR-190b/BDNF pathway.

Sperm-derived RNAs improve the efficiency of somatic cell nuclear transfer (SCNT) through promoting R-loop formation

Mammalian sperm and oocytes are haploid cells that carry parental genetic and epigenetic information for their progeny. The cytoplasm of oocytes is also capable of reprograming somatic cells to establish totipotency through somatic cell nuclear transfer (SCNT). However, epigenetic barriers seriously counteract SCNT reprogramming. Here, we found that sperm-derived RNAs elevated chromatin accessibility of nuclear donor cells concurrent with the appearance of increased RNA amount and decreased cell proliferation, instead of activating DNA damage response. Additionally, tri-methylation of lysine 9 on histone H3 (H3K9me3) and the H3K9 methyltransferase SUV39H2 were significantly downregulated by the sperm-derived RNA treatment. Our findings thus raise a fascinating possibility that sperm RNA-induced R-loops may activate gene expression and chromatin structure, thereby promoting SCNT reprogramming.

Characteristics of miRNAs Present in Bovine Sperm and Associations With Differences in Fertility

Small non-coding RNAs have been linked to different phenotypes in bovine sperm, however attempts to identify sperm-borne molecular biomarkers of male fertility have thus far failed to identify a robust profile of expressed miRNAs related to fertility. We hypothesized that some differences in bull fertility may be reflected in the levels of different miRNAs in sperm. To explore such differences in fertility that are not due to differences in visible metrics of sperm quality, we employed Next Generation Sequencing to compare the miRNA populations in Bos taurus sperm from bulls with comparable motility and morphology but varying Sire Conception Rates. We identified the most abundant miRNAs in both populations (miRs -34b-3p; -100-5p; -191-5p; -30d-4p; -21-5p) and evaluated differences in the overall levels and specific patterns of isomiR expression. We also explored correlations between specific pairs of miRNAs in each population and identified 10 distinct pairs of miRNAs that were positively correlated in bulls with higher fertility and negatively correlated in comparatively less fertile individuals. Furthermore, 8 additional miRNA pairs demonstrated the opposite trend; negatively correlated in high fertility animals and positively correlated in less fertile bulls. Finally, we performed pathway analysis to identify potential roles of miRNAs present in bull sperm in the regulation of specific genes that impact spermatogenesis and embryo development. Together, these results present a comprehensive picture of the bovine sperm miRNAome that suggests multiple potential roles in fertility.

Role of miRNAs in preimplantation embryo development and their potential as embryo selection biomarkers

CONTEXT

MicroRNAs (miRNAs) play different roles in oocyte fertilisation, degradation of maternal transcripts, embryo development, and implantation. During in vitro fertilisation (IVF), different miRNAs are released from embryos into the spent culture media (SCM) that can potentially reflect the status of the embryo.

AIMS

This study is the assessment of miRNAs, which secreted in SCM during the IVF cycles can be used as noninvasive biomarkers to predict an embryo's ability to form a blastocyst, implant, and give live birth.

METHODS

Systematic literature search was conducted to review all recent studies about miRNAs as potential non-invasive biomarkers for selecting the best embryos in the assisted reproductive technology (ART) cycle.

KEY RESULTS

Studies have shown that levels of some miRNAs in the SCM have an association with the implantation potential and pregnancy outcome of the embryo.

CONCLUSIONS

Embryo-secreted miRNAs can be used as potential non-invasive biomarkers for selecting the best embryos in the ART cycle. Unfortunately, few human studies evaluated the association between ART outcomes and miRNAs in SCM.

IMPLICATIONS

This review can pave the way for further miRNAs transcriptomic studies on human embryo culture media and introducing a specific miRNA profile as a multivariable prediction model for embryo selection in IVF cycles.

Exploring the ovine sperm transcriptome by RNAseq techniques. I Effect of seasonal conditions on transcripts abundance

Understanding the cell molecular changes occurring as a results of climatic circumstances is crucial in the current days in which climate change and global warming are one of the most serious challenges that living organisms have to face. Sperm are one of the mammals’ cells most sensitive to heat, therefore evaluating the impact of seasonal changes in terms of its transcriptional activity can contribute to elucidate how these cells cope with heat stress events. We sequenced the total sperm RNA from 64 ejaculates, 28 collected in summer and 36 collected in autumn, from 40 Manchega rams. A highly rich transcriptome (11,896 different transcripts) with 90 protein coding genes that exceed an average number of 5000 counts were found. Comparing transcriptome in the summer and autumn ejaculates, 236 significant differential abundance genes were assessed, most of them (228) downregulated. The main functions that these genes are related to sexual reproduction and negative regulation of protein metabolic processes and kinase activity. Sperm response to heat stress supposes a drastic decrease of the transcriptional activity, and the upregulation of only a few genes related with the basic functions to maintain the organisms’ homeostasis and surviving. Rams’ spermatozoids carry remnant mRNAs which are retrospectively indicators of events occurring along the spermatogenesis process, including abiotic factors such as environmental temperature.

