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Biomedical subjects

David C Taylor

Publications and source records attributed to David C Taylor.

At least 19 recordsLinked to original sources
PubMed2006

Involvement of a glycerol-3-phosphate dehydrogenase in modulating the NADH/NAD+ ratio provides evidence of a mitochondrial glycerol-3-phosphate shuttle in Arabidopsis.

A mitochondrial glycerol-3-phosphate (G-3-P) shuttle that channels cytosolic reducing equivalent to mitochondria for respiration through oxidoreduction of G-3-P has been extensively studied in yeast and animal systems. Here, we report evidence for the operation of such a shuttle in Arabidopsis thaliana. We studied Arabidopsis mutants defective in a cytosolic G-3-P dehydrogenase, GPDHc1, which, based on models described for other systems, functions as the cytosolic component of a G-3-P shuttle. We found that the gpdhc1 T-DNA insertional mutants exhibited increased NADH/NAD+ ratios compared with wild-type plants under standard growth conditions, as well as impaired adjustment of NADH/NAD+ ratios under stress simulated by abscisic acid treatment. The altered redox state of the NAD(H) pool was correlated with shifts in the profiles of metabolites concerning intracellular redox exchange. The impairment in maintaining cellular redox homeostasis was manifest by a higher steady state level of reactive oxygen species under standard growth conditions and by a significantly augmented hydrogen peroxide production under stress. Loss of GPDHc1 affected mitochondrial respiration, particularly through a diminished capacity of the alternative oxidase respiration pathway. We propose a model that outlines potential involvements of a mitochondrial G-3-P shuttle in plant cells for redox homeostasis.

Abscisic Acid↗
PubMed2005

An affinity probe for isolation of abscisic acid-binding proteins.

An affinity probe has been developed for isolation of receptor proteins that bind the plant hormone abscisic acid (ABA). The structural features required for biological activity have been preserved, and the probe has been demonstrated to bind to known ABA-binding proteins.

Abscisic Acid↗
PubMed2005

Venovenostomy for outflow venous obstruction in patients with upper extremity autogenous hemodialysis arteriovenous access.

Outflow venous obstruction is a common problem in patients with autogenous upper extremity hemodialysis access. Surgical revision to divert blood flow into the patent vein is sometimes possible to restore unobstructed flow. The result of this type of procedure is not yet well known. The purpose of this report is to describe our experience with outflow venovenostomy (VV) to salvage dysfunctional autogenous upper extremity arterial venous access (AVF) threatened by venous outflow obstruction in hemodialysis-dependent patients. All patients who underwent VV procedures between September 1999 and October 2004 were reviewed. Data regarding patient demographics, comorbidities, procedure indications, perioperative complications, as well as postoperative AVF function and patency were gathered from patient charts and dialysis records. A total of 11 patients underwent VV in the study period. The median age of the AVF prior to VV was 14 months, with a range of 4-45 months. Two patients had radial cephalic AVF, and they had VV done in the antecubital fossa. Nine patients had brachial cephalic AVF. Seven of them underwent cephalic vein transposition VV, while two patients had basilic vein transposition. Functional AVF was achieved after 1 month in 10 out of 11 patients. Five patients had no further access interventions, four patients required angioplasty at the VV site to maintain access function, and one patient had access infection requiring surgical revision during follow-up. One patient never achieved access function. Postintervention assisted functional patency was 90% +/- 9.5% at 39 months. Median follow-up after VV was 16 months. Outflow VV is a viable surgical option for selected patients with failing AVF due to venous outflow obstruction.

Aged↗
PubMed2005

Increased levels of erucic acid in Brassica carinata by co-suppression and antisense repression of the endogenous FAD2 gene.

