Ultrastructure of the mouse tracheal epithelium

The ultrastructure of mouse tracheal epithelium was examined. The three cell types, basal cells, ciliated cells and goblet cells, described for other mammalian trachea were found to be present although goblet cells occurred only rarely. A cell type, termed the nonciliated cell, not described in other mammalian trachea was frequently found in mouse tracheal epithelium. These cells contained abundant smooth and rough endoplasmic reticulum, free ribosomes, a large Golgi complex, and many mitochondria. There were many vesciles containing an electron dense material near the luminal surface of these cells; these cells were positive for PAS. These features suggested a secretory function for the cells. This, along with the scarcity of goblet cells, suggested that the nonciliated cells of mouse tracheal epithelium fulfill the function of the goblet cells found in other mammalian trachea.     

The growth and differentiation of transitional epithelium in vitro

The development of rat transitional epithelial cells grown on conventional non-permeable surfaces was compared with development on permeable collagen supports. On glass or plastic surfaces, cells grew as expanding nomolayer sheets. Once confluent, growth continued with a bilayer being formed in most areas and apical cells being continuously sloughed off. Although most cells were interconnected by desmosomes, and junctional complexes were formed, no other indications of differentiation were observed. After 2-3 wk of growth, division stopped and cel death ensued. In contrast, single-cell suspensions plated on collagen-coated nylon disks reassociated into multicellular islands and commenced growth. Mitoses were confined to the basal cells in contact with the permeable substrate. The islands developed into epithelial trilayers, tapering to monolayers along spreading edges. Once the islands were confluent, stratification was completed and appeared similar to that observed in vivo. Germinal cells formed a basal lamina, and the upper layer was composed of large, flattened cells with an unusually thick asymmetrical plasma membrane on the apical surface. Electron microscopic and radioactive tracers demonstrated "leaky" zonulae occludentes with a restricted permeability to small molecules. The movement of urea was retarded in comparison to water. Unlike the slow turnover of adult epithelium in vivo, maturation and sloughing of apical cells were measurable. Transfer of cells could be effected and growth maintained for up to 4 mo. These results may indicate the necessity of a nutrient-permeable growth surface for the polarized differentiation of adult transitional epithelium.     

Ultrastructure of the branchial epithelium of an amphibious brackish-water crab

The ultrastructure of the branchial epithelium of the amphibious brackish-water crab Uca mordax (Smith) was investigated in relation to adaptation to the salinity of the medium. No distinct differences were observed in the epithelial structure of animals adapted to either 100% sea water or to 1% sea water. Thus any interpretation of the significance of particular structures in relation to specific transport processes should be regarded with caution. Apart from strict epithelial cells, pillar cells and glycogen (presumed) storage cells were found. The epithelial cells showed very well-developed apical microvilli or lamellae and basal interdigitations with adjacent cells. Well-developed junctional complexes were seen (band desmosomes, septate desmosomes, gap junctions). The cells are extremely rich in mitochondria. Microtubules, peroxisome-like bodies, multivesicular bodies and near-nuclear Golgi complexes were present.     

Ultrastructure of the ocular ciliary epithelium of the common frog

The ultrastructure of the adult frog ciliary epithelium cells has definite regional differences. Cells of ciliary epithelium folds near the iris display morphological features characterizing its barrier and secretory functions which lead to the formation of aqueous humor. These are junctional complexes with tight junctions (zonula occludents) in the apical parts of contacting sides of cells of the inner leaf: a great quantity of mitochondria, ribosomes and various vesicles, well developed endoplasmic reticulum in the cytoplasm, much folded basal surface, gap junctions between cells of external and internal leaflets. In the mammalian inner epithelial layer different cell junctions are known to be arranged in a fixed spatial fashion. Unlike, in the frog's epithelium both zonula adherent and desmosomes may be found in any sequence. Tight junctions are formed during metamorphosis, on the place of focal junctions, whereas gap junctions, referred to earlier as "extended", start functioning between cells just on the very early stages of eye morphogenesis (Dabagyan et al., 1979). The epithelium of the posterior part of the ciliary fold and pars plana of the ciliary body have, in addition, the number of morphological sign indicating the cell involvement in the accomodational function of any eye (i. e. a majority of desmosomes binding all cells together and of zonulae adherentes, well developed intracellular skeleton of tonofilament bundles). These features are characteristic of the whole distal part of ciliary epithelium rather than of the place of attachment of zonula fiber only.