Fig 2.
Histology and ultrastructure of mammary tissue from lactating (day 6) WT and ERβ−/− mice. (A and B) Hematoxylin/eosin-stained section of lactating mammary glands. (A) WT (×10), (B) ERβ−/− (×10). In ERβ−/− mice, there is incomplete penetration of the mammary fat pad, less epithelium, and increased alveolar and ductal volume. (C and D) Electron micrograph of apical part of alveolar luminal epithelial cells. (C) Cytoplasm of a WT gland showing vesicles containing milk protein (dark spots). (D) Cytoplasm of an ERβ−/− gland showing abundant vesicles containing milk protein. (Bar = 200 nm.) (E–H) Immunohistochemical detection of α-smooth muscle actin on fixed sections from mammary glands of WT and ERβ−/− mice. Representative sections of WT and ERβ−/− lactating (day 6) mouse mammary glands, respectively; (E and G) low magnification; (F and H) high magnification. [Bar = 50 μm (E and G) or 25 μm (F and H), respectively.] (I and J) Immunohistochemical staining for Ki-67 in lactating WT (I) and ERβ−/− (J) mice. In mammary glands of WT mice, no Ki-67 expression is detectable (I). In ERβ−/− lactating mammary glands, there is Ki67 expression in the nuclei of many luminal epithelial cells (J) (percent positive cells: 58 ± 13%, n = 6). (K and L) Electron micrograph of basal part of alveolar luminal epithelial cells. The basement membrane in WT mouse shows a homogeneous layer of the lamina lucida (*) close to a myoepithelial cell (myoep) and visible collagen fibers (col) (K). The basement membrane in ERβ−/− mice shows a more translucent (arrows) lamina lucida. No collagen fibers are visible in the micrograph, and they are rarely found in the glands of ERβ−/− mice (L). (Bar = 200 nm.)