Erucic acid and its derivatives represent important industrial feedstock compounds, and there is an increasing demand for the production of high erucate oils in this regard. Our goal therefore, is to develop high erucic acid (HEA) Brassicaceae lines with increased proportions of erucic acid and very long-chain fatty acids (VLCFAs). We proposed that oleate availability may be a rate-limiting factor in the biosynthesis of erucic acid. We have tried to address this question by manipulating the expression of the endogenous FAD2 gene in B. carinata using co-supression and antisense approaches. Both methods resulted in transgenic lines exhibiting decreased proportions of polyunsaturated C18 fatty acids (18:2+18:3) and concomitant and significantly increased proportions of 18:1, 22:1 and total VLCFAs. Co-suppressed FAD2 B. carinata lines exhibited 3-18% decreases in 18:2, 22-49% decreases in 18:3 and significantly increased proportions of 18:1 (36-99%), 22:1 (12-27%) and VLCFAs (6-15%). Transgenic B. carinata lines developed using an antisense FAD2 approach exhibited decreased proportions of 18:2 and 18:3 (9-39% and 33-48%, respectively) and significantly increased proportions of 18:1 (54-130%), 22:1 (5-19%) and VLCFAs (6-21%). The possibility of using these approaches to produce prototype transgenic germplasm of the Brassicaceae accumulating seed oils with improved proportions of erucic and other VLCFAs is discussed.

Brassica↗
PubMed2004

Seed-specific heterologous expression of a nasturtium FAE gene in Arabidopsis results in a dramatic increase in the proportion of erucic acid.

The fatty acid elongase [often designated FAE or beta-(or 3-) ketoacyl-CoA synthase] is a condensing enzyme and is the first component of the elongation complex involved in synthesis of erucic acid (22:1) in seeds of garden nasturtium (Tropaeolum majus). Using a degenerate primers approach, a cDNA of a putative embryo FAE was obtained showing high homology to known plant elongases. This cDNA contains a 1,512-bp open reading frame that encodes a protein of 504 amino acids. A genomic clone of the nasturtium FAE was isolated and sequence analyses indicated the absence of introns. Northern hybridization showed the expression of this nasturtium FAE gene to be restricted to the embryo. Southern hybridization revealed the nasturtium beta-ketoacyl-CoA synthase to be encoded by a small multigene family. To establish the function of the elongase homolog, the cDNA was introduced into two different heterologous chromosomal backgrounds (Arabidopsis and tobacco [Nicotiana tabacum]) under the control of a seed-specific (napin) promoter and the tandem 35S promoter, respectively. Seed-specific expression resulted in up to an 8-fold increase in erucic acid proportions in Arabidopsis seed oil, while constitutive expression in transgenic tobacco tissue resulted in increased proportions of very long chain saturated fatty acids. These results indicate that the nasturtium FAE gene encodes a condensing enzyme involved in the biosynthesis of very long chain fatty acids, utilizing monounsaturated and saturated acyl substrates. Given its strong and unique preference for elongating 20:1-CoA, the utility of the FAE gene product for directing or engineering increased synthesis of erucic acid is discussed.

Acetyltransferases↗
PubMed2004

Gaining insight into the role of serine 282 in B. napus FAE1 condensing enzyme.

To gain some insight whether there is an absolute requirement for the serine 282 to yield a functional fatty acid elongase 1 condensing enzyme we have introduced point mutations in the FAE1 coding sequence which led to the substitution of serine 282 with several aliphatic or aromatic amino acids. The mutated FAE1 polypeptides were expressed in yeast. Gas chromatography analyses of the fatty acid methyl esters from yeast lysates and fatty acid elongase activity assays demonstrated that there is not an absolute requirement for serine at position 282 to yield a functional FAE1 condensing enzyme.

Acetyltransferases↗
PubMed2003

A new abscisic acid catabolic pathway.

