Sperm is epigenetically programmed to regulate gene transcription in embryos

Paternal immune activation by Poly I:C modulates sperm noncoding RNA profiles and causes transgenerational changes in offspring behavior

Paternal pre-conceptual environmental experiences, such as stress and diet, can affect offspring brain and behavioral phenotypes via epigenetic modifications in sperm. Furthermore, maternal immune activation due to infection during gestation can reprogram offspring behavior and brain functioning in adulthood. However, the effects of paternal pre-conceptual exposure to immune activation on the behavior and physiology of offspring (F1) and grand-offspring (F2) are not currently known. We explored effects of paternal pre-conceptual exposure to viral-like immune activation on F1 and F2 behavioral and physiological phenotypes using a C57BL/6J mouse model. Males were treated with a single injection (intraperitoneal) of the viral mimetic polyinosinic:polycytidylic acid (Poly I:C: 12 mg/kg) then bred with naïve female mice four weeks after the Poly I:C (or 0.9% saline control) injection. The F1 offspring of Poly I:C treated fathers displayed increased depression-like behavior in the Porsolt swim test, an altered stress response in the novelty-suppressed feeding test, and significant transcriptomic changes in their hippocampus. Additionally, the F1 male offspring of Poly I:C treated F0 males showed significantly increased immune responsivity after a Poly I:C immune challenge (12 mg/kg). Furthermore, the F2 male grand-offspring took longer to enter and travelled significantly shorter distances in the light zone of the light/dark box. An analysis of the small noncoding RNA profiles in sperm from Poly I:C treated males and their male offspring revealed significant effects of Poly I:C on the sperm microRNA content at the time of conception and on the sperm PIWI-interacting RNA content of the male offspring. Notably, eight miRNAs with an FDR < 0.05 (miR-141-3p, miR-126b-5p, miR-669o-5p, miR-10b-3p, miR-471-5p, miR-463-5p, miR-148b-3p, and miR-181c-5p) were found to be significantly downregulated in the sperm of Poly I:C treated males. Collectively, we demonstrate that paternal pre-conceptual exposure to a viral immune challenge results in both intergenerational and transgenerational effects on brain and behavior that may be mediated by alterations in the sperm small noncoding RNA content.

Environmental and Genetic Traffic in the Journey from Sperm to Offspring

Recent advancements in the understanding of how sperm develop into offspring have shown complex interactions between environmental influences and genetic factors. The past decade, marked by a research surge, has not only highlighted the profound impact of paternal contributions on fertility and reproductive outcomes but also revolutionized our comprehension by unveiling how parental factors sculpt traits in successive generations through mechanisms that extend beyond traditional inheritance patterns. Studies have shown that offspring are more susceptible to environmental factors, especially during critical phases of growth. While these factors are broadly detrimental to health, their effects are especially acute during these periods. Moving beyond the immutable nature of the genome, the epigenetic profile of cells emerges as a dynamic architecture. This flexibility renders it susceptible to environmental disruptions. The primary objective of this review is to shed light on the diverse processes through which environmental agents affect male reproductive capacity. Additionally, it explores the consequences of paternal environmental interactions, demonstrating how interactions can reverberate in the offspring. It encompasses direct genetic changes as well as a broad spectrum of epigenetic adaptations. By consolidating current empirically supported research, it offers an exhaustive perspective on the interwoven trajectories of the environment, genetics, and epigenetics in the elaborate transition from sperm to offspring.

Age-associated DNA methylation changes in Xenopus frogs

Age-associated changes in DNA methylation have been characterized across various animals, but not yet in amphibians, which are of particular interest because they include widely studied model organisms. In this study, we present clear evidence that the aquatic vertebrate species Xenopus tropicalis displays patterns of age-associated changes in DNA methylation. We have generated whole-genome bisulfite sequencing (WGBS) profiles from skin samples of nine frogs representing young, mature, and old adults and characterized the gene- and chromosome-scale DNA methylation changes with age. Many of the methylation features and changes we observe are consistent with what is known in mammalian species, suggesting that the mechanism of age-related changes is conserved. Moreover, we selected a few thousand age-associated CpG sites to build an assay based on targeted DNA methylation analysis (TBSseq) to expand our findings in future studies involving larger cohorts of individuals. Preliminary results of a pilot TBSeq experiment recapitulate the findings obtained with WGBS setting the basis for the development of an epigenetic clock assay. The results of this study will allow us to leverage the unique resources available for Xenopus to study how DNA methylation relates to other hallmarks of ageing.

Cryopreservation effect on DNA methylation profile in rainbow trout spermatozoa

Spermatozoa are the cells that are most commonly used for cryopreservation of valuable genetic resources in aquaculture. It is known that fish spermatozoa transmit to the embryo not only their genetic but also their epigenetic profile, especially DNA methylation. Therefore, any alteration of the DNA methylation profile in spermatozoa induces the risk of transmitting epigenetic alterations to the offspring. The aim of this study was to assess the effect of cryopreservation on DNA methylation in rainbow trout spermatozoa. To trigger variable cellular response after freezing-thawing, spermatozoa from mature males were cryopreserved with dimethyl sulfoxide, methanol or glycerol as cryoprotectant. We observed that dimethyl sulfoxide was the best to preserve thawed spermatozoa functions. Methanol only slightly preserved all the cellular parameters, while glycerol failed to protect motility and fertilization ability. The consequences on DNA methylation were assessed using Reduced Representation Bisulfite Sequencing (RRBS). Sperm cryopreservation did not thoroughly impact DNA methylation, although 335-564 differentially methylated cytosines were characterized depending on the cryoprotectant. Very few of them were shared between cryoprotectants, and no correlation with the extent of cellular damage was found. Our study showed that DNA methylation was only slightly altered after sperm cryopreservation, and this may render further analysis of the risk for the progeny very challenging.

Biological Embedding of Early-Life Adversity and a Scoping Review of the Evidence for Intergenerational Epigenetic Transmission of Stress and Trauma in Humans

Severe or chronic stress and trauma can have a detrimental impact on health. Evidence suggests that early-life adversity can become biologically embedded and has the potential to influence health outcomes decades later. Epigenetics is one mechanism that has been implicated in these long-lasting effects. Observational studies in humans indicate that the effects of stress could even persist across generations, although whether or not epigenetic mechanisms are involved remains under debate. Here, we provide an overview of studies in animals and humans that demonstrate the effects of early-life stress on DNA methylation, one of the most widely studied epigenetic mechanisms, and summarize findings from animal models demonstrating the involvement of epigenetics in the transmission of stress across generations. We then describe the results of a scoping review to determine the extent to which the terms intergenerational or transgenerational have been used in human studies investigating the transmission of trauma and stress via epigenetic mechanisms. We end with a discussion of key areas for future research to advance understanding of the role of epigenetics in the legacy effects of stress and trauma.

