An RNAi Screening of Clinically Relevant Transcription Factors Regulating Human Adipogenesis and Adipocyte Metabolism.

CONTEXT: Healthy hyperplasic (many but smaller fat cells) white adipose tissue (WAT) expansion is mediated by recruitment, proliferation and/or differentiation of new fat cells. This process (adipogenesis) is controlled by transcriptional programs that have been mostly identified in rodents. OBJECTIVE: A systemic investigation of adipogenic human transcription factors (TFs) that are relevant for metabolic conditions has not been revealed previously. METHODS: TFs regulated in WAT by obesity, adipose morphology, cancer cachexia, and insulin resistance were selected from microarrays. Their role in differentiation of human adipose tissue-derived stem cells (hASC) was investigated by RNA interference (RNAi) screen. Lipid accumulation, cell number, and lipolysis were measured for all screened factors (148 TFs). RNA (RNAseq), protein (Western blot) expression, insulin, and catecholamine responsiveness were examined in hASC following siRNA treatment of selected target TFs. RESULTS: Analysis of TFs regulated by metabolic conditions in human WAT revealed that many of them belong to adipogenesis-regulating pathways. The RNAi screen identified 39 genes that affected fat cell differentiation in vitro, where 11 genes were novel. Of the latter JARID2 stood out as being necessary for formation of healthy fat cell metabolic phenotype by regulating expression of multiple fat cell phenotype-specific genes. CONCLUSION: This comprehensive RNAi screening in hASC suggests that a large proportion of WAT TFs that are impacted by metabolic conditions might be important for hyperplastic adipose tissue expansion. The screen also identified JARID2 as a novel TF essential for the development of functional adipocytes.

Distinct PRC2 subunits regulate maintenance and establishment of Polycomb repression during differentiation.

The Polycomb repressive complex 2 (PRC2) is an essential epigenetic regulator that deposits repressive H3K27me3. PRC2 subunits form two holocomplexes-PRC2.1 and PRC2.2-but the roles of these two PRC2 assemblies during differentiation are unclear. We employed auxin-inducible degradation to deplete PRC2.1 subunit MTF2 or PRC2.2 subunit JARID2 during differentiation of embryonic stem cells (ESCs) to neural progenitors (NPCs). Depletion of either MTF2 or JARID2 resulted in incomplete differentiation due to defects in gene regulation. Distinct sets of Polycomb target genes were derepressed in the absence of MTF2 or JARID2. MTF2-sensitive genes were marked by H3K27me3 in ESCs and remained silent during differentiation, whereas JARID2-sensitive genes were preferentially active in ESCs and became newly repressed in NPCs. Thus, MTF2 and JARID2 contribute non-redundantly to Polycomb silencing, suggesting that PRC2.1 and PRC2.2 have distinct functions in maintaining and establishing, respectively, Polycomb repression during differentiation.

Using computational modelling to reveal mechanisms of epigenetic Polycomb control.

The Polycomb system is essential for stable gene silencing in many organisms. This regulation is achieved in part through addition of the histone modifications H3K27me2/me3 by Polycomb Repressive Complex 2 (PRC2). These modifications are believed to be the causative epigenetic memory elements of PRC2-mediated silencing. As these marks are stored locally in the chromatin, PRC2-based memory is a cis-acting system. A key feature of stable epigenetic memory in cis is PRC2-mediated, self-reinforcing feedback from K27-methylated histones onto nearby histones in a read-write paradigm. However, it was not clear under what conditions such feedback can lead to stable memory, able, for example, to survive the perturbation of histone dilution at DNA replication. In this context, computational modelling has allowed a rigorous exploration of possible underlying memory mechanisms and has also greatly accelerated our understanding of switching between active and silenced states. Specifically, modelling has predicted that switching and memory at Polycomb loci is digital, with a locus being either active or inactive, rather than possessing intermediate, smoothly varying levels of activation. Here, we review recent advances in models of Polycomb control, focusing on models of epigenetic switching through nucleation and spreading of H3K27me2/me3. We also examine models that incorporate transcriptional feedback antagonism and those including bivalent chromatin states. With more quantitative experimental data on histone modification kinetics, as well as single-cell resolution data on transcription and protein levels for PRC2 targets, we anticipate an expanded need for modelling to help dissect increasingly interconnected and complex memory mechanisms.

