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Biomedical subjects

F Bleicher

Publications and source records attributed to F Bleicher.

29 records · Page 2Linked to original sources
PubMed1995

Ultrastructural characterization of mesenchymal and epithelial cells co-cultured from human dental root apical explants.

Previous studies have shown the role of cell-cell and cell-matrix interactions in the differentiation of the specific secretory cells of the tooth. In order to elucidate the mechanisms implicated in root dentin formation, we developed a co-culture system of human pulpal mesenchymal and epithelial root sheath cells. Root tips of premolars were cultured in Eagle's basal Medium supplemented with fetal calf serum, ascorbic acid, antibiotics and, for some of them, with sodium beta-glycerophosphate. After 60 days of culture, cells were prepared for light and electron microscopy. Three main cell types were observed: (1) polygonal mesenchymal cells showing a functional polarity and producing a dense network of tactoid collagenous fibers. The latter had a specific circular organization that delimited small lacunae around the cells and mineralized in the presence of beta-glycerophosphate; (2) spindle-shaped mesenchymal cells mainly localized inside epithelial-mesenchymal knots and synthesizing an abundant collagenous matrix; and (3) epithelial cells lying on the plastic culture dish, on the dense collagenous matrix, or on spindle-shaped cells. Epithelial cells deposited a structured basement membrane when they were lying on the plastic culture dish or on spindle-shaped cells. On the contrary, no basement membrane was found when epithelial cells were overlying the dense collagenous network. Immunoelectron microscopic analysis of type IV collagen and laminin indicated that these two specific basement membrane components were produced by all cell types. These results show that the co-culture system should be valuable for (1) studying the in vitro formation of human dental root hard tissues, (2) characterizing cell-cell and cell-matrix interactions implicated in dental basement membrane production, and (3) isolating populations of cells implicated in dental root formation.

Adolescent↗
PubMed1993

p53 mutations and aflatoxin B1 exposure in hepatocellular carcinoma patients from Thailand.

The prevalence and type of mutations in the p53 tumour-suppressor gene have been determined in 15 hepatocellular carcinomas (HCC) originating from Thailand. Direct sequencing of exons 5-8 revealed 2 mutations, an AGG to AGT (Arg-->Ser) transversion at codon 249, and an ATC-->AAC (Ile-->Asn) transversion at codon 254. Samples from the Thai patients were analyzed for the presence of aflatoxin-liver DNA and aflatoxin-serum albumin adducts, and all but one were found negative. All the patients were genotyped for glutathione-S-transferase (GST) mu, an enzyme possibly involved in the detoxification of AFB1, and 12 out of 15 had the null genotype. In general, the level of aflatoxin-albumin adducts in sera and the prevalence of p53 mutation at codon 249 in HCC were lower than in other areas at high risk of HCC, including southern China and parts of Africa.

Adolescent↗
PubMed1993

Nonrandom distribution of O6-methylguanine in H-ras gene sequence from DNA modified with N-methyl-N-nitrosourea.

The distribution of O6-meG in the rat H-ras gene sequence was studied using PCR by transition of O6-meG to adenine during the reaction. In order to study the transition mutations the PCR product was cloned in a replicative form of phage M13mp18 and sequenced. The use of PCR for detection of O6-meG was validated by using oligonucleotides (61 bases) containing one O6-meG residue at a defined site. After treatment of rat liver DNA by N-methyl-N-nitrosourea in vitro, a striking nonrandom sequence distribution of O6-meG was observed. Sixty-eight per cent of O6-methylated Gs were found in the middle G of the sequences GGT and GGA in the H-ras gene whereas no methylation was found in the middle G of the sequences AGG, GGG, TGT, TGC, CGA and CGC. No O6-meG adduct was found in the 12th codon of H-ras (sequence GGA). The frequency of O6-meG formation as a function of two flanking nucleotides on each side of the target guanine was calculated as an approach to understanding more distant sequence effects. It was found that in the DNA sequence studied the formation of O6-meG was highest if the G was flanked by PyPu or PuPu on the 5' side (Py, pyrimidine and Pu, purine) whereas PuPu on the 3' side showed maximal inhibition of O6-meG formation.