Casting histone variants during mammalian reproduction

During mammalian reproduction, germ cell chromatin packaging is key to prepare parental genomes for fertilization and to initiate embryonic development. While chromatin modifications such as DNA methylation and histone post-translational modifications are well known to carry regulatory information, histone variants have received less attention in this context. Histone variants alter the stability, structure and function of nucleosomes and, as such, contribute to chromatin organization in germ cells. Here, we review histone variants expression dynamics during the production of male and female germ cells, and what is currently known about their parent-of-origin effects during reproduction. Finally, we discuss the apparent conundrum behind these important functions and their recent evolutionary diversification.

Nucleosomes in mammalian sperm: conveying paternal epigenetic inheritance or subject to reprogramming between generations?

The genome of mammalian sperm is largely packaged by sperm-specific proteins termed protamines. The presence of some residual nucleosomes has, however, emerged as a potential source of paternal epigenetic inheritance between generations. Sperm nucleosomes bear important regulatory histone marks and locate at gene-regulatory regions, functional elements, and intergenic regions. It is unclear whether sperm nucleosomes are retained at specific genomic locations in a deterministic manner or are randomly preserved due to inefficient exchange of histones by protamines. Recent studies indicate heterogeneity in chromatin packaging within sperm populations and an extensive reprogramming of paternal histone marks post fertilization. Obtaining single-sperm nucleosome distributions is fundamental to estimating the potential of sperm-borne nucleosomes in instructing mammalian embryonic development and in the transmission of acquired phenotypes.

Insights into the sperm chromatin and implications for male infertility from a protein perspective

Male germ cells undergo an extreme but fascinating process of chromatin remodeling that begins in the testis during the last phase of spermatogenesis and continues through epididymal sperm maturation. Most of the histones are replaced by small proteins named protamines, whose high basicity leads to a tight genomic compaction. This process is epigenetically regulated at many levels, not only by posttranslational modifications, but also by readers, writers, and erasers, in a context of a highly coordinated postmeiotic gene expression program. Protamines are key proteins for acquiring this highly specialized chromatin conformation, needed for sperm functionality. Interestingly, and contrary to what could be inferred from its very specific DNA-packaging function across protamine-containing species, human sperm chromatin contains a wide spectrum of protamine proteoforms, including truncated and posttranslationally modified proteoforms. The generation of protamine knock-out models revealed not only chromatin compaction defects, but also collateral sperm alterations contributing to infertile phenotypes, evidencing the importance of sperm chromatin protamination toward the generation of a new individual. The unique features of sperm chromatin have motivated its study, applying from conventional to the most ground-breaking techniques to disentangle its peculiarities and the cellular mechanisms governing its successful conferment, especially relevant from the protein point of view due to the important epigenetic role of sperm nuclear proteins. Gathering and contextualizing the most striking discoveries will provide a global understanding of the importance and complexity of achieving a proper chromatin compaction and exploring its implications on postfertilization events and beyond. This article is categorized under: Reproductive System Diseases > Genetics/Genomics/Epigenetics Reproductive System Diseases > Molecular and Cellular Physiology.

H4K5 Butyrylation Coexist with Acetylation during Human Spermiogenesis and Are Retained in the Mature Sperm Chromatin

Male germ cells experience a drastic chromatin remodeling through the nucleo-histone to nucleo-protamine (NH-NP) transition necessary for proper sperm functionality. Post-translational modifications (PTMs) of H4 Lys5, such as acetylation (H4K5ac), play a crucial role in epigenetic control of nucleosome disassembly facilitating protamine incorporation into paternal DNA. It has been shown that butyrylation on the same residue (H4K5bu) participates in temporal regulation of NH-NP transition in mice, delaying the bromodomain testis specific protein (BRDT)-dependent nucleosome disassembly and potentially marking retained nucleosomes. However, no information was available so far on this modification in human sperm. Here, we report a dual behavior of H4K5bu and H4K5ac in human normal spermatogenesis, suggesting a specific role of H4K5bu during spermatid elongation, coexisting with H4K5ac although with different starting points. This pattern is stable under different testicular pathologies, suggesting a highly conserved function of these modifications. Despite a drastic decrease of both PTMs in condensed spermatids, they are retained in ejaculated sperm, with 30% of non-colocalizing nucleosome clusters, which could reflect differential paternal genome retention. Whereas no apparent effect of these PTMs was observed associated with sperm quality, their presence in mature sperm could entail a potential role in the zygote.

Paternally inherited H3K27me3 affects chromatin accessibility in mouse embryos produced by round spermatid injection

Round spermatid injection (ROSI) results in a lower birth rate than intracytoplasmic sperm injection, which has hampered its clinical application. Inefficient development of ROSI embryos has been attributed to epigenetic abnormalities. However, the chromatin-based mechanism that underpins the low birth rate in ROSI remains to be determined. Here, we show that a repressive histone mark, H3K27me3, persists from mouse round spermatids into zygotes in ROSI and that round spermatid-derived H3K27me3 is associated with less accessible chromatin and impaired gene expression in ROSI embryos. These loci are initially marked by H3K27me3 but undergo histone modification remodelling in spermiogenesis, resulting in reduced H3K27me3 in normal spermatozoa. Therefore, the absence of epigenetic remodelling, presumably mediated by histone turnover during spermiogenesis, leads to dysregulation of chromatin accessibility and transcription in ROSI embryos. Thus, our results unveil a molecular logic, in which chromatin states in round spermatids impinge on chromatin accessibility and transcription in ROSI embryos, highlighting the importance of epigenetic remodelling during spermiogenesis in successful reproduction.

Increased sperm DNA damage leads to poor embryo quality and subfertility of male rats treated with methylphenidate hydrochloride in adolescence

BACKGROUND

Methylphenidate hydrochloride (MPH) is a psychostimulant widely used in the treatment of attention deficit hyperactive disorder (ADHD), as well as a performance enhancer, for at least 60 years. Despite the notable effectiveness as a psychostimulant, ADHD is a chronic disorder and has a two-third chance of accompanying the individual throughout life. Long-term use of MPH has been associated not only with an increase in the development of neurodegenerative diseases, but it also has side effects on male fertility in experimental animals.

OBJECTIVES

To investigate whether methylphenidate poses a risk to sperm DNA structure and to the quality of embryos conceived after treatment during adolescence in rats.

MATERIALS AND METHODS

Wistar rats at 38 days of age were treated either with 5 mg/kg body weight of MPH, in a single daily dose for 30 days, via gavage or with distilled water-only protocol. Levels of oxidative stress in testicular and epididymal tissues were evaluated. Sperm chromatin quality and acrosome integrity was assessed under flow cytometry. From 107 days of age, animals were mated with untreated females. The effects of the paternal contribution at two different embryo development moments - cleavage stage (2.5 days post coitum) and late gestation (20 days post coitum) - were analyzed.

RESULTS

MPH caused high levels of sperm DNA damage, which was reflected in 40% of decrease in early embryo quality and a lower number of live pups at 20 dpc.

