EZH2 Variants Differentially Regulate Polycomb Repressive Complex 2 in Histone Methylation and Cell Differentiation
ABSTRACT: Background: Polycomb repressive complex 2 (PRC2) is responsible for establishing and maintaining histone H3K27 methylation during cell differentiation and proliferation. H3K27 can be mono-, di-, or tri-methylated, resulting in differential gene regulation. However, it remains unknown how PRC2 specifies the degree and biological effects of H3K27 methylation within a given cellular context. One way to determine PRC2 specificity may be through alternative splicing of Ezh2, PRC2’s catalytic subunit, during cell differentiation and tissue maturation. Results: We fully characterized the alternative splicing of Ezh2 in somatic cells and male germ cells and found that Ezh’s exon 14 was differentially regulated during mitosis and meiosis. The Ezh2 isoform containing exon 14 (ex14-Ezh2) is upregulated during cell cycle progression, consistent with a role in maintaining H3K27 methylation during chromatin replication. In contrast, the isoform lacking exon 14 (ex14D-Ezh2) was almost exclusively present in spermatocytes when new H3K27me2 is established during meiotic differentiation. Moreover, Ezh2’s transcript is normally controlled by E2F transcription activators, but in spermatocytes, Ezh2’s transcription is controlled by the meiotic regulator MYBL1. Compared to ex14-EZH2, ex14D-EZH2 has a diminished efficiency for catalyzing H3K27me3 and promotes embryonic stem cell differentiation. Conclusions: Ezh2’s expression is regulated at transcriptional and post-transcriptional levels in a cellular context-dependent manner. EZH2 variants determine functional specificity of PRC2 in histone methylation during cell proliferation and differentiation. Overall design: ChIP-seq in wild-type and Ezh2 knock-out E14 Embryonic Stem Cells for H3k27me3 and Ezh2
Project description:We previously reported the requirement of Polycomb Repressive Complex 2 (PRC2) for spermatogenesis through transcriptional repression of somatic genes and meiosis-specific genes. To characterize how PRC2's two methyltransferase subunits, EZH1 and EZH2, regulate histone H3 lysine 27 (H3K27) methylation during germ cell development, we generated mouse models with a germline ablation of EZH1 and/or EHZ2. Only the combined loss of EZH1 and EZH2 caused a depletion of global H3K27me3 marks and meiotic arrest in spermatocytes. Genome-wide analysis of H3K27me3 in spermatogenic cells revealed that a noncanonical EZH1-PRC2 could establish and maintain this histone mark on somatic genes and certain meiotic genes. Consistent with it having active enhancers in testis, Ezh1 was not only abundant in highly differentiated spermatocytes but also in actively proliferating progenitor and stem germ cells. Taken together, our findings suggest that the expression level of Ezh1 determines the restoration of H3K27 methylation in the absence of the canonical EZH2-PRC2. Overall design: ChIP-seq of H3K27me3 in control and Ezh2 mutant spermatogenic cells isolated from 6-wk-old spermatocytes. Ezh2 was ablated in developing germ cells using the Mvh-Cre recombinase.
Project description:Polycomb-repressive complex 2 (PRC2) catalyzes the methylation of histone H3 Lys27 (H3K27) and functions as a critical epigenetic regulator of both stem cell pluripotency and somatic differentiation, but its role in male germ cell development is unknown. Using conditional mutagenesis to remove the core PRC2 subunits EED and SUZ12 during male germ cell development, we identified a requirement for PRC2 in both mitotic and meiotic germ cells. We observed a paucity of mutant spermatogonial stem cells (SSCs), which appears independent of repression of the known cell cycle inhibitors Ink4a/Ink4b/Arf. Moreover, mutant spermatocytes exhibited ectopic expression of somatic lamins and an abnormal distribution of SUN1 proteins on the nuclear envelope. These defects were coincident with abnormal chromosome dynamics, affecting homologous chromosome pairing and synapsis. We observed acquisition of H3K27me3 on stage-specific genes during meiotic progression, indicating a requirement for PRC2 in regulating the meiotic transcriptional program. Together, these data demonstrate that transcriptional repression of soma-specific genes by PRC2 facilitates homeostasis and differentiation during mammalian spermatogenesis. Examination of two different types of histone modifications (H3K27me3 and H3K4me3) in spermatocytes at two different stages of development (P12 and P17) and the DNA binding protein, EED, in spermatocytes at one stage of development, P17. At P12, there was a single replicate of H3K27me3, H3K4me3 and input. At P17, there were two replicates of H3K27me3, H3K4me3 and input and a single replicate for EED.
