Lineage committment in mammary progenitor cells. Lineage committment in mammary progenitor cells. (A) A mammary stem cell (blue) in its niche (purple). (B) Stem cells self-renew in their niche in a process that might require GATA3. Asymmetrically dividing stem cells produce transit-amplifying (light blue) daughter cells that commit to either the basal or luminal progenitor lineages. A common progenitor for ductal and alveolar cells is depicted, although there might be two different progenitors. Induction of STAT6 in response to IL4 and IL13 induces further expression of GATA3 and possibly of c-MAF, which are required for differentiation to alveolar cells. RBPJκ is required to maintain the alveolar phenotype and suppresses differentiation along the basal lineage. Christine J. Watson, and Walid T. Khaled Development 2008;135:995-1003 © 2008.