DISCUSSION

The high level of fragmentation seen in the embryos sired from the MPH group is consistent with the poor chromatin structure of the sperm, and does not seem to be a result of oxidative stress in the reproductive tissues.

CONCLUSIONS

The results presented here suggest that the subchronic use of MPH during male prepubertal phase may cause long term subfertility and compromise embryo survival. This article is protected by copyright. All rights reserved.

Parental competition for the regulators of chromatin dynamics in mouse zygotes

The underlying mechanism for parental asymmetric chromatin dynamics is still unclear. To reveal this, we investigate chromatin dynamics in parthenogenetic, androgenic, and several types of male germ cells-fertilized zygotes. Here we illustrate that parental conflicting role mediates the regulation of chromatin dynamics. Sperm reduces chromatin dynamics in both parental pronuclei (PNs). During spermiogenesis, male germ cells acquire this reducing ability and its resistance. On the other hand, oocytes can increase chromatin dynamics. Notably, the oocytes-derived chromatin dynamics enhancing ability is dominant for the sperm-derived opposing one. This maternal enhancing ability is competed between parental pronuclei. Delayed fertilization timing is critical for this competition and compromises parental asymmetric chromatin dynamics and zygotic transcription. Together, parental competition for the maternal factor enhancing chromatin dynamics is a determinant to establish parental asymmetry, and paternal repressive effects have supporting roles to enhance asymmetry.

Human Sperm Morphology as a Marker of Its Nuclear Quality and Epigenetic Pattern

Background: Human sperm chromatin condensation is a sum of epigenetic events that allows for the near-complete replacement of histones with protamines. Under high-magnification microscopy, nuclear vacuoles have been described as thumbprints with poor chromatin condensation. The objective of this study is to examine whether vacuolated spermatozoa carry specific epigenetic marks, which may influence embryo development. Methods: The presence and three-dimensional distribution of ten epigenetic marks (protamine-P2, histone-H3, H3K4me1/me2/me3, H3K9me1/me2/me3, H3K27me3, H4k20me2) were evaluated and compared in morphometrically normal spermatozoa according to the presence or absence of a large vacuole occupying more than 15% of the head surface (n = 4193). Results: Vacuolated spermatozoa were significantly more frequently labelled with H3 and H3K4me3 than normal spermatozoa (88.1% ± 2.7 and 78.5% ± 5.2 vs. 74.8% ± 4.8 and 49.1% ± 7.4, respectively; p = 0.009 and p < 0.001) and significantly less marked by P2 and H3K27me3 (50.2% ± 6.2 and 63.9% ± 6.3 vs. 82.1% ± 4.4 and 73.6% ± 5.1, respectively; p < 0.001 and p = 0.028). In three dimensions, vacuoles are nuclear concavities filled with DNA carrying the H3K4me3 marker. Conclusion: High-magnification microscopy is a simple tool to estimate in real time the sperm epigenetic profile. The selection of normal spermatozoa without vacuoles and the deselection of spermatozoa with vacuoles appear to be epigenetically favorable to embryo development and safe offspring.

Transgenerational epigenetic impacts of parental infection on offspring health and disease susceptibility

Maternal immune activation (MIA) and infection during pregnancy are known to reprogramme offspring phenotypes. However, the epigenetic effects of preconceptual paternal infection and paternal immune activation (PIA) are not currently well understood. Recent reports show that paternal infection and immune activation can affect offspring phenotypes, particularly brain function, behaviour, and immune system functioning, across multiple generations without re-exposure to infection. Evidence from other environmental exposures indicates that epigenetic inheritance also occurs in humans. Given the growing impact of the coronavirus disease 2019 (COVID-19) pandemic, it is imperative that we investigate all of the potential epigenetic mechanisms and multigenerational phenotypes that may arise from both maternal and paternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, as well as associated MIA, PIA, and inflammation. This will allow us to understand and, if necessary, mitigate any potential changes in disease susceptibility in the children, and grandchildren, of affected parents.

Paternal alcohol consumption has intergenerational consequences in male offspring

PURPOSE

Alcoholism is a heterogeneous set of disorders caused by ethanol intake. Harmful effects of paternal consumption on the offspring are poorly explored and not fully understood. We analyzed the effect of paternal alcohol consumption on both their own reproductive capacity and that of their male offspring.

METHODS

We used a model of ethanol consumption (15% v/v in drinking water) for 12 days in adult CF-1 male mice. DNA integrity and post-translational modifications of histones were assessed in sperm; testicular weight, histology, and DNA fragmentation were analyzed. Treated or untreated male mice were mated with non-treated females to obtain two cell embryos that were cultured for 7 days; morphology and embryonic cell death were evaluated. Males of both groups were mated with non-treated females. Adult male offspring was euthanized, and sperm and testicular parameters determined.

RESULTS

Paternal ethanol consumption caused histological and epigenetic changes, as well as damage in DNA integrity in the testicular germline and sperm. These alterations gave rise to deleterious effects on embryonic development and to testicular and spermatic changes in the offspring.

CONCLUSION

This study provides critical information on reproductive disturbances brought about by paternal alcohol consumption and the profound impact these could have on the male progeny. The need to explore the effects of paternal alcohol consumption in detail and warn about the importance of controlling alcohol intake for the well-being of future generations should not be underscored.

Histone Methylation Regulates Gene Expression in the Round Spermatids to Set the RNA Payloads of Sperm

Gene expression during spermatogenesis undergoes significant changes due to a demanding sequence of mitosis, meiosis, and differentiation. We investigated the contribution of H3 histone modifications to gene regulation in the round spermatids. Round spermatids were purified from rat testes using centrifugal elutriation and Percoll density-gradient centrifugation. After enzymatic chromatin shearing, immuno-precipitation using antibodies against histone marks H3k4me3 and H3K9me3 was undertaken. The immunoprecipitated DNA fragments were subjected to massive parallel sequencing. Gene expression in round spermatids and sperm was analyzed by transcriptome sequencing using next-generation sequencing methods. ChIP-seq analysis showed significant peak enrichment in H3K4me3 marks in active chromatin regions and H3K9me3 peak enrichment in repressive regions. We found 53 genes which showed overlapping peak enrichment in both H3K4me3 and H3K9me3 marks. Some of the top H3K4me3-enriched genes were involved in sperm tail formation (Odf1, Odf3, Odf4, Oaz3, Ccdc42, Ccdc63, and Ccdc181), chromatin condensation (Dync1h1, Dynll1, and Kdm3a), and sperm functions such as acrosome reaction (Acrbp and Fabp9), energy generation (Gapdhs), and signaling for motility (Tssk1b, Tssk2, and Tssk4). Transcriptome sequencing in round spermatids found 64% transcripts of the H3K4me3-enriched genes at high levels and of about 25% of H3K9me3-enriched genes at very low levels. Transcriptome sequencing in sperm found that more than 99% of the ChIP-seq corresponding transcripts were also present in sperm. H3K4me3 enrichment in the round spermatids correlates significantly with gene expression and H3K9me3 correlates with gene silencing that contribute to sperm differentiation and setting the RNA payloads of sperm.

