Figure 1

Ducts and end buds in the juvenile mouse mammary gland. (a) Photomicrograph illustrating the mammary ductal system in a 5-week-old nulliparous mouse. Note the 'open' ductal architecture, which leaves 80% or more of the gland parenchyma-free. End buds (large arrows) identify growing ducts. Those end buds that are arrayed along the right-hand side of the gland are in various stages of regression. Blunt-tipped branches (small arrows) mark growth-quiescent ducts. The nipple (asterisk) is at base of the gland. Magnification approximately ×15. (b) Photomicrograph of a longitudinal section through an end bud and subtending duct. The induction of a fibrous connective tissue sheath (large arrows) coincides with the constriction of the end bud to ductal dimensions. The alcian blue stain used in this preparation detects glycosaminoglycans and highlights the extracellular matrix/basal lamina complex at the epithelial-stromal interface (small arrows) [19]. Magnification ×250.