Project description:Using chromatin immuno-precipitation (ChIP) combined with deep sequencing (ChIP-seq) we obtained a time resolved and genome-wide map of BMAL1 binding in mouse liver, which allowed to identify over two thousand binding sites with peak binding narrowly centered around Zeitgeber time (ZT) 6. Annotation of BMAL1 targets confirms carbohydrate and lipid metabolism as the major output of the circadian clock in mouse liver. Moreover, transcription regulators are largely overrepresented, several of which also exhibit circadian activity. Genes of the core circadian oscillator stand out as strongly bound, often at promoter and distal sites. Genomic sequence analysis of the sites identified E- boxes and tandem E1-E2 consensus elements. Electromobility shift assays (EMSA) showed that E1-E2 sites are bound by a dimer of BMAL1/CLOCK heterodimers with a spacing-dependent cooperative interaction that was further validated in transactivation assays. BMAL1 target genes showed cyclic mRNA expression profiles with a phase distribution centered at ZT10. Importantly, sites with E1-E2 elements showed tighter phases both in binding and mRNA accumulation. Finally, comparing the temporal accumulation of precursor mRNA and mature mRNA helped distinguish direct BMAL1 targets from targets with more complex regulation, and showed how transcriptional and post-transcriptional regulation contribute differentially to circadian expression phase. Together, our analysis of a dynamic protein-DNA interactome uncovered how genes of the core circadian oscillator are wired together and drive phase-specific circadian output programs in a complex tissue. ChIP-Seq of BMAL1 in mouse liver during one circadian cycle at 4 hour time resolution presented in this Series (GSE26602). mRNA profiling data used in this study are already published (Kornmann et al, PLoS Biol 2007) and have been deposited on ArrayExpress repository (accession number: E-MEXP-842).
Project description:The human osteosarcoma cell line U2OS contains a functional circadian clock but expresses only a few rhythmic genes. We identified by ChIP-seq analysis 3040 binding sites of the circadian transcription factors BMAL1, CLOCK, and CRY1 in the genome of U2OS cells, comparable to the number found in highly rhythmic tissues like liver. ChIP was performed as described previously (Rey et al, 2011; doi:10.1371/journal.pbio.1000595) using confluent desynchronized U2OS cells and BMAL1, CLOCK, and CRY1-antibodies. Immunoprecipitated chromatin (10 ng DNA of 8 independent BMAL1 ChIPs with enrichment levels > 80-fold, 9 ng DNA of a CRY1 ChIP with 10-fold enrichment, and 8 ng DNA of a CLOCK ChIP with 40-fold enrichment) was used for library preparation. Three lanes of the BMAL1 library, and one lane each of the CRY1 and CLOCK library were sequenced on the Illumina Genome Analyzer IIx using Single-Read Cluster Generation Kit and 36 Cycle Sequencing Kit v2 (Lausanne Genomics Technologies Facility).
Project description:As a circadian organ, liver executes diverse functions in different phase of the circadian clock. This process is believed to be driven by a transcription program. Here, we present a TF DNA-binding activity centered multi-dimensional proteomics landscape, including DNA-binding activity of TFs, the phosphorylation pattern, ubiquitylation pattern, the nuclear sub-proteome, the whole proteome as well as the transcriptome, to portrait the hierarchical circadian clock network of mouse liver. The TF DNA-binding activity indicates diurnal oscillation in four major pathways, immune response, glucose metabolism, fatty acid metabolism, and the cell cycle. We also isolated the mouse liver Kupffer cells and measured their proteomes in the circadian clock to reveal cell type resolved circadian clock. These are the most comprehensive datasets for circadian clock in the mouse liver and provided the richest data resource for the understanding of mouse liver physiology around the circadian clock.
