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Biomedical subjects

S Maury

Publications and source records attributed to S Maury.

28 records · Page 2Linked to original sources
PubMed1999

Tobacco O-methyltransferases involved in phenylpropanoid metabolism. The different caffeoyl-coenzyme A/5-hydroxyferuloyl-coenzyme A 3/5-O-methyltransferase and caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase classes have distinct substrate specificities and expression patterns.

The biosynthesis of lignin monomers involves two methylation steps catalyzed by orthodiphenol-O-methyltransferases: caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferases (COMTs) and caffeoyl-coenzyme A (CoA)/5-hydroxyferuloyl-CoA 3/5-O-methyltransferases (CCoAOMTs). Two COMT classes (I and II) were already known to occur in tobacco (Nicotiana tabacum) and three distinct CCoAOMT classes have now been characterized. These three CCoAOMT classes displayed a maximum level of expression at different stages of stem development, in accordance with their involvement in the synthesis of lignin guaiacyl units. Expression profiles upon tobacco mosaic virus infection of tobacco leaves revealed a biphasic pattern of induction for COMT I, COMT II, and CCoAOMTs. The different isoforms were expressed in Escherichia coli and our results showed that CCoAOMTs and, more surprisingly, COMTs efficiently methylated hydroxycinnamoyl-CoA esters. COMT I was also active toward 5-hydroxyconiferyl alcohol, indicating that COMT I that catalyzes syringyl unit synthesis in planta may operate at the free acid, CoA ester, or alcohol levels. COMT II that is highly inducible by infection also accepted caffeoyl-CoA as a substrate, thus suggesting a role in ferulate derivative deposition in the walls of infected cells. Tobacco appears to possess an array of O-methyltransferase isoforms with variable efficiency toward the diverse plant o-diphenolic substrates.

Acyl Coenzyme A↗
PubMed1998

cDNA cloning, substrate specificity and expression study of tobacco caffeoyl-CoA 3-O-methyltransferase, a lignin biosynthetic enzyme.

Four caffeoyl-CoA 3-O-methyltransferase (CCoAOMT) cDNA clones were isolated from RNA extracted from TMV-infected tobacco leaves using an heterologous DNA probe. The cDNAs were 84-93% identical in their nucleotide sequences, indicating that they are the products of four closely related genes. A comparison of the CCoAOMT cDNAs with database sequences and Southern blot analysis indicated that they are encoded by a new CCoAOMT family of tobacco. Overall expression of this gene family in tobacco tissues was investigated by RNA blot analysis. The expression of each individual gene was studied by RT-PCR coupled with RFLP analysis of PCR products, taking advantage of the presence of specific restriction sites in each cloned cDNA. Two members of the CCoAOMT gene family appeared to be constitutively expressed in various plant organs and tissues whereas the two others were preferentially expressed in flower organs, after tobacco mosaic virus (TMV) infection or elicitor treatment of leaves. The CCoAOMT enzymatic protein expressed in bacteria was purified and shown to be specific for the caffeoyl-CoA and 5-hydroxyferuloyl-CoA esters and to have no activity against free caffeic acid and 5-hydroxyferulic acid. The pattern of CCoAOMT transcript accumulation during development of tobacco stem was found closely related to that of COMT I genes which have been shown to be specifically involved in lignin biosynthesis. Moreover, the inhibition of COMT I gene expression in transgenic tobacco was also shown to decrease CCoAOMT gene expression, particularly in the most lignified tissues. Thus, the expression pattern and the substrate specificity of tobacco CCoAOMT sustain a preferential role in lignin biosynthesis.

Amino Acid Sequence↗
PubMed1995

A truncated herpes simplex virus thymidine kinase phosphorylates thymidine and nucleoside analogs and does not cause sterility in transgenic mice.

Dividing eukaryotic cells expressing the herpes simplex virus type 1 thymidine kinase (TK) gene are sensitive to the cytotoxic effect of nucleoside analogs such as acyclovir or ganciclovir (GCV). Transgenic mice with cell-targeted expression of this conditional toxin have been used to create animals with temporally controlled cell-specific ablation. In these animal models, which allow the study of the physiological importance of a cell type, males are sterile. In this study, we showed that this phenomenon is due to testis-specific high-level expression of short TK transcripts initiated mainly upstream of the second internal ATG of the TK gene. This expression is DNA methylation independent. To obtain a suicide gene that does not cause male infertility, we generated and analyzed the properties of a truncated TK (delta TK) lacking the sequences upstream of the second ATG. We showed that when expressed at sufficient levels, the functional properties of delta TK are similar to those of TK in terms of thymidine or GCV phosphorylation. This translated into a similar GCV-dependent toxicity for delta TK- or TK-expressing cells, both in vitro and in transgenic mice. However, delta TK behaved differently from TK in two ways. First, it did not cause sterility in delta TK transgenic males. Second, low-level delta TK RNA expression did not confer sensitivity to GCV. The uses of delta TK in cell-specific ablation in transgenic mice and in gene therapy are discussed.

Animals↗
PubMed1994

Neural representations of abstract stimulus features in the human brain as reflected by the mismatch negativity.

Neural sensory-memory representations that encode physical properties of incoming stimuli can be probed by recording the change-specific mismatch negativity of the event-related potential (ERP). The present study was aimed at determining whether invariant stimulus features, abstracted from the continuously changing acoustic environment, are encoded in these sensory-memory representations. Regularly descending tone sequences with an occasional ascending tone or tone repetition were presented to reading subjects. A significant MMN was elicited by the ascending tones. When instead of simple tones, Shepard tones creating an illusion of a continuous pitch decrement were used in the same paradigm, the MMN was elicited by both ascending and repeating tones. It was concluded that besides physical stimulus properties, abstract stimulus features are also encoded in the neural representations of sensory memory.

Acoustic Stimulation↗
PubMed1992

[Drugs and aged subjects institutionalized in geriatric units].

Our one-year retrospective study evaluated drug use in a population of 136 patients over 60 years old hospitalized in a geriatric ward (moderate--and long-term institutionalization). After having classified the reason for hospitalization, the length of stay and the number of pathologies per patient, the number of prescribed medications was quantified by means of a drug-day unit (D-D). The mean number was 3.36 D-D, which was independent of sex, age and reason for admission. The most frequently prescribed medications treated central nervous system, cardiovascular and metabolic disorders. These results were compared to those of CREDOC 1981 and CREDES 1987. In addition, 14 iatrogenic episodes were identified in this study; aminoglycosides and cardiovascular drugs were responsible for the majority of them, despite the precautions taken in light of the therapeutic indications. The iatrogenesis thus identified was not due to biological abnormalities found in the elderly. In our opinion, this evaluation of drug use is a good predictive element for understanding iatrogenicity on a larger scale and thereby to attempt to avoid it.

Aged↗
PubMed1989

[Assays of apolipoproteins A and B as atherogenicity factors in aged patients at hospitals].

A systematic study of 100 elderly patients in a hospital geriatric unit was undertaken to analyse the relationship between clinical cardiovascular events (angina, myocardial infarction, hypertension, cerebrovascular accidents, temporo-spatial disorientation, invalidity, incontinence) and plasma lipids (total cholesterol, HDL and LDL fractions, triglycerides, apolipoprotein A and B and total cholesterol/HDL and apolipoprotein B/A ratios). The average triglyceride and apolipoprotein A concentrations were related to the patient's validity: The triglycerides were significantly higher in the group of invalid patients (+22%), p = 0.05. The apolipoprotein A levels were significantly lower in the invalid group (-12%), p = 0.05.

Aged↗