Matrix Attachment Region-Dependent Function of the Immunoglobulin μ Enhancer Involves Histone Acetylation at a Distance without Changes in Enhancer Occupancy

Abstract

Nuclear matrix attachment regions (MARs), which flank the immunoglobulin μ heavy-chain enhancer on either side, are required for the activation of the distal variable-region (V_H) promoter in transgenic mice. Previously, we have shown that the MARs extend a local domain of chromatin accessibility at the μ enhancer to more distal sites. In this report, we examine the influence of MARs on the formation of a nucleoprotein complex at the enhancer and on the acetylation of histones, which have both been implicated in contributing to chromatin accessibility. By in vivo footprint analysis of transgenic μ gene constructs, we show that the occupancy of factor-binding sites at the μ enhancer is similar in transcriptionally active wild-type and transcriptionally inactive ΔMAR genes. Chromatin immunoprecipitation experiments indicate, however, that the acetylation of histones at enhancer-distal nucleosomes is enhanced 10-fold in the presence of MARs, whereas the levels of histone acetylation at enhancer-proximal nucleosomes are similar for wild-type and ΔMAR genes. Taken together, these data indicate that the function of MARs in mediating long-range chromatin accessibility and transcriptional activation of the V_Hpromoter involves the generation of an extended domain of histone acetylation, independent of changes in the occupancy of the μ enhancer.

ACKNOWLEDGMENTS

We thank W. C. Forrester for valuable discussions. L.A.F. especially thanks Juan Galceran and Mikael Sigvardsson for their continued help and support.

L.A.F. and M.W. were holders of postdoctoral fellowships from M.E.C. of Spain and from DFG of Germany, respectively. This work was funded by a grant from the National Institutes of Health to Rudolf Grosschedl.