The estrogen-responsive Agr2 gene regulates mammary epithelial proliferation and facilitates lobuloalveolar development

► Agr2, previously implicated in breast cancer, regulates mammary gland development. ► Estrogen-induced Agr2 expression is developmentally regulated in mammary gland. ► Over-expression induces epithelial cell proliferation in virgin mammary glands. ► Over-expression induces precocious lobuloalveolar development in virgin mice. ► Agr2 deletion impairs cell proliferation and alveologenesis during pregnancy.