The Mammary Gland Microenvironment Directs Progenitor Cell Fate In Vivo

Figure 2

The mammary gland microenvironment. The major cell types of the mammary gland, luminal epithelial (luminal compartment) and myoepithelial cells (basal compartment), are separated from the stromal compartment by a basement membrane. Both the luminal epithelial and myoepithelial cell growths are mediated by adipocytes and fibroblasts located within the stroma, as well as by estrogen, progesterone, prolactin, TGF-α, TGF-β, STAT5a, STAT5b, EGF, IGF, and RANKL signaling. Wnt3A signaling regulates mammary stem cells present in the luminal compartment. IGF mediates the mammary gland’s response to estrogen, while RANKL, IGF, and Wnt4 mediate the response to progesterone. IGF additionally regulates prolactin signaling. Estrogen receptor expression is mediated by amphiregulin.