Project description:Trimethylation on H3K27 (H3K27me3) mediated by Polycomb repressive complex 2 (PRC2) has been linked to embryonic stem cell (ESC) identity and pluripotency. EZH2, the catalytic subunit of PRC2, has been reported as the sole histone methyltransferase that methylates H3K27 and mediates transcriptional silencing. Analysis of Ezh2(-/-) ESCs suggests existence of an additional enzyme(s) catalyzing H3K27 methylation. We have identified EZH1, a homolog of EZH2 that is physically present in a noncanonical PRC2 complex, as an H3K27 methyltransferase in vivo and in vitro. EZH1 colocalizes with the H3K27me3 mark on chromatin and preferentially preserves this mark on development-related genes in Ezh2(-/-) ESCs. Depletion of Ezh1 in cells lacking Ezh2 abolishes residual methylation on H3K27 and derepresses H3K27me3 target genes, demonstrating a role of EZH1 in safeguarding ESC identity. Ezh1 partially complements Ezh2 in executing pluripotency during ESC differentiation, suggesting that cell-fate transitions require epigenetic specificity. Overall design: We used ChIP-chip to reveal genome-wide locationation of Polycomb protein EZH1 and H3K27me3 mark in undifferentiated wild-type (CJ7) and Ezh2-/- mutant embryonic stem (ES) cells. DNA fragments pulled down by chromatin immunoprecipitation, amplified and hybridization on Affymetrix mouse Tiling 2.0R array sets.
Project description:The Polycomb repressive complex 2 (PRC2) catalyzes H3K27 methylation and is required for maintaining transcriptional patterns and cellular identity, but the specification and maintenance of genomic PRC2 binding and H3K27 methylation patterns remain incompletely understood. Epigenetic mechanisms have been proposed, wherein pre-existing H3K27 methylation directs recruitment and regulates the catalytic activity of PRC2 to support its own maintenance. Here we investigate if such mechanisms are required for specifying H3K27 methylation patterns in mouse embryonic stem cells. Through genetic knockouts of subunits, we find that PRC2 is responsible for all levels of H3K27 methylation, and that methylation patterns can be accurately established de novo, when a subunit is reintroduced in the absence of pre-existing H3K27 methylation and PRC2 chromatin binding. Furthermore, we find that the core-subunit SUZ12 directs genomic binding of PRC2, which is essential for establishing correct methylation patterns. Overall design: H3K27me1, H3K27me2, H3K27me3 enrichment profiles (ChIPseq) analyzed in mouse ES cells which are wildtype, knockout for Ezh1 and Ezh2 (Ezh1/Ezh2 dKO), or re-expressing wildtype EZH2 (10 samples including 1 ChIP input sample for Ezh1/Ezh2 dKO). H3K27me1, H3K27me2, H3K27me3 enrichment profiles (ChIPseq) analyzed in mouse ES cells which are wildtype, knockout for Suz12, or re-expressing either wildtype SUZ12 or one of two SUZ12 fragment (15 samples). In addition, H3K27me1, H3K27me2, H3K27me3 enrichment profiles (ChIPseq) analyzed in E14 mouse ES cells treated with Ezh2 inhibitor and followed in a timecourse study after inhibitor washout (24 samples). PRC2 subunit enrichment profiles through Suz12, Ezh2 and Flag ChIPseq in various PRC2 wildtype, knockout or mutant ES cells (9 Suz12 ChIP samples, 2 Flag ChIP samples, 2 Ezh2 ChIP samples). Differential expression analysis (RNAseq) of mouse ES cells which are wildtype (3 replicates), knockout for Ezh1 and Ezh2 (Ezh1/Ezh2 dKO) (3 replicates), or re-expressing wildtype EZH2 (3 replicates) (9 samples).
