Chromatin and extracellular vesicle associated sperm RNAs

Immunological defense mechanisms of ejaculates and the spread of viral infectious diseases through pig semen

This review focuses on the mechanisms of immune tolerance and antimicrobial defense in the male genital tract of the pig. Sperm cells are foreign to the immune system and, therefore, they must be protected from the immune system. The blood-testis-barrier is mediated by a physical barrier between adjacent Sertoli cells, several cell types within the testis, and interactions between immunomodulatory molecules. The blood-epididymal-barrier is composed of a physical barrier that is lined with principal cells having a network of junctional complexes in their apical lateral membrane and completed by specific transporters. The seminal plasma (SP) contains many signaling agents involved in establishing a state of immune tolerance in the female genital tract, which is essential for successful fertilization. Specific SP-proteins, however, also have pro-inflammatory capacities contributing to transient uterine inflammation, supporting the removal of foreign cells, possible pathogens, and excessive spermatozoa. While many different proteins and other substances present in semen can damage sperm cells, they may also protect them against viral infections. A delicate balance of these substances, therefore, needs to be maintained. Related to this, recent studies have shown the importance of extracellular vesicles (EVs), as they contain these substances and convey immune signals. Yet, viruses may use EVs to interact with the male genital tract and circumvent immune responses. For this reason, further research needs to explore the role of EVs in the male reproductive tract, as it might contribute to elucidating the pathogenesis of viral infections that might be transmitted via semen and to developing better vaccines.

Transcriptome Analysis Reveals Spermatogenesis-Related CircRNAs and LncRNAs in Goat Spermatozoa

Mammalian spermatozoa comprises both coding and non-coding RNAs, which are traditionally believed to be a residual of spermatogenesis. The differential expression level of spermatozoal RNAs is also observed between fertile and infertile human, thereby anticipated as potential molecular marker of male fertility. This study investigated the transcriptome profile of goat (Capra hircus) spermatozoa. The sperm transcriptome was analyzed by three different methods viz. RLM-RACE, long-read RNA sequencing (RNAseq) in Nanopore™ platform, and short-read RNAseq in Illumina™ platform. The Illumina™ sequencing discovered 16,604 transcripts with 357 mRNAs having FPKM (fragments per kilobase per million mapped reads) of more than five. The spermatozoal RNA suite included mRNA (94%), rRNA (3%), miscRNA (1%), circRNA (1%), miRNA (1%), etc. This study also predicted circRNAs (127), lncRNAs (655), and imprinted genes (160) that have potential role in male reproduction. The gene ontology analysis revealed the involvement of spermatozoal RNA in regulating male meiosis (TET3, STAT5B), capacitation (ACRBP, CATSPER4), sperm motility (GAS8, TEKT2), spermatogenesis (ADAMTS2, CREB3L4), etc. The spermatozoal RNA were also associated with different biological pathways viz. Wnt signaling pathway, cAMP signaling pathway, AMPK signaling pathway, and MAPK signaling pathways having potential role in spermatogenesis. Overall, this study enlightened the suite of spRNA transcripts in goat and their relevance in male fertility for diagnostic approach.

Optimized total RNA isolation from bovine sperm with enhanced sperm head lysis

Increasing evidence of sperm RNA's role in fertilization and embryonic development has provided impetus for its isolation and thorough characterization. Sperm are considered tough-to-lyse cells due to the compact condensed DNA in sperm heads. Lack of consensus among bovine sperm RNA isolation protocols introduces experimental variability in transcriptome studies. Here, we describe an optimized method for total RNA isolation from bovine sperm using the TRIzol reagent. This study critically investigated the effects of various lysis conditions on sperm RNA isolation. Sperm suspended in TRIzol were subjected to a combination of mechanical treatments (sonication and passage through a 30G needle and syringe) and chemical treatments (supplementation with reducing agents 1,4-dithiothreitol and tris(2-carboxyethyl) phosphine hydrochloride (TCEP)). Microscopic evaluation of sperm lysis confirmed preferential sperm tail versus sperm head lysis. Interestingly, only TCEP-supplemented TRIzol (both mechanical treatments) had progressive sperm head lysis and consistently yielded total sperm RNA. Furthermore, RNA integrity was confirmed based on the electrophoresis profile and an absence of genomic DNA and somatic cells (e.g., epithelial cells, spermatids, etc.) with RT-qPCR. Our findings highlighted the importance of sperm lysis, specifically of the sperm head using TCEP with mechanical treatment, in total RNA isolation and presented a bovine-specific sperm RNA isolation method to reduce experimental variabilities.

Cryostress induces fragmentation and alters the abundance of sperm transcripts associated with fertilizing competence and reproductive processes in buffalo

The study aimed to assess the influence of cryostress on RNA integrity and functional significance in sperm fertilizing ability. The fresh and post-thawed buffalo sperm (n = 6 each) samples were evaluated for their functional attributes, and sperm total RNA was subjected to transcriptome sequencing followed by validation using real-time PCR and dot blot. Overall, 6911 genes had an expression of FPKM > 1, and among these 431 genes were abundantly expressed (FPKM > 20) in buffalo sperm. These abundantly expressed genes regulate reproductive functions such as sperm motility (TEKT2, SPEM1, and PRM3, FDR = 1.10E-08), fertilization (EQTN, PLCZ1, and SPESP1, FDR = 7.25E-06) and the developmental process involved in reproduction (SPACA1, TNP1, and YBX2, FDR = 7.21E-06). Cryopreservation significantly (p < 0.05) affected the structural and functional membrane integrities of sperm. The expression levels of transcripts that regulate the metabolic activities and fertility-related functions were compromised during cryopreservation. Interestingly, cryostress induces the expression of genes involved (p < 0.05) in chemokine signaling (CX3CL1, CCL20, and CXCR4), G-protein coupled receptor binding (ADRB1, EDN1, and BRS3), translation (RPS28, MRPL28, and RPL18A), oxidative phosphorylation (ND1, ND2, and COX2), response to reactive oxygen species (GLRX2, HYAL2, and EDN1), and immune responses (CX3CL1, CCL26, and TBXA2R). These precociously expressed genes during cryopreservation alter the signaling mechanisms that govern sperm functional competence and can impact fertilization and early embryonic development.