We report the discovery of a new hydroxylated abscisic acid (ABA) metabolite, found in the course of a mass spectrometric study of ABA metabolism in Brassica napus siliques. This metabolite reveals a previously unknown catabolic pathway for ABA in which the 9'-methyl group of ABA is oxidized. Analogs of (+)-ABA deuterated at the 8'-carbon atom and at both the 8'- and 9'-carbon atoms were fed to green siliques, and extracts containing the deuterated oxidized metabolites were analyzed to determine the position of ABA hydroxylation. The results indicated that hydroxylation of ABA had occurred at the 9'-methyl group, as well as at the 7'- and 8'-methyl groups. The chromatographic characteristics and mass spectral fragmentation patterns of the new ABA metabolite were compared with those of synthetic 9'-hydroxy ABA (9'-OH ABA), in both open and cyclized forms. The new compound isolated from plant extracts was identified as the cyclized form of 9'-OH ABA, which we have named neophaseic acid (neoPA). The proton nuclear magnetic resonance spectrum of pure neoPA isolated from immature seeds of B. napus was identical to that of the authentic synthetic compound. ABA and neoPA levels were high in young seeds and lower in older seeds. The open form (2Z,4E)-5-[(1R,6S)-1-Hydroxy-6-hydroxymethyl-2,6-dimethyl-4-oxo-cyclohex-2-enyl]-3-methyl-penta-2,4-dienoic acid, but not neoPA, exhibited ABA-like bioactivity in inhibiting Arabidopsis seed germination and in inducing gene expression in B. napus microspore-derived embryos. NeoPA was also detected in fruits of orange (Citrus sinensis) and tomato (Lycopersicon esculentum), in Arabidopsis, and in chickpea (Cicer arietinum), as well as in drought-stressed barley (Hordeum vulgare) and B. napus seedlings.

Abscisic Acid↗
PubMed2003

Molecular and biochemical characterization of an aminoalcoholphosphotransferase (AAPT1) from Brassica napus: effects of low temperature and abscisic acid treatments on AAPT expression in Arabidopsis plants and effects of over-expression of BnAAPT1 in transgenic Arabidopsis.

Aminoalcoholphosphotransferases (AAPT, EC 2.7.8.1 and EC 2.7.8.2) catalyze the transfer of CDP-aminoalcohols to sn-1, 2 diacylglycerol (DAG) to form phosphatidylaminoalcohols with the release of CMP. The Brassica napus L. AAPT1 gene (designated BnAAPT1) was identified from cDNA libraries of seedlings and developing seeds. Functional characterization was accomplished by heterologous expression of BnAAPT1 in a yeast strain deficient in AAPT activities. BnAAPT1 exhibited a greater preference for utilizing CDP-choline as a substrate with Vmax of 35 [14C]phosphatidylcholine nmol h(-1) mg(-1) protein and apparent Km of 32 microM while CDP-ethanolamine had a Vmax of 13 [14C]phosphatidylethanolamine nmol h(-1) mg(-1)protein and an apparent Km of 127 microM. The enzyme was activated by Mg2+, Mn2+ and phospholipid mixtures, and inhibited by Ca2+. A CDP-alcohol phosphotransferase motif, Asp99-Gly100-(X2)-Ala103-Arg104-(X8)-Gly113-(X3)-Asp117-(X3)-Asp121, was completely conserved in BnAAPT1 and its catalytic role was confirmed by scanning alanine mutagenesis. Over-expression of BnAAPT1 under the control of the double 35S promoter in transgenic Arabidopsis thaliana (L.) Heynh. plants led to elevated levels of the corresponding transcript and enzyme activity. In four of the high over-expression transgenic lines, phospholipid and fatty acid composition analyses revealed that chloroplastidic and extrachloroplastidic membranes isolated from transgenic leaves had about a 25% increase in phosphatidylcholine and in the proportions of polyunsaturated fatty acids [18:2+18:3], relative to the control. There were also consistent, but small differences observed in the proportions of 18:3 in transgenic green siliques and in 20:1 in mature transgenic seeds of these lines. Induction of Arabidopsis AAPT transcription in response to (+)-abscisic acid and low-temperature treatments, and the cold tolerance in BnAAPT1 transgenic seedlings implies that AAPT may play a role in resistance to damage at low growth temperatures.

Abscisic Acid↗
PubMed2003

Schizophrenias and epilepsies: why? when? how?

