Hi-TrAC reveals fine-scale chromatin structures organized by transcription factors

The three-dimensional genomic structure plays a critical role in gene expression, cellular differentiation, and pathological conditions. It is pivotal to elucidate fine-scale chromatin architectures, especially interactions of regulatory elements, to understand the temporospatial regulation of gene expression. In this study, we report Hi-TrAC as a proximity ligation free, robust, and sensitive technique to profile genome-wide chromatin interactions at high-resolution among accessible regulatory elements. Hi-TrAC detects chromatin looping among accessible chromatin regions at single nucleosome resolution. With almost half-million identified loops, we constructed a comprehensive interaction network of regulatory elements across the genome. After integrating chromatin binding profiles of transcription factors, we discovered that cohesin complex and CTCF are responsible for organizing long-range chromatin loops, related to domain formation; whereas ZNF143 and HCFC1 are involved in structuring short-range chromatin loops between regulatory elements, which directly regulate gene expression. Thus, we developed a new methodology to identify a delicate and comprehensive network of cis-regulatory elements, revealing the complexity and a division of labor of TFs in chromatin looping for genome organization and gene expression.