Poised chromatin and bivalent domains facilitate the mitosis-to-meiosis transition in the male germline
ABSTRACT: 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:we identify Scml2, a subunit of a germ cell-specific polycomb repressive complex 1 (PRC1), as a critical epigenetic modifier that establishes the germline-specific epigenome through two distinct functions. One of these functions is in the stem cell phase of spermatogonia and the other is on meiotic sex chromosomes. During the stem cell phase of spermatogonia, Scml2 establishes Rnf2- dependent ubiquitination of H2A (Rnf2-ubH2A) as an epigenetic memory that subsequently ensures programmed repression of somatic genes during the late stages of spermatogenesis. Additionally, during meiosis, Scml2 interacts with γH2AX and works downstream of the DNA damage response factor Mdc1 on the sex chromosomes and, contrary to autosomes, suppresses Rnf2-ubH2A for proper epigenetic programming of the sex chromosomes. Taken together, Scml2 positively regulates Rnf2-ubH2A on autosomes and negatively regulates Rnf2-ubH2A on the sex chromosomes to establish the germline-specific epigenome in spermatogenesis. Our study reveals a novel layer of epigenetic regulation in the male germline and adds further insight into the functionality of the polycomb proteins. RNA-seq and ChIP-seq analyses using wild-type and Scml2 KO spermatogenic cells
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. Overall design: ChIP-seq, ATAC-seq and RNA-seq analyses using wild-type and Scml2-KO spermatogenic cells
Project description:Epigenetic mechanisms including DNA methylation, non-coding RNAs and histone modifications control gene expression. Studies suggest that a father's lifetime experiences can be transmitted to his offspring to affect development and health. The mechanisms underlying such epigenetic inheritance are unknown. A potential route for paternal transmission is the unique chromatin composition of spermatozoa. Unlike somatic cells and oocytes, most nucleosomes in sperm are replaced with protamine nucleoproteins. The role of residual nucleosomes, residing at gene regulatory sequences, for epigenetic control of embryonic development is unknown. Here we generated a transgenic mouse model in which over-expression of the histone H3 lysine 4 (H3K4) demethylase LSD1/KDM1A during spermatogenesis alters H3K4 methylation in sperm. Strikingly, KDM1A over-expression in one generation causes severe embryonic defects in non-transgenic descendants spanning three subsequent generations. We show for the first time that correct histone methylation homeostasis during spermatogenesis is critical for offspring development and survival over multiple generations. Identification of H3K4me2 and nucleosome occupancies in sperm of wildtype mice, KDM1A transgenic mice and their non-transgenic littermates.
Project description:We investigated genome-wide nucleosome coverage and histone methylation occupancies in somatic MEFs, intermediate pre-iPSCs and fully reprogrammed iPSCs. We found that nucleosome occupancies increased in promoter regions and decreased in intergenic regions in pre-iPSCs and then recover to an intermediate level in iPSCs. Nucleosomes in pre-iPSCs are much more phased than those in MEFs and iPSCs. Bivalent, active, repressive domains are cell type-specific and change dynamically during reprogramming. HCG and LCG promoters exhibit distinct nucleosome occupancy patterns and are dynamically marked by H3K4me3/H3K27me3 during reprogramming, correspondingly showing different gene activities. Surprisingly, Vitamin C promotes nucleosome reorganization from pre-iPSCs to iPSCs. CTCF binding sites change dynamically during reprogramming, though they share a conserved binding motif. Nucleosome occupies CTCF sites to a higher extent in pre-iPSCs than those in MEFs and iPSCs. Taken together, our study reveals that dynamic changes of nucleosome positioning and chromatin organization associated gene regulation during reprogramming. Examine dynamics of nucleosome positioning and histone modification profiles as well as gene expression regulation during somatic cell reprogramming
Project description:In higher eukaryotes, histone methylation is involved in the maintenance of cellular identity during somatic development. During spermatogenesis, Since most nucleosomes are replaced by protamines during spermatogenesis . Iit is therefore unclear whether if histone modifications function in paternal transmission of epigenetic information. Here we show that H3K4 di-methylation (H3K4me2) and H3K27 tri-methylation (H3K27me3), two modifications important for Trithorax and Polycomb-mediated gene regulation, display methylation-specific distributions at regulatory regions in human spermatozoa. H3K4 dimethylation H3K4me2-marksed promoters of genes relevant control gene functions in spermatogenesis and cellular homeostasis suggesting that this mark reflects germline transcription. In contrast, H3K27 trimethylation (H3K27me3) marks promoters of key developmental regulators in sperm like in somatic cells. Promoters of orthologous genes are similarly modified in mouse spermatozoa. Further, particularly genes with extensive H3K27me3 coverage around transcriptional start sites are never expressed during male and female gametogenesis, nor in pre-implantation embryos. These data are compatible with a function for Polycomb in repressing somatic determinants across generations. Importantly, however, we observe only modest selective retention of nucleosomes at regulatory regions in human sperm suggesting that paternal transmission of H3K27me3-encoded epigenetic information may be subjected to variegation. Identification of nucleosome containing regions in 6 human sperm samples
