ISSN:0741-0581    

DOI:10.1002/jemt.1060160102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThis article is a summary of our work of several years on the renewal of the intestinal epithelium. A combination of ultrastructural, radioautographic, and light microscopic analyses was carried out using normal tissue and tissue affected by inhibitors of RNA and protein synthesis. Measuring protein synthesis by3H‐leucine radioautography showed that the life span of the columnar (absorptive) cells in the rat small intestine was divisible into two main phases: differentiation (from stem to functional cell) and maturation (from functional to extruding cell), each phase and its subdivisions being well defined morphologically. Differentiation involved a linear rise in the rate of protein synthesis per cell and showed at the same time heterochromatinization and silencing of RNA transcription. Data from various experiments indicated that the cells functioned from stored information (RNA), part of which came from the nucleolus, which underwent marked and characteristic ultrastructural changes. Although transcription from rDNA ceased, the nucleolus released its ribosomal material, which added to the existing protein synthesis, presumably by recruiting excess stored mRNAs. Maturation involved a nearly linear decrease of the rate of protein synthesis per cell to a characteristic low value at which extrusion took place. A gradual exhaustion of the stored RNA was indicated to be the key factor in this decrease. Ultrastructurally, maturation was associated with a gradually increasing vesiculation of rER and Golgi. The results thus imply a regulatory role of cellular protein synthesis level in renewal. This would be an epigenetic response after the genes are silenced. The nucleolus seems to play a central role in this process, and this in turn is reflected in its characteristic ultrastructural changes. The work also included new observations on the epithelium of the rat ascending colon describing a hitherto unrecognized deep crypt mucus‐secretory (“DCS”) cell which is a nongoblet mature cell type apparently arising from midcrypt mitoses. In between the DCS cells, occasional slender columnar cells were seen which displayed the ultrastructural features of stem cells. These were probably reserve stem cells. We also observed nongoblet deep crypt mucous cells in the human right colon although fewer in number than in the rat. Nucleolar regulation and the presence of reserve stem cells represent new dimensions in our understanding of renewal. Electron microscopy is an essential tool in this invest

ISSN:0741-0581    

DOI:10.1002/jemt.1060160103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractRat colonic mucosae fixed in situ in Ussing chambers provided a model of the extrusion of absorptive enterocytes and less commonly of goblet and enteroendocrine cells. The cells were lost at extrusion zones midway between crypt mouths. Even in mucosae in which the number of extruding cells was large, epithelial continuity was maintained as evaluated morphologically and electrophysiologically. Beneath points of remaining contact between desquamating cells and the epithelial sheet, microfilaments of the terminal web formed band‐like structures linking adjacent junctional complexes. Freeze‐fracture replicas disclosed extensive macular regions of tight junction strands in the plasma membranes of desquamating cells. Tight junctions between newly neighboring cells were often irregular and often occurred beneath the terminal web region. Dithio‐threitol enhanced cell loss and increased basal epithelial conductance, but histological continuity was maintained and the mucosae continued to respond typically to bradykinin. These observations suggest that during the loss of senescent enterocytes, tight junctions are maintained; old junctional elements are lost, and tight junctions are formed between remaining adjacent cells. This model offers a means to study the synthesis and turnover of tight junctions and the maintenance of the colonic epithelial ba

ISSN:0741-0581    

DOI:10.1002/jemt.1060160104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe plasmalemmal glycoconjugates of the HT29‐18N2 (N2) cell line were characterized on cells grown as (1) undifferentiated multilayers in glucose‐containing culture media and (2) monolayers of columnar cells acquiring the goblet cell phenotype in glucose‐free media. Lectins were unable to bind sheets of detached N2 cells in the absence of fixation. Following fixation with aldehydes, a dramatic unmasking of lectin binding sites was seen. When fixed monolayers were stained prior to embedding, biotinylated lectins, visualized by the avidin‐biotin‐complexed peroxidase technique, were more efficient than collodial gold‐coupled lectins. Lectin binding sites could also be detected by using collodial gold‐coupled lectins to stain monolayers embedded in LR White, Lowicryl K4M, and Lowicryl HM20. The binding of 5 lectins (wheat germ,Dolichos bifluros, peanut, soybean, andUlex europeus) was found to be independent of the stage of differentiation; “pre‐differentiated” columnar cells which had prominent microvilli and no or few mucous secretory granules had identical staining patterns as well‐differentiated goblet cells with large numbers of secretory granules.Ricinus communis Iwas the only lectin whose binding was influenced by the stage of differentiation; it intensely labeled undifferentiated multilayers of N2 cells but only weakly labeled basolateral membranes of differentiated monolayers.Canavalia ensiformas(ConA) caused a moderate and even labeling of both apical and basolateral membranes of fixed monolayers stained prior to embedding, but post‐embedding labeling revealed heavy labeling along the lateral margins of all columnar cells and weak to moderate binding along the apical

