Despite 20 years since its discovery, the gene responsible for Huntington’s Disease, HTT, has still not had its function or transcriptional profile completely characterized. In response to a recent report by Ruzo et al. of several novel splice forms of HTT in human embryonic stem cell lines, we have analyzed a set of mRNA sequencing datasets from post mortem human brain from Huntington’s disease, Parkinson’s disease, and neurologically normal control subjects to evaluate support for previously observed and to identify novel splice patterns. A custom analysis pipeline produced supporting evidence for some of the results reported by two previous studies of alternative isoforms as well as identifying previously unreported splice patterns. All of the alternative splice patterns were of relatively low abundance compared to the canonical splice form. Overall design: 29 Huntington''s Disease, 29 Parkinson''s Disease, and 50 Neurologically normal control samples from human post-mortem prefrontal cortex
Evidence of Extensive Alternative Splicing in Post Mortem Human Brain HTT Transcription by mRNA Sequencing.
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View SamplesParkinson disease (PD) is a neurodegenerative disease characterized by the accumulation of alpha-synuclein (SNCA) and other proteins in aggregates termed “Lewy Bodies” within neurons. PD has both genetic and environmental risk factors, and while processes leading to aberrant protein aggregation are unknown, past work points to abnormal levels of SNCA and other proteins. Although several genome-wide studies have been performed for PD, these have focused on DNA sequence variants by genome-wide association studies (GWAS) and on RNA levels (microarray transcriptomics), while genome-wide proteomics analysis has been lacking. After appropriate filters, proteomics identified 3,558 unique proteins and 283 of these (7.9%) were significantly different between PD and controls (q-value<0.05). RNA-sequencing identified 17,580 protein-coding genes and 1,095 of these (6.2%) were significantly different (FDR p-value<0.05), but only 166 of the FDR significant protein-coding genes (0.94%) were present among the 3,558 proteins characterized. Of these 166, eight genes (4.8%) were significant in both studies, with the same direction of effect. Functional enrichment analysis of the proteomics results strongly supports mitochondrial-related pathways, while comparable analysis of the RNA-sequencing results implicates protein folding pathways and metallothioneins. Ten of the implicated genes or proteins co-localized to GWAS loci. Evidence implicating SNCA was stronger in proteomics than in RNA-sequencing analyses. Notably, differentially expressed protein-coding genes were more likely to not be characterized in the proteomics analysis, which lessens the ability to compare across platforms. Combining multiple genome-wide platforms offers novel insights into the pathological processes responsible for this disease by identifying pathways implicated across methodologies. Overall design: The study consists of mRNA-Seq (29 PD, 44 neurologically normal controls) and three-stage Mass Spectrometry Tandem Mass Tag Proteomics (12 PD, 12 neurologically normal controls) performed in post-mortem BA9 brain tissue. The proteomics samples are a subset of the RNA-Seq samples.
Integrative analyses of proteomics and RNA transcriptomics implicate mitochondrial processes, protein folding pathways and GWAS loci in Parkinson disease.
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Linking proteomic and transcriptional data through the interactome and epigenome reveals a map of oncogene-induced signaling.
Specimen part, Cell line
View SamplesEGFRvIII is the most common deletion mutant of EGFR in human cancer and its levels are highly correlated with poor prognosis in GBM. The deletion of exons 2-7 removes most of the extracellular ligand binding domain, so it is unable to bind EGF or other EGFR-binding ligands. Nevertheless, the mutant receptor is constitutively phosphorylated, and is capable of activating downstream signaling pathways at a low level.
Linking proteomic and transcriptional data through the interactome and epigenome reveals a map of oncogene-induced signaling.
Specimen part, Cell line
View SamplesThe earliest stages of Huntington’s disease are marked by changes in gene expression that are caused in an indirect and poorly understood manner by polyglutamine expansions in the huntingtin protein (HTT). To explore the hypothesis DNA methylation may be altered in cells expressing mutated HTT, we use reduced-representation bisulfite sequencing (RRBS) to map sites of DNA methylation in cells carrying either wild-type or mutant HTT. We find that a large fraction of the genes that change in expression in the presence of mutant huntingtin demonstrate significant changes in DNA methylation. Regions with low CpG content, which have previously been shown to undergo methylation changes in response to neuronal activity, are disproportionately affected. Based on the sequence of regions that change in methylation, we identify AP-1 and SOX2 as transcriptional regulators associated with DNA methylation changes, and we confirm these hypotheses using genome-wide chromatin immunoprecipitation (ChIP-Seq). Our findings suggest new mechanisms for the effects of polyglutamine-expanded HTT. These results also raise important questions about the potential effects of changes in DNA methylation on neurogenesis and at later stages, cognitive decline in Huntington’s patients. Overall design: mRNA-seq in STHdhQ7/Q7 and STHdhQ111/Q111 cells
Extensive changes in DNA methylation are associated with expression of mutant huntingtin.