Rbbp4 Suppresses Premature Differentiation of Embryonic Stem Cells.

Polycomb group (PcG) proteins exist in distinct multi-protein complexes and play a central role in silencing developmental genes, yet the underlying mechanisms remain elusive. Here, we show that deficiency of retinoblastoma binding protein 4 (RBBP4), a component of the Polycomb repressive complex 2 (PRC2), in embryonic stem cells (ESCs) leads to spontaneous differentiation into mesendodermal lineages. We further show that Rbbp4 and core PRC2 share an important number of common genomic targets, encoding regulators involved in early germ layer specification. Moreover, we find that Rbbp4 is absolutely essential for genomic targeting of PRC2 to a subset of developmental genes. Interestingly, we demonstrate that Rbbp4 is necessary for sustaining the expression of Oct4 and Sox2 and that the forced co-expression of Oct4 and Sox2 fully rescues the pluripotency of Rbbp4-null ESCs. Therefore, our study indicates that Rbbp4 links maintenance of the pluripotency regulatory network with repression of mesendoderm lineages.

An integrative model of pathway convergence in genetically heterogeneous blast crisis chronic myeloid leukemia.

Targeted therapies against the BCR-ABL1 kinase have revolutionized treatment of chronic phase (CP) chronic myeloid leukemia (CML). In contrast, management of blast crisis (BC) CML remains challenging because BC cells acquire complex molecular alterations that confer stemness features to progenitor populations and resistance to BCR-ABL1 tyrosine kinase inhibitors. Comprehensive models of BC transformation have proved elusive because of the rarity and genetic heterogeneity of BC, but are important for developing biomarkers predicting BC progression and effective therapies. To better understand BC, we performed an integrated multiomics analysis of 74 CP and BC samples using whole-genome and exome sequencing, transcriptome and methylome profiling, and chromatin immunoprecipitation followed by high-throughput sequencing. Employing pathway-based analysis, we found the BC genome was significantly enriched for mutations affecting components of the polycomb repressive complex (PRC) pathway. While transcriptomically, BC progenitors were enriched and depleted for PRC1- and PRC2-related gene sets respectively. By integrating our data sets, we determined that BC progenitors undergo PRC-driven epigenetic reprogramming toward a convergent transcriptomic state. Specifically, PRC2 directs BC DNA hypermethylation, which in turn silences key genes involved in myeloid differentiation and tumor suppressor function via so-called epigenetic switching, whereas PRC1 represses an overlapping and distinct set of genes, including novel BC tumor suppressors. On the basis of these observations, we developed an integrated model of BC that facilitated the identification of combinatorial therapies capable of reversing BC reprogramming (decitabine+PRC1 inhibitors), novel PRC-silenced tumor suppressor genes (NR4A2), and gene expression signatures predictive of disease progression and drug resistance in CP.

A Dimeric Structural Scaffold for PRC2-PCL Targeting to CpG Island Chromatin.

Diverse accessory subunits are involved in the recruitment of polycomb repressive complex 2 (PRC2) to CpG island (CGI) chromatin. Here we report the crystal structure of a SUZ12-RBBP4 complex bound to fragments of the accessory subunits PHF19 and JARID2. Unexpectedly, this complex adopts a dimeric structural architecture, accounting for PRC2 self-association that has long been implicated. The intrinsic PRC2 dimer is formed via domain swapping involving RBBP4 and the unique C2 domain of SUZ12. MTF2 and PHF19 associate with PRC2 at around the dimer interface and stabilize the dimer. Conversely, AEBP2 binding results in a drastic movement of the C2 domain, disrupting the intrinsic PRC2 dimer. PRC2 dimerization enhances CGI DNA binding by PCLs in pairs in vitro, reminiscent of the widespread phenomenon of transcription factor dimerization in active transcription. Loss of PRC2 dimerization impairs histone H3K27 trimethylation (H3K27me3) on chromatin at developmental gene loci in mouse embryonic stem cells.

Polycomb repressor complex 2 function in breast cancer (Review).

