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Figure 1 | Breast Cancer Research

Figure 1

From: Key stages in mammary gland development - The alveolar switch: coordinating the proliferative cues and cell fate decisions that drive the formation of lobuloalveoli from ductal epithelium

Figure 1

Alveolar morphogenesis. Mammary wholemounts (Carmine alum stain top row) and mammary cellular architecture (low power, middle row; high power, bottom row) in virgin, 12 days posts coitus (dpc), 18 dpc and 1 day post partum (1 dpp) murine mammary glands. Ductal epithelial cells (arrow) and myoepithelial cells (arrowhead) arise from a common mammary epithelial stem cell. Massive epithelial cell proliferation occurs at the onset of pregnancy, which is co-ordinated predominantly by prolactin and progesterone. At mid-pregnancy (12 dpc), developing alveoli continue to proliferate and polarise to form a sphere-like single layer of epithelial cells enveloping a circular lumen (indicated by X). This is followed by further cell proliferation and differentiation categorised by the expression of milk genes and the formation of cytoplasmic lipid droplets (indicated by asterisks). At 18 dpc, alveoli have large amounts of lipid and milk protein expression is increased. At parturition, tight junctions between alveolar cells close and milk proteins and lipid are secreted into the alveolar lumen (X). An expansion of the vasculature (open arrows) and reduction in the adipocyte (A) area is also apparent in the stroma.

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