The Polycomb repressive complexes (PRC) regulate self-renewal and differentiation in embryonic stem cells (ESCs). In this issue of "Cell Stem Cell," Morey et al. (2012) and O'Loghlen et al. (2012) report that dynamic interchange of PRC subunits modulates the balance between self-renewal and lineage commitment in ESCs.Stem Cell and Regenerative Biolog
