Developmental Genomics and Aging Section, Laboratory of Genetics, National Institute on Aging, Baltimore, MD 21224, USA.
In this issue of Cell Stem Cell, Pan et al. (2007) and Zhao et al. (2007) report genome-wide histone H3 trimethylations at lysines 4 and 27 in human embryonic stem (ES) cells. Similar gene sets arise via different experimental systems, advancing our understanding of stem cell epigenetics.