Epigenetic modifications are important contributors to the regulation of genes within the chromatin. The polycomb repressive complex 2 (PRC2) is a multi­subunit protein complex that is involved in silencing gene expression through the trimethylation of lysine 27 at histone 3 (H3K27me3). The dysregulation of this modification has been associated with tumorigenicity through the increased repression of tumour suppressor genes via condensing DNA to reduce access to the transcription start site (TSS) within tumor suppressor gene promoters. In the present review, the core proteins of PRC2, as well as key accessory proteins, will be described. In addition, mechanisms controlling the recruitment of the PRC2 complex to H3K27 will be outlined. Finally, literature identifying the role of PRC2 in breast cancer proliferation, apoptosis and migration, including the potential roles of long non­coding RNAs and the miR­200 family will be summarized as will the potential use of the PRC2 complex as a therapeutic target.

Histone H2AK119 Mono-Ubiquitination Is Essential for Polycomb-Mediated Transcriptional Repression.

Polycomb group proteins (PcGs) maintain transcriptional repression to preserve cellular identity in two distinct repressive complexes, PRC1 and PRC2, that modify histones by depositing H2AK119ub1 and H3K27me3, respectively. PRC1 and PRC2 exist in different variants and show a complex regulatory cross-talk. However, the contribution that H2AK119ub1 plays in mediating PcG repressive functions remains largely controversial. Using a fully catalytic inactive RING1B mutant, we demonstrated that H2AK119ub1 deposition is essential to maintain PcG-target gene repression in embryonic stem cells (ESCs). Loss of H2AK119ub1 induced a rapid displacement of PRC2 activity and a loss of H3K27me3 deposition. This preferentially affected PRC2.2 variant with respect to PRC2.1, destabilizing canonical PRC1 activity. Finally, we found that variant PRC1 forms can sense H2AK119ub1 deposition, which contributes to their stabilization specifically at sites where this modification is highly enriched. Overall, our data place H2AK119ub1 deposition as a central hub that mounts PcG repressive machineries to preserve cell transcriptional identity.

A novel member of Prame family, Gm12794c, counteracts retinoic acid differentiation through the methyltransferase activity of PRC2.

Embryonic stem cells (ESCs) fluctuate among different levels of pluripotency defined as metastates. Sporadically, metastable cellular populations convert to a highly pluripotent metastate that resembles the preimplantation two-cell embryos stage (defined as 2C stage) in terms of transcriptome, DNA methylation, and chromatin structure. Recently, we found that the retinoic acid (RA) signaling leads to a robust increase of cells specifically expressing 2C genes, such as members of the Prame family. Here, we show that Gm12794c, one of the most highly upregulated Prame members, and previously identified as a key player for the maintenance of pluripotency, has a functional role in conferring ESCs resistance to RA signaling. In particular, RA-dependent expression of Gm12794c induces a ground state-like metastate, as evaluated by activation of 2C-specific genes, global DNA hypomethylation and rearrangement of chromatin similar to that observed in naive totipotent preimplantation epiblast cells and 2C-like cells. Mechanistically, we demonstrated that Gm12794c inhibits Cdkn1A gene expression through the polycomb repressive complex 2 (PRC2) histone methyltransferase activity. Collectively, our data highlight a molecular mechanism employed by ESCs to counteract retinoic acid differentiation stimuli and contribute to shed light on the molecular mechanisms at grounds of ESCs naive pluripotency-state maintenance.

PRC2 engages a bivalent H3K27M-H3K27me3 dinucleosome inhibitor.

A lysine-to-methionine mutation at lysine 27 of histone 3 (H3K27M) has been shown to promote oncogenesis in a subset of pediatric gliomas. While there is evidence that this "oncohistone" mutation acts by inhibiting the histone methyltransferase PRC2, the details of this proposed mechanism nevertheless continue to be debated. Recent evidence suggests that PRC2 must simultaneously bind both H3K27M and H3K27me3 to experience competitive inhibition of its methyltransferase activity. In this work, we used PRC2 inhibitor treatments in a transgenic H3K27M cell line to validate this dependence in a cellular context. We further used designer chromatin inhibitors to probe the geometric constraints of PRC2 engagement of H3K27M and H3K27me3 in a biochemical setting. We found that PRC2 binds to a bivalent inhibitor unit consisting of an H3K27M and an H3K27me3 nucleosome and exhibits a distance dependence in its affinity for such an inhibitor, which favors closer proximity of the 2 nucleosomes within a chromatin array. Together, our data precisely delineate fundamental aspects of the H3K27M inhibitor and support a model wherein PRC2 becomes trapped at H3K27M-H3K27me3 boundaries.

