Unknown,Transcriptomics,Genomics,Proteomics

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SnoRNAs are a novel class of biologically relevant Myc targets

ABSTRACT: Myc proteins are essential regulators of animal growth during normal development, and their deregulation is one of the main driving factors of human malignancies. They function as transcription factors that (in vertebrates) control many growth- and proliferation-associated genes, and in some contexts contribute to global gene regulation. We combine ChIPseq and RNAseq approaches in Drosophila tissue culture cells to identify a core set of less than 500 Myc target genes, whose salient function resides in the control of ribosome biogenesis. Amongst these genes we find the non-coding snoRNA genes as a large novel class of Myc targets. All assayed snoRNAs are affected by Myc, and many of them are subject to direct transcriptional activation by Myc, both in Drosophila and in vertebrates. The loss of snoRNAs impairs growth during normal development, whereas their overexpression increases tumor mass in a model for neuronal tumors. This work shows that Myc acts as a master regulator of snoRNP biogenesis. In addition, in combination with recent observations of snoRNA involvement in human cancer, it raises the possibility that Myc’s transforming effects are partially mediated by this class of non-coding transcripts.

INSTRUMENT(S): Illumina Genome Analyzer IIx

ORGANISM(S): Drosophila melanogaster

SUBMITTER: Peter Gallant

PROVIDER: E-MTAB-3209 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Eukaryotic circadian clocks include transcriptional/translational feedback loops that drive 24-hour rhythms of transcription.These transcriptional rhythms underlie oscillations of protein abundance, thereby mediating circadian rhythms of behavior, physiology, and metabolism. Numerous studies over the last decade have employed microarrays to profile circadian transcriptional rhythms in various organisms and tissues. Here we use RNA sequencing (RNA-Seq) to profile the circadian transcriptome of *Drosophila melanogaster* brain from wild-type and *period*-null clock-defective animals. We identify several hundred transcripts whose abundance oscillates with 24-hour periods, including a number of non-coding RNAs (ncRNAs) that were not identified in previous microarray studies. Of particular interest are *U snoRNA host genes* (*Uhgs*), a family of cycling ncRNAs that encode the precursors of over 50 box C/D snoRNAs, key regulators of ribosomal biogenesis. Transcriptional profiling at the level of individual exons reveals alternative splice isoforms for many genes whose relative abundances are regulated by either *period* or circadian time, although the effect of circadian time is muted in comparison to that of *period*. Interestingly, *period* loss-of-function significantly alters the frequency of RNA editing at a number of editing sites, suggesting an unexpected link between a key circadian gene and RNA editing. We also identify tens of thousands of novel splicing events beyond those previously annotated by the modENCODE consortium, including several that affect key circadian genes. These studies demonstrate extensive circadian control of ncRNA expression, reveal the extent of clock control of alternative splicing and RNA editing, and provide a novel, genome-wide map of splicing in *Drosophila* brain. RNA-Seq transcriptional profiling of Drosophila brains from wildtype and period loss-of-function (per0) flies with time points taken over two days in constant darkness. Time points at CT24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, and 68. 10-12 brains per time point.

Project description:Background: MYC is a transcription factor encoded by the c-MYC gene (thereafter termed MYC). MYC is key transcription factor involved in many central cellular processes including ribosomal biogenesis. MYC is overexpressed in the majority of human tumours including aggressive B-cell lymphoma especially Burkitt's lymphoma. Although Burkitt's lymphoma is a highlight example for MYC overexpression due to a chromosomal translocation, no global analysis of MYC binding sites by chromatin immunoprecipitation (ChIP) followed by global next generation sequencing (ChIP-Seq) has been conducted so far in Burkitt's lymphoma. Methodology/Principal Findings: ChIP-Seq was performed with a MYC-specific antibody giving rise to 7,054 predicted MYC binding sites after bioinformatics analysis of a total of 19 million sequence reads. In line with previous findings, binding sites accumulate in gene sets known to be involved in the ribosomal biogenesis, histone acetyltransferase and methyltransferase complexes and the cell cycle demonstrating a regulatory role of MYC in these processes. Unexpectedly, MYC binding sites also accumulate in genes typically expressed in mature B-cells. To assess the functional consequences of altered MYC binding, the ChIP-Seq data were supplemented with siRNA mediated knock-downs of MYC in BL cell lines followed by gene expression profiling. Interestingly, amongst others, genes involved in B-cell function were up-regulated in response to MYC silencing. Conclusion/Significance: The 7,054 MYC-binding sites identified by our ChIP-Seq approach greatly extend the knowledge regarding MYC binding in Burkitt's lymphoma and sheds further light on the enormous complexity of the MYC regulatory network. Especially our observation that (i) many B-cell relevant genes are targeted by MYC and (ii) that MYC down-regulation leads to an up-regulation of B-cell genes highlights an interesting aspect of BurkittM-BM-4s lymphoma biology. [ChIP-Seq] Analysis of MYC DNA binding sites by ChiP-Seq in 5 BurkittM-BM-4s lymphoma cell lines (Raji, Ramos, Blue1, BL41, CA46) [mRNA expression profiling] siRNA-mediated knock-down of MYC was done employing the BL cell lines Raji, BL41 and Blue1 in order to detect MYC-driven gene expression changes. For this purpose, the cells were Amaxa-transfected using MYC smart pool siRNA and control siRNA (Thermo Scientific/Dharmacon, Erembodegem, Belgium), respectively.

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SnoRNAs are a novel class of biologically relevant Myc targets

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