Paternal methotrexate exposure affects sperm small RNA content and causes craniofacial defects in the offspring

Folate is an essential vitamin for vertebrate embryo development. Methotrexate (MTX) is a folate antagonist that is widely prescribed for autoimmune diseases, blood and solid organ malignancies, and dermatologic diseases. Although it is highly contraindicated for pregnant women, because it is associated with an increased risk of multiple birth defects, the effect of paternal MTX exposure on their offspring has been largely unexplored. Here, we found MTX treatment of adult medaka male fish (Oryzias latipes) causes cranial cartilage defects in their offspring. Small non-coding RNA (sncRNAs) sequencing in the sperm of MTX treated males identify differential expression of a subset of tRNAs, with higher abundance for specific 5' tRNA halves. Sperm RNA methylation analysis on MTX treated males shows that m5C is the most abundant and differential modification found in RNAs ranging in size from 50 to 90 nucleotides, predominantly tRNAs, and that it correlates with greater testicular Dnmt2 methyltransferase expression. Injection of sperm small RNA fractions from MTX-treated males into normal fertilized eggs generated cranial cartilage defects in the offspring. Overall, our data suggest that paternal MTX exposure alters sperm sncRNAs expression and modifications that may contribute to developmental defects in their offspring.

The emerging role of extracellular vesicles in the testis

Extracellular vesicles (EVs) are nano-sized membrane-bounded particles, released by all cells and capable of transporting bioactive cargoes, proteins, lipids, and nucleic acids, to regulate a variety of biological functions. Seminal plasma is enriched in EVs, and extensive evidence has revealed the role of EVs (e.g. prostasomes and epididymosomes) in the male genital tract. Recently, EVs released from testicular cells have been isolated and identified, and some new insights have been generated on their role in maintaining normal spermatogenesis and steroidogenesis in the testis. In the seminiferous tubules, Sertoli cell-derived EVs can promote the differentiation of spermatogonial stem cells (SSCs), and EVs secreted from undifferentiated A spermatogonia can inhibit the proliferation of SSCs. In the testicular interstitium, EVs have been identified in endothelial cells, macrophages, telocytes, and Leydig cells, although their roles are still elusive. Testicular EVs can also pass through the blood-testis barrier and mediate inter-compartment communication between the seminiferous tubules and the interstitium. Immature Sertoli cell-derived EVs can promote survival and suppress the steroidogenesis of Leydig cells. Exosomes isolated from macrophages can protect spermatogonia from radiation-induced injury. In addition to their role in intercellular communication, testicular EVs may also participate in the removal of aberrant proteins and the delivery of antigens for immune tolerance. EVs released from testicular cells can be detected in seminal plasma, which makes them potential biomarkers reflecting testicular function and disease status. The testicular EVs in seminal plasma may also affect the female reproductive tract to facilitate conception and may even affect early embryogenesis through modulating sperm RNA. EVs represent a new type of intercellular messenger in the testis. A detailed understanding of the role of testicular EV may contribute to the discovery of new mechanisms causing male infertility and enable the development of new diagnostic and therapeutic strategies for the treatment of infertile men.

Molecular insights to the sperm-cervix interaction and the consequences for cryopreserved sperm

Cryopreserved ram spermatozoa are limited in their capacity to traverse the ovine cervix and achieve fertilization. This altered interaction may be related to modified molecular communication between frozen-thawed ram spermatozoa, seminal plasma, and the female tract. As such, this review aims to identify the biological processes which underpin sperm maturation and transport throughout the female reproductive tract to elucidate factors which may alter this natural process in cryopreserved ram spermatozoa. We also assess critical barriers to ram spermatozoa specific to the ovine cervix and the role of seminal plasma in mitigating these barriers. Transcriptomics is explored as a new approach to understand the sperm-cervix interaction. Recent studies have demonstrated that both spermatozoa and seminal plasma contain a complex profile of coding and non-coding RNAs. These molecular species have clear links with functional fertility, and mounting evidence suggests they may be altered by cryopreservation. Emerging in vitro cell culture models are also investigated as a "next step" in studying this interaction, utilizing transcriptomics to identify subtle changes in female tract gene expression in response to spermatozoa. The application of such models is proposed as an exciting opportunity to investigate the unique challenges faced by cryopreserved spermatozoa traversing the ovine cervix prior to fertilization.

Proteomic changes in human spermatozoa during in vitro capacitation and acrosome reaction in normozoospermia and asthenozoospermia

BACKGROUND

The cellular and molecular mechanisms of the events that help spermatozoa acquire their fertilizing capability during capacitation and acrosome reaction are not completely understood.

OBJECTIVE

This study was performed with a postulation that the identification of sperm proteins and their changes during in vitro capacitation and acrosome reaction will unravel unknown molecular aspects of fertilization that impact male fertility.

MATERIALS AND METHODS

Spermatozoa collected from sequential conditions, that is, separation of ejaculated spermatozoa by Percoll gradient centrifugation, in vitro capacitation, and acrosome reaction were processed for tandem mass spectrometric analysis, followed by protein identification, label-free quantitation, and statistical analysis.

RESULTS AND DISCUSSION

Collectively, a total of 1088 sperm proteins were identified. In comparison to ejaculated spermatozoa, 44 and 141 proteins were differentially expressed in capacitated and acrosome reacted spermatozoa, respectively. A large number of proteins were found downregulated, including clusterin, pyruvate dehydrogenase E1 component, semenogelin-1 and 2, heat shock protein 90, beta-microseminoprotein, and keratin. It was expected as sperm-membrane-associated proteins are removed during capacitation. There were significant proteomic alterations in asthenozoospermia compared to normozoospermia; however, variation was more noticeable among proteins of acrosome reacted spermatozoa and those released during the acrosome reaction. The processes enriched among downregulated proteins in asthenozoospermia included acrosome assembly, binding of spermatozoa to zona pellucida, nucleosome assembly, flagellated sperm motility, protein folding, oxidative phosphorylation, tricarboxylic acid cycle, chromatin silencing, gluconeogenesis, glycolytic process, and glycolysis.

CONCLUSION

The dynamic information generated about proteomic alterations in spermatozoa during capacitation and acrosome reaction and their variability in asthenozoospermia will contribute not only to enhancing our understanding of processes that prepare spermatozoa to acquire fertilization capability but also help in deciphering novel factors of male infertility.

Genome-wide DNA methylation profiles and small noncoding RNA signatures in sperm with a high DNA fragmentation index

BACKGROUND

A growing number of studies have reported that sperm DNA fragmentation (SDF) is associated with male infertility. However, no studies have compared genome-wide DNA methylation profiles and sncRNA signatures between sperm with high and low sperm DNA fragmentation indices (DFIs).

METHODS

Whole-genome bisulfite sequencing (WGBS) was performed on sperm samples from a weak group (DFI ≥ 30%, n = 6) and normal group (DFI ≤ 15%, n = 7). Small noncoding RNA (sncRNA) deep sequencing was conducted for sperm samples from the weak (DFI ≥ 30%, n = 13) and normal (DFI ≤ 15%, n = 17) groups.

