Epigenetic status of human embryonic stem cells.

We examined the allele-specific expression of six imprinted genes and the methylation profiles of three imprinting control regions to assess the epigenetic status of human embryonic stem cells. We identified generally monoallelic gene expression and normal methylation patterns. During prolonged passage, one cell line became biallelic with respect to H19, but without loss of the gametic methylation imprint. These data argue for a substantial degree of epigenetic stability in human embryonic stem cells.