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A Wilde

Publications and source records attributed to A Wilde.

At least 19 recordsLinked to original sources
PubMed2001

Characterization of the cyanobacterial ycf37: mutation decreases the photosystem I content.

We have constructed and analysed a cyanobacterial mutant that lacks the putative homologue of ycf37, the chloroplast open reading frame 37, which is conserved in different algae, but missing in the plastome of higher plants. In this report we show that Ycf37 of Synechocystis sp. PCC 6803 contains three tetratrico-peptide repeat (TPR) units resembling the structural organization of Ycf3, a protein that has been suggested to function as a chaperone during photosystem (PS) I complex formation. We demonstrate a light-activated transcript accumulation of this gene. Inactivation of ycf37 leads to a lower PSI/PSII ratio and a higher phycocyanin/chlorophyll ratio in Synechocystis cells. The observed alterations in the ycf37 mutants and the structural organization of the gene product suggest a functional role in PSI stability or assembly.

Amino Acid Sequence↗
PubMed2001

Role of importin-beta in coupling Ran to downstream targets in microtubule assembly.

The guanosine triphosphatase Ran stimulates assembly of microtubule asters and spindles in mitotic Xenopus egg extracts. A carboxyl-terminal region of the nuclear-mitotic apparatus protein (NuMA), a nuclear protein required for organizing mitotic spindle poles, mimics Ran's ability to induce asters. This NuMA fragment also specifically interacted with the nuclear transport factor, importin-beta. We show that importin-beta is an inhibitor of microtubule aster assembly in Xenopus egg extracts and that Ran regulates the interaction between importin-beta and NuMA. Importin-beta therefore links NuMA to regulation by Ran. This suggests that similar mechanisms regulate nuclear import during interphase and spindle assembly during mitosis.

Animals↗
PubMed2001

Transgenic mice overexpressing human KvLQT1 dominant-negative isoform. Part I: Phenotypic characterisation.

OBJECTIVES: The KCNQ1 gene encodes the KvLQT1 potassium channel, which generates in the human heart the slow component of the cardiac delayed rectifier current, I(Ks). Mutations in KCNQ1 are the most frequent cause of the congenital long QT syndrome. We have previously cloned a cardiac KCNQ1 human isoform, which exerts a strong dominant-negative effect on KvLQT1 channels. We took advantage of this dominant-negative isoform to engineer an in vivo model of KvLQT1 disruption, obtained by overexpressing the dominant-negative subunit under the control of the alpha-myosin heavy chain promoter. RESULTS: Three different transgenic lines demonstrated a phenotype with increasing severity. Functional suppression of KvLQT1 in transgenic mice led to a markedly prolonged QT interval associated with sinus node dysfunction. Transgenic mice also demonstrated atrio-ventricular block leading to occasional Wenckebach phenomenon. The atrio-ventricular block was associated with prolonged AH but normal HV interval in His recordings. Prolonged QT interval correlated with prolonged action potential duration and with reduced K(+) current density in patch-clamp experiments. RNase protection assay revealed remodeling of K(+) channel expression in transgenic mice. CONCLUSIONS: Our transgenic mouse model suggests a role for KvLQT1 channels not only in the mouse cardiac repolarisation but also in the sinus node automaticity and in the propagation of the impulse through the AV node.

Action Potentials↗
PubMed2001

Ran stimulates spindle assembly by altering microtubule dynamics and the balance of motor activities.

The guanosine tri-phosphatase Ran stimulates assembly of microtubule spindles. However, it is not known what aspects of the microtubule cytoskeleton are subject to regulation by Ran in mitosis. Here we show that Ran-GTP stimulates microtubule assembly by increasing the rescue frequency of microtubules three- to eightfold. In addition to changing microtubule dynamics, Ran-GTP also alters the balance of motor activities, partly as a result of an increase in the amount of motile Eg5, a plus-end-directed microtubule motor that is essential for spindle formation. Thus, Ran regulates multiple processes that are involved in spindle assembly.

Animals↗
PubMed2001

Quinidine induced electrocardiographic normalization in two patients with Brugada syndrome.

