Project description:The transcription factor Ikaros represses Notch signaling. Since Ikaros and Notch treanscriptional mediator RBPJ both recognize sequences that contain the same core TGGGAA motif, it was hypothesized that Ikaros represses Notch signaling by targeting Notch response elements and competing with RBPJ for their binding. Here we used the mouse T-cell leukemia cell line T29 to compare the genomic binding profiles of Ikaros and RBPJ by ChIP-seq.
Project description:Background: Global DNA methylation contributes to genomic integrity by supressing repeat associated transposition events. Several chromatin factors are required in addition to DNA methyltransferases to maintain DNA methylation at intergenic and satellite repeats. Embryos lacking Lsh, a member of the SNF2 superfamily of chromatin helicases, are hypomethylated. The interaction of Lsh with the de novo methyltransferase, Dnmt3b, facilitates the deposition of DNA methylation at stem cell genes. We wished to determine if a similar targeting mechanism operates to maintain DNA methylation at repetitive sequences. Results: We used HELP-seq to map genome wide DNA methylation patterns in Lsh-/- and Dnmt3b-/- somatic cells. DNA methylation is predominantly lost from specific genomic repeats in Lsh-/- cells: LTR-retrotransposons, LINE-1 repeats and mouse satellites. RNA-seq experiments demonstrate that specific IAP (Intracisternal A-type particle) LTRs and satellites, but not LINE-1 elements, are aberrantly transcribed inLsh-/- cells. LTR hypomethylation in Dnmt3b-/- cells is moderate and hypomethylated repetitive elements (IAP, LINE-1 and satellite) are silent. Chromatin immunoprecipitation (ChIP) indicates that repressed LINE-1 elements gain H3K4me3, but H3K9me3 levels are unaltered in Lsh-/- cells, indicating that DNA hypomethylation alone is not permissive for their transcriptional activation. Mis-expressed IAPs and satellites lose H3K9me3 and gain H3K4me3 in Lsh-/- cells. Conclusions: Our study emphasizes that regulation of repetitive elements by DNA methylation is selective and context dependent. We propose a model where Lsh is specifically required at a precise developmental window to target de novo methylation to repeat sequences, which is subsequently maintained by Dnmt1 in somatic cells to enforce repeat silencing thus contributing to genomic integrity. Two pairs of genomic samples compared: WT and Lsh-/- DNA isolations from tail-tip fibroblasts; WT and Dnmt3b knockout DNA isolations from mouse embryonic fibroblasts.
Project description:The readout of genome information is controlled by transcriptional regulatory elements, but a comprehensive view of the combinatorial control by these DNA sequences, which bind regulatory protein and/or the modified histones in regulating gene transcription, is clearly preliminary. We have developed an experimental strategy for comprehensive determination of such functional elements in human DNA. This strategy involves the application of genome-wide location analysis, also known as ChIP-chip, to a panel of well-characterized regulatory proteins and histones with specific modifications, known to generally associate with transcriptional regulatory elements in vivo. Identification of their genomic binding sites will allow us to determine the sequence features in the human genome that carry out transcriptional regulatory function. We have designed and produced DNA microarrays to represent all the non-repetitive sequences in the 30 million basepair ENCODE regions of the human genome to map various types of transcriptional regulatory elements in three model cell types. We have identified promoters by mapping the genomic sequences associated with RNA polymerase II and the general transcription factor TFIID in cells, enhancer elements by mapping the genomic sequences associated with transcriptional co-activators and enhancer-specific chromatin modifications, and insulators by mapping the genomic sequences associated with the insulator binding protein CTCF. The raw microarray results are released periodically prior to publication. Keywords: ChIP-chip ENCODE
Project description:The readout of genome information is controlled by transcriptional regulatory elements, but a comprehensive view of the combinatorial control by these DNA sequences, which bind regulatory protein and/or the modified histones in regulating gene transcription, is clearly preliminary. We have developed an experimental strategy for comprehensive determination of such functional elements in human DNA. This strategy involves the application of genome-wide location analysis, also known as ChIP-chip, to a panel of well-characterized regulatory proteins and histones with specific modifications, known to generally associate with transcriptional regulatory elements in vivo. Identification of their genomic binding sites will allow us to determine the sequence features in the human genome that carry out transcriptional regulatory function. We have designed and produced DNA microarrays to represent all the non-repetitive sequences in the 30 million basepair ENCODE regions of the human genome to map various types of transcriptional regulatory elements in three model cell types. We have identified promoters by mapping the genomic sequences associated with RNA polymerase II and the general transcription factor TFIID in cells, enhancer elements by mapping the genomic sequences associated with transcriptional co-activators and enhancer-specific chromatin modifications, and insulators by mapping the genomic sequences associated with the insulator binding protein CTCF. The raw microarray results are released periodically prior to publication. Keywords: ChIP-chip ENCODE