RESULTS

A total of 4939 differentially methylated regions (DMRs) were identified in the weak group sperm samples relative to normal group sperm samples, with 2072 (41.95%) of them located in promoter regions. The percentages of hypermethylated DMRs were higher than those of hypomethylated DMRs in all seven examined gene annotation groups. Hypermethylated DMRs were significantly enriched in terms associated with neurons and microtubules. Compared with the normal group, the global DNA methylation level of the weak group sperm showed a downward trend, with lower correlation for methylation in the weak group sperm; therefore, the chromosomes of high-DFI sperm may be loose. On average, 40.5% of sncRNAs were annotated as rsRNAs, 19.3% as tsRNAs, 10.4% as yRNAs, and 7.1% as miRNAs. A total of 27 miRNAs, 151 tsRNAs, and 70 rsRNAs were differentially expressed between the two groups of sperm samples. Finally, 7 sncRNAs were identified as candidate sperm quality biomarkers, and the target genes of the differentially expressed miRNAs are involved in nervous system development.

CONCLUSION

Our findings suggest that genome-wide DNA methylation profiles and sncRNA signatures are significantly altered in high-DFI sperm. Our study provides potential biomarkers for sperm quality.

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.

Exosome Carrier Effects; Resistance to Digestion in Phagolysosomes May Assist Transfers to Targeted Cells; II Transfers of miRNAs Are Better Analyzed via Systems Approach as They Do Not Fit Conventional Reductionist Stoichiometric Concepts

Carrier effects of extracellular vesicles (EV) like exosomes refer to properties of the vesicles that contribute to the transferred biologic effects of their contents to targeted cells. This can pertain to ingested small amounts of xenogeneic plant miRNAs and oral administration of immunosuppressive exosomes. The exosomes contribute carrier effects on transfers of miRNAs by contributing both to the delivery and the subsequent functional intracellular outcomes. This is in contrast to current quantitative canonical rules that dictate just the minimum copies of a miRNA for functional effects, and thus successful transfers, independent of the EV carrier effects. Thus, we argue here that transfers by non-canonical minute quantities of miRNAs must consider the EV carrier effects of functional low levels of exosome transferred miRNA that may not fit conventional reductionist stoichiometric concepts. Accordingly, we have examined traditional stoichiometry vs. systems biology that may be more appropriate for delivered exosome functional responses. Exosome carrier properties discussed include; their required surface activating interactions with targeted cells, potential alternate targets beyond mRNAs, like reaching a threshold, three dimensional aspects of the RNAs, added EV kinetic dynamic aspects making transfers four dimensional, and unique intracellular release from EV that resist intracellular digestion in phagolysosomes. Together these EV carrier considerations might allow systems analysis. This can then result in a more appropriate understanding of transferred exosome carrier-assisted functional transfers. A plea is made that the miRNA expert community, in collaboration with exosome experts, perform new experiments on molecular and quantitative miRNA functional effects in systems that include EVs, like variation in EV type and surface constituents, delivery, dose and time to hopefully create more appropriate and truly current canonical concepts of the consequent miRNA functional transfers by EVs like exosomes.

Underestimated Aspects in Male Infertility: Epigenetics is A New Approach in Men with Obesity or Diabetes: A Review

Infertility is a complex multifactorial problem that affects about 7% of men and 15% of couples worldwide. Many molecular mechanisms involved in male infertility. Destructive effects of infertility on the next generations are not well understood. Approximately 60-75% of male infertility cases have idiopathic causes, and there is a need for additional investigations other than routine examinations. Molecular factors that surround DNA, which are mitotically stable and independently regulate genome activity of DNA sequences, are known as epigenetics. The known epigenetic mechanisms are DNA methylation, histone modifications and non-coding RNAs. Prevalence of metabolic diseases has been increased dramatically because of changes in lifestyle and the current levels of inactivity. Metabolic disorders, such<br />as obesity and diabetes, are prevalent reasons for male infertility; despite the association between metabolic diseases and male infertility, few studies have been conducted on the effects of epigenetic alterations associated with these diseases and sperm abnormalities. Diabetes can affect the reproductive system and testicular function at multiple levels;<br />however, there are very few molecular and epigenetic studies related to sperm from males with diabetes. On the other hand, obesity has similar conditions, while male obesity is linked to notable alterations in the sperm molecular architecture affecting both function and embryo quality. Therefore, in this review article, we presented new and developed technologies to study different patterns of epigenetic changes, and explained the exact mechanisms of epigenetic changes linked to metabolic diseases and their relationship with male infertility.

All you need to know about sperm RNAs

BACKGROUND

Spermatogenesis generates a small and highly specialised type of cell that is apparently incapable of transcription and translation. For many years, this dogma was supported by the assumption that (i) the compact sperm nucleus, resulting from the substitution of histones by protamine during spermatogenesis, renders the genome inaccessible to the transcriptional machinery; and (ii) the loss of most organelles, including endoplasmic reticulum and ribosomes, limits or prevents translational activity. Despite these observations, several types of coding and non-coding RNAs have been identified in human sperm. Their functional roles, particularly during fertilisation and embryonic development, are only now becoming apparent.

OBJECTIVE AND RATIONALE

This review aimed to summarise current knowledge of the origin, types and functional roles of sperm RNAs, and to evaluate the clinical benefits of employing these transcripts as biomarkers of male fertility and reproductive outcomes. The possible contribution of sperm RNAs to intergenerational or transgenerational phenotypic inheritance is also addressed.

SEARCH METHODS

A comprehensive literature search on PubMed was conducted using the search terms 'sperm' AND 'RNA'. Searches focussed upon articles written in English and published prior to August 2020.

OUTCOMES

The development of more sensitive and accurate RNA technologies, including RNA sequencing, has enabled the identification and characterisation of numerous transcripts in human sperm. Though a majority of these RNAs likely arise during spermatogenesis, other data support an epididymal origin of RNA transmitted to maturing sperm by extracellular vesicles. A minority may also be synthesised by de novo transcription in mature sperm, since a small portion of the sperm genome remains packed by histones. This complex RNA population has important roles in paternal chromatin packaging, sperm maturation and capacitation, fertilisation, early embryogenesis and developmental maintenance. In recent years, additional lines of evidence from animal models support a role for sperm RNAs in intergenerational or transgenerational inheritance, modulating both the genotype and phenotype of progeny. Importantly, several reports indicate that the sperm RNA content of fertile and infertile men differs considerably and is strongly modulated by the environment, lifestyle and pathological states.