Heterogeneity in the Epigenetic Landscape of Murine Testis-Specific Histone Variants TH2A and TH2B Sharing the Same Bi-Directional Promoter

Testis-specific histone variants are crucial to promote open chromatin structure to enable nucleosome disassembly in the final stages of spermiogenesis. However, even after histone replacement, mature sperm retain a proportion of these variants, the function of which is unknown. The present study aimed to understand the functional relevance of the retained H2B and H2A variants, TH2B and TH2A. While no literature is available on the phenotype of TH2A knockouts, TH2B/TH2A double knockout male mice are reported to be infertile. In this study, ChIP-seq analysis was done for TH2B and TH2A to understand the epigenomics of the retained TH2B and TH2A, using murine caudal sperm. Distribution across genomic partitions revealed ∼35% of the TH2B peaks within ±5 kb of TSS whereas TH2A peaks distribution was sparse at TSS. Gene Ontology revealed embryo development as the most significant term associated with TH2B. Also, based on genomic regions, TH2B was observed to be associated with spindle assembly and various meiosis-specific genes, which is an important finding as TH2A/TH2B DKO mice have been reported to have defective cohesin release. A comparison of mouse and human TH2B-linked chromatin revealed 26% overlap between murine and human TH2B-associated genes. This overlap included genes crucial for embryogenesis. Most importantly, heterogeneity in the epigenetic landscape of TH2A and TH2B was seen, which is intriguing as TH2B and TH2A are well reported to be present in the same nucleosomes to promote open chromatin. Additionally, unlike TH2B, TH2A was enriched on the mitochondrial chromosome. TH2A was found to be associated with Nuclear insertion of Mitochondrial DNA sequences (NUMTs) in sperm. A comprehensive analysis of these observations indicates novel functions for the sperm-retained TH2B and TH2A.

H4K20me3 marks distal intergenic and repetitive regions in human mature spermatozoa

Sperm histones represent an essential part of the paternally transmitted epigenome, but uncertainty exists about the role of those remaining in non-coding and repetitive DNA. We therefore analyzed the genome-wide distribution of the heterochromatic marker H4K20me3 in human sperm and somatic (K562) cells. To specify the function of sperm histones, we compared all H4K20me3-containing and -free loci in the sperm genome. Sperm and somatic cells possessed a very similar H4K20me3 distribution: H4K20me3 peaks occurred mostly in distal intergenic regions and repetitive gene clusters (in particular genes encoding odorant-binding factors and zinc-finger antiviral proteins). In both cell types, H4K20me3 peaks were enriched in LINEs, ERVs, satellite DNA and low complexity repeats. In contrast, H4K20me3-free nucleosomes occurred more frequently in genic regions (in particular promoters, exons, 5'-UTR and 3'-UTR) and were enriched in genes encoding developmental factors (in particular transcription activators and repressors). H4K20me3-free nucleosomes were also detected in substantial quantities in distal intergenic regions and were enriched in SINEs. Thus, evidence suggests that paternally transmitted histones may have a dual purpose: maintenance and regulation of heterochromatin and guidance towards transcription of euchromatin.

The Impact of Stress Within and Across Generations: Neuroscientific and Epigenetic Considerations

The impact of stress and trauma on biological systems in humans can be substantial. They can result in epigenetic changes, accelerated brain development and sexual maturation, and predisposition to psychopathology. Such modifications may be accompanied by behavioral, emotional, and cognitive overtones during one's lifetime. Exposure during sensitive periods of neural development may lead to long-lasting effects that may not be affected by subsequent environmental interventions. The cumulative effects of life stressors in an individual may affect offspring's methylome makeup and epigenetic clocks, neurohormonal modulation and stress reactivity, and physiological and reproductive development. While offspring may suffer deleterious effects from parental stress and their own early-life adversity, these factors may also confer traits that prove beneficial and enhance fitness to their own environment. This article synthesizes the data on how stress shapes biological and behavioral dimensions, drawing from preclinical and human models. Advances in this field of knowledge should potentially allow for an improved understanding of how interventions may be increasingly tailored according to individual biomarkers and developmental history.

Implications of cryopreservation on structural and functional attributes of bovine spermatozoa: An overview

Sperm cryopreservation is an important adjunct to assisted reproduction techniques (ART) for improving the reproductive efficiency of dairy cattle and buffaloes. Improved understanding of mechanisms and challenges of bovine semen cryopreservation is vital for artificial insemination on a commercial basis. Although cryopreservation of bovine spermatozoa is widely practiced and advanced beyond that of other species, there are still major gaps in the knowledge and technology. Upon cryopreservation, disruption of spermatozoal plasma membrane configuration due to alterations in metabolic pathways, enzymes and antioxidants activity add to lower efficiency with loss of sperm longevity and fertilising ability. Therefore, the effective amalgamation of cryo-variables like ambient temperature, cooling and thawing rates, nucleation temperature, type and concentration of the cryoprotectant, seminal plasma composition, free radicals and antioxidant status are required to optimise cryopreservation. Novel strategies like supplementation of cholesterol-loaded cyclodextrins (CLC), nanovesicles, osteopontin, antioxidants, etc., in an extender and recent techniques like nano-purification and modified packaging have to be optimised to ameliorate the cryodamage. This article is intended to describe the basic facts about the sperm cryopreservation process in bovine and the associated biochemical, biophysical, ultra-structural, molecular and functional alterations.

Control of zygotic genome activation in Xenopus

The fertilized frog egg contains all the materials needed to initiate development of a new organism, including stored RNAs and proteins deposited during oogenesis, thus the earliest stages of development do not require transcription. The onset of transcription from the zygotic genome marks the first genetic switch activating the gene regulatory network that programs embryonic development. Zygotic genome activation occurs after an initial phase of transcriptional quiescence that continues until the midblastula stage, a period called the midblastula transition, which was first identified in Xenopus. Activation of transcription is programmed by maternally supplied factors and is regulated at multiple levels. A similar switch exists in most animals and is of great interest both to developmental biologists and to those interested in understanding nuclear reprogramming. Here we review in detail our knowledge on this major switch in transcription in Xenopus and place recent discoveries in the context of a decades old problem.

Avenues of reef-building coral acclimatization in response to rapid environmental change

The swiftly changing climate presents a challenge to organismal fitness by creating a mismatch between the current environment and phenotypes adapted to historic conditions. Acclimatory mechanisms may be especially crucial for sessile benthic marine taxa, such as reef-building corals, where climate change factors including ocean acidification and increasing temperature elicit strong negative physiological responses such as bleaching, disease and mortality. Here, within the context of multiple stressors threatening marine organisms, I describe the wealth of metaorganism response mechanisms to rapid ocean change and the ontogenetic shifts in organism interactions with the environment that can generate plasticity. I then highlight the need to consider the interactions of rapid and evolutionary responses in an adaptive (epi)genetic continuum. Building on the definitions of these mechanisms and continuum, I also present how the interplay of the microbiome, epigenetics and parental effects creates additional avenues for rapid acclimatization. To consider under what conditions epigenetic inheritance has a more substantial role, I propose investigation into the offset of timing of gametogenesis leading to different environmental integration times between eggs and sperm and the consequences of this for gamete epigenetic compatibility. Collectively, non-genetic, yet heritable phenotypic plasticity will have significant ecological and evolutionary implications for sessile marine organism persistence under rapid climate change. As such, reef-building corals present ideal and time-sensitive models for further development of our understanding of adaptive feedback loops in a multi-player (epi)genetic continuum.

