Single-cell response to LPS of wild-type and cohesin-deficient macrophages.

Transcription is an intermittent process that occurs in bursts. The frequency and the number of messenger RNA (mRNA) produced by these bursts determine expression levels and shape cell-to-cell variability. Productive encounters between enhancers and promoters control burst dynamics, which the cohesin complex can facilitate through loop extrusion. Cohesin is a ring-shaped complex involved in enhancer-promoter interactions. Without cohesin, bone-marrow-derived macrophages' transcriptional response to LPS is severely impaired (Cuartero et al., 2018). Single-cell RNA sequencing (scRNAseq) showed that the frequency of cells expressing inducible transcripts (as defined in Bhatt et al., 2012) was reduced in cohesion-deficient macrophages before and after LPS stimulation. In contrast, when considering only cells expressing LPS-inducible transcripts, cohesin-deficient macrophages showed reduced mean expression at baseline and late LPS-response (8h) but not in the early response (2h). These results support a model where cohesin is implicated in the control of burst frequencies upon LPS. scRNAseq data of untreated and LPS-stimulated WT and Rad21-/- primary mouse macrophages.