Biogenesis and function of mouse mammary epithelium depends on the presence of functional alpha-catenin.

Alpha-catenin is a structural molecule and essential to the function of epithelial adherens junctions. Its role in the morphogenesis of mammary epithelium was explored using experimental mouse genetics. Since loss of alpha-catenin in mice leads to embryonic lethality, the alpha-catenin gene was flanked by loxP sites and inactivated in mammary epithelium using the WAP-Cre and MMTV-Cre transgenes. Loss of alpha-catenin arrested alveolar epithelial expansion. These cells lacked proper polarity and markers of functional differentiation, which resulted in impaired milk protein gene expression. Without alpha-catenin, increased epithelial cell death was observed at parturition and the tissue resembled an involuted gland that is normally observed after weaning. Lastly, no tumors were detected in mammary tissue lacking alpha-catenin.