Mammary basal cells: Stars of the show

Nearly all mammals rely on lactation to support their young and to ensure the continued survival of their species. Despite its importance, relatively little is known about how milk is produced and how it is ejected from the lumen of mammary alveoli and ducts. This review focuses on the latter. We discuss how a relatively small number of basal cells, wrapping around each alveolar unit, contract to forcibly expel milk from the alveolar lumen. We consider how individual basal cells coordinate their activity, the fate of these cells at the end of lactation and avenues for future deliberation and exploration. [Display omitted] •Mammary basal (or myoepithelial) cells are star-shaped cells that wrap around alveolar units in the lactating mammary gland.•Upon oxytocin stimulation alveolar and ductal basal cells contract to expel milk, making it available to a nursing neonate.•A number of genes and pathways have been identified as important in vivo regulators of milk ejection during lactation.•The plasticity and fate of alveolar basal cells at the end of lactation remain an area of active investigation.