Coding and regulatory transcriptome comparisons between fertile and infertile spermatozoa identify RNA signatures of male infertility

The aim of the present study was to identify RNA-based signatures of male infertility by sperm transcriptome analysis. In this study, deep sequencing analyses of coding (mRNA) and regulatory (miRNA) transcriptomes were performed by pooling 15 oligo/oligoasthenozoospermic infertile sperm and 9 normozoospermic fertile sperm samples. Furthermore, interesting candidates were selected for validation by real-time PCR. The comparison of miRNAs between cases and controls identified 94 differentially expressed miRNAs, of which at least 38 have known functions in spermatogenesis. In transcriptome (mRNA) data, a total of 60,505 transcripts were obtained. The comparison of coding RNAs between cases and controls revealed 11,688 differentially expressed genes. miRNA-mRNA paired analysis revealed that 94 differentially expressed miRNAs could potentially target 13,573 genes, of which 6419 transcripts were actually differentially expressed in our data. Out of these, 3303 transcripts showed inverse correlation with their corresponding regulatory miRNAs. Moreover, we found that most of the genes of miRNA-mRNA pairs were involved in male germ cell differentiation, apoptosis, meiosis, spermiogenesis and male infertility. In conclusion, we found that a number of sperm transcripts (miRNAs and mRNAs) have a very high potential of serving as infertility/sperm quality markers.

Deciphering the RNA universe in sperm in its role as a vertical information carrier

The inheritance of neurophysiologic and neuropsychologic complex diseases can only partly be explained by the Mendelian concept of genetic inheritance. Previous research showed that both psychological disorders like post-traumatic stress disorder and metabolic diseases are more prevalent in the progeny of affected parents. This could suggest an epigenetic mode of transmission. Human studies give first insight into the scope of intergenerational influence of stressors but are limited in exploring the underlying mechanisms. Animal models have elucidated the mechanistic underpinnings of epigenetic transmission. In this review, we summarize progress on the mechanisms of paternal intergenerational transmission by means of sperm RNA in mouse models. We discuss relevant details for the modelling of RNA-mediated transmission, point towards currently unanswered questions and propose experimental considerations for tackling these questions.

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.

miRNA-Profiling in Ejaculated and Epididymal Pig Spermatozoa and Their Relation to Fertility after Artificial Insemination

Simple Summary

The present study searched for the presence and abundance of porcine spermatozoa small RNA sequences (microRNAs) that have the potential to alter gene expression patterns. Four different sperm sources were compared: spermatozoa from three different sections of the ejaculate and from the caudal epididymis, also classed as spermatozoa from higher (HF) or lower (LF) fertility boars. Sperm miRNAs were compared using high-output small RNA sequencing. We identified five sperm miRNAs not previously reported in pigs. Differences in abundance of four miRNAs known to affect the expression of genes with key roles in fertility were related to boar fertility. These miRNAs could be used as fertility markers in artificial insemination programs.

Abstract

MicroRNAs (miRNAs) are short non-coding RNAs (20–25 nucleotides in length) capable of regulating gene expression by binding -fully or partially- to the 3’-UTR of target messenger RNA (mRNA). To date, several studies have investigated the role of sperm miRNAs in spermatogenesis and their remaining presence toward fertilization and early embryo development. However, little is known about the miRNA cargo in the different sperm sources and their possible implications in boar fertility. Here, we characterized the differential abundance of miRNAs in spermatozoa from the terminal segment of the epididymis and three different fractions of the pig ejaculate (sperm-peak, sperm-rich, and post-sperm rich) comparing breeding boars with higher (HF) and lower (LF) fertility after artificial insemination (AI) using high-output small RNA sequencing. We identified five sperm miRNAs that, to our knowledge, have not been previously reported in pigs (mir-10386, mir-10390, mir-6516, mir-9788-1, and mir-9788-2). Additionally, four miRNAs (mir-1285, mir-92a, mir-34c, mir-30), were differentially expressed among spermatozoa sourced from ejaculate fractions and the cauda epididymis, and also different abundance was found between HF and LF groups in mir-182, mir-1285, mir-191, and mir-96. These miRNAs target genes with key roles in fertility, sperm survival, immune tolerance, or cell cycle regulation, among others. Linking the current findings with the expression of specific sperm proteins would help predict fertility in future AI-sires.

Significance and Relevance of Spermatozoal RNAs to Male Fertility in Livestock

Livestock production contributes to a significant part of the economy in developing countries. Although artificial insemination techniques brought substantial improvements in reproductive efficiency, male infertility remains a leading challenge in livestock. Current strategies for the diagnosis of male infertility largely depend on the evaluation of semen parameters and fail to diagnose idiopathic infertility in most cases. Recent evidences show that spermatozoa contains a suit of RNA population whose profile differs between fertile and infertile males. Studies have also demonstrated the crucial roles of spermatozoal RNA (spRNA) in spermatogenesis, fertilization, and early embryonic development. Thus, the spRNA profile may serve as unique molecular signatures of fertile sperm and may play pivotal roles in the diagnosis and treatment of male fertility. This manuscript provides an update on various spRNA populations, including protein-coding and non-coding RNAs, in livestock species and their potential role in semen quality, particularly sperm motility, freezability, and fertility. The contribution of seminal plasma to the spRNA population is also discussed. Furthermore, we discussed the significance of rare non-coding RNAs (ncRNAs) such as long ncRNAs (lncRNAs) and circular RNAs (circRNAs) in spermatogenic events.