WIDER IMPLICATIONS

Transcriptional profiling has considerable potential for the discovery of fertility biomarkers. Understanding the role of sperm transcripts and comparing the sperm RNA fingerprint of fertile and infertile men could help to elucidate the regulatory pathways contributing to male factor infertility. Such data might also provide a molecular explanation for several causes of idiopathic male fertility. Ultimately, transcriptional profiling may be employed to optimise ART procedures and overcome some of the underlying causes of male infertility, ensuring the birth of healthy children.

Gene transcription profiling of astheno- and normo-zoospermic sperm subpopulations

Spermatozoa contain a repertoire of RNAs considered to be potential functional fertility biomarkers. In this study, the gene expression of human sperm subpopulations with high (F1) and low (F2) motility from healthy normozoospermic (N) and asthenozoospermic (A) individuals was evaluated using RNA microarray followed by functional genomic analysis of differentially expressed genes. Results from A–F1 versus N–F1, A–F2 versus N–F2, N–F1 versus N–F2, and A–F1 versus A–F2 comparisons showed a considerably larger set of downregulated genes in tests versus controls. Gene ontology (GO) analysis of A–F1 versus N–F1 identified 507 overrepresented biological processes (BPs), several of which are associated with sperm physiology. In addition, gene set enrichment analysis of the same contrast showed 110 BPs, 36 cellular components, and 31 molecular functions, several of which are involved in sperm motility. A leading-edge analysis of selected GO terms resulted in several downregulated genes encoding to dyneins and kinesins, both related to sperm physiology. Furthermore, the predicted activation state of asthenozoospermia was increased, while fertility, cell movement of sperm, and gametogenesis were decreased. Interestingly, several downregulated genes characteristic of the canonical pathway protein ubiquitination were involved in asthenozoospermia activation. Conversely, GO analysis of A–F2 versus N–F2 did not identify overrepresented BPs, although the gene set enrichment analysis detected six enriched BPs, one cellular component, and two molecular functions. Overall, the results show differences in gene transcription between sperm subpopulations from asthenozoospermic and normozoospermic semen samples and allowed the identification of gene sets relevant to sperm physiology and reproduction.

Epigenetic regulations in mammalian spermatogenesis: RNA-m6A modification and beyond

Emerging evidence shows that m6A, one of the most abundant RNA modifications in mammals, is involved in the entire process of spermatogenesis, including mitosis, meiosis, and spermiogenesis. "Writers" catalyze m6A formation on stage-specific transcripts during male germline development, while "erasers" remove m6A modification to maintain a balance between methylation and demethylation. The different functions of RNA-m6A transcripts depend on their recognition by "readers". m6A modification mediates RNA metabolism, including mRNA splicing, translation, and degradation, as well as the maturity and biosynthesis of non-coding RNAs. Sperm RNA profiles are easily affected by environmental exposure and can even be inherited for several generations, similar to epigenetic inheritance. Here, we review and summarize the critical role of m6A in different developmental stages of male germ cells, to understand of the mechanisms and epigenetic regulation of m6A modifications. In addition, we also outline and discuss the important role of non-coding RNAs in spermatogenesis and RNA modifications in epigenetic inheritance.

Repeated sampling facilitates within- and between-subject modeling of the human sperm transcriptome to identify dynamic and stress-responsive sncRNAs

Epidemiological studies from the last century have drawn strong associations between paternal life experiences and offspring health and disease outcomes. Recent studies have demonstrated sperm small non-coding RNA (sncRNA) populations vary in response to diverse paternal insults. However, for studies in retrospective or prospective human cohorts to identify changes in paternal germ cell epigenetics in association with offspring disease risk, a framework must first be built with insight into the expected biological variation inherent in human populations. In other words, how will we know what to look for if we don't first know what is stable and what is dynamic, and what is consistent within and between men over time? From sperm samples from a 'normative' cohort of healthy human subjects collected repeatedly from each subject over 6 months, 17 healthy male participants met inclusion criteria and completed donations and psychological evaluations of perceived stress monthly. sncRNAs (including miRNA, piRNA, and tRNA) isolated from mature sperm from these samples were subjected to Illumina small RNA sequencing, aligned to subtype-specific reference transcriptomes, and quantified. The repeated measures design allowed us to define both within- and between-subject variation in the expression of 254 miRNA, 194 tRNA, and 937 piRNA in sperm over time. We developed screening criteria to identify a subset of potential environmentally responsive 'dynamic' sperm sncRNA. Implementing complex modeling of the relationships between individual dynamic sncRNA and perceived stress states in these data, we identified 5 miRNA (including let-7f-5p and miR-181a-5p) and 4 tRNA that are responsive to the dynamics of prior stress experience and fit our established mouse model. In the current study, we aligned repeated sampling of human sperm sncRNA expression data with concurrent measures of perceived stress as a novel framework that can now be applied across a range of studies focused on diverse environmental factors able to influence germ cell programming and potentially impact offspring development.

Roles of male reproductive tract extracellular vesicles in reproduction

Extracellular vesicles (EVs) are secreted cell-derived membrane structures present in all organisms across animal, bacterial, and plant phyla. These vesicles play important roles in cell-cell communication in many processes integral to health and disease. Recent studies demonstrate that EVs and their cargo have influential and conserved roles in male reproduction. While EVs have been isolated from virtually all specialized tissues comprising the male reproductive tract, they are best characterized in the epididymis (epididymosomes) and seminal fluid (seminal fluid extracellular vesicles or prostasomes). Broadly speaking, EVs promote reproductive success through supporting sperm development and function, as well as influencing the physiology of female reproductive tract cells after mating. In this review, we present current knowledge on the composition and function of male reproductive tract EV populations in both normal physiology and pathology, and argue that their functions identify them as critical regulators of fertility and fecundity.

Male Infertility is a Women's Health Issue-Research and Clinical Evaluation of Male Infertility Is Needed

Infertility is a devastating experience for both partners as they try to conceive. Historically, when a couple could not conceive, the woman has carried the stigma of infertility; however, men and women are just as likely to contribute to the couple’s infertility. With the development of assisted reproductive technology (ART), the treatment burden for male and unexplained infertility has fallen mainly on women. Equalizing this burden requires reviving research on male infertility to both improve treatment options and enable natural conception. Despite many scientific efforts, infertility in men due to sperm dysfunction is mainly diagnosed by a semen analysis. The semen analysis is limited as it only examines general sperm properties such as concentration, motility, and morphology. A diagnosis of male infertility rarely includes an assessment of internal sperm components such as DNA, which is well documented to have an impact on infertility, or other components such as RNA and centrioles, which are beginning to be adopted. Assessment of these components is not typically included in current diagnostic testing because available treatments are limited. Recent research has expanded our understanding of sperm biology and suggests that these components may also contribute to the failure to achieve pregnancy. Understanding the sperm’s internal components, and how they contribute to male infertility, would provide avenues for new therapies that are based on treating men directly for male infertility, which may enable less invasive treatments and even natural conception.

