Gene Regulation: Activation through Space Felix Muerdter, Alexander Stark  Current Biology  Volume 26, Issue 19, Pages R895-R898 (October 2016) DOI: 10.1016/j.cub.2016.08.031 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 Enhancers and transcription bursts. Schematic view of genes activated by a weak and a strong enhancer, respectively, and the corresponding transcriptional activity profiles. Fukaya, Lim and Levine [6] report that the overall transcription rates set by different developmental enhancers in the Drosophila embryo correlate with the frequency of transcriptional bursts but not with the burst amplitudes. The number of transcripts per burst is visualized here by the number of Pol II molecules (termed Pol II convoys in Tantale et al. [7]). Note that Fukaya, Lim and Levine tested enhancers downstream of the reporter genes, leading to a situation in which they are likely traversed by the polymerase convoys. Nonetheless, bursting is equivalently observed when weaker enhancers are placed upstream of the core promoter (Michael Levine, personal communication). Current Biology 2016 26, R895-R898DOI: (10.1016/j.cub.2016.08.031) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 2 Models of enhancer function. Models of enhancer–core-promoter communication by looping-mediated, direct protein–protein contacts (A) versus an enhancer-based activating micro-environment within TAD-like chromatin domains (B). This environment could be mediated by diffusible activators at potentially very high local concentrations (indicated in red). Only the latter is consistent with coordinated rather than mutually exclusive transcriptional bursting as seen by Fukaya, Lim and Levine [6] (CP1, core promoter 1; CP2, core promoter 2). Current Biology 2016 26, R895-R898DOI: (10.1016/j.cub.2016.08.031) Copyright © 2016 Elsevier Ltd Terms and Conditions