Akt inhibition synergizes with polycomb repressive complex 2 inhibition in the treatment of multiple myeloma.

Polycomb repressive complex 2 (PRC2) components, EZH2 and its homolog EZH1, and PI3K/Akt signaling pathway are focal points as therapeutic targets for multiple myeloma. However, the exact crosstalk between their downstream targets remains unclear. We herein elucidated some epigenetic interactions following Akt inhibition and demonstrated the efficacy of the combined inhibition of Akt and PRC2. We found that TAS-117, a potent and selective Akt inhibitor, downregulated EZH2 expression at the mRNA and protein levels via interference with the Rb-E2F pathway, while EZH1 was compensatively upregulated to maintain H3K27me3 modifications. Consistent with these results, the dual EZH2/EZH1 inhibitor, UNC1999, but not the selective EZH2 inhibitor, GSK126, synergistically enhanced TAS-117-induced cytotoxicity and provoked myeloma cell apoptosis. RNA-seq analysis revealed the activation of the FOXO signaling pathway after TAS-117 treatment. FOXO3/4 mRNA and their downstream targets were upregulated with the enhanced nuclear localization of FOXO3 protein after TAS-117 treatment. ChIP assays confirmed the direct binding of FOXO3 to EZH1 promoter, which was enhanced by TAS-117 treatment. Moreover, FOXO3 knockdown repressed EZH1 expression. Collectively, the present results reveal some molecular interactions between Akt signaling and epigenetic modulators, which emphasize the benefits of targeting PRC2 full activity and the Akt pathway as a therapeutic option for multiple myeloma.

Jarid2 enhances the progression of bladder cancer through regulating PTEN/AKT signaling.

AIMS: Jumonji AT-rich interactive domain 2 (Jarid2) is an interacting component of PRC2 which catalyzes methylation of H3K27 (H3K27me3) and causes the downregulation of PTEN. In the present study, we aimed to explore whether Jarid2 could interact with H3K27me3 to regulate PTEN expression in bladder cancer. MAIN METHODS: Jarid2 expression in bladder cancer tissues and cells were determined by western blotting and RT-PCR. CCK-8, flow cytometry, transwell chamber and in vivo xenograft assays were performed to assess cell growth, apoptosis, migration and tumorigenesis, respectively. Chromatin immunoprecipitation (ChIP) assay was used to assess the methylation of PTEN. KEY FINDINGS: Jarid2 expression was increased in bladder cancer tissues and cells. Downregulation of Jarid2 with shRNA transfection obviously inhibited the proliferation, migration and tumorigenesis of bladder cancer T24 and HT-1376 cells and induced cell apoptosis. Jarid2 downregulation decreased the expression of p-AKT and increased PTEN expression. Besides, Jarid2 down-regulation repressed the epithelial-mesenchymal transition (EMT), whereas knockdown of PTEN impaired this effect. Moreover, upregulation of Jarid2 increased the combination of PTEN promoter and H3K27me3, and 5-aza-CdR rescued it. Meanwhile, 5-aza-CdR administration abolished Jarid2 roles in the promotion of EMT process and AKT activation, as well as the reduction of PTEN expression. SIGNIFICANCE: Overall, the present study elaborated that Jarid2 facilitated the progression of bladder cancer through H3K27me3-mediated PTEN downregulation and AKT activation, which might provide a new mechanism for Jarid2 in promoting bladder cancer progression.

Ezh1 arises from Ezh2 gene duplication but its function is not required for zebrafish development.

Trimethylation on H3K27 mediated by Polycomb Repressive Complex 2 (PRC2) is required to control gene repression programs involved in development, regulation of tissue homeostasis or maintenance and lineage specification of stem cells. In Drosophila, the PRC2 catalytic subunit is the single protein E(z), while in mammals this function is fulfilled by two proteins, Ezh1 and Ezh2. Based on database searches, we propose that Ezh1 arose from an Ezh2 gene duplication that has occurred in the common ancestor to elasmobranchs and bony vertebrates. Expression studies in zebrafish using in situ hybridization and RT-PCR followed by the sequencing of the amplicon revealed that ezh1 mRNAs are maternally deposited. Then, ezh1 transcripts are ubiquitously distributed in the entire embryo at 24 hpf and become more restricted to anterior part of the embryo at later developmental stages. To unveil the function of ezh1 in zebrafish, a mutant line was generated using the TALEN technology. Ezh1-deficient mutant fish are viable and fertile, but the loss of ezh1 function is responsible for the earlier death of ezh2 mutant larvae indicating that ezh1 contributes to zebrafish development in absence of zygotic ezh2 gene function. Furthermore, we show that presence of ezh1 transcripts from the maternal origin accounts for the delayed lethality of ezh2-deficient larvae.

