SUMMARY Trimethylation on histone H3 lysine 27 (H3K27me3) by Polycomb repressive complex 2 (PRC2) regulates the balance between self-renewal and differentiation of embryonic stem cells (ESCs). The mechanisms by which the activity and recruitment of PRC2 are controlled are largely unknown. Here we demonstrate that the founding member of the Jumonji-family, JMJ (JUMONJI or JARID2), is tightly associated with PRC2, colocalizes with PRC2 and H3K27me3 on chromatin, and modulates PRC2 function. In vitro JMJ inhibits PRC2 methyltransferase activity, a finding consistent with increased H3K27me3 marks at PRC2 targets in Jmj−/− ESCs. Paradoxically, JMJ is required for efficient binding of PRC2, indicating that the interplay of PRC2 and JMJ fine-tunes deposition of the H3K27me3 mark. During differentiation, activation of genes marked by H3K27me3 and lineage commitments are delayed in Jmj−/− ESCs. Our results demonstrate that dynamic regulation of Polycomb complex activity orchestrated by JMJ balances self-renewal and differentiation, further highlighting the involvement of chromatin dynamics in cell-fate transitions.

Polycomb repressive complex two (PRC2) has been implicated in embryonic stem (ES) cell pluripotency; however, the mechanistic roles of this complex are unclear. It was assumed that ES cells contain PRC2 with the same subunit composition as that identified in HeLa cells and Drosophila embryos. Here, we report that PRC2 in mouse ES cells contains at least three additional subunits: JARID2, MTF2, and a novel protein denoted esPRC2p48. JARID2, MTF2, and esPRC2p48 are highly expressed in mouse ES cells compared to differentiated cells. Importantly, knockdowns of JARID2, MTF2, or esPRC2p48 alter the level of PRC2-mediated H3K27 methylation and result in the expression of differentiation-associated genes in ES cells. Interestingly, expression of JARID2, MTF2, and esPRC2p48 together, but not individually, enhances Oct4/Sox2/Klf4-mediated reprograming of mouse embryonic fibroblasts (MEFs) into induced pluripotent stem cells, whereas knockdown or knockout of JARID2, MTF2, or esPRC2p48 significantly inhibits reprograming. JARID2, MTF2, and esPRC2p48 modulate H3K27 methylation and facilitate repression of lineage-associated gene expression when transduced into MEFs, and synergistically stimulate the histone methyl-transferase activity of PRC2 in vitro. Therefore, these studies identify JARID2, MTF2, and esPRC2p48 as important regulatory subunits of PRC2 in ES cells and reveal critical functions of these subunits in modulating PRC2’s activity and gene expression both in ES cells and during somatic cell reprograming.

Jarid2/Jumonji critically regulates developmental processes including cardiovascular development. Jarid2 knock-out mice exhibit cardiac defects including hypertrabeculation with noncompaction of the ventricular wall. However, molecular mechanisms underlying Jarid2-mediated cardiac development remain unknown. To determine the cardiac lineagespecific roles of Jarid2, we generated myocardial, epicardial, cardiac neural crest, or endothelial conditional Jarid2 knockout mice using Cre-loxP technology. Only mice with an endothelial deletion of Jarid2 recapitulate phenotypic defects observed in whole body mutants including hypertrabeculation and noncompaction of the ventricle. To identify potential targets of Jarid2, combinatorial approaches using microarray and candidate gene analyses were employed on Jarid2 knock-out embryonic hearts. Whole body or endothelial deletion of Jarid2 leads to increased endocardial Notch1 expression in the developing ventricle, resulting in increased Notch1-dependent signaling to the adjacent myocardium. Using quantitative chromatin immunoprecipitation analysis, Jarid2 was found to occupy a specific region on the endogenous Notch1 locus. We propose that failure to properly regulate Notch signaling in Jarid2 mutants likely leads to the defects in the developing ventricular chamber. The identification of Jarid2 as a potential regulator of Notch1 signaling has broad implications for many cellular processes including development, stem cell maintenance, and tumor formation.The heart is the first organ to form and function during embryogenesis. Improper formation of the heart leads to congenital heart defects, which are the most common form of human birth defects (1, 2). The formation of the heart is a complex process that requires delicate spatial and biochemical interactions among various cell types. Despite extensive studies to determine the transcriptional regulation of cardiac development, the precise mechanisms of ventricular chamber development remain largely unknown. Mice with a homozygous Jarid2 deletion (Jarid2 KO) exhibit cardiac defects mimicking human congenital cardiac defects including ventricular septal defects (VSD), 2 double outlet right ventricle (DORV), and hypertrabeculation associated with noncompaction of the ventricular wall resulting in a thin compact layer (3, 4). These mutant mice survive until birth and offer the unique opportunity to further explore the molecular mechanisms of development and late stage maturation of the ventricular chamber.Jarid2 is the founding member of the Jumonji family of proteins, all of which contain the JmjC domain that was first defined based on amino acid similarities between Jarid2, Jarid1C (Smcx), and Jarid1A (RBP2) (5-7). Proteins containing the JmjC domain generally function as histone demethylases (8). Intriguingly, Jarid2 contains mutations at key amino acids necessary for enzymatic function and is highly likely enzymatically inactive (9 -11). Recent evidence suggests that Jarid2 plays critical roles in the regulation of gene express...

Background: Jarid2 regulates Notch1 expression in the developing heart through an unidentified mechanism. Results: Regulation of Notch1 by Jarid2 is through recruitment of SETDB1, resulting in increased methylation of histone H3 lysine 9. Conclusion: Jarid2 regulation of a subset of genes during cardiac development involves histone methylation through SETDB1 recruitment. Significance: This is a novel mechanism of epigenetic regulation by Jarid2 during cardiac development.

Cardiac development is a complex biological process requiring the integration of cell specification, differentiation, migration, proliferation, and morphogenesis. Although significant progress has been made recently in understanding the molecular basis of cardiac development, mechanisms of transcriptional control of cardiac development remain largely unknown. In search for the developmentally important genes, the jumonji gene (jmj) was identified by gene trap technology and characterized as a critical nuclear factor for mouse embryonic development. Jmj has been shown to play important roles in cardiovascular development, neural tube fusion process, hematopoiesis, and liver development in mouse embryos. The amino acid sequence of the JUMONJI protein (JMJ) reveals that JMJ belongs to the AT-rich interaction domain transcription factor family and more recently has been described as a member of the JMJ transcription factor family. Here, we review the roles of jmj in multiple organ development with a focus on cardiovascular development in mice. Developmental Dynamics 232:21-32, 2005.