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Figure 2


Fig. 2. Induction of bud outgrowth. Cross-section of an embryonic mouse mammary bud at E13.5-15.5. PTHrP and BMP signalling interact to initiate mammary bud outgrowth and nipple formation. PTHrP, which is secreted from mammary epithelial cells of the mammary bud, increases BMPR1A expression in the mammary mesenchymal cells (purple shading), which can now respond to BMP4. This triggers epithelial outgrowth, elevates MSX2 expression, and inhibits hair follicle formation within the nipple sheath. Modified with permission from Hens et al. (Hens et al., 2007).