N6-methyladenosine (m6A) represents one of the most common RNA modifications in eukaryotes. Specific m6A writer, eraser, and reader proteins have been identified. As an m6A eraser, ALKBH5 specifically removes m6A from target mRNAs and inactivation of leads to male infertility in mice. However, the underlying molecular mechanism remains unknown. Here, we report that ALKBH5-mediated m6A erasure in the nuclei of spermatocytes and round spermatids is essential for correct splicing and the production of longer 3'-UTR mRNAs, and failure to do so leads to aberrant splicing and production of shorter transcripts with elevated levels of m6A that are rapidly degraded. Our study identified reversible m6A modification as a critical mechanism of posttranscriptional control of mRNA fate in late meiotic and haploid spermatogenic cells.

BackgroundEnvironmental toxicants such as DDT have been shown to induce the epigenetic transgenerational inheritance of disease (e.g., obesity) through the germline. The current study was designed to investigate the DDT-induced concurrent alterations of a number of different epigenetic processes including DNA methylation, non-coding RNA (ncRNA) and histone retention in sperm.MethodsGestating females were exposed transiently to DDT during fetal gonadal development, and then, the directly exposed F1 generation, the directly exposed germline F2 generation and the transgenerational F3 generation sperm were investigated.ResultsDNA methylation and ncRNA were altered in each generation sperm with the direct exposure F1 and F2 generations being predominantly distinct from the F3 generation epimutations. The piRNA and small tRNA were the most predominant classes of ncRNA altered. A highly conserved set of histone retention sites were found in the control lineage generations which was not significantly altered between generations, but a large number of new histone retention sites were found only in the transgenerational generation DDT lineage sperm.ConclusionsTherefore, all three different epigenetic processes were concurrently altered as DDT induced the epigenetic transgenerational inheritance of sperm epimutations. The direct exposure generations sperm epigenetic alterations were distinct from the transgenerational sperm epimutations. The genomic features and gene associations with the epimutations were investigated to help elucidate the integration of these different epigenetic processes. Observations demonstrate all three epigenetic processes are involved in transgenerational inheritance. The different epigenetic processes appear to be integrated in mediating the epigenetic transgenerational inheritance phenomenon.Electronic supplementary materialThe online version of this article (10.1186/s13072-018-0178-0) contains supplementary material, which is available to authorized users.

Epigenetic transgenerational inheritance of disease and phenotypic variation can be induced by several toxicants, such as vinclozolin. This phenomenon can involve DNA methylation, non-coding RNA (ncRNA) and histone retention, and/or modification in the germline (e.g. sperm). These different epigenetic marks are called epimutations and can transmit in part the transgenerational phenotypes. This study was designed to investigate the vinclozolin-induced concurrent alterations of a number of different epigenetic factors, including DNA methylation, ncRNA, and histone retention in rat sperm. Gestating females (F0 generation) were exposed transiently to vinclozolin during fetal gonadal development. The directly exposed F1 generation fetus, the directly exposed germline within the fetus that will generate the F2 generation, and the transgenerational F3 generation sperm were studied. DNA methylation and ncRNA were altered in each generation rat sperm with the direct exposure F1 and F2 generations being distinct from the F3 generation epimutations. Interestingly, an increased number of differential histone retention sites were found in the F3 generation vinclozolin sperm, but not in the F1 or F2 generations. All three different epimutation types were affected in the vinclozolin lineage transgenerational sperm (F3 generation). The direct exposure generations (F1 and F2) epigenetic alterations were distinct from the transgenerational sperm epimutations. The genomic features and gene pathways associated with the epimutations were investigated to help elucidate the integration of these different epigenetic processes. Our results show that the three different types of epimutations are involved and integrated in the mediation of the epigenetic transgenerational inheritance phenomenon.

The majority of circular RNAs (circRNAs) spliced from coding genes contain open reading frames (ORFs) and thus, have protein coding potential. However, it remains unknown what regulates the biogenesis of these ORF-containing circRNAs, whether they are actually translated into proteins and what functions they play in specific physiological contexts. Here, we report that a large number of circRNAs are synthesized with increasing abundance when late pachytene spermatocytes develop into round and then elongating spermatids during murine spermatogenesis. For a subset of circRNAs, the back splicing appears to occur mostly at m 6 Aenriched sites, which are usually located around the start and stop codons in linear mRNAs. Consequently, approximately a half of these male germ cell circRNAs contain large ORFs with m 6 A-modified start codons in their junctions, features that have been recently shown to be associated with protein-coding potential. Hundreds of peptides encoded by the junction sequences of these circRNAs were detected using liquid chromatography coupled with mass spectrometry, suggesting that these circRNAs can indeed be translated into proteins in both developing (spermatocytes and spermatids) and mature (spermatozoa) male germ cells. The present study discovered not only a novel role of m 6 A in the biogenesis of coding circRNAs, but also a potential mechanism to ensure stable and long-lasting protein production in the absence of linear mRNAs, i.e., through production of circRNAs containing large ORFs and m 6 A-modified start codons in junction sequences.

