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Dynamics of SREBP1 binding to DNA in mouse liver

ABSTRACT: To systematically understand how the circadian clock and the nutrient-driven rhythm integrate to regulate SREBP1 activity, we evaluated genome-wide the binding of SREBP1 to its targets along the day in wild-type (WT) C57BL/6mice. The recruitment of SREBP1 to the DNA showed a highly circadian behaviour, with a maximum during the fed status. However, the temporal expression of SREBP1 targets was not always synchronized with its binding. In particular, a different phase of expression was observed for SREBP1 target genes depending on their function, suggesting the involvement of other transcription factors in their regulation. The proper temporal expression pattern of these genes was dramatically changed in Bmal1KO mice upon time-restricted feeding, in spite of the rhythmic, although slightly delayed, binding of SREBP1. Our results show that besides the nutrient-driven regulation of SREBP1 nuclear translocation, a second layer of modulation of SREBP1 transcriptional activity exists and is strongly dependent from the circadian core clock. This system allows to fine tune the expression timing of SREBP1 target genes, thus helping to temporally separate the different physiological processes in which these genes are involved.

ORGANISM(S): Mus musculus

PROVIDER: GSE48375 | GEO | 2014/03/10

SECONDARY ACCESSION(S): PRJNA209935

REPOSITORIES: GEO

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Project description:Circadian rhythms are daily oscillations in metabolism and physiology and are generated by the circadian clock. In fruit fly Drosophila, the circadian clock is generated by a transcription-translation feedback loop in which the positive arm components Clock and Cycle activate the expression of the Period and Timeless genes of negative arm, as well as other circadian clock-regulated genes. After being retained in the cytoplasm, the Period and Timeless proteins then migrate to the nucleus to inhibit the Clock/Cycle transactivity by protein-protein interactions (PPIs). The endogenous circadian clock is synchronized with the geological (solar) clock via photoreceptors. Drosophila Cryptochrome protein functions as a circadian photoreceptor. In the early morning, exposure of Cryptochrome to light causes a conformational change in it which results in the formation of new PPIs. Light-activated Cryptochrome interacts with the core clock protein Timeless and the E3 ubiquitin ligase-substrate adaptor protein Jetlag, which results in the ubiquitylation of Timeless by Jetlag-E3 ligase complex and then degradation of Timeless within minutes by proteasome system. Rapid degradation of Timeless and then its partner protein Period, because of its instability in the absence of Timeless, relieves the inhibition on the Clock/Cycle transcription factors suddenly. Therefore, Clock/Cycle-driven expression of circadian clock-regulated genes are induced again, which is the restart of the circadian oscillation or the resetting of the clock. Following Timeless degradation, Cryptochrome is also degraded so the photoreceptor mechanism does not start a new resetting signal until all the required factors are re-synthesized in a circadian manner. Light-dependent degradation of Drosophila Cryptochrome can be observed in Drosophila S2 cell line in culture. In this project, we aimed at finding the interactome of Cryptochrome protein in Drosophila S2 cell line under light and in the dark using proximity labeling method. Because of the fast kinetics of Cryptochrome degradation, we chose the enzymes that can saturate in less than one hour. TurboID (TID) and APEX2 enzymes label proteins with biotin in the proximity even though they work with different mechanisms. They were fused to Cryptochrome protein, and proximity labeling was performed in the dark or under light. We have identified novel light-dependent or -independent interactors of Drosophila Cryptochrome and confirmed some of them using classical coimmunoprecipitation technique.

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Dynamics of SREBP1 binding to DNA in mouse liver

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