Biomedical subjects
R Dunn
Publications and source records attributed to R Dunn.
Organization and localization to chromosome 5 of the human UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I gene.
UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is a medial-Golgi enzyme essential for the synthesis of hybrid and complex N-glycans. We have isolated two overlapping genomic DNA clones which span 18 kilobases (kb) containing a single 2.5 kb exon for GlcNAc-T I. The exon includes most of the 5'-untranslated region, the complete coding sequence (1335 bases) for GlcNAc-T I (445 amino acids) and the complete 3'-untranslated region. The remaining exon (or exons) is at least 2.0 kb upstream of the intron-exon junction. Transient transfection of either clone into Lec 1 Chinese hamster ovary cell mutants (which lack GlcNAc-T I) indicates the presence of a promoter responsible for expression of a truncated transcript. Southern blot analysis indicates that the gene exists in single copy in the human genome and is located on chromosome 5. The human and rabbit enzymes are 85% similar at the nucleotide sequence level and 92% similar at the amino acid sequence level.
Molecular cloning and expression of cDNA encoding the enzyme that controls conversion of high-mannose to hybrid and complex N-glycans: UDP-N-acetylglucosamine: alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I.
UDP-GlcNAc:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GnT I; EC 2.4.1.101) catalyzes an essential first step in the conversion of high-mannose N-glycans to hybrid and complex N-glycans. Cloning of the gene encoding this enzyme was carried out by mixed oligonucleotide-primed polymerase chain reaction amplification of rabbit liver single-stranded cDNA using sense and antisense 20- to 24-base-pair (bp) primers. A rabbit liver library in phage lambda gt10 yielded a 2.5-kilobase (kb) cDNA with a 447-amino acid coding sequence. None of the nine asparagine residues were in an Asn-Xaa-(Ser or Thr) sequence, indicating that the protein is not N-glycosylated. There is no sequence homology to other previously cloned glycosyltransferases, but GnT I appears to have a domain structure typical of these enzymes--i.e., a short amino-terminal domain, a transmembrane domain, a "neck" region, and a large carboxyl-terminal catalytic domain. RNA was transcribed off the 2.5-kb cDNA, and in vitro translation with rabbit reticulocyte lysate yielded a 52-kDa protein with GnT I activity.
Limitation of retinal injury by vitreoperfusion initiated after onset of ischemia.
We tested whether vitreoperfusion, a new method of perfusing the vitreous cavity with solutions containing nutrients, can limit retinal injury if initiated after the onset of ischemia. Severe bilateral ocular ischemia was induced in cats with healed lensectomy-vitrectomy wounds; 30, 60, 90, or 120 minutes later, one eye from each of 18 cats underwent vitreoperfusion while the ischemia continued for 120 minutes. The other eye simultaneously underwent either continued untreated ischemia or reinstated circulation. The histopathologic abnormalities evident after 8 days depended on the duration of ischemia. Reinstated circulation yielded less retinal damage than continued ischemia. Nine additional cats underwent bilateral ischemia for at least 210 minutes. Vitreoperfusion was initiated in one eye after 30 minutes. In each cat, the vitreoperfused eye fared significantly better as observed histopathologically and electroretinographically. We believe that no other treatment has similarly limited retinal injury in vivo when initiated so long after total ocular ischemia has developed.
Molecular cloning of human and rabbit UDP-N-acetylglucosamine: alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I.
Explore the source record for details and available documents.
Substitutability between conditioned and primary reinforcers in discrimination acquisition.
Rats and pigeons were trained on a series of reversals of a conditional simultaneous discrimination. The percentage of reinforcement for correct trials was varied across reversals. When nonreinforced correct trials produced the same feedback as incorrect trials, the number of errors to reach an acquisition criterion was greater for smaller percentages of reinforcement, but the number of reinforcers required was either approximately constant or smaller for the smaller percentages. When a stimulus paired with food (the conditioned reinforcer) was added on nonreinforced correct trials, both measures were substantially decreased. When the same stimulus was presented, but without a history of food pairing, learning rate was similar to when no stimulus was presented on nonreinforced trials. The results provide direct evidence that conditioned reinforcers may substitute, although imperfectly, for a primary reinforcer, and that pairing with the primary reinforcer is a necessary condition for such substitutability to occur.