Cilia are cell-surface, microtubule-based organelles that project into extracellular space. Motile cilia are conserved throughout eukaryotes, and their beat induces the flow of fluid, relative to cell surfaces. In mammals, the coordinated beat of motile cilia provides highly specialized functions associated with the movement of luminal contents, as seen with metachronal waves transporting mucus in the respiratory tract. Motile cilia are also present in the male and female reproductive tracts. In the female, wave-like motions of oviductal cilia transport oocytes and embryos toward the uterus. A similar function has been assumed for motile cilia in efferent ductules of the male—i.e., to transport immotile sperm from rete testis into the epididymis. However, we report here that efferent ductal cilia in the male do not display a uniform wave-like beat to transport sperm solely in one direction, but rather exert a centripetal force on luminal fluids through whip-like beating with continual changes in direction, generating turbulence, which maintains immotile spermatozoa in suspension within the lumen. Genetic ablation of two miRNA clusters (miR-34b/c and -449a/b/c) led to failure in multiciliogenesis in murine efferent ductules due to dysregulation of numerous genes, and this mouse model allowed us to demonstrate that loss of efferent duct motile cilia causes sperm aggregation and agglutination, luminal obstruction, and sperm granulomas, which, in turn, induce back-pressure atrophy of the testis and ultimately male infertility.

Two of the most prevalent ovarian diseases affecting women’s fertility and health are Primary Ovarian Insufficiency (POI) and Polycystic Ovarian Syndrome (PCOS). Previous studies have shown that exposure to a number of environmental toxicants can promote the epigenetic transgenerational inheritance of ovarian disease. In the current study, transgenerational changes to the transcriptome and epigenome of ovarian granulosa cells are characterized in F3 generation rats after ancestral vinclozolin or DDT exposures. In purified granulosa cells from 20-day-old F3 generation females, 164 differentially methylated regions (DMRs) (P < 1 x 10−6) were found in the F3 generation vinclozolin lineage and 293 DMRs (P < 1 x 10−6) in the DDT lineage, compared to controls. Long noncoding RNAs (lncRNAs) and small noncoding RNAs (sncRNAs) were found to be differentially expressed in both the vinclozolin and DDT lineage granulosa cells. There were 492 sncRNAs (P < 1 x 10−4) in the vinclozolin lineage and 1,085 sncRNAs (P < 1 x 10−4) in the DDT lineage. There were 123 lncRNAs and 51 lncRNAs in the vinclozolin and DDT lineages, respectively (P < 1 x 10−4). Differentially expressed mRNAs were also found in the vinclozolin lineage (174 mRNAs at P < 1 x 10−4) and the DDT lineage (212 mRNAs at P < 1 x 10−4) granulosa cells. Comparisons with known ovarian disease associated genes were made. These transgenerational epigenetic changes appear to contribute to the dysregulation of the ovary and disease susceptibility that can occur in later life. Observations suggest that ancestral exposure to toxicants is a risk factor that must be considered in the molecular etiology of ovarian disease.

Prostate diseases include prostate cancer, which is the second most common male neoplasia, and benign prostatic hyperplasia (BPH), which affects approximately 50% of men. The incidence of prostate disease is increasing, and some of this increase may be attributable to ancestral exposure to environmental toxicants and epigenetic transgenerational inheritance mechanisms. The goal of the current study was to determine the effects that exposure of gestating female rats to vinclozolin has on the epigenetic transgenerational inheritance of prostate disease, and to characterize by what molecular epigenetic mechanisms this has occurred. Gestating female rats (F0 generation) were exposed to vinclozolin during E8-E14 of gestation. F1 generation offspring were bred to produce the F2 generation, which were bred to produce the transgenerational F3 generation. The transgenerational F3 generation vinclozolin lineage males at 12 months of age had an increased incidence of prostate histopathology and abnormalities compared to the control lineage. Ventral prostate epithelial and stromal cells were isolated from F3 generation 20-day old rats, prior to the onset of pathology, and used to obtain DNA and RNA for analysis. Results indicate that there were transgenerational changes in gene expression, noncoding RNA expression, and DNA methylation in both cell types. Our results suggest that ancestral exposure to vinclozolin at a critical period of gestation induces the epigenetic transgenerational inheritance of prostate stromal and epithelial cell changes in both the epigenome and transcriptome that ultimately lead to prostate disease susceptibility and may serve as a source of the increased incidence of prostate pathology observed in recent years.

Male reproductive health has been in decline for decades with dropping sperm counts and increasing infertility, which has created a significant societal and economic burden. Between the 1970s and now, a general decline of over 50% in sperm concentration has been observed in the population. Environmental toxicant-induced epigenetic transgenerational inheritance has been shown to affect testis pathology and sperm count. Sertoli cells have an essential role in spermatogenesis by providing physical and nutritional support for developing germ cells. The current study was designed to further investigate the transgenerational epigenetic changes in the rat Sertoli cell epigenome and transcriptome that are associated with the onset of testis disease. Gestating female F0 generation rats were transiently exposed during the period of fetal gonadal sex determination to the environmental toxicants, such as dichlorodiphenyltrichloroethane (DDT) or vinclozolin. The F1 generation offspring were bred (i.e. intercross within the lineage) to produce the F2 generation grand-offspring that were then bred to produce the transgenerational F3 generation (i.e. great-grand-offspring) with no sibling or cousin breeding used. The focus of the current study was to investigate the transgenerational testis disease etiology, so F3 generation rats were utilized. The DNA and RNA were obtained from purified Sertoli cells isolated from postnatal 20-day-old male testis of F3 generation rats. Transgenerational alterations in DNA methylation, noncoding RNA, and gene expression were observed in the Sertoli cells from vinclozolin and DDT lineages when compared to the control (vehicle exposed) lineage. Genes associated with abnormal Sertoli cell function and testis pathology were identified, and the transgenerational impacts of vinclozolin and DDT were determined. Alterations in critical gene pathways, such as the pyruvate metabolism pathway, were identified. Observations suggest that ancestral exposures to environmental toxicants promote the epigenetic transgenerational inheritance of Sertoli cell epigenetic and transcriptome alterations that associate with testis abnormalities. These epigenetic alterations appear to be critical factors in the developmental and generational origins of testis pathologies and male infertility.