MiR-155 inhibition ameliorates 2, 4, 6-Trinitrobenzenesulfonic acid (TNBS)-induced experimental colitis in rat via influencing the differentiation of Th17 cells by Jarid2.

Th17 cells play an important role in the immune imbalance and inflammatory state in colonic mucosa of Inflammatory Bowel Disease (IBD) and to clarify the mechanism that affect the differentiation of Th17 cells will help us find a new target for the treatment of IBD. MiR-155 which is reported to have an important role in regulating immune system function is also detected to be significantly up-regulated in colonic tissues of IBD patients. However, whether and how miR-155 affects the differentiation of Th17 cells in the colon of IBD patients is still worth studying. Here, we investigated the role of miR-155 in TNBS-induced rat colitis. Firstly, we found that the disease activity index (DAI) and Colon pathological changes were significantly reduced (P < 0.05) by using miR-155 inhibition sequences delivered by lentiviral vector, which revealed that miR-155 inhibition ameliorated TNBS-Induced experimental colitis. Then, we carried out flow cytometry, ELISA, qRT-PCR, and found that in TNBS+miR-155 inhibition group, the proportion of Th17 cells in spleens and mesenteric lymph nodes (MLNs) and the level of the Th17 cell-associated cytokines IL-6, IL-17A, IL-17F and IL-21 in colon tissues were significantly reduced (P < 0.05), which revealed that miR-155 inhibition regulated the differentiation and function of Th17 cells. Finally, we discovered that Jarid2 was significantly elevated (P < 0.05) by miR-155 inhibition and notch1 expression was inversely correlated with Jarid2 by using Immunohistochemistry and western blot. This study suggests that miR-155 inhibition ameliorates TNBS-induced colitis by regulating the Th17 cells differentiation and function and Jarid2/notch1 is closely related with the process.

Canonical PRC2 function is essential for mammary gland development and affects chromatin compaction in mammary organoids.

Distinct transcriptional states are maintained through organization of chromatin, resulting from the sum of numerous repressive and active histone modifications, into tightly packaged heterochromatin versus more accessible euchromatin. Polycomb repressive complex 2 (PRC2) is the main mammalian complex responsible for histone 3 lysine 27 trimethylation (H3K27me3) and is integral to chromatin organization. Using in vitro and in vivo studies, we show that deletion of Suz12, a core component of all PRC2 complexes, results in loss of H3K27me3 and H3K27 dimethylation (H3K27me2), completely blocks normal mammary gland development, and profoundly curtails progenitor activity in 3D organoid cultures. Through the application of mammary organoids to bypass the severe phenotype associated with Suz12 loss in vivo, we have explored gene expression and chromatin structure in wild-type and Suz12-deleted basal-derived organoids. Analysis of organoids led to the identification of lineage-specific changes in gene expression and chromatin structure, inferring cell type-specific PRC2-mediated gene silencing of the chromatin state. These expression changes were accompanied by cell cycle arrest but not lineage infidelity. Together, these data indicate that canonical PRC2 function is essential for development of the mammary gland through the repression of alternate transcription programs and maintenance of chromatin states.

The Polycomb-Dependent Epigenome Controls ß Cell Dysfunction, Dedifferentiation, and Diabetes.

To date, it remains largely unclear to what extent chromatin machinery contributes to the susceptibility and progression of complex diseases. Here, we combine deep epigenome mapping with single-cell transcriptomics to mine for evidence of chromatin dysregulation in type 2 diabetes. We find two chromatin-state signatures that track ß cell dysfunction in mice and humans: ectopic activation of bivalent Polycomb-silenced domains and loss of expression at an epigenomically unique class of lineage-defining genes. ß cell-specific Polycomb (Eed/PRC2) loss of function in mice triggers diabetes-mimicking transcriptional signatures and highly penetrant, hyperglycemia-independent dedifferentiation, indicating that PRC2 dysregulation contributes to disease. The work provides novel resources for exploring ß cell transcriptional regulation and identifies PRC2 as necessary for long-term maintenance of ß cell identity. Importantly, the data suggest a two-hit (chromatin and hyperglycemia) model for loss of ß cell identity in diabetes.

