Characterization of GJB2 cis-regulatory elements in the DFNB1 locus

Although most disease-causing variants are within coding region of genes, it is now well established that cis-acting regulatory sequences, depending on 3D-chromatin organization, are required for temporal and spatial control of gene expression. Disruptions of such regulatory elements and/or chromatin conformation are likely to play a critical role in human genetic disease. Hence, recurrent monoallelic cases of the most common hereditary type of nonsyndromic hearing loss (i.e. DFNB1) carrying out only one identified pathogenic allele, led to strongly suggest the presence of uncharacterized distal cis-acting elements in the missing allele. Herewith, we study the spatial organization of a large DFNB1 locus encompassing the gap junction protein beta 2 (GJB2) gene, the most frequently mutated gene in this inherited hearing loss, with the chromosome conformation capture carbon copy technology (5C). By combining this approach with functional activity reporter assays and mapping of CCCTC-binding factor (CTCF) along the DFNB1 locus by quantitative real-time PCR chromatin immunoprecipitation, we identify a novel set of cooperating GJB2 cis-acting elements and propose a DFNB1 three-dimensional looping regulation model. A loop chromatin forming, allows bringing closer enhancers to the GJB2 promoter, but also avoids GJB2 silencing with an enhancer-blocking insulator activity. Overall design: We mapped the interaction profile of the GJB2 promoter within the 1025 kb DFNB1 locus with 5C-seq in five HNEC samples isolated from healthy different individuals.