Modifiers of the jumonji mutation downregulate cyclin D1 expression and cardiac cell proliferation

Late-stage differentiation of embryonic pancreatic β-cells requires Jarid2

Jarid2 is a component of the Polycomb Repressor complex 2 (PRC2), which is responsible for genome-wide H3K27me3 deposition, in embryonic stem cells. However, Jarid2 has also been shown to exert pleiotropic PRC2-independent actions during embryogenesis. Here, we have investigated the role of Jarid2 during pancreas development. Conditional ablation of Jarid2 in pancreatic progenitors results in reduced endocrine cell area at birth due to impaired endocrine cell differentiation and reduced prenatal proliferation. Inactivation of Jarid2 in endocrine progenitors demonstrates that Jarid2 functions after endocrine specification. Furthermore, genome-wide expression analysis reveals that Jarid2 is required for the complete activation of the insulin-producing β-cell differentiation program. Jarid2-deficient pancreases exhibit impaired deposition of RNAPII-Ser5P, the initiating form of RNAPII, but no changes in H3K27me3, at the promoters of affected endocrine genes. Thus, our study identifies Jarid2 as a fine-tuner of gene expression during late stages of pancreatic endocrine cell development. These findings are relevant for generation of transplantable stem cell-derived β-cells.

JARID2 inhibits leukemia cell proliferation by regulating CCND1 expression

It has recently been shown that JARID2 contributes to the malignant character of solid tumors, such as epithelial-mesenchymal transition in lung and colon cancer cell lines, but its role in leukemia progression is unexplored. In this study, we explored the effect and underlying molecular mechanism of JARID2 on leukemia cell proliferation. Real-time PCR and Western assay were carried out to detect JARID2 and CCND1 expression. Cell number and cell cycle change were detected using hemocytometer and flow cytometry, and a ChIP assay was utilized to investigate JARID2 and H3K27me3 enrichment on the CCND1 promoter. JARID2 is down-regulated in B-chronic lymphocytic leukemia (B-CLL) and acute monocytic leukemia (AMOL), and knockdown of JARID2 promotes leukemia cell proliferation via acceleration of the G1/S transition. Conversely, ectopic expression of JARID2 inhibits these malignant phenotypes. Mechanistic studies show that JARID2 negatively regulates CCND1 expression by increasing H3K27 trimethylation on the CCND1 promoter. Our findings indicate that JARID2 is a negative regulator of leukemia cell proliferation, and functions as potential tumor suppressor in leukemia.

Inactive yet indispensable: the tale of Jarid2

Methylation of histone tails is believed to be important for the establishment and inheritance of gene expression programs during development. Jarid2/Jumonji is the founding member of a family of chromatin modifiers with histone demethylase activity. Although Jarid2 contains amino acid substitutions that are thought to abolish its catalytic activity, it is essential for the development of multiple organs in mice. Recent studies have shown that Jarid2 is a component of the polycomb repressive complex 2 and is required for embryonic stem (ES) cell differentiation. Here, we discuss current literature on the function of Jarid2 and hypothesize that defects resulting from Jarid2 deficiency arise from a failure to correctly prime genes in ES cells that are required for later stages in development.

Jarid2 is among a set of genes differentially regulated by Nkx2.5 during outflow tract morphogenesis

Nkx2.5, a transcription factor implicated in human congenital heart disease, is required for regulation of second heart field (SHF) progenitors contributing to outflow tract (OFT). Here, we define a set of genes (Lrrn1, Elovl2, Safb, Slc39a6, Khdrbs1, Hoxb4, Fez1, Ccdc117, Jarid2, Nrcam, and Enpp3) expressed in SHF containing pharyngeal arch tissue whose regulation is dependent on Nkx2.5. Further investigation shows that Jarid2, which has been implicated in OFT morphogenesis, is a direct target of Nkx2.5 regulation. Jarid2 expression was up-regulated in SHF mesoderm of Nkx2.5-deficient embryos. Chromatin immunoprecipitation analysis showed Nkx2.5 interaction with consensus binding sites in the Jarid2 promoter in pharyngeal arch cells. Finally, Jarid2 promoter activity and mRNA expression levels were down-regulated by Nkx2.5 overexpression. Given the role of Jarid2 as a regulator of early cardiac proliferation, these findings highlight Jarid2 as one of several potential mediators of the critical role played by Nkx2.5 during OFT morphogenesis.