Preference for conditioned reinforcement.
Pigeons were presented with a concurrent-chains schedule in which both choice alternatives led to the same terminal-link stimulus, which was followed by food. Superimposed on the food-reinforced presentations of the terminal-link stimulus was a second schedule of presentations of the same stimulus that were followed by no food. The absolute number of these no-food stimulus presentations was held constant while their relative frequency assigned to one or the other choice alternative was systematically varied. Preference for a given choice alternative tracked the relative frequency of these stimulus presentations, thus demonstrating that they served as reinforcers. These results resolve conflicts in the literature regarding the effect of conditioned reinforcement on choice.
Intravitreal U75412E: a new free radical scavenger.
Free-radical-mediated tissue damage is thought to be involved in a multitude of ophthalmic pathologies. Therefore, drugs that scavenge free radicals may find wide clinical application. A new chemical class of antiinflammatory agents, the 21-aminosteroids, has been developed as free radical scavengers. These agents are thought to inhibit lipid peroxidation and prevent the release of free arachidonic acid from injured cell membranes. In the present study, we investigated the intraocular toxicity of one of the 21-aminosteroids, U75412E. Intravitreal doses of up to 0.1 mg of U75412E were nontoxic to rabbit ocular tissues.
A unique case of congenital bilateral absence of parietal bones in a neonate.
The remains of an unidentified female neonate were discovered in a field in central Missouri. Examination revealed bilateral absence of the parietal bones. A search of the literature describing similar defects suggests that the present case represents a unique condition, described here for the first time.
Both sodium channel II and IIA alpha subunits are expressed in rat brain.
Explore the source record for details and available documents.
Functional properties of rat brain sodium channels expressed in a somatic cell line.
Transfection of Chinese hamster ovary cells with complementary DNA encoding the RIIA sodium channel alpha subunit from rat brain led to expression of functional sodium channels with the rapid, voltage-dependent activation and inactivation characteristic of sodium channels in brain neurons. The sodium currents mediated by these transfected channels were inhibited by tetrodotoxin, persistently activated by veratridine, and prolonged by Leiurus alpha-scorpion toxin, indicating that neurotoxin receptor sites 1 through 3 were present in functional form. The RIIA sodium channel alpha subunit cDNA alone is sufficient for stable expression of functional sodium channels with the expected kinetic and pharmacological properties in mammalian somatic cells.
S100 protein expression in human melanoma cells: comparison of levels of expression among different cell lines and individual cells in different phases of the cell cycle.
The synthesis of S100 protein in cultured human melanoma cells was examined using metabolic labeling with [35S]methionine, immunoprecipitation with anti-S100 protein antiserum, and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Six of seven cell lines derived from melanomas synthesized relatively large amounts of S100 protein, whereas three cell lines derived from normal melanocytes synthesized lesser amounts. Synthesis of S100 protein was not detected in 10 human cell lines of nonneuroectodermal origin. Analysis of poly(A+) RNA from one melanoma cell line by Northern blot hybridization with a probe specific for the beta subunit of rat S100 protein revealed a single mRNA species of 1.0 kb coding for the human protein. Flow cytometric analysis of individual cells of two melanoma cell lines and the rat glioma cell line C6 indicated that G0/G1 cells were heterogeneous with respect to S100 protein expression, while almost all the cells in S + G2 + M expressed S100 protein. These results suggest that expression of S100 protein in G0/G1 could be a prerequisite for progression of the cells through the cell cycle.
Grouping students for instruction: effects of learning style on achievement and attitudes.
The present study examined the effects of matching and mismatching American middle-school students with a preference for learning alone or learning with peers with selected instructional treatments in order to determine the impact upon their attitudes and achievement in social studies. Analysis revealed that the learning-alone preference performed significantly better in the learning-alone condition and that the learning-with-peers preference performed significantly better in the learning-with-peers condition. However, no-preference students also performed significantly better in the learning-alone condition than with peers. In addition, data revealed that the learning-alone and the learning-with-peers students had significantly more positive attitudes when matched with their preferred learning style; the nopreference students had more positive attitudes in the learning-alone condition.
Resolution of recent evolutionary divergence among Escherichia coli from related lineages: the application of pulsed field electrophoresis to molecular epidemiology.
