Biomedical subjects

R D Thompson

Publications and source records attributed to R D Thompson.

At least 55 records · Page 3Linked to original sources

PubMed1992

The S locus of flowering plants: when self-rejection is self-interest.

In certain families of flowering plants, a self-incompatibility (SI) locus prevents self-fertilization, by a specific interaction between the S-gene product produced in the pistil and the S-gene products borne on or expressed by the male gametophyte, the pollen grain. The female S-locus gene products for two families showing different types of SI have been putatively identified as major pistil glycoproteins (the S-locus-specific glycoproteins of the Brassicaceae and the S-RNases of the Solanaceae). However, they are distinct in sequence and mode of action. The nature of the S-locus gene product borne by the pollen is still uncertain in both systems.

Brassica↗

PubMed1991

Restriction fragment length polymorphism-mediated targeting of the ml-o resistance locus in barley (Hordeum vulgare).

The ml-o locus in barley confers resistance to all known races of the fungus Erysiphe graminis f.sp. hordei. Since the molecular mechanisms underlying ml-o-mediated resistance are currently undefined, experiments have been initiated to isolate the gene by means of its map position. A collection of backcross lines containing ml-o alleles derived from six barley genotypes allowed us to identify a set of DNA markers very tightly linked to the resistance locus. These markers span an unexpectedly small segment of 8.6 centimorgans on chromosome 4 that includes the Ml-o locus. Two of the markers cosegregate with the resistance locus on the basis of 44 homozygous resistant plants identified within a segregating F2 population derived from an intravarietal cross. Colinearity of the resistance-linked markers was confirmed in an F2 mapping population derived from a wide cross between Hordeum vulgare subsp. vulgare and Hordeum vulgare subsp. spontaneum. The two markers cosegregating with the resistance locus in the former cross define in the latter cross an interval of 2.4 centimorgans within which Ml-o is most probably situated. The set of linked markers opens up the possibility of carrying out a bidirectional chromosomal walk or jump to the gene.

Journal Article↗

PubMed1991

The maize regulatory locus Opaque-2 encodes a DNA-binding protein which activates the transcription of the b-32 gene.

The maize locus, Opaque-2, controls the expression in developing endosperm of structural genes encoding a family of storage proteins, the 22 kd zeins, and an abundant albumin, termed b-32. It is shown that the promoter of the b-32 gene is activated in vivo in the presence of the O2 gene product and that the information necessary for this activation resides in a 440 bp DNA fragment containing five O2 binding sites (GATGAPyPuTGPu). Two of these sites are embedded in copies of the 'endosperm box', a motif thought to be involved in endosperm-specific expression, which is also represented in 22 kd zein promoters. The O2 protein is also shown to be capable of binding in vitro and activating in vivo, its own promoter.

Base Sequence↗

PubMed1991

Sequence variability and gene structure at the self-incompatibility locus of Solanum tuberosum.

Allelic complexity is a key feature of self-incompatibility (S) loci in gametophytic plants. We describe in this report the allelic diversity and gene structure of the S locus in Solanum tuberosum revealed by the isolation and characterization of genomic and cDNA clones encoding S-associated major pistil proteins from three alleles (S1, Sr1, S2). Genomic clones encoding the S1 and S2 proteins provide evidence for a simple gene structure: Two exons are separated by a small intron of 113 (S1) and 117 bp (S2). Protein sequences deduced from cDNA clones encoding S1 and Sr1 proteins show 95% homology, 15 of the 25 residues that differ between these S1 and Sr1 alleles are clustered in a short hypervariable protein segment (amino acid positions 44-68), which corresponds in the genomic clones to DNA sequences flanking the single intron. In contrast, these alleles are only 66% homologous to the S2 allele, with the residues that differ between the alleles being scattered throughout the sequence. DNA crosshybridization experiments identify a minimum of three classes of potato S alleles: one class contains the alleles S1, Sr1 and S3, the second class S2 and an allele of the cultivar Roxy, and the third class contains at present only S4. It is proposed that these classes reflect the origin of the S alleles from a few ancestral S sequence types.

Alleles↗

PubMed1991

Molecular analysis of the Bg-rbg transposable element system of Zea mays L.

