CpG hypomethylation in a large domain encompassing the embryonic beta-like globin genes in primitive erythrocytes.

There is little evidence addressing the role of CpG methylation in transcriptional control of genes that do not contain CpG islands. This is reflected in the ongoing debate about whether CpG methylation merely suppresses retroelements or if it also plays a role in developmental and tissue-specific gene regulation. The genes of the beta-globin locus are an important model of mammalian developmental gene regulation and do not contain CpG islands. We have analyzed the methylation status of regions in the murine beta-like globin locus in uncultured primitive and definitive erythroblasts and other cultured primary and transformed cell types. A large ( approximately 20-kb) domain is hypomethylated only in primitive erythroid cells; it extends from the region just past the locus control region to before beta-major and encompasses the embryonic genes Ey, beta h1, and beta h0. Even retrotransposons in this region are hypomethylated in primitive erythroid cells. The existence of this large developmentally regulated domain of hypomethylation supports a mechanistic role for DNA methylation in developmental regulation of globin genes.