Nuclear matrix attachment regions antagonize methylation-dependent repression of long-range enhancer-promoter interactions.

Abstract

The immunoglobulin intragenic mu enhancer region acts as a locus control region that mediates transcriptional activation over large distances in germ line transformation assays. In transgenic mice, but not in transfected tissue culture cells, the activation of a variable region (V(H)) promoter by the mu enhancer is dependent on flanking nuclear matrix attachment regions (MARs). Here, we examine the effects of DNA methylation, which occurs in early mouse development, on the function of the mu enhancer and the MARs. We find that methylation of rearranged mu genes in vitro, before transfection, represses the ability of the mu enhancer to activate the V(H) promoter over the distance of 1.2 kb. However, methylation does not affect enhancer-mediated promoter activation over a distance of 150 bp. In methylated DNA templates, the mu enhancer alone induces only local chromatin remodeling, whereas in combination with MARs, the mu enhancer generates an extended domain of histone acetylation. These observations provide evidence that DNA methylation impairs the distance independence of enhancer function and thereby imposes a requirement for additional regulatory elements, such as MARs, which facilitate long-range chromatin remodeling.