The two components of the Bg-rbg transposable element system of maize have been cloned. The Bg element, isolated from the mutable allele wx-m32:: Bg is inserted in the intron of the Waxy (Wx) gene between exons 12 and 13. The length of the element is of 4869 bp. Bg has 5 bp terminal inverted repeats, and generates upon insertion an 8 bp direct duplication of the target sequence. Both ends of the Bg element contain a 76 bp direct repeat adjacent to the terminal inverted repeats. The hexamer motif TATCGGC is here repeated several times in direct or inverse orientation. The rbg element was isolated from the mutable allele o2m(r) where it is located in the promoter region of the Opaque-2 (O2) gene. rbg is approximately 4.5 kb in length, has terminal inverted repeats identical to those of the Bg element, and is also flanked by an 8 bp direct duplication at the target site. Like Bg, rbg carries the 76 bp direct repeats. Restriction enzyme analysis reveals that, compared to Bg, the receptor element is distinguishable by small deletion and insertion events. Sequence data indicate that not more than 75% homology exists at the DNA level between the rbg element and the autonomous Bg element.

Alleles↗

PubMed1991

Investigation of a self-compatible mutation in Solanum tuberosum clones inhibiting S-allele activity in pollen differentially.

A self-compatible (SC) mutation, identified in dihaploid lines of Solanum tuberosum, was investigated. It has previously been proposed that this mutation arose by translocation of an S-allele (S1) to a new chromosomal location. When present in pollen grains of genotype Sx, it overcomes the incompatibility reaction normally seen on styles carrying the Sx allele. However, when present in S1-bearing pollen grains, the normal incompatibility reaction on styles carrying S1 is still observed. Using probes for the potato (S. tuberosum L.) S-linked glycoprotein (SLG) genes, it is shown that no sequence derived from SLG allele S1 can be linked to the presence of the SC mutation. The polypeptide product of the SLG allele S1 is also not detectable in SC mutant lines unless the S1 allele is also present. It is concluded that the SC mutation arose in a sequence other than that encoding the SLG S1 polypeptide, either in a part of the S-locus that is distinct from the S-gene, or at a different locus, giving rise to an inhibitor.

Alleles↗

PubMed1991

Cardiovascular actions of adenosines, but not adenosine receptors, differ in rat and guinea pig.

This study compared the structure-activity relationships of 16 analogues at the A1 and A2 adenosine receptors (A1AR, A2AR) of rat and guinea pig. Radioligand binding studies revealed no marked differences in the affinities of each analogue at the A1AR of brain cortex or the A2AR of brain striatum. Bioassay employing Langendorff heart preparations showed that the guinea pig is more sensitive than the rat to A1AR-mediated slowing of conduction through the atrioventricular node and, in some instances, to A2AR-mediated coronary vasodilation. That difference could reflect factors such as receptor density or efficacy of coupling to effector systems.

Adenosine↗

PubMed1991

2-Alkoxyadenosines: potent and selective agonists at the coronary artery A2 adenosine receptor.

A Langendorff guinea pig heart preparation served for the assay of agonist activity of a series of 24 2-alkoxyadenosines at the A1 and A2 adenosine receptors of, respectively, the atrioventricular node (conduction block) and coronary arteries (vasodilation). Activities are low at the A1 receptor and do not show a clear relationship to the size or hydrophobicity of the C-2 substituent. All the analogues are more potent at the A2 receptor, activity varying directly with the size and hydrophobicity of the alkyl group. The most potent analogue in this series, 2-(2-cyclohexylethoxy)adenosine has an EC50 of 1 nM for coronary vasodilation and is 8700-fold selective for the A2 receptor.

Adenosine↗

PubMed1991

2-aralkoxyadenosines: potent and selective agonists at the coronary artery A2 adenosine receptor.

A Langendorff guinea pig heart preparation served for the assay of agonist potency of a series of 26 2-aralkoxyadenosines at the A1 and A2 receptors of, respectively, the atrioventricular node (conduction block) and coronary arteries (vasodilation). All of the analogues are weak agonists at the A1 receptor, requiring concentrations greater than 9 microM to cause second degree heart block. At the A2 receptor 2-phenethoxyadenosine is the most potent of the 2-phenylalkyladenosines. The activity of ring-substituted (F, Cl, CH3, and OCH3) 2-phenethoxyadenosines increases ortho less than meta less than para. The EC50s of coronary vasoactivity of several para-substituted analogues are in the subnanomolar range. The most potent analogue, 2-[2-(4-methylphenyl)ethoxy]adenosine 19, has an EC50 for coronary vasodilation of 190 pM and an A1/A2 selectivity ratio of 44,000. Aryl groups such as thienyl, indoloyl, or naphthyl also support A2 agonist activity. Although 2-oxoadenosine is 3 times more vasoactive than 2-aminoadenosine, the activities of the phenyl derivatives are markedly different; 2-phenoxyadenosine is 23 times weaker than 2-(phenylamino)adenosine (CV-1808).