Heterogenic Origin of Micro RNAs in Atlantic Salmon (Salmo salar) Seminal Plasma

The origin and contribution of seminal plasma RNAs into the whole semen RNA repertoire are poorly known, frequently being overlooked or neglected. In this study, we used high-throughput sequencing and RT-qPCR to profile microRNA (miRNA) constituents in the whole semen, as well as in fractionated spermatozoa and seminal plasma of Atlantic salmon (Salmo salar). We found 85 differentially accumulated miRNAs between spermatozoa and the seminal plasma. We identified a number of seminal plasma-enriched and spermatozoa-enriched miRNAs. We localized the expression of some miRNAs in juvenile and mature testes. Two abundant miRNAs, miR-92a-3p and miR-202-5p, localized to both spermatogonia and somatic supporting cells in immature testis, and they were also highly abundant in somatic cells in mature testis. miR-15c-5p, miR-30d-5p, miR-93a-5p, and miR-730-5p were detected only in mature testis. miRs 92a-3p, 202-5p, 15c-5p, and 30d-5p were also detected in a juvenile ovary. The RT-qPCR experiment demonstrated lack of correlation in miRNA transcript levels in seminal plasma versus blood plasma. Our results indicate that salmon semen is rich in miRNAs, which are present in both spermatozoa and seminal plasma. Testicular-supporting somatic cells are likely the source of seminal plasma enrichment, whereas blood plasma is unlikely to contribute to the seminal plasma miRNA repertoire.

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

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

Transgenerational epigenetic reprogramming of early embryos: a mechanistic model

The notion that epigenetic information can be transmitted across generations is supported by mounting waves of data, but the underlying mechanisms remain elusive. Here, a model is proposed which combines different lines of experimental evidence. First, it has been shown that somatic tissues exposed to stressing stimuli release circulating RNA-containing extracellular vesicles; second, epididymal spermatozoa can take up, internalize and deliver the RNA-containing extracellular vesicles to oocytes at fertilization; third, early embryos can process RNA-based information. These elements constitute the building blocks upon which the model is built. The model proposes that a continuous stream of epigenetic information flows from parental somatic tissues to the developing embryos. The flow can cross the Weismann barrier, is mediated by circulating vesicles and epididymal spermatozoa, and has the potential to generate epigenetic traits that are then stably acquired in the offspring. In a broader perspective, it emerges that a natural 'assembly line' operates continuously, aiming at passing the parental epigenetic blueprint in growing embryos.

Characterization and functional roles of paternal RNAs in 2-4 cell bovine embryos

Embryos utilize oocyte-donated RNAs until they become capable of producing RNAs through embryonic genome activation (EGA). The sperm's influence over pre-EGA RNA content of embryos remains unknown. Recent studies have revealed that sperm donate non-genomic components upon fertilization. Thus, sperm may also contribute to RNA presence in pre-EGA embryos. The first objective of this study was to investigate whether male fertility status is associated with the RNAs present in the bovine embryo prior to EGA. A total of 65 RNAs were found to be differentially expressed between 2-4 cell bovine embryos derived from high and low fertility sires. Expression patterns were confirmed for protein phosphatase 1 regulatory subunit 36 (PPP1R36) and ataxin 2 like (ATXN2L) in three new biological replicates. The knockdown of ATXN2L led to a 22.9% increase in blastocyst development. The second objective of this study was to characterize the parental origin of RNAs present in pre-EGA embryos. Results revealed 472 sperm-derived RNAs, 2575 oocyte-derived RNAs, 2675 RNAs derived from both sperm and oocytes, and 663 embryo-exclusive RNAs. This study uncovers an association of male fertility with developmentally impactful RNAs in 2-4 cell embryos. This study also provides an initial characterization of paternally-contributed RNAs to pre-EGA embryos. Furthermore, a subset of 2-4 cell embryo-specific RNAs was identified.

Paternal Contributions to Offspring Health: Role of Sperm Small RNAs in Intergenerational Transmission of Epigenetic Information

The most fundamental process for the perpetuation of a species is the transfer of information from parent to offspring. Although genomic DNA contributes to the majority of the inheritance, it is now clear that epigenetic information −information beyond the underlying DNA sequence − is also passed on to future generations. However, the mechanism and extent of such inheritance are not well-understood. Here, I review some of the concepts, evidence, and mechanisms of intergenerational epigenetic inheritance via sperm small RNAs. Recent studies provide evidence that mature sperm are highly abundant in small non-coding RNAs. These RNAs are modulated by paternal environmental conditions and potentially delivered to the zygote at fertilization, where they can regulate early embryonic development. Intriguingly, sperm small RNA payload undergoes dramatic changes during testicular and post-testicular maturation, making the mature sperm epigenome highly unique and distinct from testicular germ cells. I explore the mechanism of sperm small RNA remodeling during post-testicular maturation in the epididymis, and the potential role of this reprograming in intergenerational epigenetic inheritance.

The effects of di-butyl phthalate exposure from medications on human sperm RNA among men

Endocrine disruptors, such as phthalates, are suspected of affecting reproductive function. The Mesalamine and Reproductive Health Study (MARS) was designed to address the physiological effect of in vivo phthalate exposure on male reproduction in patients with Inflammatory Bowel Disease (IBD). As part of this effort, the effect on sperm RNAs to DBP exposure were longitudinally assessed using a cross-over cross-back binary design of high or background, exposures to DBP. As the DBP level was altered, numerous sperm RNA elements (REs) were differentially expressed, suggesting that exposure to or removal from high DBP produces effects that require longer than one spermatogenic cycle to resolve. In comparison, small RNAs were minimally affected by DBP exposure. While initial study medication (high or background) implicates different biological pathways, initiation on the high-DBP condition activated oxidative stress and DNA damage pathways. The negative correlation of REs with specific genomic repeats suggests a regulatory role. Using ejaculated sperm, this work provides insight into the male germline's response to phthalate exposure.

