Alveolar-like Structures Research Articles

The surfactant system of human fetal lung organotypic cultures: Ultrastructural preservation by a lipid‐carbohydrate retention method

Human fetal lung organotypic cultures consisted of epithelial elements (congruent to 40- 100 micrometer in diameter) formed by the reaggregation of single cells from a monodisperse suspension of enzymatically dissociated fetal lung. These elements, termed alveolar-like structures, were composed primarily of type II alveolar epithelial cells whose apical surfaces bordered the central lumen of the alveolar-like structure. Pulmonary surfactant secreted by the type II cells was retained within the lumen and accumulated in close association with the epithelium. These characteristics made this culture system an advantageous model for the morphological study of human pulmonary surfactant in vitro. A lipid-carbohydrate retention procedure which reduced the extraction of tissue components and thus provided improved preservation of multilamellar bodies and tubular myelin surfactant was used in an ultrastructural study of organotypically cultured surfactant. Human surfactant was observed for the first time with most of its structural components intact. In vitro human surfactant was found to be similar to in vivo rodent and non-human primate surfactant, but with certain differences. Long surfactant tubules were not observed. There were more transformed multilamellar bodies present with more foci undergoing transformation. Each focus contained fewer layers of tubular myelin surfactant than occurs in rodent surfactant. No epiphase-hypophase areas were observed, only tubular myelin surfactant. In addition, a previously unreported intrasurfactant matrix material was observed.

The isolation and rotation-suspension culture of alveolar-like structures from fetallung organotypic cultures

The isolation and rotation-suspension culture of alveolar-like structures from fetallung organotypic cultures

Maintenance and induction of morphological differentiation in dissociated mammary epithelium on floating collagen membranes.

Dissociated normal mammary epithelial cells from prelactating mice were plated on different substrates in various medium-serum-hormone combinations to find conditions that would permit maintenance of morphological differentiation. Cells cultured on floating collagen membranes in medium containing insulin, hydrocortisone and prolactin maintain differentiation through 1 month in culture. The surface cells form a continous epithelial pavement. Some epithelial cells below the surface layer rearrange themselves to form alveolus-like structures. Cells at both sites display surface polarization; microvilli and tight junctions are present at their medium-facing of luminal surface and a basal lamina separates the epithelial components from the gel and stromal cells. Occasional myoepithelial cells, characterized by myofilaments and plasmalemmmal vesicles, are identified at the basal surface of the secretory epithelium. In contrast, cells cultured on plastic, glass or collagen gels attached to Petri dishes form a confluent epithelial sheet showing surface polarization, but lose secretory and myoepithelial specializations. If these dedifferentiated cells are subsequently maintained on floating collagen membranes, they redifferentiate. There is little DNA synthesis in cells on collagen gels, in contrast to Petri-dish controls. Protein synthesis in cells on floating collagen membranes increases over TO values and remains constant through 7 days in culture whereas it decreases on attached gels; however, if the gels are freed to float, protein synthesis increases sharply and parallels that seen on floating membranes.

The formation of histotypic structures from monodisperse fetal rat lung cells cultured on a three-dimensional substrate

Enzymatically dissociated lungs from rat fetuses at 19-days gestation yield single cells which reaggregate to form alveolar-like structures when cultured on gelatin sponge discs. These structures form within 2 days and have been maintained in vitro for as long as 6 weeks. They are composed primarily of type II pneumonocytes as characterized by large, lightly stained nuclei and cytoplasmic inclusion bodies. The lamellar structure of these inclusion bodies has been confirmed by electron microscopy. The dynamic formation of inclusion bodies is suggested by the presence of lamellar bodies in the extra-cellular space and the appearance of new inclusions in the cytoplasm of the type II pneumonocytes. The formation and long-term maintenance of histotypic lung structures in vitro provides a model system for the study of lung development and synthesis of surfactant by type II alveolar pneumonocytes.

An organotypic in vitro model system for studying pulmonary surfactant production by type II alveolar pneumonocytes.

This report describes an in vitro model system in which monodisperse fetal rat lung cells reorganize to form alveolar-like structures when cultured on a gelatin sponge matrix. The alveolar-like structures are composed of cells that have morphologic characteristics like those of the type II alveolar pneumonocytes of intact lung. These morphologic characteristics include lightly stained nuclei, microvilli on the apical surface, and osmiophilic lamellar bodies in the cytoplasm. The presence of osmiophilic lamellar bodies and tubular myelin in the lumen of the alveolar-like structures suggests that the cells in these structures are producing pulmonary surfactant. The formation and long-term maintenance of these alveolar-like structures provide a unique in vitro model system for studies of the synthesis, storage, and secretion of pulmonary surfactant.

Carcinogenesis in pulmonary epithelia in mice on different levels of vitamin A

Lungs from 82 fetal or neonat BALB/c mice were minced and implanted with 20-methylcholanthrene (MCA) into right posterior thigh muscles of 159 adult males of the same strain. At these sites, bronchial, bronchiolar and alveolar-like structures developed. Metaplastic changes are illustrated. Squamous cell carcinomas arose at these sites in 9 of 56 hosts maintained on an adequate diet supplemented with injections of vitamin A palmitate, in 4 of 58 hosts maintained on an adequate diet without supplementary vitamin A, but in none of 25 hosts on a diet deficient in vitamin A. With the lowest tested dose of MCA, there were numerous adenocarcinomas and a few poorly differentiated squamous cell carcinomas. Well-differentiated squamous cell carcinomas were obtained with larger doses of MCA. Both well-differentiated and poorly differentiated squamous cell carcinomas were found in mice on the high level of vitamin A.

The origin and structure of the tertiary envelope in thick-shelled eggs of the brine shrimp, Artemia

The shell glands of the brine shrimp Artemia are composed of clusters of shell gland units. Each unit usually consists of two rather oblong cells separated by a lumen. Each lumen communicates with the uterus by a duct, formed by a neck cell and a small number of duct cells. Often, two or more ducts join before entering the uterus. The plasma membrane facing the lumen between gland cells is thrown into short microvilli. Elsewhere, the plasmalemma lacks such specializations. The two gland cells are joined together by maculae adhaerentes and septate desmosomes. The nuclei of these cells are large and contain abundant chromatin, arranged in a reticular pattern. The cytoplasmic matrix contains glycogen, lipids, mitochondria, a few microtubules, Golgi complexes, and large amounts of rough endoplasmic reticulum. When Artemia produces thick-shell eggs, the material for the outer portion of the shell (the tertiary envelope) is synthesized in the shell glands. During this synthesis numerous membrane-bounded secretory granules are formed that contain lipoprotein. Prior to their liberation the granules show a decrease in density and their membranes fuse with the plasmalemma adjacent to the lumen between the gland cells. Other granules fuse with those already being liberated, thereby enlarging the lumen of the shell gland unit. The tertiary envelope that is deposited around an embryo is at first homogeneous. Later it becomes filled with alveolus-like structures, the surfaces of which are composed of hexagonal porous units, through which the alveoli interconnect. Still later, in the gastrula stage, these interconnections are lost, and a more homogeneous outer layer is added.