Single-allele chromatin interactions identify regulatory hubs in dynamic compartmentalized domains [Hi-C]

The genome is organized into self-interacting chromatin domains containing genes and the cis-regulatory elements controlling their expression. How these domains form and how elements within them interact is unknown. We have developed Tri-C, a sensitive, high-resolution Chromosome Conformation Capture (3C) approach to identify concurrent chromatin interactions in single cells. Combining Tri-C with conventional 3C and polymer modeling, we show that, rather than folding into stable pre-formed loops, self-interacting domains form dynamic compartmentalized chromatin structures, delimited by CTCF/Cohesin boundaries. Within these tissue-specific domains, all regions of chromatin contact each other, but preferential structures are formed in which multiple enhancers and promoters interact simultaneously. Flanking CTCF/Cohesin-bound elements are excluded from these interactions and form distinct structures. These observations are best explained by a dynamic loop extrusion mechanism and subsequent stabilization of enhancer-promoter interactions, rather than the current view of long-range interactions occurring via the formation of discrete pre-formed chromatin loops. Two replicates of C57BL/6 mice erythroid cells from phenylhydrazine treated spleen, sequenced with Hi-C , and analyzed to give an intra-chromosomal interaction matrix.