Polycomb repressive complex 2 regulates normal hematopoietic stem cell function in a developmental-stage-specific manner.

Recent studies point to a pivotal role of Polycomb repressive complex 2 (PRC2) in stem cell function and cancer. Loss-of-function approaches targeting individual PRC2 subunits have, however, generated findings that are difficult to reconcile. Here, we prevent assembly of both Ezh1- and Ezh2-containing PRC2 complexes by conditional deletion of Eed, a core subunit, and assess hematopoiesis. We find that deletion of Eed exhausts adult bone marrow hematopoietic stem cells (HSCs), although fetal liver HSCs are produced in normal numbers. Eed-null neonatal HSCs express HSC signature genes but are defective in maintenance and differentiation. Comparative gene expression profiling revealed that neonatal and adult HSCs lacking Eed upregulated gene sets of conflicting pathways. Deletion of Cdkn2a, a PRC2 target gene, in Eed-null mice enhances hematopoietic stem/progenitor cell (HSPC) survival but fails to restore HSC functions. Taken together, our findings define developmental-stage-specific requirements for canonical PRC2 complexes in normal HSC function.

Xie H ，Xu J ，Hsu JH ，Nguyen M ，Fujiwara Y ，Peng C ，Orkin SH ... -  《-》

Dependency on the polycomb gene Ezh2 distinguishes fetal from adult hematopoietic stem cells.

Mochizuki-Kashio M ，Mishima Y ，Miyagi S ，Negishi M ，Saraya A ，Konuma T ，Shinga J ，Koseki H ，Iwama A ... -  《-》

Deletion of Polycomb Repressive Complex 2 From Mouse Intestine Causes Loss of Stem Cells.

The polycomb repressive complex 2 (PRC2) regulates differentiation by contributing to repression of gene expression and thereby stabilizing the fate of stem cells and their progeny. PRC2 helps to maintain adult stem cell populations, but little is known about its functions in intestinal stem cells. We studied phenotypes of mice with intestine-specific deletion of the PRC2 proteins embryonic ectoderm development (EED) (a subunit required for PRC2 function) and enhancer of zeste homolog 2 (EZH2) (a histone methyltransferase). We performed studies of AhCre;EedLoxP/LoxP (EED knockout) mice and AhCre;Ezh2LoxP/LoxP (EZH2 knockout) mice, which have intestine-specific disruption in EED and EZH2, respectively. Small intestinal crypts were isolated and subsequently cultured to grow organoids. Intestines and organoids were analyzed by immunohistochemical, in situ hybridization, RNA sequence, and chromatin immunoprecipitation methods. Intestines of EED knockout mice had massive crypt degeneration and lower numbers of proliferating cells compared with wild-type control mice. Cdkn2a became derepressed and we detected increased levels of P21. We did not observe any differences between EZH2 knockout and control mice. Intestinal crypts from EED knockout mice had signs of aberrant differentiation of uncommitted crypt cells-these differentiated toward the secretory cell lineage. Furthermore, crypts from EED-knockout mice had impaired Wnt signaling and concomitant loss of intestinal stem cells, this phenotype was not reversed upon ectopic stimulation of Wnt and Notch signaling in organoids. Analysis of gene expression patterns from intestinal tissues of EED knockout mice showed dysregulation of several genes involved in Wnt signaling. Wnt signaling was regulated directly by PRC2. In intestinal tissues of mice, PRC2 maintains small intestinal stem cells by promoting proliferation and preventing differentiation in the intestinal stem cell compartment. PRC2 controls gene expression in multiple signaling pathways that regulate intestinal homeostasis. Sequencing data are available in the genomics data repository GEO under reference series GSE81578; RNA sequencing data are available under subseries GSE81576; and ChIP sequencing data are available under subseries GSE81577.

Koppens MA ，Bounova G ，Gargiulo G ，Tanger E ，Janssen H ，Cornelissen-Steijger P ，Blom M ，Song JY ，Wessels LF ，van Lohuizen M ... -  《-》

Polycomb repressive complex 2 component Suz12 is required for hematopoietic stem cell function and lymphopoiesis.

Polycomb repressive complex 2 (PRC2) is a chromatin modifier that regulates stem cells in embryonic and adult tissues. Loss-of-function studies of PRC2 components have been complicated by early embryonic dependence on PRC2 activity and the partial functional redundancy of enhancer of zeste homolog 1 (Ezh1) and enhancer of zeste homolog 2 (Ezh2), which encode the enzymatic component of PRC2. Here, we investigated the role of PRC2 in hematopoiesis by conditional deletion of suppressor of zeste 12 protein homolog (Suz12), a core component of PRC2. Complete loss of Suz12 resulted in failure of hematopoiesis, both in the embryo and the adult, with a loss of maintenance of hematopoietic stem cells (HSCs). In contrast, partial loss of PRC2 enhanced HSC self-renewal. Although Suz12 was required for lymphoid development, deletion in individual blood cell lineages revealed that it was dispensable for the development of granulocytic, monocytic, and megakaryocytic cells. Collectively, these data reveal the multifaceted role of PRC2 in hematopoiesis, with divergent dose-dependent effects in HSC and distinct roles in maturing blood cells. Because PRC2 is a potential target for cancer therapy, the significant consequences of modest changes in PRC2 activity, as well as the cell and developmental stage-specific effects, will need to be carefully considered in any therapeutic context.

Lee SC ，Miller S ，Hyland C ，Kauppi M ，Lebois M ，Di Rago L ，Metcalf D ，Kinkel SA ，Josefsson EC ，Blewitt ME ，Majewski IJ ，Alexander WS ... -  《-》

Ezh1 is required for hematopoietic stem cell maintenance and prevents senescence-like cell cycle arrest.

Polycomb group (PcG) proteins are key epigenetic regulators of hematopietic stem cell (HSC) fate. The PcG members Ezh2 and Ezh1 are important determinants of embryonic stem cell identity, and the transcript levels of these histone methyltransferases are inversely correlated during development. However, the role of Ezh1 in somatic stem cells is largely unknown. Here we show that Ezh1 maintains repopulating HSCs in a slow-cycling, undifferentiated state, protecting them from senescence. Ezh1 ablation induces significant loss of adult HSCs, with concomitant impairment of their self-renewal capacity due to a potent senescence response. Epigenomic and gene expression changes induced by Ezh1 deletion in senesced HSCs demonstrated that Ezh1-mediated PRC2 activity catalyzes monomethylation and dimethylation of H3K27. Deletion of Cdkn2a on the Ezh1 null background rescued HSC proliferation and survival. Our results suggest that Ezh1 is an important histone methyltransferase for HSC maintenance.

Hidalgo I ，Herrera-Merchan A ，Ligos JM ，Carramolino L ，Nuñez J ，Martinez F ，Dominguez O ，Torres M ，Gonzalez S ... -  《-》