Electron microscopic observations of cell division in Mycobacterium vaccae V1

Cell division of Mycobacterium vaccae was initiated by deposition of new wall material in the cross wall. The surface layers of the old wall remained continuous until septum formation was complete. Subsequently, rupture of the outer cell wall layers occurred circumferentially, leaving rings on the cell wall. The two daughter cells remained connected with each other at the new pole and bent to form V-shaped structures at the connecting point.     

Electron microscopic observations on a new cell type in the fundus mucosa of the mouse stomach

Summary In the course of electron microscopic investigations of the fundus mucosa of the mouse stomach, a few cells of an unknown type were found by chance in the deep portions of the glands. These cells are characterized by two different kinds of specific granules in their cytoplasm, one of which being large and less dense, and the other one being small and dense. The large less dense granules resemble zymogen granules of the chief cell, which are formed by the rough endoplasmic reticulum and Golgi system. The small dense granules are quite similar to the secretory granules of the basal granulated cell, and are considered to be formed in the Golgi complex. Release figures of the small dense granule were not observed, numerous granules, however, were observed in close contact with the basal cell membrane. The occurrence of these two kinds of granules in one cell suggests that the basal granulated cell and the zymogenic cell originate from the same entodermal stem element.The author cordially thanks Professor Dr. Hisao Fujita, Department of Anatomy, Hiroshima University School of Medicine, for his kind advices and criticisms.     

Electron microscopic study of cell surface rings during cell division and morphogenesis of Arthrobacter crystallopoietes.

The whole cell ultrastructure during cell division and morphogenesis of Arthrobacter crystallopoietes was monitored using electron microscopic techniques. Glucose-grown spherical cells were inoculated into succinate-based medium. In this medium, the organism undergoes a morphogenetic cycle consisting of elongation of spheres to rods, exponential growth as rods, and fragmentation of rods to spherical cells. Raised bands or rings that encircled the cells were evident on the cell surface of both sphere- and rod-shaped cells. Many rod-shaped cells possessed two or more rings arranged adjacent to each other in a parallel orientation. At each cell division a new ring was formed on both siblings. However, as predicted by the proposed model of unidirectional cell growth and by maintaining a ring from the previous generation, unequal numbers of rings were observed on sibling cells. Only one ring was visible on most of the spherical inoculum cells, but in some cases a second ring perpendicular to the other ring was observed. Parallel rings were found on spherical cells resulting from fragmentation or reductive cell division of rods during the stationary growth phase. Thus, these spheres could be distinguished from inoculum spheres containing a single ring or perpendicular orientation of rings. The number of rings per cell and arrangement of rings on the cell surface of sibling cells after cell division, but before cell separation, are discussed with respect to cell age, cell division, and sphere-rod-sphere morphogenesis of A. crystallopoietes.     

Electron microscopic observations on absorption in the epithelium of the guinea pig gall bladder

Summary The fine structure of the epithelium of the gall bladder in the guinea pig has been examined after the resorption of Thorotrast. Vesicles at the apex of the epithelial cells containing Thorotrast give evidence of pinocytosis and particles are also found in the intercellular spaces and in dense cytoplasmic bodies. The epithelium exhibits interdigitating lateral cell membranes which are correlated with its function of resorbing large amounts of water.     

Electron microscopic studies on the small intestine of rats after mechanical intestinal obstruction.

The morphologic changes of the small intestine after the mechanical obstruction were studied by light and electron microscopy. After the ligation of the upper small intestine, segments of jejunum, both proximal and distal to the site of obstruction, were removed at intervals varying from 45 min to 24 h. The essential changes were found in the epithelial cells of the tips of villi, and few morphologic differences were recognized between samples proximal and distal to the site of obstruction. The most remarkable changes in the mucosa were the pseudopodlike extension of the cytoplasm, vacuolar alteration of the villus epithelial cells, desquamation of these degenerated cells, and the dilatation of the epithelial intercellular spaces. A few epithelial cells showed hypertrophy of the smooth endoplasmic reticulum. In the submucosa, vascular stasis and edema were observed throughout the course. The mechanism of fluid loss into the intestinal lumen was discussed briefly.     