Project description:Polycomb repressive complex 2 (PRC2-EZH2) methylates histone H3 at lysine 27 (H3K27). PRC2 is required to maintain gene repression during development and differentiation and misregulation of PRC2 is linked to a range of neoplastic malignancies, activities that are believed to involve H3K27 methylation. The full spectrum of non-histone substrates of PRC2, however, is not known, and it is not known which other substrates might also contribute to the biological functions of PRC2. We characterized the target recognition specificity and substrate diversity of PRC2, and identified more than one hundred potential novel nuclear targets of PRC2. The RNA polymerase II (Pol II) transcription elongation factor, Elongin A (EloA), is an in vivo target of PRC2. Mutation of the EloA residue that is methylated by PRC2 decreases repression of numerous PRC2 target genes. We propose that this functional crosstalk between PRC2 and EloA tunes the level of repression of targeted genes and contributes to the biological functions of PRC2. Overall design: We examined the genome-wide distribution of PRC2 catalytic subunit, EZH2, in mES cell by ChIP-seq
Project description:Polycomb Repressor Complex 2 (PRC2) is a multi-protein epigenetic regulator complex that plays critical roles in early development and tissue differentiation. The complex catalyzes the methylation of histone H3 lysine 27 (H3K27). The tri-methyl state (H3K27me3) is well studied as an agent of gene repression, but more recently distinct roles for the mono- and di-methyl states have been discovered. In order to more fully understand how PRC2-associated factors might influence H3K27 status, we screened for physical associations of PRC2 subunits. Knockdown of these factors was used to produce functional interaction maps focused on H3K27 methylation, including proteins that have positive and negative effects on the levels each histone mark.
Project description:The Wnt/b-catenin signaling inhibits adipogenesis. Genome-wide profiling studies have revealed the enrichment of histone H3K27 methyltransferase PRC2 on Wnt genes. However, the functional significance of such a direct link between the two types of developmental regulators in mammalian cells, and the role of PRC2 in adipogenesis, remain unclear. Here we show PRC2 and its H3K27 methyltransferase activity are required for adipogenesis. PRC2 directly represses Wnt1, 6, 10a and 10b genes in preadipocytes and during adipogenesis. Deletion of the enzymatic Ezh2 subunit of PRC2 eliminates H3K27me3 on Wnt promoters and de-represses Wnt expression, which leads to activation of Wnt/b-catenin signaling and inhibition of adipogenesis. Ectopic expression of the wild type Ezh2, but not the enzymatically inactive F667I mutant, prevents the loss of H3K27me3 and the defects in adipogenesis in Ezh2-/- preadipocytes. The adipogenesis defects in Ezh2-/- cells can be rescued by expression of adipogenic transcription factors PPARa, C/EBPb, or inhibitors of Wnt/b-catenin signaling. Interestingly, Ezh2-/- cells show marked increase of H3K27 acetylation globally as well as on Wnt promoters. These results indicate that H3K27 methyltransferase PRC2 directly represses Wnt genes to facilitate adipogenesis, and suggest that acetylation and trimethylation on H3K27 play opposing roles in regulating Wnt expression. To identify additional PRC2-regulated genes in preadipocytes, we performed microarray analysis in Ezh2flox/flox preadipocytes infected with retroviruses expressing Cre or vector alone.