Two patients with Brugada syndrome are presented. The ECGs showed right precordial J waves and ST-segment elevation. Patient 1 was resuscitated from nocturnal ventricular fibrillation, patient 2 was asymptomatic. In only patient 1, flecainide was infused causing monomorphic "malignant" ventricular extrasystoles (R on T), demonstrating the deleterious effect of Class IC antiarrhythmic drugs in Brugada syndrome. However, administration of the Class Ia antiarrhythmic drug quinidine caused normalization of the ECG in both patients. Based on in vitro experiments, agents that reduce the magnitude of Ito-mediated phase 1 have been suggested to normalize ST-segment elevation in Brugada syndrome. This is the first clinical report of such a quinidine induced ECG normalization.

Adult↗
PubMed2000

The role of Xgrip210 in gamma-tubulin ring complex assembly and centrosome recruitment.

The gamma-tubulin ring complex (gammaTuRC), purified from the cytoplasm of vertebrate and invertebrate cells, is a microtubule nucleator in vitro. Structural studies have shown that gammaTuRC is a structure shaped like a lock-washer and topped with a cap. Microtubules are thought to nucleate from the uncapped side of the gammaTuRC. Consequently, the cap structure of the gammaTuRC is distal to the base of the microtubules, giving the end of the microtubule the shape of a pointed cap. Here, we report the cloning and characterization of a new subunit of Xenopus gammaTuRC, Xgrip210. We show that Xgrip210 is a conserved centrosomal protein that is essential for the formation of gammaTuRC. Using immunogold labeling, we found that Xgrip210 is localized to the ends of microtubules nucleated by the gammaTuRC and that its localization is more distal, toward the tip of the gammaTuRC-cap structure, than that of gamma-tubulin. Immunodepletion of Xgrip210 blocks not only the assembly of the gammaTuRC, but also the recruitment of gamma-tubulin and its interacting protein, Xgrip109, to the centrosome. These results suggest that Xgrip210 is a component of the gammaTuRC cap structure that is required for the assembly of the gammaTuRC.

Amino Acid Sequence↗
PubMed2000

NGF signals through TrkA to increase clathrin at the plasma membrane and enhance clathrin-mediated membrane trafficking.

Neurotrophin (NT) signals may be moved from axon terminals to neuron cell bodies via signaling endosomes-organelles in which NTs continue to be bound to their activated receptors. Suggesting that clathrin-coated membranes serve as one source of signaling endosomes, in earlier studies we showed that nerve growth factor (NGF) treatment increased clathrin at the plasma membrane and resulted in colocalization of clathrin with TrkA, the receptor tyrosine kinase for NGF. Strikingly, however, we also noted that most clathrin puncta at the surface of NGF-treated cells did not colocalize with TrkA, raising the possibility that NGF induces a general increase in clathrin-coated membrane formation. To explore this possibility further, we examined the distribution of clathrin in NGF- and BDNF-treated cells. NGF signaling in PC12 cells robustly redistributed the adaptor protein AP2 and the clathrin heavy chain (CHC) to surface membranes. Using confocal and epifluorescence microscopy, as well as biochemical assays, we showed the redistribution of clathrin to be attributable to the activation of TrkA. Significantly, NGF signaled through TrkA to induce an increase in clathrin-mediated membrane trafficking, as revealed in the increased endocytosis of transferrin. In that BDNF treatment increased AP2 and clathrin at the surface membranes of hippocampal neurons, these findings may represent a physiologically significant response to NTs. We conclude that NT signaling increases clathrin-coated membrane formation and clathrin-mediated membrane trafficking and speculate that this effect contributes to their trophic actions via the increased internalization of receptors and other proteins that are present in clathrin-coated membranes.

Adaptor Protein Complex 2↗
PubMed2000

Complete reconstitution of clathrin basket formation with recombinant protein fragments: adaptor control of clathrin self-assembly.

Clathrin polymerization into a polyhedral basket, surrounding budding membrane vesicles, mediates protein sorting during endocytosis and organelle biogenesis. Adaptor proteins target clathrin assembly to specific membrane sites and sequester receptors into the clathrin coat. We have reconstituted complete clathrin basket formation from recombinantly expressed fragments of clathrin and adaptors. This reconstitution reveals a hierarchy of clathrin self-assembly interactions and demonstrates that adaptors control basket formation by alignment of the distal domains of the clathrin triskelion leg through their binding to the terminal domain.

Clathrin↗
PubMed1999

Homozygous premature truncation of the HERG protein : the human HERG knockout.

