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Interactions between transcriptional promoters and their distal regulatory elements play an important role in transcriptional regulation; however, the extent to which these interactions are subject to rapid modulations in response to signals is unknown. Here, we use promoter capture Hi-C to demonstrate a rapid reorganization of promoter-anchored chromatin loops within 4 hr after inducing differentiation of 3T3-L1 preadipocytes. The establishment of new promoter-enhancer loops is tightly coupled to activation of poised (histone H3 lysine 4 mono- and dimethylated) enhancers, as evidenced by the acquisition of histone H3 lysine 27 acetylation and the binding of MED1, SMC1, and P300 proteins to these regions, as well as to activation of target genes. Intriguingly, formation of loops connecting activated enhancers and promoters is also associated with extensive recruitment of corepressors such as NCoR and HDACs, indicating that this class of coregulators may play a previously unrecognized role during enhancer activation., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Transcription factors have recently been shown to colocalize in hotspot regions of the genome, which are further clustered into super-enhancers. However, the detailed molecular organization of transcription factors at hotspot regions is poorly defined. Here, we have used digital genomic footprinting to precisely define factor localization at a genome-wide level during the early phase of 3T3-L1 adipocyte differentiation, which allows us to obtain detailed molecular insight into how transcription factors target hotspots. We demonstrate the formation of ATF-C/EBP heterodimers at a composite motif on chromatin, and we suggest that this may be a general mechanism for integrating external signals on chromatin. Furthermore, we find evidence of extensive recruitment of transcription factors to hotspots through alternative mechanisms not involving their known motifs and demonstrate that these alternative binding events are functionally important for hotspot formation and activity. Taken together, these findings provide a framework for understanding transcription factor cooperativity in hotspots., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)

It is becoming increasingly clear that transcription factors operate in complex networks through thousands of genomic binding sites, many of which bind several transcription factors. However, the extent and mechanisms of crosstalk between transcription factors at these hotspots remain unclear. Using a combination of advanced proteomics and genomics approaches, we identify ∼12,000 transcription factor hotspots (∼400 bp) in the early phase of adipogenesis, and we find evidence of both simultaneous and sequential binding of transcription factors at these regions. We demonstrate that hotspots are highly enriched in large super-enhancer regions (several kilobases), which drive the early adipogenic reprogramming of gene expression. Our results indicate that cooperativity between transcription factors at the level of hotspots as well as super-enhancers is very important for enhancer activity and transcriptional reprogramming. Thus, hotspots and super-enhancers constitute important regulatory hubs that serve to integrate external stimuli on chromatin., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)