Cell Contacts in the Mouse Mammary Gland

Abstract

The nature and distribution of cell contacts have been examined in thin sections and freeze-fracture replicas of mammary gland samples from female C3H/Crgl mice at stages from birth through pregnancy, lactation, and postweaning involution. Epithelial cells of major mammary ducts at all stages examined are linked at their luminal borders by junctional complexes consisting of tight junctions, variable intermediate junctions, occasional small gap junctions, and one or more series of desmosomes. Scattered desmosomes and gap junctions link ductal epithelial and myoepithelial cells in all combinations; hemidesmosomes attach myoepithelial cells to the basal lamina. Freeze-fracture replicas confirm the erratic distribution of gap junctions and reveal a loose, irregular network of ridges comprising the continuous tight-junctional belts. Alveoli develop early in gestation and initially resemble ducts. Later, as alveoli and small ducts become actively secretory, they lose all desmosomes and most intermediate junctions, whereas tight and gap junctions persist, The tight-junctional network becomes compact and orderly, its undulating ridges oriented predominantly parallel to the luminal surface. It is suggested that these changes in junctional morphology, occurring in secretory cells around parturition, may be related to the greatly enhanced rate of movement of milk precursors and products through the lactating epithelium, or to the profound and recurrent changes in shape of secretory cells that occur in relation to myoepithelial cell contraction, or to both.

Assembly of Gap Junctions During Amphibian Neurulation

“…Although the visualization of gap junctions has been enhanced by utilizing heavy metal tracers and stains (11,22,24,30,32,33,34,63), negative staining (4,30,55,81), and freeze fracturing (12,22,30,46,47,55,61,74,81), these studies have contributed little in describing their construction in developing or mature tissues. While some gap junctions are diminutive and macular (22,47,64,65,66), others exhibit a diversity of contours: some are long, particulate chains such as those in the outer plexiform layer of the retina (62), and still others are small, amorphous, particle aggregates similar to those of normal and transformed fibroblasts (28,58,64).…”

“…21) suggests that strong intramolecular forces exist between components of both. That gap junctions are intercalated within the confines of other occluding zonules further emphasizes the probability of an intimate relationship between the structural components of the two elements (22,30,31,41,47,61).…”

On the presence and function of closed lymphatic stomata in the diaphragm of the golden hamster

“…Closed stomata are composed of parquets of lymphatic endothelial cells which are adjoined with various junctional abutments. According to recent observations on cell-to-cell connections, even desmosomes and tight junctions are not necessarily stable but separable under certain conditions (Pitelka et al, 1973;Decker and Friend, 1974), and this is especially true for intercellular junctions in the lymphatic endothelium (Casley-Smith, 1980). We are inclined to think that shrinkage of the tissue during critical-point drying may artifactually separate the intercellular junctions of closed stomata.…”

Introduction: Hormonal Regulation of Mammary Development and Milk Protein Gene Expression at the Whole Animal and Molecular Levels

“…Ultimately the work in the CRGL moved mostly to a focus on breast cancer, but we reprint two additional articles from this laboratory in this issue [6,7].…”