Project description:We have identified the distinct effects on neuronal differentiation of two different mutations of ATRX. We generated E14 mouse embryonic stem cell lines with mutations in the histone binding domain of ATRX (PHDmut) or in the helicase domain (K1584R). Neurodifferentiation is both delayed and compromised in PHDmut and K1584R, and manifest differently from complete ATRX loss. We performed ATRX ChIP-seq which showed changes in occupancy of ATRX in PHDmut and K1584R. Our CUT&RUN and RNA-Seq reveal that mutations or deficiency of ATRX result in separate patterns of dysregulation in gene expression and PRC2 binding, suggesting different roles of each ATRX domain in neuronal differentiation
Project description:Here, we report that ATRX co-localizes with the H3K9-methyl transferase SETDB1 (also known as ESET), the co-repressor TRIM28 (also known as KAP1), and the transcription factor ZNF274 at 3â exons of Zinc Finger Genes (ZNFs) containing an atypical H3K9me3/H3K36me3 chromatin signature. Disruption of ATRX and ZNF274 leads to a significant reduction of H3K9me3, particularly at the 3â ZNF exons and other atypical chromatin regions, higher percentages of DNA damage, and defects in cell cycle. Taken together, our studies suggest that ATRX binds the 3â exons of ZNFs to maintain genomic stability through the regulation of their H3K9me3 levels XL-MNase ChIP-seq of ATRX was performed in the erythroleukemic cell line K562 and the Neuroblastoma cell line LAN6. Two independent replicates using different ATRX antibodies were performed in K562. Additionally, Native ChIP-seq of H3K9me3 in LAN6, ATRX WT and ATRX KO K562 cells was performed. Input samples were sequenced as control.
Project description:The genome consists of non-B-DNA structures such as G-quadruplexes (G4) that are involved in the regulation of genome stability and transcription. Telomeric-repeat containing RNA (TERRA) is capable of folding into G-quadruplex and interacting with chromatin remodeler ATRX. Here we show that TERRA modulates ATRX occupancy on repetitive sequences and over genes, and maintains DNA G-quadruplex structures at TERRA target and non-target sites in mouse embryonic stem cells. TERRA prevents ATRX from binding to subtelomeric regions and represses H3K9me3 formation. G4 ChIP-seq reveals that G4 abundance decreases at accessible chromatin regions, particularly at transcription start sites (TSS) after TERRA depletion; such G4 reduction at TSS is associated with elevated ATRX occupancy and differentially expressed genes. Loss of ATRX alleviates the effect of gene repression caused by TERRA depletion. Immunostaining analyses demonstrate that knockdown of TERRA diminishes DNA G4 signals, whereas silencing ATRX elevates G4 formation. Our results uncover an epigenetic regulation by TERRA that sequesters ATRX and preserves DNA G4 structures.
Project description:<p>Many tumors maintain chromosome ends through a telomerase-independent, homologous recombination based mechanism called alternative lengthening of telomeres (ALT). While ALT occurs in only a subset of tumors, it is strongly associated with mutations in the genes encoding components of the histone H3.3 chaperone complex, ATRX and DAXX. To date the mechanistic role of ATRX and particularly DAXX mutations in potentiating ALT remains poorly understood. We identify an osteosarcoma cell line, G292, with a unique chromosomal translocation resulting in loss of DAXX function, while retaining functional ATRX. Using this distinctive resource, we demonstrate that introduction of wild type DAXX suppresses the ALT phenotype and restores localization of the ATRX/DAXX complex to PML bodies. This provides the first direct molecular evidence that ongoing DAXX deficiency is essential for maintenance of the ALT phenotype and highlights the potential for therapeutic targeting of this oncogenic pathway.</p>
Project description:CHIP is a neuroprotective E3-ubiquitin ligase that supports longevity and healthy ageing. Loss of CHIP function has a major impact on life expectancy in animal models, whilst in humans’ mutations that compromise the E3-ligase activity of CHIP are causative for forms of Spinocerebellar Ataxia (SCA) that are accompanied by cognitive decline and/or dementia. The pathways regulated by CHIP to maintain neuronal health remain to be discovered. Gene-edited neuroblastoma cells were produced and used as a model to study the effects of CHIP loss on the steady state proteome in the absence of proteotoxic stress. Label free quantitative proteomic analysis (SWATH-MS) highlighted VGF, a member of the neuropeptide precursor family of proteins, as being a dominant protein responding to loss of CHIP function. By studying the dependence of VGF expression on CHIP using SILAC and RNA-Seq we have defined a role for the ligase in regulated neuropeptide expression.