Project description:As a circadian organ, liver executes diverse functions in different phase of the circadian clock. This process is believed to be driven by a transcription program. Here, we present a TF DNA-binding activity centered multi-dimensional proteomics landscape, including DNA-binding activity of TFs, the phosphorylation pattern, ubiquitylation pattern, the nuclear sub-proteome, the whole proteome as well as the transcriptome, to portrait the hierarchical circadian clock network of mouse liver. The TF DNA-binding activity indicates diurnal oscillation in four major pathways, immune response, glucose metabolism, fatty acid metabolism, and the cell cycle. We also isolated the mouse liver Kupffer cells and measured their proteomes in the circadian clock to reveal cell type resolved circadian clock. These are the most comprehensive datasets for circadian clock in the mouse liver and provided the richest data resource for the understanding of mouse liver physiology around the circadian clock.
Project description:The human osteosarcoma cell line U2OS contains a functional circadian clock but expresses only a few rhythmic genes. We identified by ChIP-seq analysis 3040 binding sites of the circadian transcription factors BMAL1, CLOCK, and CRY1 in the genome of U2OS cells, comparable to the number found in highly rhythmic tissues like liver.
Project description:The molecular clock is a transcriptional oscillator present in brain and peripheral cells that coordinates behavior and physiology with the solar cycle. Here we reveal that the clock gates insulin secretion through genome-wide transcriptional control of the pancreatic exocyst across species. Clock transcription factors bind to unique enhancer sites in cycling genes in beta cells that diverge from those in liver, revealing the dynamics of inter-tissue clock control of genomic and physiologic processes important in glucose homeostasis. ChIP-Seq in Beta-TC6 mouse beta cells
Project description:Identification of liver transcription factors binding sites by ChIP-chip using HepG2 cells. Inference of binding sites at base pair resolution was achieved by using bioinformatic tools on the generated data sets.
Project description:Over the past decade, genome-wide assays have underscored the broad sweep of circadian gene expression. A substantial fraction of the transcriptome undergoes oscillations in many organisms and tissues, which governs the many biochemical, physiological and behavioral functions under circadian control. Based predominantly on the transcription feedback loops important for core circadian timekeeping, it is commonly assumed that this widespread mRNA cycling reflects circadian transcriptional cycling. To address this issue, we directly measured dynamic changes in mouse liver transcription using Nascent-Seq. Many genes are rhythmically transcribed over the 24h day, which include precursors of several non-coding RNAs as well as the expected set of core clock genes. Surprisingly however, nascent RNA rhythms overlap poorly with mRNA abundance rhythms assayed by RNA-seq. This is because most mouse liver genes with rhythmic mRNA expression manifest poor transcriptional rhythms, indicating a prominent role of post-transcriptional regulation in setting mRNA cycling amplitude. To gain further insight into circadian transcriptional regulation, we also characterized the rhythmic transcription of liver genes targeted by the transcription factors CLOCK and BMAL1; they directly target other core clock genes and sit at the top of the molecular circadian clock hierarchy in mammals. CLK:BMAL1 rhythmically bind at the same discrete phase of the circadian cycle to all target genes, which not surprisingly have a much higher percentage of rhythmic transcription than the genome as a whole. However, there is a surprisingly heterogeneous set of cycling transcription phases of direct target genes, which even include core clock genes. This indicates a disconnect between rhythmic DNA binding and the peak of transcription, which is likely due to other transcription factors that collaborate with CLK:BMAL1. In summary, the application of Nascent-Seq to a mammalian tissue provides surprising insights into the rhythmic control of gene expression and should have broad applications beyond the analysis of circadian rhythms. Mouse liver nascent RNA profile over 6 time points of the 24h light:dark cycle, in duplicate, sequenced using Ilumina GAII (Nascent-Seq); Mouse liver mRNA profile over 6 time points of the 24h light:dark cycle, in duplicate, sequenced using Ilumina HiSeq2000 (RNA-Seq); CLK and BMAL1 DNA binding profile in the mouse liver at ZT8, sequenced along an Input sample using GAII (ChIP-Seq); Mouse liver strand-specific nascent RNA profile over 6 time points of the 24h light:dark cycle, in duplicate, sequenced using Ilumina HiSeq2000 (Strand-specific Nascent-Seq);