Histone H1 depletion in mammals alters global chromatin structure but causes specific changes in gene regulation

Linker histone H1 plays an important role in chromatin folding in vitro. To study the role of H1 in vivo, mouse embryonic stem cells null for three H1 genes were derived and were found to have 50% of the normal level of H1. H1 depletion caused dramatic chromatin structure changes, including decreased global nucleosome spacing, reduced local chromatin compaction, and decreases in certain core histone modifications. Surprisingly, however, microarray analysis revealed that expression of only a small number of genes is affected. Many of the affected genes are imprinted or are on the X chromosome and are therefore normally regulated by DNA methylation. Although global DNA methylation is not changed, methylation of specific CpGs within the regulatory regions of some of the H1 regulated genes is reduced. These results indicate that linker histones can participate in epigenetic regulation of gene expression by contributing to the maintenance or establishment of specific DNA methylation patterns.