DNase I-hypersensitive sites surround the mouse acetylcholine receptor delta-subunit gene

The mouse skeletal muscle acetylcholine receptor is regulated, at least in part, by transcriptional mechanisms. As a first step toward defining the cis- and trans-acting factors involved in acetylcholine receptor transcriptional regulation, we examined mouse muscle and fibroblast cells for the presence of DNase I-hypersensitive sites in the chromatin surrounding the delta-subunit gene. We detect six DNase I-hypersensitive sites in muscle DNA blots hybridized with a mouse delta-subunit cDNA. Two hypersensitive sites lie distantly 5' to the delta gene, one lies near the 5' end of the delta gene, one lies near its 3' end, and two hypersensitive sites lie distantly 3'. The pair of distantly 3' hypersensitive sites should by analogy to chicken and human genomes lie near the gamma-subunit gene. Only the distantly 5' pair of hypersensitive sites is present in fibroblasts; the remainder is muscle specific. Two hypersensitive sites, one at the 3' end of the delta gene and one distantly 3', appear only after terminal muscle differentiation and, therefore, are developmentally regulated, similarly to receptor subunit mRNAs. All four muscle-specific hypersensitive sites are excellent candidates for regulatory loci for the delta- and gamma-subunit genes of mouse acetylcholine receptor.