Extensive Chromatin Remodeling and Establishment of Transcription Factor 'Hotspots' during Early Adipogenesis. Mus musculus

Adipogenesis is tightly controlled by a complex network of transcription factors acting at different stages of differentiation. Peroxisome proliferator-activated receptor gamma (PPAR gamma) and CCAAT/enhancer binding protein (C/EBP) family members are key regulators of this process. We have employed DNase I hypersensitive site analysis to investigate the genome-wide changes in chromatin structure that accompany the binding of adipogenic transcription factors. These analyses revealed a dramatic and dynamic modulation of the chromatin landscape during the first hours of adipocyte differentiation that coincides with cooperative binding of multiple early transcription factors (including glucocorticoid receptor, retinoid X receptor, Stat5a, C/EBPbeta and -delta) to transcription factor 'hotspots'. Our results demonstrate that C/EBPbeta marks a large number of these transcription factor 'hotspots' prior to induction of differentiation and chromatin remodeling and is required for their establishment. Furthermore, a subset of early remodeled C/EBP binding sites persists throughout differentiation and is later occupied by PPAR gamma , indicating that early C/EBP family members, in addition to their well established role in activation of PPAR gamma transcription, may act as pioneering factors for PPAR gamma binding. Overall design: DNase I hypersensitive chromatin regions and transcription factor binding sites were identified at various time points of 3T3-L1 differentiation using DHS-seq and ChIP-seq, respectively.