The tight junction proteins expression in the epithelium of the small intestines in a rat

Proteins' expression of tight junction proteins in rat small intestine was analyzed by means of immunohistochemistry and Western blotting. Claudins -1, -2, -3, -4, -5, -7 and occludin were analyzed. Confocal laser-scanning microscopy revealed differences in the subcellular distributions of these proteins. Claudins-1, -2, -3, -4, -5, and -7 were localized within the tight junction complex and were also detectable in subjunctional regions. Distributed subcellular localization of these proteins may reflect their different roles during formation of epithelial cell layers as well as in paracellular transport of ions in the small intestine.     

Activation of Paneth cell alpha-defensins in mouse small intestine.

Paneth cells in small intestine crypts secrete microbicidal alpha-defensins, termed cryptdins, as components of enteric innate immunity. The bactericidal activity of cryptdins requires proteolytic activation of precursors by matrix metalloproteinase-7 (MMP-7; matrilysin) (Wilson, C. L., Ouellette, A. J., Satchell, D. P., Ayabe, T., Lopez-Boado, Y. S., Stratman, J. L., Hultgren, S. J., Matrisian, L. M., and Parks, W. C. (1999) Science 286, 113-117). Here, we report on the intracellular processing of cryptdin proforms in mouse Paneth cells. Peptide sequencing of MMP-7 digests of purified natural procryptdins identified conserved cleavage sites in the proregion between Ser(43) and Val(44) as well as at the cryptdin peptide N terminus between Ser(58) and Leu(59). Immunostaining co-localized precursor prosegments and mature cryptdin peptides to Paneth cell granules, providing evidence of their secretion. Extensive MMP-7-dependent procryptdin processing occurs in Paneth cells, as shown by Western blot analyses of intestinal crypt proteins and proteins from granule-enriched subcellular fractions. The addition of soluble prosegments to in vitro antimicrobial peptide assays inhibited the bactericidal activities of cryptdin-3 and -4 in trans, suggesting possible cytoprotective effects by prosegments prior to secretion. Levels of activated cryptdins were normal in small bowel of germ-free mice and in sterile implants of fetal mouse small intestine grown subcutaneously. Thus, the initiation of procryptdin processing by MMP-7 does not require direct bacterial exposure, and the basal MMP-7 content of germ-free Paneth cells is sufficient to process and activate alpha-defensin precursors. MMP-7-dependent procryptdin activation in vivo provides mouse Paneth cells with functional peptides for apical secretion into the small intestine lumen.     

Freeze-etch appearance of the tight junctions in the epithelium of small and large intestine of mice

Summary The ultrastructure of the central layer and the contributing plasma membranes of tight junctions has been studied in epithelia of the jejunum and colon of mice.Examination of freeze-etched plasma membranes of epithelial cells has revealed that they consist of a central layer, with fracturing characteristics similar to bimolecular lipid leaflets, which is covered on both sides with a layer of particles.The fusion of the outer membrane surfaces of adjacent cells in the region of the tight junction leads to the formation of a new common structure consisting of a meshwork of fibrils embedded in a matrix substance. The fibrils probably contain protein. They have a diameter of 65 ± 10 Å and are linked together so that they form around the distal end of each cell a continuous belt-like meshwork which is extended proximally at the joints where three cells meet. As the fibrillar mesh appears to be strongly attached to the central lipid layer of the two adjoining membranes, in contrast to the weakly bound surrounding matrix, it is believed that the fibrils forming the continuous meshwork could be the mechanical coupling and the sealing elements of the tight junction. Their arrangement in the form of a concertinalike mesh would make the whole structure very flexible. In the region of the junction the membranes are constricted along the lines of attachment to the fibrils and bulge outwards,i.e. towards the cytoplasm, in the areas of the matrix material. In the resulting grooves on the cytoplasmic side of the plasma membranes regularly spaced particles with a diameter of 90 ± 10 Å can be detected. Various observations suggest that these particles could be connected through the central layer of the membranes to the fibrils on the other side. This would offer a possible explanation for the known abhesion properties of tight junctions. The described structures are also evaluated in terms of current theories of cell communication.     

