(1/739) Regulatory sequences of the mouse villin gene that efficiently drive transgenic expression in immature and differentiated epithelial cells of small and large intestines.
Villin is an early marker of epithelial cells from the digestive and urogenital tracts. Indeed villin is expressed in the stem cells and the proliferative cells of the intestinal crypts. To investigate the underlying molecular mechanisms and particularly those responsible for the restricted tissue specificity, a large genomic region of the mouse villin gene has been analyzed. A 9-kilobase (kb) regulatory region of the mouse villin gene (harboring 3.5 kb upstream the transcription start site and 5.5 kb of the first intron) was able to promote transcription of the LacZ reporter gene in the small and large intestines of transgenic mice, in a transmissible manner, and thus efficiently directed subsequent beta-galactosidase expression in epithelial cells along the entire crypt-villus axis. In the kidney, the transgene was also expressed in the epithelial cells of the proximal tubules but is likely sensitive to the site of integration. A construct lacking the first intron restricted beta-galactosidase expression to the small intestine. Thus, the 9-kb genomic region contains the necessary cis-acting elements to recapitulate the tissue-specific expression pattern of the endogenous villin gene. Hence, these regulatory sequences can be used to target heterologous genes in immature and differentiated epithelial cells of the small and/or large intestinal mucosa. (+info)
(2/739) Cellular uptake of biotin: mechanisms and regulation.
This review describes our knowledge of biotin transport in the small intestine of humans and other mammals and presents recent findings in the area. Previous studies have shown that biotin transport across the brush border membrane of the small intestinal absorptive cells occurs via a carrier-mediated, Na+ gradient-dependent, electroneutral mechanism. Exit of biotin out of the enterocyte, i.e., transport across the basolateral membrane, also occurs via a carrier-mediated process, but the process is Na+ independent and electrogenic. Recent studies from our laboratory have shown that the uptake process of biotin in Caco-2 cells, a human-derived cultured intestinal epithelial cell line, are under the cellular regulation of both a protein kinase C- and a Ca/calmodulin-mediated pathway. In addition, the uptake process is shared by another water-soluble vitamin, pantothenic acid. For the first time, other recent studies have detected the existence of a Na+-dependent, carrier-mediated mechanism for biotin uptake at the apical membrane of colonocytes, which could theoretically mediate absorption of the biotin synthesized by colonic microflora. This system was again found to be shared by pantothenic acid, which is also synthesized by the normal microflora of the large intestine. (+info)
(3/739) Prolonged large bowel transit increases serum deoxycholic acid: a risk factor for octreotide induced gallstones.
BACKGROUND: Treatment of acromegaly with octreotide increases the proportion of deoxycholic acid in, and the cholesterol saturation of, bile and induces the formation of gallstones. Prolongation of intestinal transit has been proposed as the mechanism for the increase in the proportion of deoxycholic acid in bile. AIMS: To study the effects of octreotide on intestinal transit in acromegalic patients during octreotide treatment, and to examine the relation between intestinal transit and bile acid composition in fasting serum. METHODS: Mouth to caecum and large bowel transit times, and the proportion of deoxycholic acid in fasting serum were measured in non-acromegalic controls, acromegalic patients untreated with octreotide, acromegalics on long term octreotide, and patients with simple constipation. Intestinal transit and the proportion of deoxycholic acid were compared in acromegalic patients before and during octreotide. RESULTS: Acromegalics untreated with octreotide had longer mouth to caecum and large bowel transit times than controls. Intestinal transit was further prolonged by chronic octreotide treatment. There were significant linear relations between large bowel transit time and the proportion of deoxycholic acid in the total, conjugated, and unconjugated fractions of fasting serum. CONCLUSIONS: These data support the hypothesis that, by prolonging large bowel transit, octreotide increases the proportion of deoxycholic acid in fasting serum (and, by implication, in bile) and thereby the risk of gallstone formation. (+info)
(4/739) D-tagatose has low small intestinal digestibility but high large intestinal fermentability in pigs.
The digestibility of D-tagatose, its effect on the digestibility of macronutrients and the metabolic response of the microbiota of the gastrointestinal tract to the ingestion of this carbohydrate were studied in pigs. Eight pigs were fed a low fiber diet comprising 15% sucrose (control group). Another eight pigs were fed a similar diet except that 100 g sucrose per kg diet was replaced by D-tagatose (test group). After 18 d, the pigs were killed and the gastrointestinal contents removed for analysis. The digestibility of D-tagatose was 25.8 +/- 5.6% in the distal third of the small intestine. The small intestinal digestibilities of dry matter (86.9 +/- 1.3 vs. 92.9 +/- 0.9%), gross energy (74.4 +/- 1.6 vs. 80.7 +/- 1.8%) and sucrose (90.4 +/- 2.5 vs. 98.0 +/- 0.5%) were lower (P < 0. 05) in the pigs fed D-tagatose. Digestibilities of starch, protein and fat did not differ between groups. D-Tagatose, sucrose and starch were fully digested in the large intestine. The fecal digestibilities of energy, dry matter and fat did not differ between the two groups, whereas D-tagatose reduced the fecal digestibility of protein (91.1 +/- 0.6 vs. 93.5 +/- 0.7%, P < 0.05). D-Tagatose served as a substrate for the microbiota in the cecum and proximal colon as indicated by a reduced pH, and a greater ATP concentration, adenylate energy charge (AEC) ratio and concentration of short-chain fatty acids. In particular, the increase in the concentrations of propionate, butyrate and valerate suggests possible health benefits of this monosaccharide. (+info)
(5/739) Estimation of growth rates of Escherichia coli BJ4 in streptomycin-treated and previously germfree mice by in situ rRNA hybridization.
