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D Swallow

Publications and source records attributed to D Swallow.

At least 19 recordsLinked to original sources
PubMed2001

Polymorphism of the human muc genes.

Mucins encoded by the MUC genes share the common feature of having an extensive tandem repeat region that encompasses a large proportion of the coding sequence. In many of the genes this tandem repeat region shows a great deal of allelic length variation and recently studies have demonstrated person to person variation in pattern of nucleotide or amino-acid changes in the repeat units. The length and sequence variability will be discussed in this review, as will its role in disease susceptibility.

Humans↗
PubMed1996

A limited upstream region of the human sucrase-isomaltase gene confers glucose-regulated expression on a heterologous gene.

We have previously shown that glucose can exert a repressive effect on the transcription of the sucrase-isomaltase (SI) gene in the differentiated enterocyte-like human colon carcinoma cell lines HT-29 and Caco-2. To characterize the region through which glucose exerts this effect, three different-length fragments of the 5'-flanking region of the human SI gene were linked to the reporter gene luciferase in an episomal vector carrying a hygromycin resistance gene. These fragments were used for transfection into a clone of the Caco-2 cell line, PF11, which has high glucose consumption and only expresses SI at high levels when cultured in the presence of a low supply of glucose. By using the stably transformed PF11 cells grown either in standard high glucose (25 mM) or in low glucose (1 mM) it was possible to show that the smallest fragment of the SI promoter, extending from bases -370 to +30, contains all the information required for the glucose repression of the reporter gene luciferase.

Base Sequence↗
PubMed1994

Mosaic regulation of lactase in human adult-type hypolactasia.

BACKGROUND/AIMS: We have previously shown that in the proximal-jejunum of hypolactasic humans, just a few villus enterocytes express lactase protein and activity. In the present study, we compared the distribution of lactase messenger RNA (mRNA), protein, and activity in villus enterocytes in tissues obtained from subjects with persistent high lactase activity and those with hypolactasia. METHODS: Immunohistochemical and enzymohistochemical staining was performed on closely adjacent sections of human proximal jejunum from 5 individuals with persistent high lactase activity and 32 with hypolactasia. In all the persistent and in 9 hypolactasic samples, in situ hybridization was also performed using a digoxygenin-labeled RNA probe. RESULTS: In persistent tissues, lactase mRNA, protein, and activity were present in all villus enterocytes. In hypolactasic tissues, lactase mRNA was detected only in some villus enterocytes; some of them also expressed protein and activity, whereas others did not. In 8 of these hypolactasic samples, a variable number of villus enterocytes with lactase mRNA and protein did not express lactase activity. CONCLUSIONS: Various types of enterocytes are present even on a single villus from individuals with adult-type hypolactasia. These results show that different mechanisms control lactase expression in enterocytes on the same villus.

Adult↗
PubMed1993

Monensin and forskolin inhibit the transcription rate of sucrase-isomaltase but not the stability of its mRNA in Caco-2 cells.

Treatment of Caco-2 cells with forskolin (25 microM) or monensin (1 microM) has previously been shown to cause a marked decrease in the level of sucrase-isomaltase (SI) mRNA, without any effect on the expression of dipeptidylpeptidase IV (DPP-IV). In the present work, we report that there is no significant difference in the stability of SI mRNA between control and treated cells. On the other hand, we demonstrate a decrease in the transcription rate of SI mRNA which is sufficient to account for the decrease in the steady-state level of SI mRNA both in forskolin- and monensin-treated Caco-2 cells.

Blotting, Northern↗
PubMed1993

Mosaic differentiation of human villus enterocytes: patchy expression of blood group A antigen in A nonsecretors.

BACKGROUND: The authors have shown that a mosaicism of brush border antigens may occur spontaneously on enterocytes of small intestine in human adult-type hypolactasia. The present paper gives another example of spontaneously occurring mosaicism as indicated by the patchy expression of blood group antigens on villus enterocytes. METHODS: Thirty-five individuals were examined by immunomorphological techniques with antibodies against blood group antigens. RESULTS: In 4 of 16 A blood group individuals, the blood group antigens were expressed only in some villus enterocytes. The individuals with this mosaic pattern were all shown to be nonsecretors. The A antigen in the positive enterocytes of these individuals was only present as the ALe(b) structure, whereas ALe(y) and ALe(d) were also present in the secretors. The patches of positive enterocytes were randomly distributed along the villus wall. CONCLUSIONS: A nonsecretor individuals express the blood group antigens only in some villus enterocytes; this mosaicism does not arise from a heterogeneous population of stem cells within the crypts but rather reflects subtle differences in the pattern of differentiation between monoclonally derived epithelial cells on the villus.