Phosphorylation of EZH2 by AMPK Suppresses PRC2 Methyltransferase Activity and Oncogenic Function.

Sustained energy starvation leads to activation of AMP-activated protein kinase (AMPK), which coordinates energy status with numerous cellular processes including metabolism, protein synthesis, and autophagy. Here, we report that AMPK phosphorylates the histone methyltransferase EZH2 at T311 to disrupt the interaction between EZH2 and SUZ12, another core component of the polycomb repressive complex 2 (PRC2), leading to attenuated PRC2-dependent methylation of histone H3 at Lys27. As such, PRC2 target genes, many of which are known tumor suppressors, were upregulated upon T311-EZH2 phosphorylation, which suppressed tumor cell growth both in cell culture and mouse xenografts. Pathologically, immunohistochemical analyses uncovered a positive correlation between AMPK activity and pT311-EZH2, and higher pT311-EZH2 correlates with better survival in both ovarian and breast cancer patients. Our finding suggests that AMPK agonists might be promising sensitizers for EZH2-targeting cancer therapies.

Cis and trans determinants of epigenetic silencing by Polycomb repressive complex 2 in Arabidopsis.

Disruption of gene silencing by Polycomb protein complexes leads to homeotic transformations and altered developmental-phase identity in plants. Here we define short genomic fragments, known as Polycomb response elements (PREs), that direct Polycomb repressive complex 2 (PRC2) placement at developmental genes regulated by silencing in Arabidopsis thaliana. We identify transcription factor families that bind to these PREs, colocalize with PRC2 on chromatin, physically interact with and recruit PRC2, and are required for PRC2-mediated gene silencing in vivo. Two of the cis sequence motifs enriched in the PREs are cognate binding sites for the identified transcription factors and are necessary and sufficient for PRE activity. Thus PRC2 recruitment in Arabidopsis relies in large part on binding of trans-acting factors to cis-localized DNA sequence motifs.

Slow Chromatin Dynamics Allow Polycomb Target Genes to Filter Fluctuations in Transcription Factor Activity.

Genes targeted by Polycomb repressive complex 2 (PRC2) are regulated in cis by chromatin modifications and also in trans by diffusible regulators such as transcription factors. Here, we introduce a mathematical model in which transcription directly antagonizes Polycomb silencing, thereby linking these cis- and trans-regulatory inputs to gene expression. The model is parameterized by recent experimental data showing that PRC2-mediated repressive chromatin modifications accumulate extremely slowly. The model generates self-perpetuating, bistable active and repressed chromatin states that persist through DNA replication, thereby ensuring high-fidelity transmission of the current chromatin state. However, sufficiently strong, persistent activation or repression of transcription promotes switching between active and repressed chromatin states. We observe that when chromatin modification dynamics are slow, transient pulses of transcriptional activation or repression are effectively filtered, such that epigenetic memory is retained. Noise filtering thus depends on slow chromatin dynamics and may represent an important function of PRC2-based regulation.

Stage- and subunit-specific functions of polycomb repressive complex 2 in bladder urothelial formation and regeneration.

Urothelium is the protective lining of the urinary tract. The mechanisms underlying urothelial formation and maintenance are largely unknown. Here, we report the stage-specific roles of PRC2 epigenetic regulators in embryonic and adult urothelial progenitors. Without Eed, the obligatory subunit of PRC2, embryonic urothelial progenitors demonstrate reduced proliferation with concomitant dysregulation of genes including Cdkn2a (p16), Cdkn2b (p15) and Shh. These mutants display premature differentiation of keratin 5-positive (Krt5+) basal cells and ectopic expression of squamous-like differentiation markers. Deletion of Ezh2, the major enzymatic component of PRC2, causes upregulation of Upk3a+ superficial cells. Unexpectedly, Eed and Eed/Ezh2 double mutants exhibit delayed superficial cell differentiation. Furthermore, Eed regulates the proliferative and regenerative capacity of adult urothelial progenitors and prevents precocious differentiation. Collectively, these findings uncover the epigenetic mechanism by which PRC2 controls urothelial progenitor cell fate and the timing of differentiation, and further suggest an epigenetic basis of urothelial maintenance and regeneration.