Specimen part, Cell line, Subject
View SamplesThe Alternative Lengthening of Telomeres (ALT) pathway stimulates telomere elongation and prevents cellular senescence in approximately 60% of osteosarcoma. While the precise mechanisms underlying the ALT pathway are unclear, mutations in the chromatin remodeling protein ATRX, histone chaperone DAXX, and the histone variant H3.3, correlate with ALT status. ATRX and DAXX facilitate deposition of the histone variant H3.3 within heterochromatic regions including the telomere suggesting that loss of ATRX, DAXX, and/or H3.3 lead to defects in heterochromatin maintenance at telomeres, ultimately contributing to ALT activity. Previous studies have detected genetic mutations in ATRX, DAXX, and H3.3 in ALT cell lines and tumor samples. However, a subset of ALT samples show loss of ATRX or DAXX protein expression or localization without evidence of genetic alterations, indicating a role for other defects in ATRX/DAXX/H3.3 function. Here, using Next Generation Sequencing, we identified a novel gene fusion event between DAXX and the kinesin motor protein, KIFC3, which leads to the translation of a chimeric DAXX-KIFC3 fusion protein. Here, we demonstrate that the fusion of KIFC3 to DAXX leads to defects in DAXX function and likely perpetuates ALT activity. These data highlight a previously unrecognized mechanism of DAXX inactivation in ALT positive osteosarcoma and provide rationale for thorough and comprehensive analyses of ATRX/DAXX/H3.3 proteins in ALT positive cancers. Overall design: 13 cell lines sequenced in triplicate, totaling 39 sequencing samples
Identification of a novel gene fusion in ALT positive osteosarcoma.
Cell line, Subject
View SamplesDiet-induced obesity (DIO) predisposes individuals to insulin resistance, and adipose tissue has a major role in the disease. Insulin resistance can be induced in cultured adipocytes by a variety of treatments, but what aspects of the in vivo responses are captured by these models remains unknown. We use global RNA sequencing to investigate changes induced by TNF-a, hypoxia, dexamethasone, high insulin, and a combination of TNF-a and hypoxia, comparing the results to the changes in white adipose tissue from DIO mice. We found that different in vitro models capture distinct features of DIO adipose insulin resistance, and a combined treatment of TNF-a and hypoxia is most able to mimic the in vivo changes. Using genome-wide DNase I hypersensitivity followed by sequencing, we further examined the transcriptional regulation of TNF-a-induced insulin resistance, and we found that C/EPBß key regulator of adipose insulin resistance. Overall design: RNA-seq for 6 insulin resistance conditions and 2 control conditions, Dnase hypersensitivity-seq of 4 conditions and 1 control condition, ChIP-seq on p65 after TNFa treatment.
Analysis of in vitro insulin-resistance models and their physiological relevance to in vivo diet-induced adipose insulin resistance.
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Direct recruitment of polycomb repressive complex 1 to chromatin by core binding transcription factors.
Specimen part, Cell line
View SamplesPolycomb repressive complexes (PRCs) play key roles in developmental epigenetic regulation. Yet the mechanisms that target PRCs to specific loci in mammalian cells remain incompletely understood. In this study, we show that Bmi1, a core component of Polycomb Repressive Complex 1 (PRC1), binds directly to the Runx1/CBFbeta transcription factor complex. Genome-wide studies in megakaryocytic cells demonstrate considerable chromatin occupancy overlap between the PRC1 core component Ring1b and Runx1/CBFbeta and functional regulation of a significant fraction of commonly bound genes. Bmi1/Ring1b and Runx1/CBFbeta deficiency generate partial phenocopies of one another in vivo. We also show that Ring1b occupies key Runx1 binding sites in primary murine thymocytes and that this occurs via Polycomb Repressive Complex 2 (PRC2) independent mechanisms. Genetic depletion of Runx1 results in reduced Ring1b binding at these sites in vivo. These findings provide evidence for site-specific PRC1 chromatin recruitment by core binding transcription factors in mammalian cells.
Direct recruitment of polycomb repressive complex 1 to chromatin by core binding transcription factors.
Specimen part, Cell line
View SamplesTranscriptional dysregulation is an early feature of Huntington''s disease (HD). We observed gene-specific changes in H3K4me3 at transcriptionally repressed promoters in R6/2 mouse and human HD brain. Genome-wide analysis showed a novel chromatin signature for this mark. Reducing the levels of the H3K4 demethylase SMCX/Jarid1c in primary neurons reversed down-regulation of key neuronal genes caused by mutant Huntingtin (Htt) expression. Finally, reduction of SMCX/Jarid1c in primary neurons from BACHD mice or the single Jarid1 in a Drosophila HD model was protective. Therefore, targeting this epigenetic signature may be an effective strategy to ameliorate the consequences of HD. Overall design: mRNA-seq in wild type and R6/2 cortex and striatum at 8 and 12 weeks.
Targeting H3K4 trimethylation in Huntington disease.
Age, Specimen part, Subject
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