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Comparing genome-wide chromatin profiles using ChIP-chip or ChIP-seq

ABSTRACT: The goal of the ChIP-seq study was to investigate the distribution of the TATA-binding protein (TBP) across the human genome. TBP is the DNA-binding subunit of the basal transcription factor TFIID for RNA polymerase II (pol II) and it also participates in other complexes for the other RNA polymerase. The BTAF1 ATPase forms a stable complex with TBP and regulates its activity in pol II transcription. BTAF1 is believed to mobilize TBP from promoter and non-promoter sites. To test this hypothesis, TBP ChIP samples were prepared from human HeLa cervix carcinoma cells after knock-down of BTAF1 expression and compared to HeLa cells with a control knock-down of GAPDH. GAPDH is a cytosolic enzyme that participates in glycolysis, and its inactivation is not expected to affect the genomic distribution of TBP, and acts as negative control. ChIP samples were sequenced using SOLiD technology along with the INPUT sample to normalize the distribution of background signals within each of the two chromatin samples.

ORGANISM(S): Homo sapiens

PROVIDER: GSE17937 | GEO | 2010/03/02

SECONDARY ACCESSION(S): PRJNA119875

REPOSITORIES: GEO

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Project description:The conserved core domain of the TATA binding protein (TBP) interacts with multiple partners forming the complexes required for transcription by RNA Polymerases I, II and III. We use genetically modified mouse embryonic fibroblasts to show that many TBP core domain mutants complement loss of endogenous TBP, but this often results in a slow growth phenotype. Two TBP mutations, R188E and K243E, disrupt the TBP-BTAF1 interaction and B-TFIID complex formation. Transcriptome and ChIP-seq analyses show that loss of B-TFIID does not affect global genomic distribution of TBP, but positively or negatively affects TBP and/or RNA Polymerase II (Pol II) recruitment to a selected set of promoters. We identify a set of promoters where wild-type TBP assembles a partial inactive preinitiation complex lacking Pol II and TAF1. Our results suggest that an exchange of the B-TFIID complex in wild-type cells for TFIID in R188E and K243E mutant cells at these primed promoters recruits Pol II to activate their expression. We also observe that both Wt and mutant TBP can occupy promoters without concurrent Pol II recruitment and active transcription. Our data reveal a novel regulatory mechanism involving the formation of a partial preinitiation complex that primes the promoter for productive preinitiation complex formation in mammalian cells. Using homologous recombination, we generated ES cells and mice harbouring a null allele in the Tbp gene by insertion of a hygromycin resistance cassette in exon III and a floxed allele, in which exon III is surrounded by LoxP sites. From these mice, we generated an embryonic fibroblast Tbplox/- cell line in which TBP expression can be inactivated by expression of the Cre recombinase leading to cell death. We adopted a two-step strategy to generate Tbp-/- cell lines expressing human (h)TBP. Cells were first infected with pBABE retrovirus vectors expressing Wt hTBP or a series of mutants in the TBP core region, all of which carry a Flag-HA tag on their N-terminus. Cells expressing endogenous mTBP and exogenous hTBP were then infected with a second retrovirus expressing the 4 hydroxy-tamoxifen (OHT) inducible Cre-ERT2. Subsequently, multiple clonal populations from the OHT treated cells were isolated and genotyped by PCR to identify the Tbp-/-clones. At least two independent clones where expression of the endogenous mTBP was lost and replaced by the exogenous hTBP were isolated.

Project description:The mouse Btaf1 gene, an ortholog of yeast MOT1, encodes a highly conserved general transcription factor. The function of this SNF-2 like ATPase has been studied mainly in yeast and human cells, which has revealed that it binds directly to TBP, forming the B-TFIID complex. This complex binds to core promoters of RNA polymerase II- transcribed genes and, of crucial importance, BTAF1-TBP interactions have been shown to affect the kinetics of TBP-promoter interactions. Here we report the isolation of a mouse line carrying a Btaf1 allele containing an ENU-induced point mutation that causes a substitution mutation in the BTAF1 ATPase domain. Embryos homozygous for this loss-of-function mutation appear to be morphologically normal until early somite stages, but die between embryonic day 9 and 10.5 displaying growth arrest and edema. Analyses in vitro suggest that the altered protein is less stable and, independent from this, functionally impaired in releasing of TBP from chromatin, but not in binding to TBP. A microarray screen for genes with altered expression in the Btaf V1330M mutant as compared to WT embryos was performed with RNA from whole embryos. We compared mRNA transcripts from pools of Btaf1-/- and Btaf1+/+ embryos. Where possible, we used 3-5-somite embryos, a stage we considered to be immediately prior to the emergence of a perceptible phenotype. The experiments were done in duplo, i.e. two sets of comparisons were made: in one case stage matching (i.e. number of somites counted) was the highest priority, in the other case the pools were designed such that a maximum number of litter mates were compared while a difference of up to five somites was allowed. cDNAs were synthesized and Cy-3/Cy-5 labeled cRNAs were generated by using a Low RNA Input Fluorescent Linear Amplification Kit (Agilent Technologies, Santa Clara, CA). The labeled cRNAs were hybridized on 4X44K Agilent Whole Mouse Genome Dual Color Microarrays (G4122F). Two dye-swap experiments were performed, resulting in four individual arrays. Microarray signal and background information were retrieved with Feature Extraction (V9.5.3, Agilent technologies). All data analyses were performed by using ArrayAssist (5.5.1, Stratagene Inc, La Jolla, CA) and Microsoft Excel (Microsoft Corporation, Redmont, WA). Genetic background: C57BL/6J were mutagenized, and crossed against FVB/NJ mice for positional mapping. The background of the mice used in the experiment is hybrid C57BL/6J *FVB/NJ with a percentage FVB between 50 and 90%.

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Comparing genome-wide chromatin profiles using ChIP-chip or ChIP-seq

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