Adenosine↗

PubMed1991

N6,9-disubstituted adenines: potent, selective antagonists at the A1 adenosine receptor.

N6-Substituted 9-methyladenines are potent antagonists of the activation of A1 adenosine receptors. The present study assessed the effect of N6 and N-9 substituents on the binding of adenines to the A1 and A2 receptors, respectively, of rat brain cortex and striatum and also on the antagonism of the A2 receptor mediated stimulation of the adenylate cyclase of PC12 cells by N-ethyladenosine-5'-uronamide. The potency ranking of 9-substituted adenines varied directly with the hydrophobicity of the substituent: cyclopentyl greater than phenyl greater than tetrahydrofuryl greater than ethyl greater than methyl greater than 2-hydroxyethyl. The 9-substituted adenines showed little selectivity for either receptor and the R enantiomer of N6-(1-phenyl-2-propyl)-9-methyladenine was only 4-fold more potent than the S enantiomer at the A1 receptor. An N6-cyclopentyl substituent increased potency at the A1 receptor and decreased potency at the A2 receptor, resulting in selectivity for the A1 receptor of up to 39-fold. The N6-cyclopentyl group completely overshadowed the effect of the hydrophobicity of the 9-substituent. A 2-chloro substituent did not alter the potency of an N6-substituted 9-methyladenine.

Adenine↗

PubMed1991

Activity of N6-substituted 2-chloroadenosines at A1 and A2 adenosine receptors.

Radioligand binding studies of N6-substituted adenosines at the A1 and A2 adenosine receptors of rat brain cortex and rat brain striatum, respectively, show that a 2-chloro substituent does not consistently change the affinity or the selectivity of these analogues for the A1 receptor. A 2-chloro substituent lowers the characteristic stereoselectivity of the A1 receptor toward the R diastereomer of N6-(1-phenyl-2-propyl)adenosine. A 2-chloro substituent consistently increases potency of N6-substituted adenosines as agonists at an adenosine A2 receptor stimulatory to adenylate cyclase in PC12 cell membranes.

2-Chloroadenosine↗

PubMed1990

A prospective evaluation of a simplified captopril test for the detection of renovascular hypertension.

Renovascular hypertension is potentially curable but of low prevalence. A previous retrospective study has demonstrated the use of a potentiated increase in plasma renin activity after captopril administration as a diagnostic test for renovascular hypertension; this requires two blood samples for plasma renin activity determination and three inclusive criteria for a positive test result. We applied this test prospectively to screen 100 hypertensive patients for renovascular hypertension. We evaluated 29 patients with renovascular hypertension; the remainder were diagnosed as having essential hypertension. In our patient population, a postcaptopril plasma renin activity of 5.7 ng of angiotensin per milliliter per hour (ngAl.mL-1.h-1) or greater had a 100% sensitivity and an 80% specificity for renovascular hypertension. An absolute increase in plasma renin activity with captopril of 4.7 ngAl.mL-1.h-1 or greater had a lower sensitivity of 90% and a specificity of 87%, whereas a fractional increase in plasma renin activity after captopril of 150% or higher had the lowest sensitivity of 69% and a specificity of 86%. A subgroup analysis of 38 patients who were receiving diuretic therapy demonstrated that the test sensitivity was unchanged but the specificity was reduced. In conclusion, a single postcaptopril plasma renin activity value of 5.7 ngAl.mL-1.h-1 or greater is a simplified screening test for renovascular hypertension, with excellent sensitivity and acceptable specificity. This test is well tolerated, inexpensive, and easy to perform.

Captopril↗

PubMed1989

Determination of thymol in halothane anaesthetic preparations by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) procedure has been developed for the isolation and quantification of thymol, a stabilizing agent present in halothane anaesthetic preparations. The method offers improvements in specificity and simplicity with respect to a current official procedure for thymol in halothane. Results for commercial preparations obtained by the proposed procedure demonstrate excellent precision and accuracy with RSD values for replicate analysis ranging from 0.11 to 0.74% and recoveries via fortification from 99.6 to 100.1%. The HPLC method was compared to compendial procedures for thymol bulk substance and halothane products. Chromatographic separation of other related phenolic preservatives used in pharmaceuticals suggests a more extensive application of the proposed procedure.

Chromatography, High Pressure Liquid↗

PubMed1989

Tissue-specific expression of a wheat high molecular weight glutenin gene in transgenic tobacco.