Background-In long-QT syndrome (LQTS), heterozygosity for a mutation in 1 of the K(+) channel genes leads to prolongation of the cardiac action potential, because the aberrant protein exhibits "loss of function." HERG, which is involved in LQT2, is the gene encoding the rapid component of the delayed rectifier, I(Kr). Methods and Results-In a consanguineous family, a stillbirth was followed by the premature birth of a child in distress due to ventricular arrhythmia in the presence of QT prolongation. LQTS was diagnosed, beta-blocker therapy was begun, and a pacemaker was implanted. She developed well and remained symptom-free for 1.5 years. In the index patient, we identified a duplication of bp 558 to 600 in exon 4 of HERG on both alleles. This will result in a frameshift and a premature stop codon before the S1 domain of the HERG protein. Because it is present on both alleles, no functional I(Kr) is anticipated. The same mutation was found heterozygously in both parents and homozygously in the stillborn brother. Conclusions-It is concluded that absence of I(Kr) gives rise to a severe cardiac phenotype, with no indication of malfunction of any other organ.

Cation Transport Proteins↗
PubMed1999

Stimulation of microtubule aster formation and spindle assembly by the small GTPase Ran.

Ran, a small guanosine triphosphatase, is suggested to have additional functions beyond its well-characterized role in nuclear trafficking. Guanosine triphosphate-bound Ran, but not guanosine diphosphate-bound Ran, stimulated polymerization of astral microtubules from centrosomes assembled on Xenopus sperm. Moreover, a Ran allele with a mutation in the effector domain (RanL43E) induced the formation of microtubule asters and spindle assembly, in the absence of sperm nuclei, in a gammaTuRC (gamma-tubulin ring complex)- and XMAP215 (Xenopus microtubule associated protein)-dependent manner. Therefore, Ran could be a key signaling molecule regulating microtubule polymerization during mitosis.

Animals↗
PubMed1999

EGF receptor signaling stimulates SRC kinase phosphorylation of clathrin, influencing clathrin redistribution and EGF uptake.

Epidermal growth factor (EGF) binding to its receptor causes rapid phosphorylation of the clathrin heavy chain at tyrosine 1477, which lies in a domain controlling clathrin assembly. EGF-mediated clathrin phosphorylation is followed by clathrin redistribution to the cell periphery and is the product of downstream activation of SRC kinase by EGF receptor (EGFR) signaling. In cells lacking SRC kinase, or cells treated with a specific SRC family kinase inhibitor, EGF stimulation of clathrin phosphorylation and redistribution does not occur, and EGF endocytosis is delayed. These observations demonstrate a role for SRC kinase in modification and recruitment of clathrin during ligand-induced EGFR endocytosis and thereby define a novel effector mechanism for regulation of endocytosis by receptor signaling.

Amino Acid Sequence↗
PubMed1999

Secondary tonsillectomy haemorrhage and non-steroidal anti-inflammatory drugs.

Modern non-steroidal anti-inflammatory drugs (NSAIDs), are now widely accepted analgesics for post-tonsillectomy patients, but their effect on secondary haemorrhage has not been fully evaluated. This study attempts to evaluate the influence of NSAIDs on the secondary haemorrhage rate, and also whether mode of dissection is an important factor. The records of 557 consecutive patients undergoing tonsillectomy were studied to determine if there was a relationship between the secondary haemorrhage rate and discharge prescription of NSAIDs. There was an overall secondary haemorrhage rate of 5.2 per cent (29) and a significantly increased secondary haemorrhage rate in those taking regular NSAIDs, 11 per cent, compared to those not taking NSAIDs, 1.47 per cent, (chi 1(2) = 41.25, p < 0.001). There was a higher rate of secondary haemorrhages with bipolar dissection than with standard dissection for both those taking and not taking NSAIDs (13 per cent vs seven per cent and 2.75 per cent vs 0.87 per cent) however this was not statistically significant (chi 1(2) = 1.17, p = 0.19 and chi 1(2) = 0.773, p = 0.17). Both bipolar dissection and standard dissection individually showed very significant increases in secondary haemorrhage rate when on regular NSAIDs (chi 1(2) = 14.03, p = 0.004 and chi 1(2) = 6.19, p = 0.003). Although NSAIDs are very good analgesics, they may cause an increased secondary haemorrhage rate, and should be prescribed at discharge prescription with caution.

Adult↗