Sperm RNA code programmes the metabolic health of offspring

Mammalian sperm RNA is increasingly recognized as an additional source of paternal hereditary information beyond DNA. Environmental inputs, including an unhealthy diet, mental stresses and toxin exposure, can reshape the sperm RNA signature and induce offspring phenotypes that relate to paternal environmental stressors. Our understanding of the categories of sperm RNAs (such as tRNA-derived small RNAs, microRNAs, ribosomal RNA-derived small RNAs and long non-coding RNAs) and associated RNA modifications is expanding and has begun to reveal the functional diversity and information capacity of these molecules. However, the coding mechanism endowed by sperm RNA structures and by RNA interactions with DNA and other epigenetic factors remains unknown. How sperm RNA-encoded information is decoded in early embryos to control offspring phenotypes also remains unclear. Complete deciphering of the 'sperm RNA code' with regard to metabolic control could move the field towards translational applications and precision medicine, and this may lead to prevention of intergenerational transmission of obesity and type 2 diabetes mellitus susceptibility.

A history of why fathers' RNA matters

Having been debated for many years, the presence and role of spermatozoal RNAs is resolving, and their contribution to development is now appreciated. Data from different species continue show that sperm contain a complex suite of coding and noncoding RNAs that play a role in an individual's life course. Mature sperm RNAs provide a retrospective of spermatogenesis, with their presence and abundance reflecting sperm maturation, fertility potential, and the paternal contribution to the developmental path the offspring may follow.Sperm RNAs delivered upon fertilization provide some of the initial contacts with the oocyte, directly confront the maternal with the paternal contribution as a prelude to genome consolidation. Following syngamy, early embryo development may in part be modulated by paternal RNAs that can include epidydimal passengers. This provides a direct path to relay an experience and then initiate a paternal response to the environment to the oocyte and beyond. Their epigenetic impact is likely felt prior to embryonic genome activation when the population of sperm delivered transcripts markedly changes. Here, we review the insights gained from sperm RNAs over the years, the subtypes, and the caveats of the RNAs described. We discuss the role of sperm RNAs in fertilization and embryo development, and their possible mechanism(s) influencing offspring phenotype. Approaches to meet the future challenges as the study of sperm RNAs continues, include, elucidating the potential mechanisms underlying how paternal allostatic load, the constant adaptation of health to external conditions, may be relayed by sperm RNAs to affect future generations.

A RNA-Seq Analysis to Describe the Boar Sperm Transcriptome and Its Seasonal Changes

Understanding the molecular basis of cell function and ultimate phenotypes is crucial for the development of biological markers. With this aim, several RNA-seq studies have been devoted to the characterization of the transcriptome of ejaculated spermatozoa in relation to sperm quality and fertility. Semen quality follows a seasonal pattern and decays in the summer months in several animal species. The aim of this study was to deeply profile the transcriptome of the boar sperm and to evaluate its seasonal changes. We sequenced the total and the short fractions of the sperm RNA from 10 Pietrain boars, 5 collected in summer and 5 five sampled in winter, and identified a complex and rich transcriptome with 4,436 coding genes of moderate to high abundance. Transcript fragmentation was high but less obvious in genes related to spermatogenesis, chromatin compaction and fertility. Short non-coding RNAs mostly included piwi-interacting RNAs, transfer RNAs and microRNAs. We also compared the transcriptome of the summer and the winter ejaculates and identified 34 coding genes and 7 microRNAs with a significantly distinct distribution. These genes were mostly related to oxidative stress, DNA damage and autophagy. This is the deepest characterization of the boar sperm transcriptome and the first study linking the transcriptome and the seasonal variability of semen quality in animals. The annotation described here can be used as a reference for the identification of markers of sperm quality in pigs.

RNA element discovery from germ cell to blastocyst

Recent studies have shown that tissue-specific transcriptomes contain multiple types of RNAs that are transcribed from intronic and intergenic sequences. The current study presents a tool for the discovery of transcribed, unannotated sequence elements from RNA-seq libraries. This RNA Element (RE) discovery algorithm (REDa) was applied to a spectrum of tissues and cells representing germline, embryonic, and somatic tissues and examined as a function of differentiation through the first set of cell divisions of human development. This highlighted extensive transcription throughout the genome, yielding previously unidentified human spermatogenic RNAs. Both exonic and novel X-chromosome REs were subject to robust meiotic sex chromosome inactivation, although an extensive de-repression occurred in the post-meiotic stages of spermatogenesis. Surprisingly, 2.4% of the 10,395 X chromosome exonic REs were present in mature sperm. Transcribed genomic repetitive sequences, including simple centromeric repeats, HERVE and HSAT1, were also shown to be associated with RE expression during spermatogenesis. These results suggest that pervasive intergenic repetitive sequence expression during human spermatogenesis may play a role in regulating chromatin dynamics. Repetitive REs switching repeat classes during differentiation upon fertilization and embryonic genome activation was evident.

Adolescence and the next generation

Adolescent growth and social development shape the early development of offspring from preconception through to the post-partum period through distinct processes in males and females. At a time of great change in the forces shaping adolescence, including the timing of parenthood, investments in today's adolescents, the largest cohort in human history, will yield great dividends for future generations.

Epigenetic reprogramming during spermatogenesis and male factor infertility

Infertility is an often devastating diagnosis encountered by around one in six couples who are trying to conceive. Moving away from the long-held belief that infertility is primarily a female issue, it is now recognised that half, if not more, of these cases may be due to male factors. Recent evidence has suggested that epigenetic abnormalities in chromatin dynamics, DNA methylation or sperm-borne RNAs may contribute to male infertility. In light of advances in deep sequencing technologies, researchers have been able to increase the coverage and depth of sequencing results, which in turn has allowed more comprehensive analyses of spermatozoa chromatin dynamics and methylomes and enabled the discovery of new subsets of sperm RNAs. This review examines the most current literature related to epigenetic processes in the male germline and the associations of aberrant modifications with fertility and development.

Glycosylation of extracellular vesicles: current knowledge, tools and clinical perspectives

It is now acknowledged that extracellular vesicles (EVs) are important effectors in a vast number of biological processes through intercellular transfer of biomolecules. Increasing research efforts in the EV field have yielded an appreciation for the potential role of glycans in EV function. Indeed, recent reports show that the presence of glycoconjugates is involved in EV biogenesis, in cellular recognition and in the efficient uptake of EVs by recipient cells. It is clear that a full understanding of EV biology will require researchers to focus also on EV glycosylation through glycomics approaches. This review outlines the major glycomics techniques that have been applied to EVs in the context of the recent findings. Beyond understanding the mechanisms by which EVs mediate their physiological functions, glycosylation also provides opportunities by which to engineer EVs for therapeutic and diagnostic purposes. Studies characterising the glycan composition of EVs have highlighted glycome changes in various disease states, thus indicating potential for EV glycans as diagnostic markers. Meanwhile, glycans have been targeted as molecular handles for affinity-based isolation in both research and clinical contexts. An overview of current strategies to exploit EV glycosylation and a discussion of the implications of recent findings for the burgeoning EV industry follows the below review of glycomics and its application to EV biology.