ABO Blood-Group System↗
PubMed1993

Differential expression of the human mucin genes MUC1 to MUC5 in relation to growth and differentiation of different mucus-secreting HT-29 cell subpopulations.

Mucin expression was analysed, in relation to cell growth, in parental HT-29 cells and in two populations of mucus-secreting HT-29 cells selected by adaptation to methotrexate (HT29-MTX) or 5-fluorouracil (HT29-FU). These two populations express mature mucins that differ in their immunoreactivity to antibodies against gastric (HT29-MTX) or colonic mucins (HT29-FU). In the parental population, at late confluency, only very few cells produce mucins or the MUC1 glycoprotein, this being consistent with the low level of expression of the mRNAs corresponding to the MUC1 to MUC5C mucin genes. In the HT29-MTX and HT29-FU populations, the appearance of mucus droplets, as shown by histochemistry and immunofluorescence, starts a few days after confluency, progressively involving a greater proportion of cells and reaching a steady state at late confluency. The MUC1 glycoprotein appears earlier, already being detectable in preconfluent cells. Its distribution is restricted to the apical surface of the cells and is distinct from that of the mucus droplets. In both populations the growth-related levels of MUC1 mRNA are concordant with the apparent levels of expression of the MUC1 glycoprotein. The levels of MUC2, MUC3, MUC4 and MUC5C mRNAs differ from one population to another and, within each population, according to the stage of the culture. The highest levels of MUC2 and MUC4 mRNAs are found in the HT29-FU cells, whereas the highest levels of MUC3 and MUC5C are found in the HT29-MTX cells, suggesting that the differences observed in the mature mucins expressed by either population may be related to which MUC genes are expressed. In both populations significant or even high levels of MUC mRNAs are already present in early cultures, i.e. at a stage when the mature mucins are not yet detectable, suggesting that mucin maturation is a later event.

Blotting, Northern↗
PubMed1992

Sequence of the complete cDNA and the 5' structure of the human sucrase-isomaltase gene. Possible homology with a yeast glucoamylase.

The complete sequence of the 6 kb cDNA and the 5' genomic structure are reported for the gene coding for the human intestinal brush border hydrolase sucrase-isomaltase. The human sucrase-isomaltase cDNA shows a high level of identity (83%) with that of the rabbit enzyme, indicating that the protein shares the same structural domains in both species. In addition to the previously reported homology with lysosomal alpha-glucosidase, the sucrase and isomaltase subunits also appear to be homologous to a yeast glucoamylase. A 14 kb human genomic clone has been isolated which includes the first three exons and the first two introns of the gene, as well as 9.5 kb 5' to the major start site of transcription. The first exon comprises 62 bp of untranslated sequence and the second starts exactly at the initiation ATG codon. Typical CAAT and TATA boxes are seen upstream of the first exon. A genetic polymorphism is described which involves a PstI site in the second intron. Southern blotting, sequencing and mRNA studies indicate that the structures of the sucrase-isomaltase gene and its mRNA are unaltered in the two human colon cancer cell lines Caco-2 and HT-29 in comparison with normal human small intestine.

Amino Acid Sequence↗
PubMed1992

Patchy expression of lactase protein in adult rabbit and rat intestine.

Enzymatic and immunohistological analyses of lactase were performed at different stages of development and within different regions of the small intestine of the rabbit and rat. As previously reported, there seems to be a sharp decline of lactase activity on weaning but variable and higher levels of activity are seen in adult animals. Two monoclonal antibodies to rat lactase were available to study the protein in rats. Four monoclonal antibodies to human lactase were shown to cross-react with rabbit lactase and used for the rabbit studies. Immunohistological analysis of small intestine of adult rabbits and rats showed residual lactase protein within the enterocytes throughout the small intestine. In the middle of the small intestine (lower jejunum, upper ileum), uniform staining of the brush border was observed. In the proximal and distal regions, a patchy pattern of staining was observed. This pattern, which resembles that observed in adult hypolactasic humans, indicates an underlying heterogeneity of enterocyte differentiation.