The growth physiology of Escherichia coli during colonization of the intestinal tract was studied with four animal models: the streptomycin-treated mouse carrying a reduced microflora, the monoassociated mouse with no other microflora than the introduced strain, the conventionalized streptomycin-treated mouse, and the conventionalized monoassociated mouse harboring a full microflora. A 23S rRNA fluorescent oligonucleotide probe was used for hybridization to whole E. coli cells fixed directly after being taken from the animals, and the respective growth rates of E. coli BJ4 in the four animal models were estimated by correlating the cellular concentrations of ribosomes with the growth rate of the strain. The growth rates thus estimated from the ribosomal content of E. coli BJ4 in vivo did not differ in the streptomycin-treated and the monoassociated mice. After conventionalization there was a slight decrease of the bacterial growth rates in both animal models. (+info)
(6/739) Extrathymic derivation of gut lymphocytes in parabiotic mice.
In adult mice, c-kit+ stem cells have recently been found in their liver, intestine and appendix, where extrathymic T cells are generated. A major population of such thymus-independent subsets among intraepithelial lymphocytes is T-cell receptor (TCR)gamma delta+ CD4- CD8alpha alpha+(beta-) cells, but the origins of other lymphocyte subsets are still controversial. In this study, we examined what type of lymphocyte subsets were produced in situ by such stem cells in the small intestine, large intestine and appendix. To investigate this subject, we used parabiotic B6.Ly5.1 and B5.Ly5. 2 mice which shared the same circulation by day 3. The origin of lymphocytes was identified by anti-Ly5.1 and anti-Ly5.2 monoclonal antibodies in conjunction with immunofluorescence tests. Lymphocytes in Peyer's patches and lamina propria lymphocytes (especially B cells and CD4+ T cells) in the small intestine became a half-and-half mixture of Ly5.1+ and Ly5.2+ cells in each individual of parabiotic pairs of mice by day 14. However, the mixture was low in CD8alpha alpha+, CD8alpha beta+ and gamma delta T cells in the small and large intestines and in CD3+ CD8+ B220+ cells in the appendix. These cells might be of the in situ origin. When one individual of a pair was irradiated before parabiosis, the mixture of partner cells was accelerated. However, a low-mixture group always continued to show a lower mixture pattern than did a high-mixture group. The present results suggest that extrathymic T cells in the digestive tract may arise from their own pre-existing precursor cells and remain longer at the corresponding sites. (+info)
(7/739) Functional significance of the variations in the geometrical organization of tight junction networks.
Using freeze-fracture techniques, we have examined the morpholog of tight junction networks found along the length of the alimentary tract of Xenopus laevis before and after metamorphosis. We have developed the hypothesis, based on these observations, that the geometrical organization of the network determined by the stress-induced shape changes normally experienced by the cells linked by the network. Consistent with this theory, tight junctions can be classified into two distinct types of network organization which differ in their response normal and experimentally induced stress conditions: (a) loosely interconnected networks which can stretch or compress extensively under tension, thereby adapting to stress changes in the tissue; and (b) evenly cross-linked networks which retain their basic morphology under normal stress conditions. The absorptive cells of the large intestine as well as the mucous cells of the gastrointestine or stomach are sealed by the first, flexible type of tight junction. The second type of junctional organization, the evenly cross-connected network, is found between absorptive cells of the small intestine and ciliated cells of the esophagus, and reflects in its constant morphology the relative stability of the apical region of both of these cell types. Networks intermediate between these two types arise when a cell which would normally form a lossely interconnected network borders a cell which tends to form a more evenly cross-linked network, as is found in the esophagus where ciliated and goblet cells adjoin. Despite the change in the animal's diet during metamorphosis from herbivorous to carnivorous, the basic gemetrical organization of the networks associated with each tissue of the alimentary tract remains the same. (+info)
(8/739) Coordinate expression of cytokeratins 7 and 20 in feline and canine carcinomas.
Forty-seven feline and 60 canine epithelial tumors were studied to test the coordinate expression of cytokeratin 7 (CK 7) and cytokeratin 20 (CK 20) using commercially available monoclonal antibodies and an avidin-biotin immunoperoxidase staining technique. Previously, the distribution of both cytokeratins was examined in normal tissues from 4 cats and 4 dogs. The pattern of distribution of CK 7 in normal tissues was similar, with minor differences, to that described in humans, whereas the reactivity pattern of CK 20 in cats and dogs was wider than that in humans. The subset of tumors strongly expressing CK 7 and CK 20 included pancreatic adenocarcinomas (100%), transitional cell carcinomas (75%), and endometrial carcinomas (67%) in the cat. None of the canine tumors had this immunophenotype. Feline (50%) and canine (56%) mammary gland carcinomas and canine cholangiocarcinomas (67%) were the only tumors presenting the CK 7 +/CK 20- immunophenotype, whereas the CK 7-/CK 20+ immunophenotype included thyroid carcinomas (100%), intestinal adenocarcinomas (60%), bronchioloalveolar carcinomas (50%), and renal carcinomas (50%) in the cat and intestinal adenocarcinomas (56%), gastric adenocarcinomas (50%), and ovarian carcinomas (50%) in the dog. The CK 7-/CK 20- immunophenotype included the rest of the analyzed tumors. The immunohistochemical evaluation of coordinate expression of both CK 7 and CK 20 in feline and canine carcinomas using monoclonal antibodies provides important information that can help to discriminate among carcinomas from different primary sites and could be particularly helpful in the determination of the primary site of origin of carcinomas presenting as metastatic disease. (+info)