Twists and turns in the development and maintenance of the mammalian small intestine epithelium

Experimental studies during the last decade have revealed a number of signaling pathways that are critical for the development and maintenance of the intestinal epithelium and that demonstrate the molecular basis for a variety of diseases. The Notch-Delta, Wnt, Hedge Hog, TGF-beta, and other signaling pathways have been shown to form and steadily maintain the crypt-villus system, generating the proper quantities of highly-specialized cells, and ultimately defining the architectural shape of the system. Based on the characterized phenotypes and functional defects of mice resulting from various targeted knockouts, and overexpression and misexpressions of genes, a picture is emerging of the sequence of gene expression events from within the epithelium, and in the underlying mesenchyme that contribute to the regulation of cell differentiation and proliferation. This review focuses on the contributions of multiple signaling pathways to intestinal epithelial proliferation, differentiation, and structural organization, as well as the possible opportunities for cross-talk between pathways. The Notch pathway's potential ability to maintain and regulate the intestinal epithelial stem cell is discussed, in addition to its role as the primary mediator of lineage specification. Recent research that has shed light on the function of Wnt signaling and epithelial-mesenchymal cross-talk during embryonic and postnatal development is examined, along with data on the interplay of heparan sulfate proteoglycans in the signaling process.     

Differential regulation of tight junction permeability during development of the retinal pigment epithelium

The retinalpigment epithelium (RPE) is an epithelial region of the blood-brainbarrier. During embryogenesis, permeability of the barrier graduallydecreases. A culture model of RPE development revealed differences inhow tight junctions regulate the paracellular diffusion of ionic andnonionic solutes (Ban Y and Rizzolo LJ. Mol Vis 3: 18, 1997). To examine these differences, the permeation of ionic andnonionic monosaccharides was compared with mannitol, and the permeationof the alkali metals was compared with sodium. The order of permeationwas 3-O-methlyglucose = glucosamine = mannitol > N-acetylneuraminic acid. The ratio ofN-acetylneuraminic acid to mannitol permeability decreasedwith embryonic age of the RPE or exposure to retinal-conditionedmedium. Neither the ratio nor the permeability was affected byinhibiting transcytosis. The ratio increased if tight junctions weredisrupted in low-calcium medium. The permeation of cations followed thesequence cesium > rubidium > potassium = sodium > lithium and was unaffected by embryonic age or retinal-conditionedmedium. These results are considered in terms of a model in which thesize distribution, charge, or number of open junctional pores could bemodulated. It suggests that different subpopulations of pores can beregulated independently during development.

     

Electron microscopic observations on ciliated epithelium of tracheal organ cultures infected with Bordetella bronchiseptica

Using mouse tracheal organ cultures, the pathogenic effect of Bordetella bronchiseptica to epithelial cells was studied by electron microscopy. The ultrastructure of epithelial cells in uninfected tracheal rings was preserved well for longer than 3 days. In mouse tracheal rings infected with graded doses (3 x 10(5) to 10(7) CFU/ml) of phase I B. bronchiseptica, the colonization in the interciliary spaces of ciliated epithelial cells was observed after a 20-hr infection period. The infected tracheal rings showed swelling of nonciliated cells as well as ciliated cells, rupture of cell membrane of cilia, swelling and disappearance of cilia, and atrophic cytomorphosis of epithelial cells. The severity of these changes occurred depending on the infection doses. These changes were essentially similar to those observed previously in the tracheal epithelia of the B. bronchiseptica-infected mice. The usefulness of this in vitro model was suggested for studying the pathogenesis of Bordetella infection.