Detailed studies of the association between the epilepsies and the schizophrenias extend over 40 years. Recent studies are abundant and make fertile use of new technologies. However, the pathological changes described in schizophrenias are quite varied. Studies fail to recognize that "epilepsies" and "schizophrenias" have varied in definition over time, and have always been weak categories with which to do science. Now that it is possible to measure deficits in brain structure, it would be better to see what behavioral problems are associated with specific cerebral pathology. It would be wise to be very precise in describing the behaviors and the nature and timing of their emergence rather than using terms such as psychoses. Schizophrenias have neurological, neuropsychological, and behavioral antecedents in childhood. Those associated with later epilepsies show biases, persistent in many studies over a number of years, toward relative excess of females, left temporal lobe structural deficits, and non-right-handedness. Schizophrenia should now be a predictable eventuality in certain people with epilepsies, an important factor in medical and surgical treatment.

Chronic Disease↗
PubMed2003

Expression of the Arabidopsis ADS1 gene in Brassica juncea results in a decreased level of total saturated fatty acids.

Brassica juncea plants transformed with the Arabidopsis ADS1 gene, which encodes a plant homologue of the mammalian and yeast acyl-CoA Delta9 desaturases and the cyanobateria acyl-lipid Delta9 desaturase, were found to have a statistically significant decrease in the level of saturated fatty acids in seeds. The decrease in the level of saturated fatty acids is largely attributable to decreases in palmitic acid (16:0) and stearic acid (18:0), although arachidic acid (20:0), behenic acid (22:0) and lignoceric acid (24:0) were also decreased in the transgenic seeds compared to the negative control lines. As a result, the level of oleic acid (18:1) was slightly increased in the transgenic seed lines compared to the non-transformed controls. However, a decrease in saturated fatty acid is not always accompanied by the corresponding increase in mono-unsaturated fatty acids. For example, palmitoleic acid (16:1), gondoic acid (20:1) and nervonic acid (24:1) were all found to be decreased in transgenic seeds. The levels of linoleic acid (18:2) and linolenic acid (18:3) were also notably changed in the transgenic lines compared to the controls. The present study provides preliminary experimental data suggesting that the Arabidopsis ADS1 encodes a fatty acid Delta9 desaturase and could be useful in genetic engineering for modifying the level of saturated fatty acids in oilseed crops. However, the effect of ADS1 gene expression on seed oil fatty acid composition is beyond the changes of total saturated and mono-unsaturated fatty acids, which suggests a complex mechanism is involved in the regulation of fatty acid metabolism.

Journal Article↗
PubMed2003

Biochemical and physiological studies of Arabidopsis thaliana transgenic lines with repressed expression of the mitochondrial pyruvate dehydrogenase kinase.

Pyruvate dehydrogenase kinase (PDHK), a negative regulator of the mitochondrial pyruvate dehydrogenase complex (mtPDC), plays a pivotal role in controlling mtPDC activity, and hence, the TCA cycle and cell respiration. Previously, the cloning of a PDHK cDNA from Arabidopsis thaliana and the effects of constitutively down-regulating its expression on plant growth and development has been reported. The first detailed analyses of the biochemical and physiological effects of partial silencing of the mtPDHK in A. thaliana using antisense constructs driven by both constitutive and seed-specific promoters are reported here. The studies revealed an increased level of respiration in leaves of the constitutive antisense PDHK transgenics; an increase in respiration was also found in developing seeds of the seed-specific antisense transgenics. Both constitutive and seed-specific partial silencing of the mtPDHK resulted in increased seed oil content and seed weight at maturity. Feeding 3-(14)C pyruvate to bolted stems containing siliques (constitutive transgenics), or to isolated siliques or immature seeds (seed-specific transgenics) confirmed a higher rate of incorporation of radiolabel into all seed lipid species, particularly triacylglycerols. Neither constitutive nor seed-specific partial silencing of PDHK negatively affected overall silique and seed development. Instead, oil and seed yield, and overall plant productivity were improved. These findings suggest that a partial reduction of the repression of the mtPDC by antisense PDHK expression can alter carbon flux and, in particular, the contribution of carbon moieties from pyruvate to fatty acid biosynthesis and storage lipid accumulation in developing seeds, implicating a role for mtPDC in fatty acid biosynthesis in seeds.

Antisense Elements (Genetics)↗