PubMed Health⌕ Search

Biomedical subjects

T A Jones

Publications and source records attributed to T A Jones.

At least 19 recordsLinked to original sources
PubMed1992

Subcortical deterioration after cortical damage: effects of diazepam and relation to recovery of function.

Agents which enhance the activity of gamma-aminobutyric acid (GABA) can severely disrupt behavioral recovery in rats following damage to the neocortex if delivered during a sensitive postoperative period. The mechanisms of this disruption have not been found. It has been suggested previously that the ipsilateral striatum and related structures may be transiently disabled after cortical lesions and that diazepam may interfere with restoration of function in these areas. In the present experiment, the subcortical anatomical effects of chronic (3 weeks) administration of diazepam, an indirect GABAergic agonist, were assessed following unilateral lesions of the anteromedial cortex (AMC) or the sensorimotor cortex (SMC) in rats. Atrophic and degenerative changes were examined in the striatum, substantia nigra and thalamus. Following either AMC or SMC lesions, there was a reduction in the size of the ipsilateral striatum and thalamus and a loss of neurons in the ipsilateral substantia nigra pars reticulata (SNr). After AMC lesions, striatal atrophy and neuron loss in the SNr were increased by the diazepam regimen relative to vehicle-treated controls. In addition, diazepam interfered with the behavioral recovery from somatic-sensorimotor asymmetries in AMC-lesioned rats. After SMC lesions, the sites of striatal and thalamic atrophy were different from that observed after AMC lesions, and the extent of atrophy and neuron loss was not exaggerated by diazepam treatment. Consistent with these data, diazepam did not significantly affect recovery from SMC lesions. These findings suggest that the long-term disruptive effects of diazepam on recovery of function after AMC lesions may be related to an augmentation of lesion-induced degeneration.

Animals↗
PubMed1992

Overgrowth and pruning of dendrites in adult rats recovering from neocortical damage.

Unilateral lesions to the forelimb representation (FL) area of the rat sensorimotor cortex caused a time-dependent increase in the dendritic arborization of layer V pyramidal neurons in the contralateral homotopic cortex. The increase in arborization was maximum at 2-3 weeks after the lesion, following which there was a partial reduction in dendritic branching. These neural morphological changes may be related to post-lesion behavioral changes in the use of the forelimbs.

Analysis of Variance↗
PubMed1992

Mutating the charged residues in the binding pocket of cellular retinoic acid-binding protein simultaneously reduces its binding affinity to retinoic acid and increases its thermostability.

Three-dimensional modeling of the complex between retinoic acid-binding protein (CRABP) and retinoic acid suggests that binding of the ligand is mediated by interaction between the carboxyl group of retinoic acid and two charged amino acids (Arg-111 and Arg-131) whose side chains project into the barrel of the protein. To assess the contribution of these amino acids to protein-ligand interaction, amino acid substitutions were made by oligonucleotide-directed, site-specific mutagenesis. The wild-type and mutant proteins were expressed in E. coli and subsequently purified. Like wild-type CRABP, the mutant proteins are composed mainly of beta-strands as determined by circular dichroism in the presence and absence of ligand, and thus presumably are folded into the same compact barrel structure as the wild-type protein. Mutants in which Arg-111 and Arg-131 are replaced by glutamine bind retinoic acid with significantly lower affinity than the wild-type protein, arguing that these two residues indeed interact with the ligand. The mutant proteins are more resistant to thermal denaturation than wild-type CRABP in the absence of retinoic acid, but they are not as thermostable as the CRABP-retinoic acid complex. These data suggest a model for CRABP-retinoic acid interaction in which the repulsive forces between the positively-charged arginine residues provide conformational flexibility to the native protein for retinoic acid to enter the binding pocket. Elimination of the positively-charged pair of amino acids produces a protein that is more thermostable than wild-type CRABP but less effective at ligand-binding.

Amino Acid Sequence↗
PubMed1992

Investigation of the function of mutated cellulose-binding domains of Trichoderma reesei cellobiohydrolase I.

The function of the cellulose-binding domain (CBD) of the cellobiohydrolase I of Trichoderma reesei was studied by site-directed mutagenesis of two amino acid residues identified by analyzing the 3D structure of this domain. The mutant enzymes were produced in yeast and tested for binding and activity on crystalline cellulose. Mutagenesis of the tyrosine residue (Y492) located at the tip of the wedge-shaped domain to alanine or aspartate reduced the binding and activity on crystalline cellulose to the level of the core protein lacking the CBD. However, there was no effect on the activity toward small oligosaccharide (4-methylumbelliferyl beta-D-lactoside). The mutation tyrosine to histidine (Y492H) lowered but did not destroy the cellulose binding, suggesting that the interaction of the pyranose ring of the substrate with an aromatic side chain is important. However, the catalytic activity of this mutant on crystalline cellulose was identical to the other two mutants. The mutation P477R on the edge of the other face of the domain reduces both binding and activity of CBHI. These results support the hypothesis that both surfaces of the CBD are involved in the interaction of the binding domain with crystalline cellulose.