ISSN:0741-0581    

DOI:10.1002/jemt.1060160105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractIn the present study, we modified the technique described by Altman et al. (J. Histochem. Cytochem., 32:1217–1223, 1984) for rapid embedding of tissues in Lowicryl K4M. To attain good sections of the small intestine that contained villi, crypts, submucosa, and external muscle layers, we cut 100 μm slices of the full thickness of the wall with a vibratome before embedment and then deoxygenated the resin and tissue before polymerization. The sections we obtained compared favorably with the quality of sections from conventional resi

ISSN:0741-0581    

DOI:10.1002/jemt.1060160106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractDifferent regions of small bowel were examined in five groups of rats in three separate experiments. The effects on mucosal morphology of position along the bowel, induced hypoproliferation (due to fasting), and induced hyperproliferation (due to streptozotocin diabetes) were investigated.Intestines fixed by in situ perfusion with buffered glutaraldehyde were sampled by strictly randomised procedures. Pieces of tissue from segments of roughly equal length were processed for electron microscopy and embedded in resin. Complete transverse sections were cut for light microscopy and estimates of villous surface areas were obtained by stereological methods devised for the purpose. Ultrathin sections from random sectors of the same tissue blocks were sampled systematically to obtain micrographs of the villous surface. These were analysed for quantitative information about microvilli (length, diameter, surface area, and number). Structural quantities from individual segments were pooled to provide values for the entire small bowel.Significant regional differences in villous and microvillous dimensions were found in all groups. The numbers of microvilli per bowel were remarkably constant in all control groups. Other variables were estimated reproducibly in rats of the same sex, strain, and average body weight.Effective absorptive surfaces did not show a linear gradient but tended to peak in middle segments. Neither fasting nor induced diabetes altered the mean length, diameter, or packing density of microvilli. However, surfaces due to villi and microvilli altered commensurately during fasting and induced diabetes. Therefore cell number seems to be the key quantity for determining villous and microvillous surface areas.The findings are discussed in the context of kinetic, biochemical, and physiological changes found in different adaptive states.

ISSN:0741-0581    

DOI:10.1002/jemt.1060160107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe polymorphism of the endoplasmic reticulum (ER) in epithelial cells with different transport functions such as the enterocyte suggests that the ER may be involved in some way in molecular transport. To further access this possibility, we examined the ER from the intestine of winter flounder,Pseudopleuronectes americanus, a species which undergoes an annual fast of approximately 6 months' duration, a time during which previous work indicates nutrient carrier number does not change. Fish from June (feeding) and January (8–10 weeks fasted) were sampled. Tissues from the pyloric caeca, foregut, midgut, and hindgut were prepared for electron microscopy using two techniques of staining. Cell height was unaltered in any section, although microvillar length shortened variably. Cellular organization, including position of nuclei, number and distribution of mitochondria, and presence of basolateral membranes, did not change. The ER appeared equally abundant in June and January. However, use of the osmium impregnation technique, which is specific for ER cisternal contents, revealed a change in the impregnation of ER, from a heavily impregnated network in summer to little or no impregnation in winter. These results suggest that a shift in function of the ER had occurred when nutrient transport ceased, and supports a role of the ER in nutrient transpor

ISSN:0741-0581    

DOI:10.1002/jemt.1060160108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPaneth cells in the following species were observed under an electron microscope: human, rhesus monkey, hare, guinea pig, rat, nude rat, mouse, golden hamster, and insect feeder bat. Secretory granules containing homogeneous electron‐dense materials were observed in the Paneth cells of humans, monkeys, hares, guinea pigs, and bats; mouse Paneth‐cell granules were bipartite (central core and peripheral halo), and the Paneth cells in rats and golden hamsters had secretory granules showing various electron densities. In humans, monkeys, and bats, immature granules near the Golgi apparatus sometimes showed bipartite substructure. The number and size of secretory granules were also diverse among various animal species. Some lysosome‐like bodies were commonly observed in peri‐ or supranuclear regions, though the size and shape of the bodies differed from cell to cell. In apical cytoplasm, small clear vesicles (100–200 nm diameter) were more‐or‐less observed in all species examined, and it was especially note that rat Paneth cells contained many clear vesicles. Small dense‐cored vesicles (150–200 nm diameter) were rare. It is unlikely that the various ultrastructural features of Paneth cells correlate with the phylogenetic

ISSN:0741-0581    

DOI:10.1002/jemt.1060160109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060160110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060160111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY