FoxP1 “Tspans” Quiescence and Activation of Mammary Stem Cells

Stem cells can enter a reversible cell-cycle arrest state termed quiescence. In this issue of Developmental Cell , Fu et al. report that the transcription factor FoxP1 is necessary for postnatal mammary gland development and relieves Tspan8-dependent quiescence in basal mammary stem cells.