Cell Polarity in Mammary Gland Morphogenesis and Breast Cancer

Epithelial cells form organized structures such as tubes and alveoli, the organization of which is controlled by conserved complexes of polarity proteins. Mammary gland development requires extensive epithelial remodeling coordinated with proliferation and apoptosis to generate the highly branched epithelial ductal network that extends into a complex fatty stroma. Mammary epithelial cells dynamically regulate cell polarity during branching morphogenesis, and therefore the mammary gland represents a unique model to understand epithelial remodeling during normal development. Moreover, the mammary gland undergoes extensive remodeling during the progression of breast cancer, which is associated with a loss of apical-basal polarity and epithelial organization. In this chapter, we present the mammary gland as a model to understand unique roles for polarity proteins in epithelial remodeling. We also discuss novel signaling pathways regulated by polarity proteins that function in normal mammary gland development, as well as breast cancer initiation, invasion, and metastasis.