Adsorption↗
PubMed1992

Vestibular short latency responses to pulsed linear acceleration in unanesthetized animals.

Linear acceleration transients were used to elicit vestibular compound action potentials in non-invasively prepared, unanesthetized animals for the first time (chicks, Gallus domesticus, n = 33). Responses were composed of a series of up to 8 dominant peaks occurring within 8 msec of the stimulus. Response amplitudes for 1.0 g stimulus ranged from 1 to 10 microV. A late, slow, triphasic, anesthesia-labile component was identified as a dominant response feature in unanesthetized animals. Amplitudes increased and latencies decreased as stimulus intensity was increased (MANOVA P less than 0.05). Linear regression slope ranges were: amplitudes = 1.0-5.0 microV/g; latencies = -300 to -1100 microseconds/g. Thresholds for single polarity stimuli (0.035 +/- 0.022 g, n = 11) were significantly lower than those of alternating polarity (0.074 +/- 0.028 g, n = 18, P less than 0.001). Bilateral labyrinthectomy eliminated responses whereas bilateral extirpation of cochleae did not significantly change response thresholds. Intense acoustic masking (100/104 dB SL) produced no effect in 2 animals, but did produce small to moderate effects on response amplitudes in 7 others. Changes were attributed to effects on vestibular end organs. Results of unilateral labyrinth blockade (tetrodotoxin) suggest that P1 and N1 preferentially reflect ipsilateral eighth nerve compound action potentials whereas components beyond approximately 2 msec reflect activity from vestibular neurons that depend on both labyrinths. The results demonstrate that short latency vestibular compound action potentials can be measured in unanesthetized, non-invasively prepared animals.

Acceleration↗
PubMed1992

Recovery of vestibular function following hair cell destruction by streptomycin.

Can the vestibular periphery of warm-blooded vertebrates recover functionally from severe sensory hair cell loss? Recent findings in birds suggest a mechanism for recovery but in fact no direct functional evidence has been reported. We produced vestibular hair cell lesions using the ototoxic agent streptomycin sulfate (600 mg/kg/day, 8 days, chicks, Gallus domesticus). Compound action potentials of the vestibular nerve were used as a direct measure of peripheral vestibular function. Vestibular thresholds, neural activation latencies and amplitudes were documented. Eight days of drug treatment elevated thresholds significantly (P < 0.001) and eliminated all but remnants of vestibular activity. Virtually complete physiological recovery occurred in all animals studied over a period of 70 days following treatment. Thresholds recovered within two weeks of drug treatment whereas the return of response morphologies including activation latencies and amplitudes required an additional 6-8 weeks.

Action Potentials↗
PubMed1992

A somatic cell hybrid panel for regional mapping of human chromosome 18.

We have produced and characterized a panel of seven somatic cell hybrids defining eight potential intervals on human chromosome 18. Using 24 markers that have previously been assigned to this chromosome, we have placed markers into six of these regions. The gene for alpha 2-plasmin inhibitor (PLI) and the anonymous DNA segment locus D18S23 are excluded from this chromosome.

Animals↗
PubMed1992

Major surgery of oral and oropharyngeal carcinoma.

Thirty-two composite resections were carried out in the Department of Otolaryngology at Groote Schuur Hospital for oral and oro-pharyngeal squamous carcinoma over the 10-year period, 1977-1986. Three patients were lost to review but all others were followed up to death or to five years. Twenty-seven patients underwent surgery as their primary procedure and five for recurrence after primary radiotherapy. The overall survival was 16 patients at three years and eight at five years. Only one of the five patients who underwent salvage surgery after failed radiotherapy was alive at five years and all five experienced serious postoperative complications. All those surviving over five years had had either N0 or N1 disease at the time of presentation for surgery.

Adult↗
PubMed1991

Folate-binding protein is a marker for ovarian cancer.

