Development of DNase I Hypersensitive Sites during Adipocyte Differentiation on a Genome-Wide Scale

Siersbæk, R. (Foredragsholder)

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The main components of the transcriptional network that controls the development of adipocytes (fat cells) from preadipocytes have now been identified, and it is clear that the peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding proteins (C/EBPs) are key regulators of this differentiation process. Recent reports from our group[1] and the Lazar group[2] have identified the binding sites for these transcription factors on a genome-wide scale. Interestingly, the two C/EBP family members C/EBPβ and C/EBPα appear to bind proximal to PPARγ early and late in differentiation, respectively, and these three transcription factors together appear to coordinate the expression of most of the proteins involved in the function of the mature adipocyte. However, it is not clear how the chromatin structure changes during adipocyte differentiation at PPARγ/C/EBP target sites and how this impacts on the binding and function of PPARγ and C/EBPs.

It is now well established that the chromatin template in which the DNA is imbedded plays a major role in the regulation of gene expression. In addition to serving as a scaffold for DNA, histone proteins, which constitute the core of the chromatin template, are subject to extensive modifications (e.g. acetylation, methylation, and phosphorylation), which may serve as docking sites for transcriptional regulators. In addition, histone modifications and remodeling factors determine the way the DNA wraps around the histones and the position of histones along the DNA, thereby regulating the accessibility of the DNA template for sequence-specific transcription factors. The susceptibility of DNA to DNase I cutting can be used as a measure of the accessibility of the chromatin template3. Chromosomal regions that have an open chromatin structure are hypersensitive to DNase I cutting and are consequently called DNase I hypersensitive sites.

In this study we investigate how the chromatin landscape3 changes during adipocyte differentiation in terms of DNase I sensitivity and correlate these changes to the binding profiles of PPARγ and C/EBPs. Specifically, we want to determine if the early binding of C/EBPβ to PPARγ/C/EBP target sites increases the DNA accessibility at these loci, thereby assisting subsequent binding by PPARγ and C/EBPα later in adipocyte differentiation.

[1] Nielsen R, Pedersen TA, Hagenbeek D, Moulos P, Siersbæk R, Megens E, Denissov S, Børgesen M, Francoijs KJ, Mandrup S, Stunnenberg HG. (2008); Genome-wide profiling of PPARγ:RXR and RNA polymerase II occupancy reveals temporal activation of distinct metabolic pathways and changes in RXR dimer composition during adipogenesis. Genes Dev.; 22(21); 2953-2967

[2] Lefterova MI, Zhang Y, Steger DJ, Schupp M, Schug J, Cristancho A, Feng D, Zhuo D, Stoeckert CJ Jr, Liu XS, Lazar MA. (2008); PPARγ and C/EBP factors orchestrate adipocyte biology via adjacent binding on a genome-wide scale. Genes Dev.; 22(21); 2941-2952

3 John,S., Sabo,P.J., Johnson,T.A., Sung,M.H., Biddie,S.C., Lightman,S.L., Voss,T.C., Davis,S.R., Meltzer,P.S., Stamatoyannopoulos,J.A., and Hager,G.L. (2008). Interaction of the glucocorticoid receptor with the global chromatin landscape. Mol. Cell 29, 611-624.

Periode25. aug. 2009
BegivenhedstitelSpetses Summer School on Nuclear Receptor Signalling: From Molecular Mechanisms to Integrative Physiology
PlaceringSpetses, Grækenland