Canonical WNT Signaling Promotes Mammary Placode Development and Is Essential for Initiation of Mammary Gland Morphogenesis

The study found that the canonical WNT/β-catenin signaling pathway was crucial for the initiation of mammary gland morphogenesis in embryonic mice. Activation of this pathway coincided with the start of mammary morphogenesis, with WNT activity localizing to mammary placodes and buds. The presence of WNT3A or lithium chloride (LiCl) in cultured embryos accelerated placode formation, while the WNT inhibitor Dickkopf 1 completely blocked placode development. These findings suggested that WNT signaling was essential for mammary placode development and might also be important for the formation of other skin appendages, such as hair follicles.