Project description:Despite being expressed in most tissues, a number of mammalian process-specific transcriptional regulators, such as those involved in cell cycle and immune responses, often have profound tissue-specific phenotypes. The mechanism underlying this effect is poorly understood. We chose to investigate on a genome-wide basis how the cell cycle master regulator E2F4, a key regulator of proliferation and differentiation in G0 cells, controls gene expression in multiple mammalian tissues. We identified potential direct targets of E2F4 in primary mouse and human tissues using chromatin immunoprecipitation. E2F4 binds a core set of genes in most mouse tissues that includes a substantial number of previously identified direct targets, and these common targets are highly enriched in the canonical binding sequence. Comparison of the genes bound in mouse tissues versus those bound in comparable human tissues revealed that, consistent with previous results, a core set of targets was bound in both species, and contains a substantial overrepresentation of cell-cycle genes.
Project description:Genome-wide chromatin-immunoprecipitation (ChIP-chip) detects binding of transcriptional regulators to DNA in vivo at low resolution. Motif discovery algorithms can be used to discover sequence patterns in the bound regions that may be recognized by the immunoprecipitated protein. However, the discovered motifs often do not agree with the binding specificity of the protein, when it is known. RESULTS: We present a powerful approach to analyzing ChIP-chip data, called THEME, that tests hypotheses concerning the sequence specificity of a protein. Hypotheses are refined using constrained local optimization. Cross-validation provides a principled standard for selecting the optimal weighting of the hypothesis and the ChIP-chip data and for choosing the best refined hypothesis. We demonstrate how to derive hypotheses for proteins from 36 domain families. Using THEME together with these hypotheses, we analyze ChIP-chip datasets for 14 human and mouse proteins. In all the cases the identified motifs are consistent with the published data with regard to the binding specificity of the proteins.
Project description:An experiment was performed to understand its role in cell type specification, we have determined the human genomic binding sites of MLL1. MLL1 localizes with Pol II to the 5' end of actively transcribed genes, where histone H3 lysine 4 (H3-K4) trimethylation occurs. The ability of MLL1 to serve as a start site-specific global transcriptional regulator and to participate in larger chromatin domains at the Hox genes reveals the dual roles MLL1 plays in maintenance of cellular identity.
Project description:Hormones and nutrients often induce genetic programs via signaling pathways that interface with gene-specific activators. Activation of the cAMP pathway, for example, stimulates cellular gene expression by means of the PKA-mediated phosphorylation of cAMP-response element binding protein (CREB) at Ser-133. Here, we use genome-wide approaches to characterize target genes that are regulated by CREB in different cellular contexts. CREB was found to occupy approximately 4,000 promoter sites in vivo, depending on the presence and methylation state of consensus cAMP response elements near the promoter. The profiles for CREB occupancy were very similar in different human tissues, and exposure to a cAMP agonist stimulated CREB phosphorylation over a majority of these sites. Only a small proportion of CREB target genes was induced by cAMP in any cell type, however, due in part to the preferential recruitment of the coactivator CREB-binding protein to those promoters. These results indicate that CREB phosphorylation alone is not a reliable predictor of target gene activation and that additional CREB regulatory partners are required for recruitment of the transcriptional apparatus to the promoter.
Project description:The NF-KappaB family of transcription factors plays a critical role in numerous cellular processes, particularly the immune response. Our understanding of how the different NF-kappaB subunits act coordinately to regulate gene expression is based on a limited set of genes. We used genome-scale location analysis to identify targets of all five NF-kappaB proteins before and after stimulation of monocytic cells with bacterial lipopolysaccharide (LPS). In unstimulated cells, p50 and p52 bound to a significant number of gene promoters. p50 occupied genes together with RNA polymerase II and defined a set of genes to which other NF-kappaB proteins bound after LPS induction. In stimulated cells, genes bound by multiple NF-kappaB subunits exhibited the greatest increases in RNA polymerase II occupancy and gene expression. This study identifies novel NF-kappaB target genes, reveals how the different NF-kappaB proteins coordinate their activity and maps transcriptional regulatory networks that underlie the host response to infection.