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"Calling Cards" for DNA-binding proteins in mammalian cells

ABSTRACT: The ability to chronicle transcription factor binding events throughout the development of an organism would facilitate mapping of transcriptional networks that control cell fate decisions. We describe a method for permanently recording protein-DNA interactions in mammalian cells. We endow transcription factors with the ability to deposit a transposon into the genome near to where they bind. The transposon becomes a “Calling Card” the transcription factor leaves behind to record its visit to the genome. The locations of the Calling Cards can be determined by massively-parallel DNA sequencing. We show that the transcription factor SP1 fused to the piggyBac transposase directs insertion of the piggyBac transposon near SP1 binding sites. The locations of transposon insertions are highly reproducible, and agree with sites of SP1-binding determined by ChIP-seq. Genes bound by SP1 are more likely to be expressed in the HCT116 cell line we used, and SP1-bound CpG islands show a strong preference to be unmethylated. This method has the potential to trace transcription factor binding throughout cellular and organismal development in a way that has heretofore not been possible.

ORGANISM(S): Homo sapiens

PROVIDER: GSE34791 | GEO | 2011/12/31

SECONDARY ACCESSION(S): PRJNA151051

REPOSITORIES: GEO

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Project description:Transcription factors direct gene expression, and so there is much interest in mapping their genome-wide binding locations. M-BM- Current methods do not allow for the multiplexed analysis of TF binding, and this limits their throughput. We describe a novel method for determining the genomic target genes of multiple transcription factors simultaneously. DNA-binding proteins are endowed with the ability to direct transposon insertions into the genome near to where they bind. The transposon becomes a M-bM-^@M-^\Calling CardM-bM-^@M-^] marking the visit of the DNA-binding protein to that location. A unique sequence M-bM-^@M-^\barcodeM-bM-^@M-^] in the transposon matches it to the DNA-binding protein that directed its insertion. The sequences of the DNA flanking the transposon (which reveal where in the genome the transposon landed) and the barcode within the transposon (which identifies the TF that put it there) are determined by massively-parallel DNA sequencing. To demonstrate the methodM-bM-^@M-^Ys feasibility, we determined the genomic targets of eight transcription factors in a single experiment. The Calling Card method promises to significantly reduce the cost and labor needed to determine the genomic targets of many transcription factors in different environmental conditions and genetic backgrounds. These data contain Ty5 insertion sites mapped by an Illumina GAII analyzer in the S. cerevisiae genome for the background strain without any Sir4 present (1 run), in strains expressing Sir4-tagged copies of three well-characterized TFs: Gal4, Leu3, and Gcn4 (1 run each), and a multiplex of eight Sir4-tagged TFs pooled in a single experiment (2 biological replicates), and insertions from the Thi2-Sir4 fusion expressed from its native locus in two conditions (1 run each). The format of each insertions file is [chromosome number] [position of genomic base] [direction of insertion] [number of reads at that position]. Raw sequencing data comes in two varieties. Paired-end data contains a 5 bp barcode at the beginning of read #2. Single-end data contains a 2 bp barcode on the beggining of read #1.

Project description:Sp1 is a transcription factor able to regulate many genes through its DNA binding domain, containing three zinc fingers. We were interested in identifying target genes regulated by Sp1, with a special emphasis to those involved in proliferation and cancer. Our approach was to treat HeLa cells with a siRNA directed against Sp1 mRNA (siSp1) to decrease the expression of Sp1 and, in turn, the genes activated by this transcription factor. Sp1 siRNA treatment led to a great number of differentially expressed genes as determined by whole genome cDNA microarray analysis. Underexpressed genes were selected since they represent putative genes activated by Sp1. These underexpressed genes were classified in six Gene Onthology categories, namely proliferation and cancer, mRNA processing, lipidic metabolism, glucidic metabolism, transcription and translation. Putative Sp1 binding sites were found in the promoters of the selected genes using the MatchTM software. After literature mining, 11 genes were selected for further validation of their expression levels using RT-real time PCR. Underexpression was confirmed for the 11 genes plus Sp1 in HeLa cells after siSp1 treatment. Additionally, EMSA and chromatin immunoprecipitation assays were performed to test for binding between Sp1 and the promoters of these genes. We observed binding of Sp1 to the promoters of RAB20, FGF21, IHPK2, ARHGAP18, NPM3, SRSF7, CALM3, PGD and Sp1 itself. Finally, the mRNA levels of RAB20, FGF21 and IHPK2, three genes related with proliferation and cancer, were determined after overexpression of Sp1 in HeLa cells, to confirm their relationship with Sp1. The aim of our study was to evaluate, by using whole genome microarrays, the effects of a siRNA against the transcription factor of Sp1 in HeLa cells. Using this methodology genes activated by Sp1 could be downregulated. The obtective was to determine new genes regulated at the cellular level. Triplicate samples were hybridized for each experimental condition (6 samples in total). The samples provided were analyzed using the specific software GeneSpring GX.

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"Calling Cards" for DNA-binding proteins in mammalian cells

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