Age Factors↗
PubMed1991

Mosaic pattern of lactase expression by villous enterocytes in human adult-type hypolactasia.

Immunohistological analysis of the expression of lactase protein in adults with hypolactasia has been carried out using monoclonal antibodies. Eight different antibodies that recognize at least three distinct epitopes on the lactase protein each gave the same result. Strong brush border staining was observed in all the lactase-persistent adults. No staining at all was detected in 9 of the hypolactasic subjects. In the remaining 12 individuals a mosaic pattern of expression was observed: small patches of enterocytes stained strongly, whereas the surrounding areas showed no staining at all. Sucrase-isomaltase, in contrast, showed no such mosaicism in these or in any of the other individuals. The mosaicism observed in the 12 hypolactasic individuals suggests that the differentiation of the columnar cells along the villus is not homogeneous. Furthermore, the existence of two patterns of expression of the lactase protein in the lactase-deficient individuals (i.e., absence of protein and mosaicism), if characteristic of the entire length of the intestine of the individuals tested, would suggest the existence of two phenotypes of adult-type hypolactasia in the population studied.

Antibodies, Monoclonal↗
PubMed1991

Identification of a conserved epitope in class I alcohol dehydrogenase isoenzymes using monoclonal antibodies.

Two monoclonal antibodies raised against native horse alcohol dehydrogenase (HADH) bind preferentially to the enzyme attached to solid supports and recognize the denatured and carboxymethylated HADH subunits. Both antibodies cross-react with the human class I isoenzymes but do not recognize the class III ADH isoenzyme. Protease digestion, electrophoresis and HPLC have been used to identify the linear epitope which is contained in the sequence Pro344-Glu357 of the HADH subunit.

Alcohol Dehydrogenase↗
PubMed1989

Reversible forskolin-induced impairment of sucrase-isomaltase mRNA levels, biosynthesis, and transport to the brush border membrane in Caco-2 cells.

Hybridization analysis of mRNA with a cDNA probe for human sucrase-isomaltase, pulse-chase experiments with L-[35S]-methionine followed by SDS-PAGE, and immunofluorescence detection of sucrase-isomaltase were used to analyze the level(s) at which forskolin interferes with the expression of the enzyme in Caco-2 cells in culture. Three effects are observed in Caco-2 cells treated with forskolin: 1) a marked decrease in the level of sucrase-isomaltase mRNA, 2) a marked decrease in the biosynthesis of the enzyme without any alteration of its stability, and 3) an almost total inhibition of its transport to the brush border membrane. All three effects are reversible when the drug is removed from the culture medium, though this reversibility is asynchronous: transport to the brush border membrane resumes after 24 h, sucrase-isomaltase mRNA levels are back to the normal after 5 days, whereas the biosynthesis of the enzyme, although increasing progressively, remains lower than in control cells, even 10 days after removal of the drug. The possibility that some effects are directly dependent on cAMP and others a consequence of changes in glucose metabolism is discussed.

Biological Transport↗
PubMed1987

Isolation of a cDNA probe for a human jejunal brush-border hydrolase, sucrase-isomaltase, and assignment of the gene locus to chromosome 3.

We report the nucleotide sequence and derived amino acid sequence of a cDNA clone encoding most of the N-terminal, isomaltase region of human sucrase-isomaltase (SI). A plasmid containing this cDNA, pS12, identifies a 6-kb mRNA found in human jejunum and the human colon carcinoma cell line Caco-2. This human SI cDNA shows extensive overall homology with recently published rabbit SI cDNA. Using pS12 to probe DNA from a panel of somatic cell hybrids, we have assigned the gene encoding human SI to chromosome 3.

Amino Acid Sequence↗
PubMed1987

Clinical diversity in glycogenosis type II. Biosynthesis and in situ localization of acid alpha-glucosidase in mutant fibroblasts.