Histone H3 lysine 4 trimethylation in sperm is transmitted to the embryo and associated with diet-induced phenotypes in the offspring

A father's lifestyle impacts offspring health; yet, the underlying molecular mechanisms remain elusive. We hypothesized that a diet that changes methyl donor availability will alter the sperm and embryo epigenomes to impact embryonic gene expression and development. Here, we demonstrate that a folate-deficient (FD) diet alters histone H3 lysine 4 trimethylation (H3K4me3) in sperm at developmental genes and putative enhancers. A subset of H3K4me3 alterations in sperm are retained in the pre-implantation embryo and associated with deregulated embryonic gene expression. Using a genetic mouse model in which sires have pre-existing altered H3K4me2/3 in sperm, we show that a FD diet exacerbates alterations in sperm H3K4me3 and embryonic gene expression, leading to an increase in developmental defect severity. These findings imply that paternal H3K4me3 is transmitted to the embryo and influences gene expression and development. It further suggests that epigenetic errors can accumulate in sperm to worsen offspring developmental outcomes.

Sperm-oocyte interplay: an overview of spermatozoon's role in oocyte activation and current perspectives in diagnosis and fertility treatment

The fertilizing spermatozoon is a highly specialized cell that selects from millions along the female tract until the oocyte. The paternal components influence the oocyte activation during fertilization and are fundamental for normal embryo development; however, the sperm-oocyte interplay is in a continuous debate. This review aims to analyze the available scientific information related to the role of the male gamete in the oocyte activation during fertilization, the process of the interaction of sperm factors with oocyte machinery, and the implications of any alterations in this interplay, as well as the advances and limitations of the reproductive techniques and diagnostic tests. At present, both PLCζ and PAWP are the main candidates as oocyte activated factors during fertilization. While PLCζ mechanism is via IP₃, how PAWP activates the oocyte still no clear, and these findings are important to study and treat fertilization failure due to oocyte activation, especially when one of the causes is the deficiency of PLCζ in the sperm. However, no diagnostic test has been developed to establish the amount of PLCζ, the protocol to treat this type of pathologies is broad, including treatment with ionophores, sperm selection improvement, and microinjection with PLCζ protein or RNA.

Genome-wide occupancy reveals the localization of H1T2 (H1fnt) to repeat regions and a subset of transcriptionally active chromatin domains in rat spermatids

Background

H1T2/H1FNT is a germ cell-specific linker histone variant expressed during spermiogenesis specifically in round and elongating spermatids. Infertile phenotype of homozygous H1T2 mutant male mice revealed the essential function of H1T2 for the DNA condensation and histone-to-protamine replacement in spermiogenesis. However, the mechanism by which H1T2 imparts the inherent polarity within spermatid nucleus including the additional protein partners and the genomic domains occupied by this linker histone are unknown.

Results

Sequence analysis revealed the presence of Walker motif, SR domains and putative coiled-coil domains in the C-terminal domain of rat H1T2 protein. Genome-wide occupancy analysis using highly specific antibody against the CTD of H1T2 demonstrated the binding of H1T2 to the LINE L1 repeat elements and to a significant percentage of the genic regions (promoter-TSS, exons and introns) of the rat spermatid genome. Immunoprecipitation followed by mass spectrometry analysis revealed the open chromatin architecture of H1T2 occupied chromatin encompassing the H4 acetylation and other histone PTMs characteristic of transcriptionally active chromatin. In addition, the present study has identified the interacting protein partners of H1T2-associated chromatin mainly as nucleo-skeleton components, RNA-binding proteins and chaperones.

Conclusions

Linker histone H1T2 possesses unique domain architecture which can account for the specific functions associated with chromatin remodeling events facilitating the initiation of histone to transition proteins/protamine transition in the polar apical spermatid genome. Our results directly establish the unique function of H1T2 in nuclear shaping associated with spermiogenesis by mediating the interaction between chromatin and nucleo-skeleton, positioning the epigenetically specialized chromatin domains involved in transcription coupled histone replacement initiation towards the apical pole of round/elongating spermatids.

Environmental impacts on sperm and oocyte epigenetics affect embryo cell epigenetics and transcription to promote the epigenetic inheritance of pathology and phenotypic variation

Previous studies have demonstrated that exposure to environmental factors can cause epigenetic modifications to germ cells, particularly sperm, to promote epigenetic and transcriptome changes in the embryo. These germ cell and embryo cell epigenetic alterations are associated with phenotypic changes in offspring. Epigenetic inheritance requires epigenetic changes (i.e. epimutations) in germ cells that promote epigenetic and gene expression changes in embryos. The objective of this perspective is to examine the evidence that germ cell epigenome modifications are associated with embryo cell epigenetic and transcriptome changes that affect the subsequent development of all developing somatic cells to promote phenotype change. Various epigenetic changes in sperm, including changes to histone methylation, histone retention, non-coding RNA expression and DNA methylation, have been associated with alterations in embryo cell epigenetics and gene expression. Few studies have investigated this link for oocytes. The studies reviewed herein support the idea that environmentally induced epigenetic changes in germ cells affect alterations in embryo cell epigenetics and transcriptomes that have an important role in the epigenetic inheritance of pathology and phenotypic change.

Dynamics of paternal contributions to early embryo development in large animals

This review focuses on current knowledge of paternal contributions to preimplantation embryonic development with particular emphasis on large animals. Specifically, the included content aims to summarize genomic and epigenomic contributions of paternally expressed genes, their regulation, and chromatin structure that are indispensable for early embryo development. The accumulation of current knowledge will summarize conserved allelic function among species to include functional molecular and genomic studies across large domestic animals in context with reference to founding experimental models.