Hepatitis C virus core protein up-regulates anergy-related genes and a new set of genes, which affects T cell homeostasis

Hepatitis C virus (HCV) infection is the main cause for chronic hepatitis, leading to cirrhosis and hepatic carcinoma. Virally induced immune dysfunction has been called as the cause for viral persistence. Previous results demonstrate that CD4 Jurkat cells stably expressing the HCV core protein show an increased activation of NFAT transcription factor and an impaired IL-2 promoter activity, affecting intracellular signaling pathways in a manner that mimics clonal anergy. We had shown previously that NFAT activates a transcriptional program, ensuing in immunological tolerance. In the present work, we have engineered lentiviral vectors expressing the HCV core to analyze the events, which unfold in the initial phase of HCV core-induced anergy. We show that genes initially described to be up-regulated by ionomycin-induced anergy in mice are also up-regulated in humans, not only by ionomycin but also by HCV core expression. We also show that HCV core is sufficient to cause NFAT nuclear translocation and a slow-down in cell-cycle progression, and using whole genome microarrays, we identify novel genes up-regulated in Jurkat cells expressing HCV core. The relevance of our results is highlighted by the presence of HCV in CD4 T cells from HCV chronically infected patients.

Characterization of zinc finger protein 496 that interacts with Jumonji/Jarid2

Jumonij (JMJ)/Jarid2 plays important roles in embryonic development and functions as a transcriptional repressor. Using yeast two-hybrid screening, we have identified a cofactor of JMJ, the zinc finger protein 496 (Zfp496) that contains a SCAN, KRAB and zinc finger domain. Our molecular analyses indicate that Zfp496 functions as a transcriptional activator. Further, Zfp496 inhibits the transcriptional repression of JMJ and JMJ represses the transcriptional activation of Zfp496. This study demonstrates that JMJ physically and functionally interacts with Zfp496, which will provide important insights into endogenous target gene regulation by both factors.

ATM-mediated transcriptional and developmental responses to gamma-rays in Arabidopsis

ATM (Ataxia Telangiectasia Mutated) is an essential checkpoint kinase that signals DNA double-strand breaks in eukaryotes. Its depletion causes meiotic and somatic defects in Arabidopsis and progressive motor impairment accompanied by several cell deficiencies in patients with ataxia telangiectasia (AT). To obtain a comprehensive view of the ATM pathway in plants, we performed a time-course analysis of seedling responses by combining confocal laser scanning microscopy studies of root development and genome-wide expression profiling of wild-type (WT) and homozygous ATM-deficient mutants challenged with a dose of γ-rays (IR) that is sublethal for WT plants. Early morphologic defects in meristematic stem cells indicated that AtATM, an Arabidopsis homolog of the human ATM gene, is essential for maintaining the quiescent center and controlling the differentiation of initial cells after exposure to IR. Results of several microarray experiments performed with whole seedlings and roots up to 5 h post-IR were compiled in a single table, which was used to import gene information and extract gene sets. Sequence and function homology searches; import of spatio-temporal, cell cycling, and mutant-constitutive expression characteristics; and a simplified functional classification system were used to identify novel genes in all functional classes. The hundreds of radiomodulated genes identified were not a random collection, but belonged to functional pathways such as those of the cell cycle; cell death and repair; DNA replication, repair, and recombination; and transcription; translation; and signaling, indicating the strong cell reprogramming and double-strand break abrogation functions of ATM checkpoints. Accordingly, genes in all functional classes were either down or up-regulated concomitantly with downregulation of chromatin deacetylases or upregulation of acetylases and methylases, respectively. Determining the early transcriptional indicators of prolonged S-G2 phases that coincided with cell proliferation delay, or an anticipated subsequent auxin increase, accelerated cell differentiation or death, was used to link IR-regulated hallmark functions and tissue phenotypes after IR. The transcription burst was almost exclusively AtATM-dependent or weakly AtATR-dependent, and followed two major trends of expression in atm: (i)-loss or severe attenuation and delay, and (ii)-inverse and/or stochastic, as well as specific, enabling one to distinguish IR/ATM pathway constituents. Our data provide a large resource for studies on the interaction between plant checkpoints of the cell cycle, development, hormone response, and DNA repair functions, because IR-induced transcriptional changes partially overlap with the response to environmental stress. Putative connections of ATM to stem cell maintenance pathways after IR are also discussed.

Roles of jumonji and jumonji family genes in chromatin regulation and development

The jumonji (jmj) gene was identified by a mouse gene trap approach and has essential roles in the development of multiple tissues. The Jmj protein has a DNA binding domain, ARID, and two conserved jmj domains (jmjN and jmjC). In many diverse species including bacteria, fungi, plants, and animals, there are many jumonji family proteins that have only the jmjC domain or both jmj domains. Recently, Jmj protein was found to be a transcriptional repressor. Several proteins in the jumonji family are involved in transcriptional repression and/or chromatin regulation. Most recently, one of the human members has been shown to be a histone demethylase, and the jmjC domain is essential for the demethylase activity. Meanwhile, more and more evidence indicating that the jumonji family proteins play important roles during development is accumulating. Many proteins in the jumonji family may regulate chromatin and gene expression, and control development through various signaling pathways. Here, we highlight the roles of jmj and jumonji family proteins in chromatin regulation and development.

Roles of JUMONJI in mouse embryonic 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.