Escherichia coli infecting the urinary tract and other extraintestinal sites are often identical in many phenotypic and genotypic characteristics. To discriminate among pathogenic E. coli isolates, chromosomal DNA was digested with restriction endonucleases that recognize eight base pair sequences and the resulting 20-25 fragments were resolved by pulsed field gel electrophoresis (PFGE). Different restriction fragment profiles were detected for isolates obtained from different patients, including isolates of the same evolutionary lineage that were identical in electrophoretic type, serotype, and antibiotic sensitivities. In contrast, isolates obtained from separate sites of infection within the same patient had identical restriction profiles. These results indicate that PFGE can resolve recent evolutionary divergence within E.coli lineages and, consequently, offers a powerful new means for precisely performing molecular epidemiology. In addition, these studies provide genetic evidence that E. coli urinary tract infection within a given patient is typically due to the expansion of a single bacterial clone.
Myelin-associated glycoprotein gene expression in the presence and absence of Schwann cell-axonal contact.
The distal segments of the crush-injured and permanently transected sciatic nerve provide models to study Schwann cell activity in the presence and absence of Schwann cell-axonal contact, respectively. We examined the quantity and quality of transcript coding for the myelin-associated glycoprotein (MAG) over a 3-week period following crush injury and at 35 days after transection to investigate possible regulation of this gene during nerve injury and subsequent repair. Northern blot and slot blot analysis indicated a sharp decrease in levels of MAG mRNA 2 days after crush injury which was followed by a progressive increase in levels of message between 7 and 21 days after injury. Western blot analysis showed that levels of MAG protein decreased substantially 7 days after crush injury, which returned to 70% of the adult value by 21 days after injury. MAG mRNA and protein were undetectable by Northern and Western analysis, respectively, in the distal segment of the sciatic nerve 35 days after permanent transection. This infers distinct down-regulation of MAG gene expression after permanent transection of a peripheral nerve. These comparative studies of MAG transcripts and encoded protein may indicate regulation of MAG gene expression at the level of transcription, and possibly at the level of post-transcription in these experimental models of peripheral neuropathies.
Bias over substance: a critical analysis of Kavale and Forness' report on modality-based instruction.
Explore the source record for details and available documents.
Timeout from concurrent schedules.
Response-contingent timeouts of equal duration and frequency were added to both alternatives of unequal concurrent schedules of reinforcement. For each of 4 pigeons in Experiment 1, relative response rates generally became less extreme as the frequency of timeout increased. In Experiment 2, relative response rates consistently approached indifference as the duration of timeout was increased. Variation in time allocation was less consistent in both experiments. Absolute response rates did not vary with the timeout contingency in either experiment. In a third experiment, neither measure of choice varied systematically when the duration of a postreinforcement blackout was varied. In contrast to the present results, preference has been shown to vary directly with the parameters of shock delivery in related procedures. The pattern of results in the first two experiments follows that obtained with other manipulations of the overall rate of reinforcement in concurrent schedules. The results of the third experiment suggest that an intertrial interval following reinforcement is not a critical feature of the overall rate of reinforcement.
Choice with uncertain outcomes: conditioned reinforcement effects.
Pigeons responded on concurrent chains with equal initial- and terminal-link durations. In all conditions, the terminal links of one chain ended reliably in reinforcement; the terminal links on the alternative chain ended in either food or blackout. In Experiment 1, the terminal-link stimuli were correlated with (signaled) the outcome, and the durations of the initial and terminal links were varied across conditions. Preference did not vary systematically across conditions. In Experiment 2, terminal-link durations were varied under different stimulus conditions. The initial links were variable-interval 80-s schedules. Preference for the reliable alternative was generally higher in unsignaled than in signaled conditions. Preference increased with terminal-link durations only in the unsignaled conditions. There were no consistent differences between conditions with and without a common signal for reinforcement on the two chains. In the first series of conditions in Experiment 3, a single response was required in the initial links, and the stimulus conditions during 50-s terminal links were varied. Preference for the reliable outcome approached 1.0 in unsignaled conditions and was considerably lower (below .50 for 3 of 5 subjects) in signaled conditions. In a final series of signaled conditions with relatively long terminal links, preference varied with duration of the initial links. The results extend previous findings and are discussed in terms of the delay reduction signaled by terminal-link stimuli.