The expression of a wheat genomic clone containing the entire coding sequence of the high molecular weight glutenin subunit 12 gene flanked by 2.6 kilobases of 5' and 1.5 kilobases of 3' sequences has been studied after introduction into tobacco. Seeds of different tobacco plants containing the full-length wheat genomic clone accumulated different amounts of intact high molecular weight glutenin subunit mRNA and of a polypeptide displaying the solubility, molecular weight, and antigenic properties of the high molecular weight glutenin subunit 12. The wheat protein accumulated without obvious degradation products and constituted up to approximately 0.1% of the total tobacco endosperm protein. Restriction fragments corresponding to 2.6 kilobases, 1.4 kilobases, and 433 base pairs of high molecular weight glutenin 5' upstream sequence were fused to the coding sequence of the chloramphenicol acetyltransferase (CAT) gene in the vector polyCATter and transferred into tobacco. Chloramphenicol acetyltransferase enzyme activity was detected only in the seed endosperm tissue of the transformed plants. It was detected in tobacco seeds 8 days after anthesis and persisted until seed maturity. It is concluded that 433 base pairs of high molecular weight glutenin upstream sequence are sufficient to confer endosperm-specific expression of this monocot gene in the dicot tobacco.

Chloramphenicol O-Acetyltransferase↗

PubMed1988

Determination of coumarin as an adulterant in vanilla flavoring products by high-performance liquid chromatography.

A high-performance liquid chromatographic procedure was developed for the isolation and quantitation of coumarin from vanilla-based liquid flavorings of Mexican origin. Forty products representing fourteen different Mexican brands were assayed for coumarin, vanillin, and ethyl vanillin by the proposed method. The procedure has been adapted to the analysis of other products including domestic vanilla extracts and imitation vanilla flavorings for vanillin, ethyl vanillin, 4-hydroxybenzaldehyde and piperonal. Chromatographic retention data for thirty-seven compounds associated with vanillin and vanilla products employing two mobile phase systems are presented.

Benzaldehydes↗

PubMed1988

Loss of corticomedullary demarcation on magnetic resonance imaging: an index of biopsy-proven acute renal transplant dysfunction.

A prospective study of 19 cadaveric renal allograft recipients with suspected graft rejection was undertaken to compare the histological findings of the renal transplant biopsy with the results of magnetic resonance imaging (MRI). All 19 patients underwent a biopsy of the transplant allograft. Biopsy results included acute cellular rejection, acute vascular rejection, chronic vascular rejection (CVR), and acute tubular necrosis (ATN). Recipients of cadaveric renal allografts with normal function served as controls. The control showed distinct corticomedullary demarcation (CMD) on T1-weighted imaging. In contrast, CMD was absent or diminished in all the patients with suspected allograft rejection. Unfortunately, the loss of CMD did not correlate with a specific biopsy diagnosis. Patients with biopsy evidence of acute and chronic rejection or ATN demonstrated loss of CMD with similar image patterns. In conclusion, MRI is capable of detecting renal allograft dysfunction, but does not permit the determination of a specific cause.

Adult↗

PubMed1988

Determination of isosorbide dinitrate in pharmaceutical products by HPLC.

A high-performance liquid chromatographic (HPLC) assay for isosorbide dinitrate in pharmaceutical formulations is described. The method employs a reversed-phase C18 column with a mobile phase containing methanol/water/acetate buffer and is specific for isosorbide dinitrate with respect to its 2- and 5-mononitrate degradation products and other organic polynitrate esters. The method is applicable to the analysis of the diluted bulk drug and dosage forms, including sublingual, oral, chewable, and timed-release preparations.

Chromatography, High Pressure Liquid↗

PubMed1987

Localization of sequences in wheat endosperm protein genes which confer tissue-specific expression in tobacco.

The developing cereal grain accumulates large quantities of proteins which are unique to the endosperm tissue. The DNA sequences which determine their endosperm-specific expression have not yet been identified. In the absence of a suitable transformation-regeneration system for cereals, we have investigated whether chimaeric genes consisting of low mol. wt (LMW) and high mol. wt (HMW) glutenin gene upstream sequences coupled to the coding region of the bacterial chloramphenicol acetyl transferase (CAT) gene could be specifically expressed in transgenic tobacco. The fusions, made in a Ti-derived binary vector, were introduced into tobacco via Agrobacterium tumefaciens-mediated transformation and their activity assayed. Both the LMW and HMW glutenin chimaeric genes exhibited endosperm-specific CAT activity in the transformed plants. In addition, a deletion series of the LMW glutenin sequence indicated that sequences present between 326 bp and 160 bp upstream of the transcription start point are necessary to confer endosperm-specific CAT activity.

Journal Article↗