Project description:The regulation of gene expression is controlled in part by post-translational modifications to histone proteins. Methylation at histone H3, lysine 27 (H3K27), which is catalyzed by Polycomb repressive complex 2 (PRC2), is associated with silenced chromatin. Previous studies have identified dysregulation of H3K27 methylation in pediatric diffuse intrinsic pontine gliomas (DIPGs), the majority of which feature mutation of lysine 27 to methionine. This “oncohistone” potently inhibits PRC2 activity and leads to a global reduction in H3K27 methylation. Similar to DIPG, posterior fossa type A (PFA) ependymomas also show low levels of H3K27 methylation. Although PFAs do not possess the H3K27M oncohistone mutation, they do show increased expression of Cxorf67. Interestingly, Cxorf67 contains a C-terminal sequence that resembles the sequence surrounding H3K27, and we find that this portion of Cxorf67 inhibits PRC2 activity to an even greater extent than the H3K27M oncohistone. Thus, we suggest re-naming Cxorf67 as EZHIP (Enhancer of Zeste Homologs Inhibitory Protein). Furthermore, when expressed in 293T cells, Cxorf67 interacts with several members of PRC2 and induces changes in H3K27 methylation patterns that mirror the changes in H3K27 methylation induced by expression of H3K27M. We propose that PFAs have dysregulated H3K27 methylation by a mechanism that involves inhibition of PRC2 by Cxorf67, which could drive tumorigenesis.
Project description:The Wnt/b-catenin signaling inhibits adipogenesis. Genome-wide profiling studies have revealed the enrichment of histone H3K27 methyltransferase PRC2 on Wnt genes. However, the functional significance of such a direct link between the two types of developmental regulators in mammalian cells, and the role of PRC2 in adipogenesis, remain unclear. Here we show PRC2 and its H3K27 methyltransferase activity are required for adipogenesis. PRC2 directly represses Wnt1, 6, 10a and 10b genes in preadipocytes and during adipogenesis. Deletion of the enzymatic Ezh2 subunit of PRC2 eliminates H3K27me3 on Wnt promoters and de-represses Wnt expression, which leads to activation of Wnt/b-catenin signaling and inhibition of adipogenesis. Ectopic expression of the wild type Ezh2, but not the enzymatically inactive F667I mutant, prevents the loss of H3K27me3 and the defects in adipogenesis in Ezh2-/- preadipocytes. The adipogenesis defects in Ezh2-/- cells can be rescued by expression of adipogenic transcription factors PPARa, C/EBPb, or inhibitors of Wnt/b-catenin signaling. Interestingly, Ezh2-/- cells show marked increase of H3K27 acetylation globally as well as on Wnt promoters. These results indicate that H3K27 methyltransferase PRC2 directly represses Wnt genes to facilitate adipogenesis, and suggest that acetylation and trimethylation on H3K27 play opposing roles in regulating Wnt expression. Overall design: To identify additional PRC2-regulated genes in preadipocytes, we performed microarray analysis in Ezh2flox/flox preadipocytes infected with retroviruses expressing Cre or vector alone.
Project description:Alternative splicing (AS) represents a powerful resource to amplify the coding potential of eukaryotic genomes and to finely tune gene expression during cell differentiation and development. Notably, high-throughput transcriptome analyses identified testis among the tissues displaying the highest proportion of AS events and profiling of whole testis transcriptome during the first wave of mouse spermatogenesis highlighted some AS events that are timely regulated during this process. Thus, AS modulation likely contributes to the fine-tuned regulation of gene expression that occurs during the male germ cell differentiation. In particular, meiotic spermatocytes and post-meiotic spermatids are known to express a highly specific repertoire of protein variants. However, no study has directly investigated whether global splicing-changes occur during the trans-meiotic phases of spermatogenesis to date. Spermatocytes undergo two consecutive meiotic divisions to yield haploid post-meiotic spermatids, which then differentiate into highly specialized and motile spermatozoa. Herein, to achieve a comprehensive characterization of the splicing changes occurring during trans-meiotic differentiation of male germ cells, we performed high-throughput RNA sequencing (RNA-seq) analyses of polyA+ RNA isolated from highly purified populations of meiotic spermatocytes and post-meiotic spermatids. Our analysis uncovered a robust intron retention (IR) program in meiotic spermatocytes. Intron-retaining genes were strongly enriched in functional categories related to differentiation and properties of the male gamete. We found that meiotic intron-retaining transcripts are long-lived mRNAs, which are preserved in the nucleus until they need to be translated. Thus, our study reveals an unexpected physiological role for IR in ensuring proper and timely control of gene expression during male germ cell differentiation. Overall design: RNA‐Seq data for purified spermatocytes and spermatids