Developmental origins of transgenerational sperm histone retention following ancestral exposures

Numerous environmental toxicants have been shown to induce the epigenetic transgenerational inheritance of disease and phenotypic variation. Alterations in the germline epigenome are necessary to transmit transgenerational phenotypes. In previous studies, the pesticide DDT (dichlorodiphenyltrichloroethane) and the agricultural fungicide vinclozolin were shown to promote the transgenerational inheritance of sperm differential DNA methylation regions, non-coding RNAs and histone retention, which are termed epimutations. These epimutations are able to mediate this epigenetic inheritance of disease and phenotypic variation. The current study was designed to investigate the developmental origins of the transgenerational differential histone retention sites (called DHRs) during gametogenesis of the sperm. Vinclozolin and DDT were independently used to promote the epigenetic transgenerational inheritance of these DHRs. Male control lineage, DDT lineage and vinclozolin lineage F3 generation rats were used to isolate round spermatids, caput epididymal spermatozoa, and caudal sperm. The DHRs distinguishing the control versus DDT lineage or vinclozolin lineage samples were determined at these three developmental stages. DHRs and a reproducible core of histone H3 retention sites were observed using an H3 chromatin immunoprecipitation-sequencing (ChIP-Seq) analysis in each of the germ cell populations. The chromosomal locations and genomic features of the DHRs were analyzed. A cascade of epigenetic histone retention site alterations was found to be initiated in the round spermatids and then further modified during epididymal sperm maturation. Observations show that in addition to alterations in sperm DNA methylation and ncRNA expression previously identified, the induction of differential histone retention sites (DHRs) in the later stages of spermatogenesis also occurs. This novel component of epigenetic programming during spermatogenesis can be environmentally altered and transmitted to subsequent generations through epigenetic transgenerational inheritance.

Epigenetic homogeneity in histone methylation underlies sperm programming for embryonic transcription

Sperm contributes genetic and epigenetic information to the embryo to efficiently support development. However, the mechanism underlying such developmental competence remains elusive. Here, we investigated whether all sperm cells have a common epigenetic configuration that primes transcriptional program for embryonic development. Using calibrated ChIP-seq, we show that remodelling of histones during spermiogenesis results in the retention of methylated histone H3 at the same genomic location in most sperm cell. This homogeneously methylated fraction of histone H3 in the sperm genome is maintained during early embryonic replication. Such methylated histone fraction resisting post-fertilisation reprogramming marks developmental genes whose expression is perturbed upon experimental reduction of histone methylation. A similar homogeneously methylated histone H3 fraction is detected in human sperm. Altogether, we uncover a conserved mechanism of paternal epigenetic information transmission to the embryo through the homogeneous retention of methylated histone in a sperm cells population.

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 Lysine Demethylases KDM5B and KDM5C Modulate Genome Activation and Stability in Porcine Embryos

The lysine demethylases KDM5B and KDM5C are highly, but transiently, expressed in porcine embryos around the genome activation stage. Attenuation of KDM5B and KDM5C mRNA hampered embryo development to the blastocyst stage in fertilized, parthenogenetically activated and nuclear transfer embryos. While KDM5B attenuation increased H3K4me2-3 levels on D3 embryos and H3K4me1-2-3 on D5 embryos, KDM5C attenuation increased H3K9me1 on D3 embryos, and H3K9me1 and H3K4me1 on D5 embryos. The relative mRNA abundance of EIF1AX and EIF2A on D3 embryos, and the proportion of D4 embryos presenting a fluorescent signal for uridine incorporation were severely reduced in both KDM5B- and KDM5C-attenuated compared to control embryos, which indicate a delay in the initiation of the embryo transcriptional activity. Moreover, KDM5B and KDM5C attenuation affected DNA damage response and increased DNA double-strand breaks (DSBs), and decreased development of UV-irradiated embryos. Findings from this study revealed that both KDM5B and KDM5C are important regulators of early development in porcine embryos as their attenuation altered H3K4 and H3K9 methylation patterns, perturbed embryo genome activation, and decreased DNA damage repair capacity.

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.

Insights into the roles of sperm in animal cloning

Somatic cell nuclear transfer (SCNT) has shown a wide application in the generation of transgenic animals, protection of endangered animals, and therapeutic cloning. However, the efficiency of SCNT remains very low due to some poorly characterized key factors. Compared with fertilized embryos, somatic donor cells lack some important components of sperm, such as sperm small noncoding RNA (sncRNA) and proteins. Loss of these factors is considered an important reason for the abnormal development of SCNT embryo. This study focused on recent advances of SCNT and the roles of sperm in development. Sperm-derived factors play an important role in nucleus reprogramming and cytoskeleton remodeling during SCNT embryo development. Hence, considering the role of sperm may provide a new strategy for improving cloning efficiency.

Transgenerational Inheritance of Environmentally Induced Epigenetic Alterations during Mammalian Development

Genetic studies traditionally focus on DNA as the molecule that passes information on from parents to their offspring. Changes in the DNA code alter heritable information and can more or less severely affect the progeny's phenotype. While the idea that information can be inherited between generations independently of the DNA's nucleotide sequence is not new, the outcome of recent studies provides a mechanistic foundation for the concept. In this review, we attempt to summarize our current knowledge about the transgenerational inheritance of environmentally induced epigenetic changes. We focus primarily on studies using mice but refer to other species to illustrate salient points. Some studies support the notion that there is a somatic component within the phenomenon of epigenetic inheritance. However, here, we will mostly focus on gamete-based processes and the primary molecular mechanisms that are thought to contribute to epigenetic inheritance: DNA methylation, histone modifications, and non-coding RNAs. Most of the rodent studies published in the literature suggest that transgenerational epigenetic inheritance through gametes can be modulated by environmental factors. Modification and redistribution of chromatin proteins in gametes is one of the major routes for transmitting epigenetic information from parents to the offspring. Our recent studies provide additional specific cues for this concept and help better understand environmental exposure influences fitness and fidelity in the germline. In summary, environmental cues can induce parental alterations and affect the phenotypes of offspring through gametic epigenetic inheritance. Consequently, epigenetic factors and their heritability should be considered during disease risk assessment.

Bisphenol AF compromises blood-testis barrier integrity and sperm quality in mice

The profound influence of environmental chemicals on human health including inducing life-threatening gene mutation has been publicly recognized. Being a substitute for the extensively used endocrine-disrupting chemical BPA, Bisphenol AF (BPAF) has been known as teratogen with developmental toxicities and therefore potentially putting human into the risk of biological hazards. Herein, we deciphered the detrimental effects of BPAF on spermatogenesis and spermiotiliosis in sexual maturity of mice exposing to BPAF (5, 20, 50 mg/kg/d) for consecutive 28 days. BPAF exposure significantly compromises blood-testis barrier integrity and sperm quantity and quality in a dose-dependent manner. Sperms from BPAF exposure mice are featured by severe DNA damage, altered SUMOylation and ubiquitination dynamics and interfered epigenetic inheritance with hypermethylation of H3K27me3 presumably due to the aggregation of cellular reactive oxygen species (ROS). Furthermore, BPAF treatment (50 μM for 24 h) compromises cytoskeleton architecture and tight junction permeability in primary cultured Sertoli cells evidenced by dysfunction of actin regulatory proteins (e.g. Arp3 and Palladin) via activation of ERK signaling, thereby perturbing the privilege microenvironment created by Sertoli cells for spermatogenesis. Overall, our study determines BPAF is deleterious for male fertility, leading to a better appreciation of its toxicological features in our life.