The molecular basis of clinical diversity in glycogenosis type II (Pompe's disease) was investigated by comparing the nature of acid alpha-glucosidase deficiency in cultured fibroblasts from 30 patients. Biosynthetic forms of acid alpha-glucosidase with different molecular mass were separated electrophoretically and identified by immunoblotting. Immuno-electron microscopy was employed to determine the intracellular localization of mutant enzyme. Our studies illustrate that maturation of acid alpha-glucosidase is associated with transport to the lysosomes. Deficiency of catalytically active mature enzyme in lysosomes is common to all clinical phenotypes but, in the majority of cases, is more profound in early onset than in late onset forms of the disease. Thus, the results suggest that the clinical course of glycogenosis type II is primarily determined by the amount of functional acid alpha-glucosidase. The role of secondary factors can, however, not be excluded because three adult patients were identified with very low activity and little enzyme in the lysosomes.

Adult↗
PubMed1982

Lactase polymorphism in adult British natives: estimating allele frequencies by enzyme assays in autopsy samples.

In an attempt to estimate allele frequencies of lactase persistence in adult British natives, sucrase was assayed simultaneously with lactase under conditions that gave optimal activities for both enzymes. A trimodal distribution in the ratios of enzyme activities was demonstrated. Circumstantial evidence and statistical analyses suggest that the trimodal distribution is due to the different levels of lactase activity in the three genotypes--homozygous persistent, heterozygous, and homozygous nonpersistent, and that it is possible to correct for "nongenetic" variation by using sucrase as an internal standard. The allele frequency for lactase persistence was estimated to be .747. The implications of our findings on the genetic mechanisms involved in lactase persistence are discussed.

Adult↗
PubMed1981

alpha-L-Fucosidase in cystic fibrosis: analysis of skin fibroblasts and liver.

The lysosomal enzyme alpha-L-fucosidase has been examined by thin layer gel and column isoelectric focusing in skin fibroblasts and liver from patients with cystic fibrosis and controls. All three common phenotypes of the enzyme were observed in both control and CF fibroblasts. When individuals of the same alpha-L-fucosidase phenotype were compared, no major differences between the isozyme profiles of cystic fibrosis patients and controls were detected in either fibroblasts or liver tissue.

Adolescent↗
PubMed1979

Assignment of the human acid alpha-glucosidase gene (alphaGLU) to chromosome 17 using somatic cell hybrids.

Hybrid clones (MOGs) were made between the mouse line RAG and a primary fibroblast line from an individual of the rare alphaGLU 2 phenotype. Fifteen independent primary clones and 32 subclones were tested for the presence of human alphaGLU after separation of the human and rodent enzymes by starch gel electrophoresis. Twenty-three other human-mouse hybrids from six different crosses were analysed for the presence of human alphaGLU by exploiting a difference in the thermostability of the human and mouse enzymes. The hybrids were also analysed for up to 25 other enzymes which were used as markers for different human chromosomes. Two of the MOG hybrids were karyotyped and karyotype data were already available for a number of the other hybrids. The combined results demonstrate that alphaGLU is located on chromosome 17, and probably on 17q.

Animals↗
PubMed1979

Sialidosis type 1: cherry red spot-myoclonus syndrome with sialidase deficiency and altered electrophoretic mobilities of some enzymes known to be glycoproteins. 1. Clinical findings.

A family is described with three affected brothers, two of whom were examined, born to consanguineous parent, who in early adult life began to experience ataxia, intention myoclonus, and progressive visual failure. The brothers examined had cherry red spots at the maculae and cataracts. They were of normal intelligence. The intention myoclonus responded partially to treatment with clonazepam and pheneturide, but not to 5-hydroxytryptophan in combination with carbidopa or to sodium valproate. Studies in one patient showed the excretion of large quantities of sialylated oligosaccharides in the urine. Both patients showed deficient sialidase activity in their cultured fibroblasts. Further studies on cultured skin fibroblasts revealed increased electrophoretic mobility of six glycoprotein enzymes that was returned approximately to normal by treatment with sialidase. The clinical and biochemical findings indicate that these patients are further cases of the newly described condition sialidosis type 1.

Adult↗