Do Gametes Woo? Evidence for Their Nonrandom Union at Fertilization

A fundamental tenet of inheritance in sexually reproducing organisms such as humans and laboratory mice is that gametes combine randomly at fertilization, thereby ensuring a balanced and statistically predictable representation of inherited variants in each generation. This principle is encapsulated in Mendel's First Law. But exceptions are known. With transmission ratio distortion, particular alleles are preferentially transmitted to offspring. Preferential transmission usually occurs in one sex but not both, and is not known to require interactions between gametes at fertilization. A reanalysis of our published work in mice and of data in other published reports revealed instances where any of 12 mutant genes biases fertilization, with either too many or too few heterozygotes and homozygotes, depending on the mutant gene and on dietary conditions. Although such deviations are usually attributed to embryonic lethality of the underrepresented genotypes, the evidence is more consistent with genetically-determined preferences for specific combinations of egg and sperm at fertilization that result in genotype bias without embryo loss. This unexpected discovery of genetically-biased fertilization could yield insights about the molecular and cellular interactions between sperm and egg at fertilization, with implications for our understanding of inheritance, reproduction, population genetics, and medical genetics.

Sperm RNA elements as markers of health

Idiopathic infertility, an etiology not identified as part of standard clinical assessment, represents approximately 20% of all infertility cases. Current male infertility diagnosis focuses on the concentration, motility, and morphology of spermatozoa. This is of limited value when predicting birth success and of limited utility when selecting the optimum treatment. At fertilization, spermatozoa provide their genomic contribution, as well as a set of RNAs and proteins that have distinct roles in development. The potential of spermatozoal RNAs to be used as a prognostic of live birth has been shown [Jodar et al. (2015) Science Translational Medicine 7(295):295re6]. This relied on a set of 648 sperm RNA elements derived from 285 genes that are perhaps indicative of future health status. To address this tenet, the present study correlated the levels of each transcript among all samples to assess linkage between transcript absence, birth success, and possible disease association. Correlations between transcript levels of the 285 genes were analyzed amongst themselves, and within the context of the entire transcript population for these samples. The transcripts ACE, GIGYF2, and ODF2 had many negative correlations and form the majority of correlations, suggesting an important function for these transcripts. Eleven of the 285 queried genes had disease-associated variants within a sperm RNA element. Three genes, GPX4, NDRG1, and RPS24 had SREs were absent in at least one individual from the test cohort. GPX4 and RPS24 are associated with developmental defects and/or neonatal lethality. This leaves the intriguing possibility that, while sperm RNAs delivered to the oocyte inform the success of live birth, they may also be predictors of human health.

ABBREVIATIONS

GO: Gene Ontology; ART: assisted reproductive technology; IVF: in vitro fertilization; ICSI: intra-cytoplasmic sperm injection; RNA-seq: RNA-sequencing; TIC: timed intercourse; IUI: intrauterine insemination; SRE: sperm RNA elements; HPA: Human Protein Atlas; SMDS: sedaghatian-type spondylometaphyseal dysplasia; DBA: Diamond-Blackfan anemia; RPKM: reads per kilobase per million; TPM: transcripts per million; IPA: Ingenuity Pathway Analysis; OMIM: Online Mendelian Inheritance in Man.

Potential sperm contributions to the murine zygote predicted by in silico analysis

Paternal contributions to the zygote are thought to extend beyond delivery of the genome and paternal RNAs have been linked to epigenetic transgenerational inheritance in different species. In addition, sperm–egg fusion activates several downstream processes that contribute to zygote formation, including PLC zeta-mediated egg activation and maternal RNA clearance. Since a third of the preimplantation developmental period in the mouse occurs prior to the first cleavage stage, there is ample time for paternal RNAs or their encoded proteins potentially to interact and participate in early zygotic activities. To investigate this possibility, a bespoke next-generation RNA sequencing pipeline was employed for the first time to characterise and compare transcripts obtained from isolated murine sperm, MII eggs and pre-cleavage stage zygotes. Gene network analysis was then employed to identify potential interactions between paternally and maternally derived factors during the murine egg-to-zygote transition involving RNA clearance, protein clearance and post-transcriptional regulation of gene expression. Ourin silicoapproach looked for factors in sperm, eggs and zygotes that could potentially interact co-operatively and synergistically during zygote formation. At least five sperm RNAs (Hdac11,Fbxo2,Map1lc3a,Pcbp4andZfp821) met these requirements for a paternal contribution, which with complementary maternal co-factors suggest a wider potential for extra-genomic paternal involvement in the developing zygote.

Spermatogenesis disruption by dioxins: Epigenetic reprograming and windows of susceptibility

Dioxins are a group of highly persistent chemicals that are generated as by-products of industrial and natural processes. Reduction in sperm counts is among the most sensitive endpoints of dioxin toxicity. The exact mechanism by which dioxins reduce sperm counts is not known. Recent data implicate the role of epididymal factors rather than disruption of spermatogenesis. Studies reviewed here demonstrate that dioxins induce the transfer of environmental conditions to the next generation via male germline following exposures during the window of epigenetic reprogramming of primordial germ cells. Increased incidence of birth defects in offspring of male veterans exposed to dioxin containing, Agent Orange, suggest that dioxins may induce epigenomic changes in male germ cells of adults during spermatogenesis. This is supported by recent animal data that show that environmental conditions can cause epigenetic dysregulation in sperm in the context of specific windows of epigenetic reprogramming during spermatogenesis.

Exogenous Molecule and Organelle Delivery in Oogenesis

Recent discoveries on the delivery of small- and large-size molecules and organelles to the oocytes/eggs from external sources, such as surrounding somatic cells, body fluids, and sperm, change our understanding of female germ cells' (oocytes and eggs) self-containment and individuality. In this chapter, we will summarize present-day knowledge on sources and presumptive functions of different types of exogenous molecules and organelles delivered to the animal oocytes and eggs.

