Fig. 1

Model for the epigenetic regulation of lineage commitment within the mammary gland epithelium. Mammary stem cells (MaSC) located in the basal compartment can give rise to both the myoepithelial and luminal/alveolar lineages. Bipotent MaSCs may only be present during embryonic development and when basal stem cells are taken out of their physiological context (for example, upon dissociation and transplantation or culture). Epigenetic modifiers that have been shown to be involved in cell fate decisions are shown. Cells within the basal compartment (including stem, progenitor, and differentiated myoepithelial cells) have an epigenetic landscape that allows basal identity genes to be turned on and luminal identity genes to be turned off. Luminal progenitor cells have intermediate epigenetic features between basal and mature luminal cells. Mature luminal cells have repressive epigenetic features in basal and luminal progenitor identity genes and active epigenetic features in mature luminal identity genes. Red = repressed, orange = poised, green = active chromatin modifications. Open circles represent unmethylated promoter DNA; closed circles represent methylated promoter DNA