We describe the isolation of a complementary DNA (cDNA) sequence encoding the ovarian cancer-associated antigen recognized by monoclonal antibody MOv18 and its identification as a high-affinity folate-binding protein (FBP). Functional cDNA clones were isolated using mRNA from the ovarian carcinoma cell line SKOV3 and colon carcinoma cell line HT29, by transient expression in WOP cells and selection of expressing cells by adhesion to antibody-coated magnetic beads. The cDNAs differed in the lengths of 5'- and 3'-noncoding regions, but they encoded identical peptides. A database search clearly showed them to be adult high-affinity FBPs with amino acid sequences identical with those isolated from normal placenta and several carcinoma cell lines. Reactivity of cell lines with MOv18 was quantitatively consistent with the expression of FBP mRNA. Southern hybridizations show evidence of a family of related genes and/or pseudogenes and were mapped to chromosome 11q13.3-14.1 by fluorescent in situ hybridization using cosmid clones containing part of this region. Also identified were two PstI polymorphisms of four and three alleles, respectively, and a two-allele MspI polymorphism. The folate-binding protein locus was not amplified in any of the 16 carcinoma cell lines tested and in only 1 of 10 serous adenocarcinomas, indicating that overexpression of FBP in ovarian cancer cannot, in general, be due to gene amplification.

Amino Acid Sequence↗
PubMed1991

Three-dimensional structure of fatty-acid-binding protein from bovine heart.

The complex of fatty-acid-binding protein (FABP) from bovine heart (cFABP, pI4.9) with endogenous lipid was crystallized in the presence of ammonium sulfate as precipitant. The needle-shaped crystals belong to the monoclinic space group C2, with unit-cell constants a = 5.262(6) nm, b = 7.631(8) nm, c = 3.945(5) nm and beta = 94.47(9) degrees. A native data set to 0.35 nm resolution was collected using synchrotron radiation and film methods. An initial model for the three-dimensional structure of the protein was constructed based on the crystal structure of the related bovine P2 myelin protein [Jones, T.A., Bergfors, T., Sedzik, J. & Unge, T. (1988) EMBO J. 7, 1597-1604] to which the amino acid sequence of bovine cFABP was adapted. Energy minimizations were carried out under different conditions using both an all-atom and a united-atom force field. The optimized models were used to determine the crystal structure of cFABP by molecular-replacement techniques. The structure was refined by simulated annealing to R = 0.267. As the bound lipid is heterogeneous, it could not be located in the electron-density map and/or the attained resolution was not sufficient. Bovine cFABP is composed of ten antiparallel beta strands forming a beta barrel, and by two alpha helices. The structural features are similar to those of other members of the superfamily of hydrophobic molecule transporters.

Amino Acid Sequence↗
PubMed1991

Improved methods for building protein models in electron density maps and the location of errors in these models.

Map interpretation remains a critical step in solving the structure of a macromolecule. Errors introduced at this early stage may persist throughout crystallographic refinement and result in an incorrect structure. The normally quoted crystallographic residual is often a poor description for the quality of the model. Strategies and tools are described that help to alleviate this problem. These simplify the model-building process, quantify the goodness of fit of the model on a per-residue basis and locate possible errors in peptide and side-chain conformations.

Chemical Phenomena↗
PubMed1991

Fine mapping of probes in the adenomatous polyposis coli region of chromosome 5 by in situ hybridization.

The gene for adenomatous polyposis coli has been localized to 5q21-22. We have mapped six probes from this region using isotopic or nonisotopic in situ hybridization. Using tritium-labeled probes we localized II227 (D5S37) to 5q14-15 and ECB27 (D5S98) to 5q21. Following hybridization with biotin-labeled probes, the positions of signals along the chromosomes were measured as fractional length relative to the length of the chromosome arm from centromere to qter (FLcen-qter). Ninety-five percent confidence limits, compared with standard karyotypes, provided the corresponding band localization. By this method we localized Cllpll (D5S71) to FLcen-qter 0.407-0.452 (5q21.1-21.3), ECB27 to FLcen-qter 0.426-0.473 (5q21.3), YN5.48 (D5S81) to FLcen-qter 0.459-0.496 (5q21.3-22.2), and ECB134 (D5S97) to FLcen-qter 0.509-0.533 (5q22.3-23.1). ECB220 had three sites of hybridization, a major site at FLcen-qter 0.460-0.492 (5q21.3-22.1) and minor sites at FLcen-qter 0.299-0.339 (5q14.3-15) and FLcen-qter 0.629-0.691 (5q23.3-31.2). We have shown that the chromosome 5 breakpoint in a t(5;15) translocation from a patient with Gardner's syndrome (GM03314) is between Cllpll and ECB27. Linkage data are presented suggesting that ECB27 is located on the same side of the APC locus as II227. These and published results including data on several constitutional deletions (M, SD, and brothers PW and ND) give a probable order of [cen] - [II227, proximal SD breakpoint] - [Cllpll] - [proximal PW/ND, M breakpoint(s), GM03314 breakpoint] - [ECB27] - [APC] - [YN5.48] - [distal PW/ND breakpoint] - [ECB134] - [distal M breakpoint] - [qter]. The major site of ECB220 appears to be between ECB27 and the distal PW/ND breakpoint; the distal SD breakpoint is distal to YN5.48.

