A DNA signal from the Thy-1 gene defines de novo methylation patterns in embryonic stem cells.

Although DNA can be extensively methylated de novo when introduced into pluripotent cells, the CpG island in the Thy-1 gene does not become methylated either in the mouse embryo or in embryonic stem cells. A 214-base-pair region near the promoter of the Thy-1 gene protects itself as well as heterologous DNA sequences from de novo methylation. We propose that this nucleotide sequence is representative of a class of important signals that limits de novo methylation in the embryo and establishes the pattern of hypomethylated CpG dinucleotides found in somatic tissues.