Laminin-binding integrins are essential for the maintenance of functional secretory epithelium in lactation

Integrin dimers α3/β1, α6/β1 and α6/β4 are the mammary epithelial cell receptors for laminins, which are major components of the basement membrane, a specialized extracellular matrix surrounding the mammary epithelium. The roles of specific basement membrane components and their integrin receptors in the regulation of functional gland development have not been analyzed in detail. To investigate the functions of laminin-binding integrins, we obtained mutant mice with mammary luminal cell-specific deficiencies of the α3 and α6 integrin chains generated by the Cre-Lox approach. During pregnancy, mutant mice displayed low levels of luminal progenitor activity and retarded lobulo-alveolar development, whereas their mammary glands seemed to be functional at the onset of lactation. Myoepithelial cell morphology was markedly altered in mutant glands, suggesting cellular compensation mechanisms involving cytoskeleton reorganization. However, lactation was not sustained in mutant mice, and the glands underwent precocious involution. Inactivation of the p53 gene rescued the growth defects but did not restore lactogenesis in mutant mice. This study reveals an essential role for laminin-binding integrins in functional mammary gland development. Ctrl basal cells (4 biological replicates) /a3a6KO basal cells (3 biological replicates)