Adenomatous Polyposis Coli↗
PubMed1991

Molecular cloning of human lysyl oxidase and assignment of the gene to chromosome 5q23.3-31.2.

Lysyl oxidase (EC 1.4.3.13) initiates the crosslinking of collagens and elastin by catalyzing oxidative deamination of the epsilon-amino group in certain lysine and hydroxylysine residues. We report here on the isolation and characterization of cDNA clones for the enzyme from human placenta and rat aorta lambda gt11 cDNA libraries. A cDNA clone for human lysyl oxidase covers all the coding sequences, 230 nucleotides of the 5' and 299 nucleotides, of the 3' untranslated sequences, including a poly(A) tail of 23 nucleotides. This cDNA encodes a polypeptide of 417 amino acid residues, including a signal peptide of 21 amino acids. Sequencing of two rat lysyl oxidase cDNA clones indicated six differences between the present and the previously published sequence for the rat enzyme [Trackman et al. (1990) Biochemistry 29: 4863-4870], resulting in frameshifts in the translated sequence. The human lysyl oxidase sequence was found to be 78% identical to the revised rat sequence at the nucleotide level and 84% identical at the amino acid level, with the degree of identity unevenly distributed between various regions of the coded polypeptide. Northern blot analysis of human skin fibroblasts RNA indicated that the human lysyl oxidase cDNA hybridizes to at least four mRNA species; their sizes are about 5.5, 4.3, 2.4, and 2.0 kb. Analysis of a panel of 25 human x hamster cell hybrids by Southern blotting mapped the human lysyl oxidase gene to chromosome 5, and in situ hybridization mapped it to 5q23.3-31.2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Isolation of probes specific to human chromosomal region 6p21 from immunoselected irradiation-fusion gene transfer hybrids.

A hybrid cell line (R21/B1) containing a truncated human chromosome 6 (6pter-6q21) and a human Y chromosome on a hamster background was irradiated and fused to A23 (TK-) or W3GH (HPRT-) hamster cells. Clones containing expressed HLA class I genes (4/40) were selected using monoclonal antibodies. These clones were recloned and analyzed with a panel of probes from the HLA region. One hybrid (4G6) contained the entire HLA complex. Two other hybrids (4J4 and 4H2) contained only the HLA class I region, while the fourth hybrid (5P9) contained HLA class I and III genes in addition to other genes located in the 6p21 chromosomal region. In situ hybridization showed that the hybrid cells contained more than one fragment of human DNA. Alu and LINE PCR products were derived from these cells and compared to each other as well as to products from two somatic cell hybrids having the 6p21 region in common. The PCR fragments were then screened on conventional Southern blots of the somatic cell hybrids to select a panel of novel probes encompassing the 6p21 region. In addition, the origin of the human DNA fragments in hybrid 4J4 was determined by regional mapping of PCR products.

Animals↗
PubMed1991

Regional assignment of the human gene coding for a multifunctional polypeptide (P4HB) acting as the beta-subunit of prolyl 4-hydroxylase and the enzyme protein disulfide isomerase to 17q25.

Prolyl 4-hydroxylase, an alpha 2 beta 2 tetramer, catalyzes the formation of 4-hydroxyproline in collagens and related proteins by hydroxylating proline residues in peptide linkages. The beta-subunit of prolyl 4-hydroxylase (P4HB) is a highly unusual multifunctional polypeptide that is identical to the enzyme protein disulfide isomerase and a major cellular thyroid hormone-binding protein and is highly similar to a glycosylation site-binding polypeptide of oligosaccharyl transferase. We report here the regional assignment of the gene for this multifunctional polypeptide. In situ hybridization mapped the gene to 17q25. Southern blot analyses of restricted DNA from a chromosome-mediated gene transfer transfectant panel suggested that the P4HB gene is located distal to the gene for thymidine kinase, either between the genes for thymidine kinase and galactokinase or on the telomeric side of both these genes.

Blotting, Southern↗
PubMed1990

Three-dimensional structure of cellobiohydrolase II from Trichoderma reesei.

The enzymatic degradation of cellulose is an important process, both ecologically and commercially. The three-dimensional structure of a cellulase, the enzymatic core of CBHII from the fungus Trichoderma reesei reveals an alpha-beta protein with a fold similar to but different from the widely occurring barrel topology first observed in triose phosphate isomerase. The active site of CBHII is located at the carboxyl-terminal end of a parallel beta barrel, in an enclosed tunnel through which the cellulose threads. Two aspartic acid residues, located in the center of the tunnel are the probable catalytic residues.

Amino Acid Sequence↗