DNA methylation stability in fish spermatozoa upon external constraint: Impact of fish hormonal stimulation and sperm cryopreservation

Highly differentiated mature spermatozoa carry not only genetic but also epigenetic information that is to be transmitted to the embryo. DNA methylation is one epigenetic actor associated with sperm nucleus compaction, gene silencing, and prepatterning of embryonic gene expression. Therefore, the stability of this mark toward reproductive biotechnologies is a major issue in animal production. The present work explored the impact of hormonal induction of spermiation and sperm cryopreservation in two cyprinids, the goldfish (Carassius auratus) and the zebrafish (Danio rerio), using LUminometric Methylation Assay (LUMA). We showed that while goldfish hormonal treatment did increase sperm production, it did not alter global DNA methylation of spermatozoa. Different sperm samples repeatedly collected from the same males for 2 months also showed the same global DNA methylation level. Similarly, global DNA methylation was not affected after cryopreservation of goldfish spermatozoa with methanol, whereas less efficient cryoprotectants (dimethylsulfoxide and 1,2-propanediol) decreased DNA methylation. In contrast, cryopreservation of zebrafish spermatozoa with methanol induced a slight, but significant, increase in global DNA methylation. In the less compact nuclei, that is, goldfish fin somatic cells, cryopreservation did not change global DNA methylation regardless of the choice of cryoprotectant. To conclude, global DNA methylation is a robust parameter with respect to biotechnologies such as hormonal induction of spermiation and sperm cryopreservation, but it can be altered when the best sperm manipulation conditions are not met.

Redox Regulation and Oxidative Stress: The Particular Case of the Stallion Spermatozoa

Redox regulation and oxidative stress have become areas of major interest in spermatology. Alteration of redox homeostasis is recognized as a significant cause of male factor infertility and is behind the damage that spermatozoa experience after freezing and thawing or conservation in a liquid state. While for a long time, oxidative stress was just considered an overproduction of reactive oxygen species, nowadays it is considered as a consequence of redox deregulation. Many essential aspects of spermatozoa functionality are redox regulated, with reversible oxidation of thiols in cysteine residues of key proteins acting as an “on–off” switch controlling sperm function. However, if deregulation occurs, these residues may experience irreversible oxidation and oxidative stress, leading to malfunction and ultimately death of the spermatozoa. Stallion spermatozoa are “professional producers” of reactive oxygen species due to their intense mitochondrial activity, and thus sophisticated systems to control redox homeostasis are also characteristic of the spermatozoa in the horse. As a result, and combined with the fact that embryos can easily be collected in this species, horses are a good model for the study of redox biology in the spermatozoa and its impact on the embryo.

Sperm cryopreservation reduces offspring growth

Sperm cryopreservation is routinely used in reproductive medicine, livestock production and wildlife management. Its effect on offspring performance is often assumed to be negligible, but this still remains to be confirmed in well-controlled within-subject experiments. We use a vertebrate model that allows us to experimentally separate parental and environmental effects to test whether sperm cryopreservation influences offspring phenotype under stress and non-stress conditions, and whether such effects are male-specific. Wild brown trout (Salmo trutta) were stripped for their gametes, and a portion of each male's milt was cryopreserved. Then, 960 eggs were simultaneously fertilized with either non-cryopreserved or frozen-thawed semen and raised singly in the presence or absence of a pathogen. We found no significant effects of cryopreservation on fertilization rates, and no effects on growth, survival nor pathogen resistance during the embryo stage. However, fertilization by cryopreserved sperm led to significantly reduced larval growth after hatching. Males varied in genetic quality as determined from offspring performance, but effects of cryopreservation on larval growth were not male-specific. We conclude that cryopreservation causes a reduction in offspring growth that is easily overlooked because it only manifests itself at later developmental stages, when many other factors affect growth and survival too.

Functions and mechanisms of epigenetic inheritance in animals

The idea that epigenetic determinants such as DNA methylation, histone modifications or RNA can be passed to the next generation through meiotic products (gametes) is long standing. Such meiotic epigenetic inheritance (MEI) is fairly common in yeast, plants and nematodes, but its extent in mammals has been much debated. Advances in genomics techniques are now driving the profiling of germline and zygotic epigenomes, thereby improving our understanding of MEI in diverse species. Whereas the role of DNA methylation in MEI remains unclear, insights from genome-wide studies suggest that a previously underappreciated fraction of mammalian genomes bypass epigenetic reprogramming during development. Notably, intergenerational inheritance of histone modifications, tRNA fragments and microRNAs can affect gene regulation in the offspring. It is important to note that MEI in mammals rarely constitutes transgenerational epigenetic inheritance (TEI), which spans multiple generations. In this Review, we discuss the examples of MEI in mammals, including mammalian epigenome reprogramming, and the molecular mechanisms of MEI in vertebrates in general. We also discuss the implications of the inheritance of histone modifications and small RNA for embryogenesis in metazoans, with a particular focus on insights gained from genome-wide studies.

Advances in Cryopreservation of Bull Sperm

Cryopreservation of semen and artificial insemination have an important, positive impact on cattle production, and product quality. Through the use of cryopreserved semen and artificial insemination, sperm from the best breeding bulls can be used to inseminate thousands of cows around the world. Although cryopreservation of bull sperm has advanced beyond that of other species, there are still major gaps in the knowledge and technology bases. Post-thaw viability of sperm is still low and differs significantly among the breeding bulls. These weaknesses are important because they are preventing advances both in fundamental science of mammalian gametes and reproductive biotechnology. Various extenders have been developed and supplemented with chemicals to reduce cryodamage or oxidative stress with varying levels of success. More detailed insights on sperm morphology and function have been uncovered through application of advanced tools in modern molecular and cell biology. This article provides a concise review of progress in the cryopreservation of bull sperm, advances in extender development, and frontiers using diverse techniques of the study of sperm viability. This scientific resource is important in animal biotechnology because with the advances in discovery of sperm fertility markers, there is an urgent need to improve post-thaw viability and fertility of sperm through enhanced cryopreservation for precision agriculture to produce food animals to ensure food security on the global scale.

Paternal benzo[a]pyrene exposure alters the sperm DNA methylation levels of imprinting genes in F0 generation mice and their unexposed F1-2 male offspring

BACKGROUND

Benzo[a]pyrene (BaP) is an environmental pollutant known to cause teratogenesis. However, the mechanism underlying this teratogenic effect is not fully understood. Recently, the alteration of DNA methylation of imprinting genes has emerged as a specific epigenetic mechanism linking the impact of environmental pollutants on embryonic development to paternal exposures. The aim of this study was to investigate the transgenerational effects of paternal BaP exposure on the imprinting genes in mouse sperm DNA.

METHODS

Male C57BL/6J mice received BaP (1.0 or 2.5 mg/kg) or olive oil twice a week for 12 weeks. The methylation status of 6 imprinting genes (H19, Meg3, Peg1, Peg3, Igf2 and Snrpn) was examined by bisulfite pyrosequencing of the sperm DNA of BaP-exposed F0 generation and their offspring.

