Retinoic acid signaling and the initiation of mammary gland development

► RA signaling participates in mammary gland initiation at appropriate time. ► RA prevents Lef1 expression possibly via effects on Wnt10b signalling. ► Raldh2 expression in leads to production of RA required for Tbx3 expression. ► RA signaling act Tbx3 expression via control of Fgf10 expression in somite. ► Tbx3 on Raldh2 protect the epithelium of developing mammary gland from RA.