Project description:The male germline transcriptome changes dramatically during the mitosis-to-meiosis transition to activate late spermatogenesis genes and to transiently suppress genes commonly expressed in somatic lineages and spermatogenesis progenitor cells, termed somatic/progenitor genes. These changes reflect epigenetic regulation. Induction of late spermatogenesis genes during spermatogenesis is facilitated by poised chromatin established in the stem cell phases of spermatogonia, whereas silencing of somatic/progenitor genes during meiosis and postmeiosis is associated with formation of bivalent domains which also allows the recovery of the somatic/progenitor program after fertilization. Importantly, during spermatogenesis mechanisms of epigenetic regulation on sex chromosomes are different from autosomes: X-linked somatic/progenitor genes are suppressed by meiotic sex chromosome inactivation without deposition of H3K27me3. Our results suggest that bivalent H3K27me3 and H3K4me2/3 domains are not limited to developmental promoters (which maintain bivalent domains that are silent throughout the reproductive cycle), but also underlie reversible silencing of somatic/progenitor genes during the mitosis-to-meiosis transition in late spermatogenesis. 29 samples analyzed by ChIP-Seq
Project description:The male germline transcriptome changes dramatically during the mitosis-to-meiosis transition to activate late spermatogenesis genes and to transiently suppress genes commonly expressed in somatic lineages and spermatogenesis progenitor cells, termed somatic/progenitor genes. These changes reflect epigenetic regulation. Induction of late spermatogenesis genes during spermatogenesis is facilitated by poised chromatin established in the stem cell phases of spermatogonia, whereas silencing of somatic/progenitor genes during meiosis and postmeiosis is associated with formation of bivalent domains which also allows the recovery of the somatic/progenitor program after fertilization. Importantly, during spermatogenesis mechanisms of epigenetic regulation on sex chromosomes are different from autosomes: X-linked somatic/progenitor genes are suppressed by meiotic sex chromosome inactivation without deposition of H3K27me3. Our results suggest that bivalent H3K27me3 and H3K4me2/3 domains are not limited to developmental promoters (which maintain bivalent domains that are silent throughout the reproductive cycle), but also underlie reversible silencing of somatic/progenitor genes during the mitosis-to-meiosis transition in late spermatogenesis.
Project description:Bivalent domains marked with repressive H3K27me3 and activating H3K4me2/3 are a molecular signature of totipotency in stem cells and development. While bivalent domains are retained throughout the germline to recover totipotency in the next generation, the mechanisms establishing bivalent domains remains unknown. Here we demonstrate that a germline-specific Polycomb protein, SCML2, binds to chromatin containing hypomethylated DNA to induce H3K27me3, thereby initiating the establishment of germline-specific bivalent domains in mice. SCML2 regulates two distinct classes of autosomal bivalent domains, the first are maintained constitutively through spermatogenesis (Class I), and the second are specifically established during meiosis (Class II). In postmeiotic spermatids, the loss of H3K27me3 leads to an increase of H3K4me2/3 on bivalent domains and disorganization of pericentromic heterochromatin. We propose that SCML2 regulates dynamic bivalent domains in the germline as a molecular imprint to recover totipotency after fertilization.
Project description:Tissue homeostasis depends on the activities of tissue-specific adult stem cells to maintain a balance between proliferation and differentiation and ensure DNA damage repair. Here, we use the Drosophila male germline stem cell lineage to study how a chromatin factor, Enhancer of Polycomb [E(Pc)], regulates the proliferation-to-differentiation (mitosis-to-meiosis) transition and DNA damage repair. We identified two critical target genes of E(Pc). First, E(Pc) directly represses CycB transcription through modulating H4 acetylation. Second, E(Pc) is required for accumulation of an important germline differentiation factor, Bag-of-marbles (Bam) protein, through post-transcriptional regulation. When E(Pc) is downregulated, increased CycB transcription and decreased Bam protein are both responsible for defective mitosis-to-meiosis transition in germ cells. Moreover, E(Pc) is required for the DNA double-strand break repair, the failure of which leads to germ cell death. Finally, compromising the activity of Tip60, a histone acetyltransferase, leads to germline defects similar to E(Pc) loss-of-function, suggesting that E(Pc) acts cooperatively with Tip60 . Together, our data demonstrate that E(Pc) has pleiotropic roles in maintaining male germline activity and genome integrity. E(Pc) is highly conserved with implications in cancers; consequently, our findings will help elucidate the in vivo mechanisms of E(Pc), in turn making this chromatin factor a promising target for cancer treatment.
