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The polycomb proteins EZH1 and EZH2 co-regulate chromatin accessibility and nephron progenitor cell lifespan in mice.

ABSTRACT: SIX2 (SIX homeobox 2)-positive nephron progenitor cells (NPCs) give rise to all epithelial cell types of the nephron, the filtering unit of the kidney. NPCs have a limited lifespan and are depleted near the time of birth. Epigenetic factors are implicated in the maintenance of organ-restricted progenitors such as NPCs, but the chromatin-based mechanisms are incompletely understood. Here, using a combination of gene targeting, chromatin profiling, and single-cell RNA analysis, we examined the role of the murine histone 3 Lys-27 (H3K27) methyltransferases EZH1 (enhancer of zeste 1) and EZH2 in NPC maintenance. We found that EZH2 expression correlates with NPC growth potential and that EZH2 is the dominant H3K27 methyltransferase in NPCs and epithelial descendants. Surprisingly, NPCs lacking H3K27 trimethylation maintained their progenitor state but cycled slowly, leading to a smaller NPC pool and formation of fewer nephrons. Unlike Ezh2 loss of function, dual inactivation of Ezh1 and Ezh2 triggered overexpression of the transcriptional repressor Hes-related family BHLH transcription factor with YRPW motif 1 (Hey1), down-regulation of Six2, and unscheduled activation of Wnt4-driven differentiation, resulting in early termination of nephrogenesis and severe renal dysgenesis. Double-mutant NPCs also overexpressed the SIX family member Six1 However, in this context, SIX1 failed to maintain NPC stemness. At the chromatin level, EZH1 and EZH2 restricted accessibility to AP-1-binding motifs, and their absence promoted a regulatory landscape akin to differentiated and nonlineage cells. We conclude that EZH2 is required for NPC renewal potential and that tempering of the differentiation program requires cooperation of both EZH1 and EZH2.

SUBMITTER: Liu H

PROVIDER: S-EPMC7450110 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Bulk ATAC_seq on GFP expressing FACS-isolated cells from E16.5 and P0 Six2TGC and compound Ezh1 and Ezh2 mutant kidneys( Six2TGC_Ezh2-/- , Ezh1+/-; Six2TGC_Ezh2-/-; and Ezh1-/- ; scRNA-seq analysis of NPCs (Six2/GFP+ cells) from E16.5 as well as P2 kidneys. Genotypes analyzed: Six2TGC (E16.5&P2), Six2TGCEzh2-/- (E16.5), Ezh1+/-;Six2TGCEzh2-/- (E16.5), and Ezh2-/-;Six2TGCEzh2-/- (E16.5) Six2/GFP+ nephron progenitor cells (NPCs) give rise to all epithelial cell types of the nephron, the filtering unit of the kidney. NPCs have a limited lifespan and are consumed near the time of birth. Pre-term birth or prenatal stress further shorten the lifespan of NPCs and result in nephron deficit and chronic kidney disease. Accordingly, there is a pressing need to better understand the factors that regulate NPC lifespan in order to develop novel regenerative strategies. Epigenetic factors are implicated in maintenance of organ-restricted progenitors such as NPCs, but the chromatin-based mechanisms are not well understood. In this study, we examined the role of the H3K27 methyltransferases, Enhancer of zeste (Ezh1 and Ezh2), in NPC maintenance using a combination of gene targeting, chromatin profiling, and single-cell RNA analysis. We find that Ezh2 expression correlates with NPC growth potential, and that Ezh2 is the dominant H3K27 methyltransferase in NPCs and epithelial descendants. Surprisingly, NPCs lacking H3K27me3 maintain their progenitor state albeit cycle slowly leading to formation of fewer nephrons. Unlike Ezh2 loss-of-function, dual inactivation of Ezh1 and Ezh2 triggers overexpression of the transcriptional repressor Hey1 and downregulation of Six2 and result in unscheduled activation of Wnt4-driven differentiation, early termination of nephrogenesis and severe renal dysgenesis. Double-mutant NPCs also overexpress the Six family member, Six1. However, in this context, Six1 is unable to access the closed Six2 enhancer and fails to maintain NPC stemness. At the chromatin level, Ezh1 and Ezh2 act by restricting accessibility of AP1 factors to their genomic binding motifs and their absence provokes a regulatory landscape akin of differentiated and non-lineage cells. We conclude that Ezh2 is required for NPC renewal potential, while maintenance of NPC lifespan and tempering the differentiation program require cooperation of both Ezh1 and Ezh2.

Project description:BACKGROUND & AIMS:Little is known about mechanisms that underlie postnatal hepatocyte maturation and fibrosis at the chromatin level. We investigated the transcription of genes involved in maturation and fibrosis in postnatal hepatocytes of mice, focusing on the chromatin compaction the roles of the Polycomb repressive complex 2 histone methyltransferases EZH1 and EZH2. METHODS:Hepatocytes were isolated from mixed background C57BL/6J-C3H mice, as well as mice with liver-specific disruption of Ezh1 and/or Ezh2, at postnatal day 14 and 2 months after birth. Liver tissues were collected and analyzed by RNA sequencing, H3K27me3 chromatin immunoprecipitation sequencing, and sonication-resistant heterochromatin sequencing (a method to map heterochromatin and euchromatin). Liver damage was characterized by histologic analysis. RESULTS:We found more than 3000 genes differentially expressed in hepatocytes during liver maturation from postnatal day 14 to month 2 after birth. Disruption of Ezh1 and Ezh2 in livers caused perinatal hepatocytes to differentiate prematurely and to express genes at postnatal day 14 that would normally be induced by month 2 and differentiate prematurely. Loss of Ezh1 and Ezh2 also resulted in liver fibrosis. Genes with H3K27me3-postive and H3K4me3-positive euchromatic promoters were prematurely induced in hepatocytes with loss of Ezh1 and Ezh2-these genes included those that regulate hepatocyte maturation, fibrosis, and genes not specifically associated with the liver lineage. CONCLUSIONS:The Polycomb repressive complex 2 proteins EZH1 and EZH2 regulate genes that control hepatocyte maturation and fibrogenesis and genes not specifically associated with the liver lineage by acting at euchromatic promoter regions. EZH1 and EZH2 thereby promote liver homeostasis and prevent liver damage. Strategies to manipulate Polycomb proteins might be used to improve hepatocyte derivation protocols or developed for treatment of patients with liver fibrosis.

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The polycomb proteins EZH1 and EZH2 co-regulate chromatin accessibility and nephron progenitor cell lifespan in mice.

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