1. Normal mammary morphogenesis is accomplished by a stratified epithelium.
Normal mammary morphogenesis is accomplished by a stratified epithelium. (A) Carmine-Red-stained 10-week-old mouse mammary gland. Mammary ducts are elongated during puberty by specialized structures at the end of the duct, terminal end buds (TEBs). (B) Resting mammary ducts have a bilayered organization, with luminal epithelial cells, connected by extensive intercellular junctions, and basally located myoepithelial cells. (C) Normal ducts in vivo have a simple epithelial organization when not actively growing. Zona occludens 1 (ZO-1) is localized to the apico-lateral surface of the luminal epithelial cells and β-catenin to the basolateral surfaces. (D) Mammary ducts are elongated during puberty by TEBs, stratified epithelial structures with many luminal cell layers. β-catenin localizes to all basolateral surfaces and is only excluded from lumen-facing surfaces. ZO-1 localizes to the lumen lining surfaces of both the main lumen and isolated micro-lumens. (E–E″) Primary mammary ducts can be isolated and grown in 3D Matrigel gels. Without the addition of growth factor all ducts form simple cysts. These cysts are bilayered, with a single luminal (Lum) cell layer and a single myoepithelial (Myo) layer. The lumen has electron dense secretory material (arrows), microvilli (MV), and tight junctions (TJ). Both luminal and myoepithelial cells are connected by desmosomes (Des). (F–H) Polarized cysts in 3D culture localize PAR3 to apical surfaces (F) and both scribble (G) and numb (H) to basolateral surfaces. All TEM images are from high-pressure frozen, freeze-substituted samples that were pre-fixed with 4% glutaraldehyde.
Andrew J. Ewald et al. J Cell Sci 2012;125:
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