DNASE I HYPERSENSITIVE SITES IN THE CHROMATIN OF THE CHICKEN MSX2 GENE DIFFER IN ANTERIOR AND POSTERIOR LIMB MESENCHYME, CALVARIAL OSTEOBLASTS AND EMBRYONIC FIBROBLASTS

To identify candidate cis-acting regulatory regions involved in regula tion of the Msx2 gene in anterior limb mesenchyme and calvarial osteob lasts, DNase I hypersensitive sites (DHSs) from -6.1 kb to +8.4 kb rel ative to the translation start site of the chicken Msx2 gene were iden tified in anterior and posterior limb mesenchyme, calvarial osteoblast s, and embryonic fibroblasts. A total of 12 DHSs were detected. Except for the DHS in the basal promoter region, none of the other DHSs were present in all four tissues, suggesting that the chromatin structure in the Msx2 gene locus is differently organized in these four cell typ es. One DHS was unique to Msx2 expressing cells and a second site to n onexpressing cells. Anterior and posterior limb mesenchyme had similar patterns of DHSs that were much more complex than observed in calvari al osteoblasts possibly reflecting differences in the complexity of Ms x2 regulation in these two tissues.