Collagen involvement in branching morphogenesis of embryonic lung and salivary gland

Submersion culture of the intact fetal lung

Intact whole lungs from 14 d rat fetuses were explanted to organ culture and maintained fully submerged in medium or positioned at the gas-fluid interface. Striking differences were observed in the morphological development of submersion cultured and interface cultured explants after 7 d in vitro. Submersion cultured lung developed as an expanded hollow organ, whereas the tissue of interface cultures was glandular in appearance and attenuated against the culture substrate. This difference in the development of the cultured lung may be attributed to the influence of surface tension forces at the gas-fluid interface versus the fluid immersed environment. In submersion culture the fetal lung followed a unique pattern of morphogenetic development. Under these culture conditions the lung expanded in three dimensions and retained its discrete lobar structure. The primitive bronchial epithelial tree of the fetal lung at explantation exhibited substantial histoarchitectural changes in vitro. Progressive branching of the epithelium into the surrounding lung mesenchyme gave rise to a pulmonary parenchyma bearing characteristics of the presumptive alveolar region of the late gestation fetal lung. The epithelium consisted predominantly of large, glycogen rich cuboidal cells interspersed with numerous structurally differentiated type II cells, containing lamellar bodies. The pulmonary parenchyma of the submersion cultured explant occupied a narrow margin of the lung wall, surrounding a large central lumen. This unique form of the cultured lung made it possible to examine the pulmonary epithelium by scanning electron microscopy. Data from the present study suggest that submersion culture of the intact fetal lung may provide a useful model system for study of the maturation of epithelial cell surface features during pulmonary development.

Synthesis of basement membrane proteins by rat mammary epithelial cells

A mammary epithelial cell line, Rama 25, growing on plastic, deposits fibronectin, type IV collagen, and laminin in punctate structures located beneath the basal surface of the cells. When grown on the surface of collagen gels, Rama 25 cells deposit these basement membrane proteins in a continuous layer between the basal surface of the cells and the surface of the collagen matrix. Rama 25 cells also penetrate the collagen matrix forming rudimentary duct-like structures. These structures are surrounded by a discontinuous layer of basement membrane proteins. The ducts of fetal and neonatal rat mammary glands contain few mature myoepithelial cells and our results suggest that some mammary epithelial cells, in contact with a collagenous stroma, are capable of synthesizing a basal lamina-like structure.

Involvement of glycoproteins in the development of early mouse embryos: effect of tunicamycin and alpha, alpha' dipyridyl in vitro

Early mouse embryos grown in tissue culture were treated with tunicamycin, an inhibitor of protein glycosylation or with alpha, alpha' dipyridyl, an inhibitor of collagen secretion. Neither treatment blocked development of cleavage stage embryos nor did either interfere with blastocyst formation, hatching, or adhesion to the substratum at low concentrations. However, both treatments caused marked and specific changes in the morphology of the blastocyst outgrowth. Treatment of embryos with tunicamycin caused severe deterioration of the trophoblast layer and subsequent disintegration of the inner cell mass. Tunicamycin completely inhibited the incorporation of mannose into proteins. Treatment with alpha, alpha' dipyridyl caused dose dependent retardation of the inner cell mass while the trophoblast cells were virtually unaffected. These alterations in morphogenesis occurred only in embryos treated at the blastocyst stage or later in development. Changes caused by alpha, alpha' dipyridyl could be partially reversed by addition of collagen to the culture. These findings might indicate the involvement of extracellular matrix macromolecules in embryonic organization.