Segment-specific regulation of epididymal gene expression

The epididymis is necessary for post-testicular sperm maturation. During their epididymal transit, spermatozoa gain ability for progressive movement and fertilization. The epididymis is composed of several segments that have distinct gene expression profiles that enable the establishment of the changing luminal environment required for sperm maturation. The epididymal gene expression is regulated by endocrine, lumicrine, and paracrine factors in a segment-specific manner. Thus, in addition to its importance for male fertility, the epididymis is a valuable model tissue for studying the regulation of gene expression. This review concentrates on recent advances in understanding the androgen, small RNA, and epigenetically mediated regulation of segment-specific gene expression in the epididymis.

Post-Testicular Sperm Maturation: Centriole Pairs, Found in Upper Epididymis, are Destroyed Prior to Sperm's Release at Ejaculation

The fertilizing sperm’s lengthiest unchartered voyage is through the longest, least-investigated organ in a man’s body – the Epididymis. Over six meters long in men, ~80 meters in stallions and over one-hundred times a mouse’s body length, there are few functions known aside from sperm storage and nutrition. While spermatogenesis is completed in the testes, here we demonstrate sperm centriole reduction occurs within the epididymis. Investigations of GFP-CENTR mice and controls demonstrate both the presence of centriole pairs in the upper caput region of the epididymis and, the destruction, first, of the distal and, then, of the proximal centriole as the sperm transits to the cauda and vas deferens in preparation for its climactic release. These centrioles can neither recruit γ-tubulin nor nucleate microtubules when eggs are inseminated or microinjected, yet numerous maternally-nucleated cytasters are found. These sperm centrioles appear as vestigial basal bodies, destroyed in the mid-to-lower corpus. Post-testicular sperm maturation, in which sperm centrioles found in the caput are destroyed prior to ejaculation, is a newly discovered function for the epididymis.

Nuclease Footprints in Sperm Project Past and Future Chromatin Regulatory Events

Nuclear remodeling to a condensed state is a hallmark of spermatogenesis. This is achieved by replacement of histones with protamines. Regions retaining nucleosomes may be of functional significance. To determine their potential roles, sperm from wild type and transgenic mice harboring a single copy insert of the human protamine cluster were subjected to Micrococcal Nuclease-seq. CENTIPEDE, a hierarchical Bayesian model, was used to identify multiple spatial patterns, "footprints", of MNase-seq reads along the sperm genome. Regions predicted by CENTIPEDE analysis to be bound by a regulatory factor in sperm were correlated with genomic landmarks and higher order chromatin structure datasets to identify potential roles for these factors in regulating either prior or post spermatogenic, i.e., early embryonic events. This approach linked robust endogenous protamine transcription and transgene suppression to its chromatin environment within topologically associated domains. Of the candidate enhancer-bound regulatory proteins, Ctcf, was associated with chromatin domain boundaries in testes and embryonic stem cells. The continuity of Ctcf binding through the murine germline may permit rapid reconstitution of chromatin organization following fertilization. This likely reflects its preparation for early zygotic genome activation and comparatively accelerated preimplantation embryonic development program observed in mouse as compared to human and bull.

Environmental Susceptibility of the Sperm Epigenome During Windows of Male Germ Cell Development

Male germ cells require multiple epigenetic reprogramming events during their lifespan to achieve reproductive capacity. An emerging body of compelling data demonstrates that environmental exposures can be embodied within the developing male germ cell as epigenetic marks. In turn, these epigenetic marks can impart information at fertilization to affect the trajectory of offspring health and development. While it is recognized that in utero epigenetic reprogramming of male germ cells is a particularly susceptible window to environmental exposures, other such windows exist during germ cell development. The objective of this review is to discuss epigenetic reprogramming events during male germ cell development and to provide supporting evidence from animal and human studies that during specific periods of development, germ cells are susceptible to environmentally induced epigenetic errors. Moving forward, the nascent field of sperm epigenetics research is likely to advance our understanding of paternal environmental determinants of offspring health and development.

Increased N6-methyladenosine in Human Sperm RNA as a Risk Factor for Asthenozoospermia

Male infertility is a worldwide medical problem. Asthenozoospermia is a common cause of infertility. Epigenetic modifications of DNA and histones have been shown to influence human infertility, but no research has explored whether N(6)-methyladenosine (m(6)A) level in RNA is associated with asthenozoospermia. Here, we collected a total of 52 semen samples, including 20 asthenozoospermia patients and 32 healthy controls. An LC-ESI-MS/MS method was used to detect m(6)A contents in sperm RNA, and real-time PCR was performed to determine the mRNA expression of demethylase (FTO, ALKBH5), methyltransferase (METTL3, METTL14, WTAP) and an m(6)A-selective-binding protein (YTHDF2). We found that m(6)A content (p = 0.033) and the mRNA expression of METTL3 (p = 0.016) and METTL14 (p = 0.025) in asthenozoospermia patients were significantly higher than those of controls. Increased m(6)A content was a risk factor for asthenozoospermia (odds ratio (OR) 3.229, 95% confidence interval (CI) 1.178 - 8.853, p = 0.023). Moreover, m(6)A content was correlated with the expression of METTL3 (r = 0.303, p = 0.032) and with sperm motility (progressive motility: r = -0.288, p = 0.038; non-progressive motility: r = -0.293, p = 0.037; immotility: r = 0.387, p = 0.005). Our data suggest that increased m(6)A content is a risk factor for asthenozoospermia and affects sperm motility. Methyltransferases, particularly METTL3, play key roles in increasing m(6)A contents in sperm RNA.

Long non-coding RNA regulation of reproduction and development

Noncoding RNAs (ncRNAs) have long been known to play vital roles in eukaryotic gene regulation. Studies conducted over a decade ago revealed that maturation of spliced, polyadenylated coding mRNA occurs by reactions involving small nuclear RNAs and small nucleolar RNAs; mRNA translation depends on activities mediated by transfer RNAs and ribosomal RNAs, subject to negative regulation by micro RNAs; transcriptional competence of sex chromosomes and some imprinted genes is regulated in cis by ncRNAs that vary by species; and both small-interfering RNAs and piwi-interacting RNAs bound to Argonaute-family proteins regulate post-translational modifications on chromatin and local gene expression states. More recently, gene-regulating noncoding RNAs have been identified, such as long intergenic and long noncoding RNAs (collectively referred to as lncRNAs)--a class totaling more than 100,000 transcripts in humans, which include some of the previously mentioned RNAs that regulate dosage compensation and imprinted gene expression. Here, we provide an overview of lncRNA activities, and then review the role of lncRNAs in processes vital to reproduction, such as germ cell specification, sex determination and gonadogenesis, sex hormone responses, meiosis, gametogenesis, placentation, non-genetic inheritance, and pathologies affecting reproductive tissues. Results from many species are presented to illustrate the evolutionarily conserved processes lncRNAs are involved in.