SRA

The genome is organized via CTCF/cohesin binding sites, which partition chromosomes into 1-5Mb topologically associated domains (TADs), and further into smaller contact sub-domains within TADs (sub-TADs; 40-1000kb). Here we examined in vivo an ~80kb sub-TAD, containing the mouse a-globin gene cluster, lying within a ~1Mb TAD. We find that the sub-TAD is flanked by predominantly convergent CTCF/cohesin sites which are ubiquitously bound by CTCF but only interact during erythropoiesis, defining a self-interacting erythroid compartment. Whereas the a-globin regulatory elements normally act solely on promoters downstream of the enhancers, removal of a conserved upstream CTCF/cohesin boundary extends the sub-TAD to the adjacent upstream CTCF/cohesin binding site. The a-globin enhancers now interact with the flanking chromatin, upregulating expression of genes within this extended sub-TAD. Rather than acting solely as a barrier to chromatin modification, CTCF/cohesin boundaries in this sub-TAD regulate both directionality and specificity of enhancer interactions with surrounding promoters. Overall design: ATAC-seq on chromatin isolated from primary erythroid ter119+ cells obtained from the spleens of acetylphenylhydrazine treated mice. Wild-type C57BL/6 mice were comparied with mice containing deletions for HS-29 (D29) or HS-38 and/or HS-39 (D38, D39,D3839) CTCF binding sites. Experiments are performed in duplicate in mutant and WT mice.