Abstract
Refining transcriptional levels via active repression in an euchromatic context represents a critical regulatory process. While the molecular players of active repression are well described, their dynamics remain obscure. Here, we used snail expression dynamics as a paradigm to uncover how repression, mediated by the Snail (Sna) repressor, can be imposed within a developing tissue. Combining live imaging and mathematical modeling, we show that Sna-mediated repression is cooperative and that cooperativity is primarily mediated by the distal enhancer. Repression shifts transcription bursting dynamics from a two-state ON/OFF regime to a three-state repressed regime with two temporally distinct OFF states. Mutating Sna binding sites suggests that repression introduces the long-lasting inactive state, which is stabilized by cooperativity. Our approach offers quantitative insights into the dynamics of repression and how transcription factor cooperativity coordinates cell fate decisions within a tissue.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
1-We generated a new protein null CRISPR Sna allele to directly prove that Sna TF autoregulates its transcription in nc14 (negative feedback loop) (new Figure 1 and new Supplementary Figure 2). 2-We discovered that Sna cooperative action responsible for its auto-repression is primarily mediated by the distal enhancer (new Figure 4). 3-We dissected the bursting kinetics of Sna-mediated repression at the distal enhancer through a series of sna-distal-enhancer<MS2 transgenes, with mutations in Sna binding sites (new Figure 5). This analysis suggests that Sna-mediated repression introduces a new long inactive promoter state (long OFF, lasting minutes), linked to Sna cooperative binding. 4- we revisited our mathematical modelling predictions (new Figure 6). The criticality of high cooperativity to drive a more synchronized repression at the tissue level remains valid considering our enhanced perspective on the mechanism of Snail repressor TF action.