RESULTS

BaP exposure reduced the methylation levels in the imprinting genes H19 and Meg3 and increased the methylation levels of Peg1 and Peg3; however, no significant differences was observed for the methylation levels of Igf2 or Snrpn in the sperm DNA. Furthermore, BaP-exposed male mice were mated with unexposed female mice to generate F1-2 generations. The methylation levels of the 6 genes in the sperm DNA from F1-2 offspring showed a similar pattern as that of the F0 male. The effects were attenuated in F1-2 generations.

CONCLUSIONS

Paternal BaP exposure altered the methylation levels of imprinting genes, implicating that imprinting genes are susceptible to environmental toxicants. Furthermore, a similar alteration was observed in the F1-2 generations although the attenuated in methylation in F2 generation, revealing a potential transgenerational effect.

TUNEL assay: Establishing a sperm DNA fragmentation cut-off value for Egyptian infertile men

Male factor infertility is responsible for half of all infertility cases. Conventional semen analysis is inadequate to evaluate male fertility. Sperm DNA fragmentation (SDF) test can be done by: direct methods such as Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) and Comet assay, or indirect like Sperm Chromatin Structure Assay (SCSA) and Sperm Chromatin Dispersion (SCD). TUNEL assay measures both single- and double-strand breaks and is technically less demanding, while SCSA tests for the susceptibility for nuclear DNA denaturation and samples should be sent to the reference lab. Studies showed that a single cut-off value does not fit all. Therefore, this study aimed at establishing a cut-off value to discriminate between fertile and infertile Egyptian men. We enrolled 354 infertile men and 40 proven fertile volunteers.TUNEL assay was performed using Apo-Direct kit and bench top flow cytometer.The calculated SDF cut-off value was 20.3% with a sensitivity of 96.6% and specificity of 87.5%, and the overall accuracy of the test was 95.7%. Sperm DNA fragmentation Test using TUNEL assay is valuable tool for male infertility evaluation, and it assists in offering the best treatment options based on it's results.

In the human sperm nucleus, nucleosomes form spatially restricted domains consistent with programmed nucleosome positioning

In human sperm, a fraction of its chromatin retains nucleosomes that are positioned on specific sequences containing genes and regulatory units essential for embryonic development. This nucleosome positioning (NP) feature provides an inherited epigenetic mark for sperm. However, it is not known whether there is a structural constraint for these nucleosomes and, if so, how they are localized in a three-dimensional (3D) context of the sperm nucleus. In this study, we examine the 3D organization of sperm chromatin and specifically determine its 3D localization of nucleosomes using structured illumination microscopy. A fraction of the sperm chromatin form nucleosome domains (NDs), visible as microscopic puncta ranging from 40 μm to 700 μm in diameter, and these NDs are precisely localized in the post acrosome region (PAR), outside the sperm's core chromatin. Further, NDs exist mainly in sperm from fertile men in a pilot survey with a small sample size. Together, this study uncovers a new spatially-restricted sub-nuclear structure containing NDs that are consistent with NPs of the sperm, which might represent a novel mark for healthy sperm in human.

Transcriptome analysis reveals that fertilization with cryopreserved sperm downregulates genes relevant for early embryo development in the horse

Artificial insemination with cryopreserved spermatozoa is a major assisted reproductive technology in many species. In horses, as in humans, insemination with cryopreserved sperm is associated with lower pregnancy rates than those for fresh sperm, however, direct effects of sperm cryopreservation on the development of resulting embryos are largely unexplored. The aim of this study was to investigate differences in gene expression between embryos resulting from fertilization with fresh or cryopreserved sperm. Embryos were obtained at 8, 10 or 12 days after ovulation from mares inseminated post-ovulation on successive cycles with either fresh sperm or frozen-thawed sperm from the same stallion, providing matched embryo pairs at each day. RNA was isolated from two matched pairs (4 embryos) for each day, and cDNA libraries were built and sequenced. Significant differences in transcripts per kilobase million (TPM) were determined using (i) genes for which the expression difference between treatments was higher than 99% of that in the random case (P < 0.01), and (ii) genes for which the fold change was ≥ 2, to avoid expression bias in selection of the candidate genes. Molecular pathways were explored using the DAVID webserver, followed by network analyses using STRING, with a threshold of 0.700 for positive interactions. The transcriptional profile of embryos obtained with frozen-thawed sperm differed significantly from that for embryos derived from fresh sperm on all days, showing significant down-regulation of genes involved in biological pathways related to oxidative phosphorylation, DNA binding, DNA replication, and immune response. Many genes with reduced expression were orthologs of genes known to be embryonic lethal in mice. This study, for the first time, provides evidence of altered transcription in embryos resulting from fertilization with cryopreserved spermatozoa in any species. As sperm cryopreservation is commonly used in many species, including human, the effect of this intervention on expression of developmentally important genes in resulting embryos warrants attention.

Sperm-inherited H3K27me3 impacts offspring transcription and development in C. elegans

Paternal epigenetic inheritance is gaining attention for its growing medical relevance. However, the form in which paternal epigenetic information is transmitted to offspring and how it influences offspring development remain poorly understood. Here we show that in C. elegans, sperm-inherited chromatin states transmitted to the primordial germ cells in offspring influence germline transcription and development. We show that sperm chromosomes inherited lacking the repressive histone modification H3K27me3 are maintained in that state by H3K36me3 antagonism. Inheritance of H3K27me3-lacking sperm chromosomes results in derepression in the germline of somatic genes, especially neuronal genes, predominantly from sperm-inherited alleles. This results in germ cells primed for losing their germ cell identity and adopting a neuronal fate. These data demonstrate that histone modifications are one mechanism through which epigenetic information from a father can shape offspring gene expression and development.

The mechanisms of paternal epigenetic inheritance and its influence on offspring are still poorly understood. Here the authors provide evidence that in C. elegans, sperm-inherited chromatin states influence transcription and cell identity in the germ cells of offspring.

Genetic and epigenetic architecture of paternal origin contribute to gestation length in cattle

The length of gestation can affect offspring health and performance. Both maternal and fetal effects contribute to gestation length; however, paternal contributions to gestation length remain elusive. Using genome-wide association study (GWAS) in 27,214 Holstein bulls with millions of gestation records, here we identify nine paternal genomic loci associated with cattle gestation length. We demonstrate that these GWAS signals are enriched in pathways relevant to embryonic development, and in differentially methylated regions between sperm samples with long and short gestation length. We reveal that gestation length shares genetic and epigenetic architecture in sperm with calving ability, body depth, and conception rate. While several candidate genes are detected in our fine-mapping analysis, we provide evidence indicating ZNF613 as a promising candidate for cattle gestation length. Collectively, our findings support that the paternal genome and epigenome can impact gestation length potentially through regulation of the embryonic development.

Lingzhao Fang et al. studied the paternal genetic variants that affect gestational length in cattle. They found that paternal genes from pathways involved in embryonic development were associated with gestation length, and that these were often found in differentially methylated regions of the genome.