Project description:Gene regulation in the germline ensures the production of high-quality gametes, long-term maintenance of the species, and speciation. Germline transcriptomes undergo dynamic changes after the mitosis-to-meiosis transition in males and have been subject to evolutionary divergence among mammals. However, the mechanism that underlies germline regulatory divergence remains undetermined. Here, we show that endogenous retroviruses influence species-specific germline transcriptomes in mammals. We show that the endogenous retroviruses function as active enhancers to drive evolutionarily young (mouse or rodent specific) spermatogenesis-specific genes after the mitosis-to-meiosis transition in male mice. These ERV loci bear binding motifs for critical regulators of spermatogenesis such as A-MYB. The genome-wide transposition of ERVs might have rewired germline gene expression in a species-specific manner. Notably, these features are present in human spermatogenesis, but independently evolved ERVs are associated with expression of germline genes, demonstrating the prevalence of ERV-driven mechanisms in mammals. Together, we propose a model whereby species-specific transcriptomes are fine-tuned by endogenous retroviruses in the mammalian germline.
Project description:The bivalent domain at promoter region is a unique epigenetic feature poised for activation or repression during cell differentiation in embryonic stem cell. However, the function of bivalent domains in already differentiated cells remains exclusive. By profiling the epigenetic landscape of endothelial cells during VEGFA stimulation, we discovered that bivalent domains are widespread in endothelial cells and preferentially marked genes responsive to VEGFA. The bivalent domains responsive to VEGFA have more permissive chromatin environment comparing to other bivalent domains. The initial activation of bivalent genes depends on RNAPII pausing release induced by EZH1 rather than removal of H3K27me3. The later suppression of bivalent gene expression depended on KDM5A recruitment by its interaction with PRC2. Importantly, EZH1 promoted both in vitro and in vivo angiogenesis by upregulating EGR3, whereas KDM5A dampened angiogenesis. Collectively, this study demonstrated a novel dual function of bivalent domains in endothelial cells to control VEGF responsiveness and angiogenesis.
Project description:Bivalent H3K4me3 and H3K27me3 chromatin domains in embryonic stem cells keep active developmental regulatory genes expressed at very low levels and poised for activation. Here, we show an alternative and previously unknown bivalent modified histone signature in lineage-committed mesenchymal stem cells and preadipocytes that pairs H3K4me3 with H3K9me3 to maintain adipogenic master regulatory genes (Cebpa and Pparg) expressed at low levels yet poised for activation when differentiation is required. We show lineage-specific gene-body DNA methylation recruits H3K9 methyltransferase SETDB1 which methylates H3K9 immediately downstream of transcription start sites marked with H3K4me3 to establish the bivalent domain. At the Cebpa locus, this prevents transcription factor C/EBPβ binding, histone acetylation, and further H3K4me3 deposition and is associated with pausing of RNA polymerase II, which limits Cebpa gene expression and adipogenesis. H3K4me3, H3K27me3, H3K9me3, SETDB1, MBD1, and Pol II ChIP-seq. m5CpG pull-down using recombinant MBD domain of MBD1 followed by next-generation sequencing.
Project description:To investigate the relationship between chromatin organization and meiotic processes, we used Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) to map open chromatin during the transition from mitosis to meiosis in the budding yeast Saccharomyces cerevisiae.
Project description:By mapping the genomic enrichments of H3K4me3 and H3K27me3 modifications in pure populations of hESCs during the G2, mitotic and G1 phases of the cell cycle, we characterize cell cycle-dependent variations in the epigenetic landscape of bivalent genes, altering the current view of mitotic inheritance in pluripotent cells. We identified novel classes of bivalent domains that are highly enriched with H3K4me3 during mitosis, depleted during G1 only, and ubiquitously bivalent. These bivalent domains are associated with specific genes and expression patterns during differentiation. These cell cycle-dependent epigenetic profiles are unique to hESCs and are not observed following initiation of phenotype commitment. Our results establish a new dimension in cell cycle-dependent chromatin regulation that advances understanding of contributions the pluripotent epigenetic landscape to hESC identity. Study of two histone modifications, H3K4me3 and H3K27me3, during three cell cycle phases in two cell types. Study of gene expression from these two cell types in asynchronous cells.