Animals↗
PubMed1988

Promoter vectors with restriction-site banks.

New vectors harboring the promoter for the chloramphenicol acetyl transferase gene (cat promoter) have been constructed. These vectors are all derived from pJRD184 [Heusterspreute et al., Gene 39 (1985) 299-304], which contains a restriction-site bank. The cat promoter has been inserted at various positions and in reverse orientations so that almost all the restriction sites originally present on JRD184 can be used in cloning experiments. The expression of the aceK gene of Escherichia coli cloned under the control of the cat promoter has been tested. A large increase in the synthesis of the isocitrate dehydrogenase kinase, the aceK gene product, has demonstrated the efficiency of the newly constructed vectors.

Acetyltransferases↗
PubMed1988

Nucleotide sequence and expression of the aceK gene coding for isocitrate dehydrogenase kinase/phosphatase in Escherichia coli.

The flow of isocitrate through the glyoxylate bypass in Escherichia coli is regulated via the phosphorylation-dephosphorylation of isocitrate dehydrogenase mediated by a bifunctional enzyme: isocitrate dehydrogenase kinase/phosphatase. The aceK gene coding for this enzyme is part of the polycistronic ace operon, which also includes the aceB and aceA genes coding, respectively, for malate synthase and isocitrate lyase, the two glyoxylate bypass enzymes. The complete nucleotide sequence of a 2,214-base-pair DNA fragment containing the aceK gene and its 5' flanking region has been determined. In vivo experiments based on gene expression in a minicell system and protein fusion with beta-galactosidase, as well as in vitro assays with a plasmid-directed transcription-translation coupled system, have shown that the aceK gene extends over 1,731 nucleotides encoding a 66,528-dalton protein. The 5' flanking region presents an unusual intercistronic structural pattern consisting of two consecutive long dyad symmetries, almost identical in sequence, which can yield very stable stem-loop units. These structures are probably responsible for the drastic downshifting in expression observed in acetate-grown bacteria between the aceK gene and the aceA gene located immediately upstream in the ace operon.

Amino Acid Sequence↗
PubMed1987

Effect of bacteriophage M13 infection on phosphorylation of dnaK protein and other Escherichia coli proteins.

1. The effects of infection with the filamentous phage M13 on the phosphorylation of Escherichia coli proteins were studied. Phosphorylated proteins were labeled with [32P]orthophosphate and analyzed by the O'Farrell two-dimensional gel technique and autoradiography. 2. Phage infection was shown to induce significant changes in the pattern of protein phosphorylation. At least eight different proteins were found to be phosphorylated to a larger extent while seven others were, by contrast, much less labeled than in uninfected bacteria. 3. Labeling experiments with [35S]methionine demonstrated that these quantitative changes in protein phosphorylation were not connected, in any case, with changes in the amount of protein synthesized. They rather seemed to result from a variation of the phosphorylating capacity of the relevant protein kinase(s). 4. The individual proteins, whose phosphorylation was affected by phage infection, were characterized by both their molecular mass and isoelectric point. One of them, whose phosphorylation was increased by a factor of 7, was identified as the dnaK protein which is necessary for both cellular and phage DNA replication. 5. The chemical analysis of the phosphorylated moiety of dnaK protein showed that it was modified exclusively at serine residues during normal growth of cells, and mostly at threonine residues after phage infection. These results were discussed in terms of stimulation of the protein activity by phosphorylation.

Bacterial Proteins↗
PubMedDate not supplied

Utilization of acetate in Escherichia coli: structural organization and differential expression of the ace operon.

Growth of Escherichia coli on acetate as the sole source of carbon and energy requires operation of the glyoxylate bypass in connection with the expression of the polycistronic ace operon. The structural organization of this operon is presented, including the 3 structural genes coding respectively for malate synthase (aceB), isocitrate lyase (aceA) and isocitrate dehydrogenase kinase/phosphatase (aceK), and the surrounding genes iclR and metA. In addition, the differential expression of genes aceB, aceA, and aceK has been tested both in vivo in a minicell system and in vitro in a plasmid-directed transcription-translation coupled system. Moreover, the codon usage and adaptation to transfer RNA frequencies during translation of the corresponding messenger RNAs have been measured.

Acetates↗