Project description:Nucleosomes are the principal packaging units of chromatin and critical for gene regulation and genome stability. In mammals, a subset of nucleosomes fail to be replaced by protamines during spermatogenesis and are retained in mature spermatozoa providing opportunities for paternal epigenetic transmission. In humans, the remaining 10% localize at regulatory elements of genes. To assess evolutionary conservation and to dissect the molecular logic underlying nucleosome retention, we determined the genome wide nucleosome occupancy in mouse spermatozoa that only contain 1% residual histones. In striking contrast to mammalian somatic cells and haploid round spermatids, we observe high enrichment of nucleosomes at CpG-rich sequences throughout the genome, at conserved regulatory sequences as well as at intra- and intergenic regions and repetitive DNA. This preferred occupancy occurs mutually exclusive with DNA methylation both in mouse and human sperm. At unmethylated CpG-rich sequences, residing nucleosomes are largely composed of the H3.3 histone variant, and trimethylated at lysine 4 (H3K4me3). Both canonical H3.1/H3.2 and H3.3 variant histones are present at promoters marked by Polycomb-mediated H3K27me3, which is strongly predictive for gene repression in pre-implantation embryos. Our data indicate important roles of DNA sequence composition, DNA methylation, variant H3.3 and canonical H3.1/H3.2 histones and associated modifications in nucleosome retention versus eviction during the histone-to-protamine remodeling process in elongating spermatids and potentially in epigenetic inheritance by nucleosomes between generations. Identification of histone, histone variant and histone modification states in round spermatids and sperm
Project description:The EZH2 histone methyltransferase is highly expressed in germinal center (GC) B-cells and targeted by somatic mutations in B-cell lymphomas. Here we find that EZH2 deletion or pharmacologic inhibition suppresses GC formation and functions in mice. EZH2 represses proliferation checkpoint genes and helps establish bivalent chromatin domains at key regulatory loci to transiently suppress GC B-cell differentiation. Somatic mutations reinforce these physiological effects through enhanced silencing of EZH2 targets in B-cells, and in human B-cell lymphomas. Conditional expression of mutant EZH2 in mice induces GC hyperplasia and accelerated lymphomagenesis in cooperation with BCL2. GCB-type DLBCLs are mostly addicted to EZH2, regardless of mutation status, but not the more differentiated ABC-type DLBCLs, thus clarifying the therapeutic scope of EZH2 targeting. RNA sequencing and H3K27me3 ChIP sequencing of human DLBCL cell lines and murine BCL1 cell line. RNA sequencing, H3K27me3 and H3K4me3 ChIP sequencing of B cells from de-identified human tonsills.
Project description:Using the Fucci cell cycle indicator system in hESCs, we evaluated the patterns of bivalent histone marks and enhancer histone marks during the cell cycle by ChIP-seq. We further evaluated how the chromatin architecture changed during the cell cycle. We found that bivalent domains are cell cycle regulated, and H3K4me3 specifically peaks during the late G1 stage of the cell cycle. H3K27me3, however, is largely unchanged during the cell cycle. Cell cycle-regulated bivalent domains interact with enhancers and form cell cycle regulated chromatin interactions. FACS-isolated cell cycle fractions (DN, early G1; KO2, late G1; AzL, S-phase; and AzH, G2/M) from Fucci hESCs were subject to ChIP-seq for H3K4me3, H3K27me3, H3K27ac and H3K4me1, and used for sequencing along with input controls for each of the 4 cell cycle fractions (20 samples total), using Illumina platform, or 4C-seq for each cell cycle fraction using viewpoints neighboring the GATA6 or SOX17 promoters.
Project description:PRDM9, a histone methyltransferase, initiates meiotic recombination by binding DNA at recombination hotspots and directing the position of DNA double-strand breaks (DSB). The DSB repair mechanism suggests that hotspots should eventually self-destruct, yet genome-wide recombination levels remain constant, a conundrum known as the hotspot paradox. To test if PRDM9 drives this evolutionary erosion, we compared activity of the Prdm9Cst allele in two Mus musculus subspecies, M.m. castaneus, in which Prdm9Cst arose, and M.m. domesticus, into which Prdm9Cst was introduced. Comparing these two strains, we find that haplotype differences at hotspots leads to qualitative and quantitative changes in PRDM9 binding and activity. Most variants affecting PRDM9Cst binding arose and were fixed in M.m castaneus, suppressing hotspot activity. Furthermore, M.m castaneus x M.m domesticus F1 hybrids exhibit novel hotspots, representing sites of historic evolutionary erosion. Together these data support a model where haplotype-specific PRDM9 binding directs biased gene conversion at hotspots, ultimately leading to hotspot erosion. Identify position of meiotic H3K4me3 from various sub-species of mice and F1 hybrids from crosses between subspecies. In addition, perform ChIP-seq analysis on the meiosis-specific methyltransferase PRDM9.
Project description:To determine the dynamics of open chromatin at a genomic resolution during spermatogenesis, we performed ATAC-seq and detected genomic regions of accessible chromatin by Tn5 transposase during spermatogenesis. We analyzed four representative stages of spermatogenesis: Thy1+ undifferentiated spermatogonia, which contains spermatogonial stem cells and progenitor cells; c-Kit+ differentiating spermatogonia from P7 testes; purified pachytene spermatocytes (PS) undergoing meiosis; and postmeiotic round spermatids (RS) from adult testes Overall design: ATAC-seq analyses using purified spematogenic cells from wild-type mice and Scml2 knockout mice