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Regulatory Changes in Glioblastoma Brain Tumors and Xenografts

ABSTRACT:

Non-coding elements in our genomes that play critical roles in complex disease are frequently marked by highly unstable RNA species. Sequencing nascent RNAs attached to an actively transcribing RNA polymerase complex can identify unstable RNAs, including those templated from gene-distal enhancers (eRNAs). However, nascent RNA sequencing techniques remain challenging to apply in some cell lines and especially to intact tissues, limiting broad applications in fields such as cancer genomics and personalized medicine. Here we report the development of chromatin run-on and sequencing (ChRO-seq), a novel run-on technology that maps the location of RNA polymerase using virtually any frozen tissue sample, including samples with degraded RNA that are intractable to conventional RNA-seq. We used ChRO-seq to develop the first maps of nascent transcription in 23 human glioblastoma (GBM) brain tumors and patient derived xenografts. Remarkably, >90,000 distal enhancers discovered using the signature of eRNA biogenesis within primary GBMs closely resemble those found in the normal human brain, and diverge substantially from GBM cell models. Despite extensive overall similarity, 12% of enhancers in each GBM distinguish normal and malignant brain tissue. These enhancers drive regulatory programs similar to the developing nervous system and are enriched for transcription factor binding sites that specify a stem-like cell fate. These results demonstrate that GBMs largely retain the enhancer landscape associated with their tissue of origin, but selectively adopt regulatory programs that are responsible for driving stem-like cell properties. We also identified enhancers and their associated transcription factors that regulate genes characteristic of each known GBM subtype, and discovered a core group of transcription factors that control the expression of genes associated with clinical outcomes. This study uncovers new insights into the molecular etiology of GBM and introduces ChRO-seq which can now be used to map regulatory programs contributing to a variety of complex diseases.

PROVIDER: phs001646 | dbGaP |

REPOSITORIES: dbGaP

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			Action	DRS
	GapExchange_phs001646.v1.p1.xml	Xml
	dbGaPEx2.1.5.xsd	Other
	Study_Report.phs001646.GB_Tumors_Xenografts.v1.p1.MULTI.pdf	Pdf
	manifest_phs001646.GB_Tumors_Xenografts.v1.p1.c1.DS-BT-IRB.pdf	Pdf
	datadict_v2.xsl	Other

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Project description:During development histone modifying enzymes are required for cell identity and lineage commitment, however little is known about the regulatory origins of the epigenome during embryonic development. Here we generate a comprehensive set of embryonic epigenome reference maps, which we use to determine the extent to which maternal factors shape chromatin state in Xenopus embryos. Using Î±-amanitin to inhibit zygotic transcription, we find that the majority of H3K4me3 and H3K27me3-enriched regions form a maternally defined epigenetic regulatory space with an underlying logic of hypomethylated islands. This maternal regulatory space extends to a substantial proportion of neurula stage-activated promoters. In contrast, p300-recruitment to distal regulatory regions requires embryonic transcription at most loci. The results show that H3K4me3 and H3K27me3 are part of a regulatory space that exerts an extended maternal control well into post-gastrulation development, and highlight the combinatorial action of maternal and zygotic factors through proximal and distal regulatory sequences. We have performed ChIP-sequencing of eight histone modifications, RNA polymerase II (RNAPII) and the enhancer protein p300 at five stages of development: blastula (st. 9), gastrula (st. 10.5, 12.5), neurula (st. 16) and tailbud (st. 30). These experiments allow identification of enhancers (H3K4me1, p300), promoters (H3K4me3, H3K9ac), transcribed regions (H3K36me3, RNAPII) and repressed and heterochromatic domains (H3K27me3, H3K9me2, H3K9me3, H4K20me3). In addition we generated pre-MBT (st. 8) maps for three histone modifications (H3K4me3, H3K9ac, H3K27me3) and single-base resolution DNA methylome maps using whole genome bisulfite sequencing of blastula and gastrula (st. 9 and 10.5) embryos. To determine the maternal and zygotic contributions to chromatin state, we used alpha-amanitin to block embryonic transcription. Fertilised eggs were injected with 2.3 nl of 2.67 ng/ul alpha-amanitin and developed until the control embryos reached mid-gastrulation. Alpha-amanitin and control embryos were used for RNA-seq and ChIP-seq of RNAPII, H3K4me3, H3K27me3 and p300. For all ChIP-seq samples of the epigenome reference maps and RNAPII ChIP-seq samples of the Î±-amanitin experiments three biological replicates of different chromatin isolations of 45 embryos were pooled. Two biological replicates for H3K4me3 (Î±-amanitin injected: resp. 90 and 56 embryo equivalents (eeq); control: resp. 45 and 67 eeq), H3K27me3 (Î±-amanitin injected: resp. 90 and 180 eeq; control: resp. 45 and 202 eeq) and p300 (Î±-amanitin injected: resp. 112 and 56 eeq; control: resp. 112 and 67 eeq) ChIP-seq samples of the Î±-amanitin experiments were generated. For RNA-seq samples of the Î±-amanitin experiments RNA from 5 embryos from one biological replicate was isolated and depleted of ribosomal RNA

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Regulatory Changes in Glioblastoma Brain Tumors and Xenografts

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