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Biomedical subjects

G E Jones

Publications and source records attributed to G E Jones.

At least 37 records · Page 2Linked to original sources
PubMed1999

The dynamics of the vestibulo-ocular reflex after peripheral vestibular damage. I. Frequency-dependent asymmetry.

Accurate performance by the vestibulo-ocular reflex (VOR) is necessary to stabilize visual fixation during head movements. VOR performance is severely affected by peripheral vestibular damage; after one horizontal semicircular canal is plugged, the horizontal VOR is asymmetric and its amplitude is reduced. The VOR recovers partially. We investigated the limits of recovery by measuring the VOR's response to ipsilesional and contralesional rotation after unilateral peripheral damage in cats. We found that the VOR's response to rotation at high frequencies remained asymmetric after recovery was complete. When the stimulus was a pulse of head velocity comprising a dynamic overshoot followed by a plateau, gain was partially restored and symmetry completely restored within 30 days after the plug, but only for the plateau response. The overshoot in eye velocity remained asymmetric. The asymmetry was independent of stimulus velocity throughout the known linear velocity range of primary vestibular afferents. Sinusoidal rotation at 0.05-8 Hz revealed that, within this range, the persistent asymmetry was significant only at frequencies above 2 Hz. Asymmetry was independent of the peak head acceleration over the range of 50-500 degrees/s2. When both horizontal canals were plugged, a small residual VOR was observed, suggesting residual signal transduction by plugged semicircular canals. However, transduction by plugged canals could not explain the enhancement of the VOR gain, at high frequencies, for rotation away from the plugged side compared with rotation toward the plug. Also, the high-frequency asymmetry was present after recovery from a unilateral labyrinthectomy. These results suggest that high-frequency asymmetry after unilateral damage is not due to residual function in the plugged canal. The findings are discussed in the context of a bilateral model of the VOR that includes central filtering.

Acceleration↗
PubMed1999

Model studies on a synthetically facile series of N-substituted phenyl-N'-pyridin-3-yl ureas leading to 1-(3-pyridylcarbamoyl) indolines that are potent and selective 5-HT(2C/2B) receptor antagonists.

A model series of 5-HT2C antagonists have been prepared by rapid parallel synthesis. These N-substituted phenyl-N'-pyridin-3-yl ureas were found to have a range of 5-HT2C receptor affinities and selectivities over the closely related 5-HT2A receptor. Extrapolation of simple SAR, derived from this set of compounds, to the more active but synthetically more complex 1-(3-pyridylcarbamoyl)indoline series allowed us to target optimal substitution patterns and identify potent and selective 5-HT(2C/2B) antagonists.

Animals↗
PubMed1999

Effects of the presentation of false heart-rate feedback on the performance of two common heartbeat-detection tasks.

Research has indicated that performance on heartbeat counting tasks may be influenced by beliefs about heart rate. Sixty male subjects were administered the Schandry heartbeat counting task after viewing fast, slow, or no heart rate feedback. Subjects were also administered the Whitehead signal-detection type task. Results indicated that subjects who received fast or no heartbeat feedback performed better on the Schandry task than subjects who received slow feedback. Feedback presentation did not affect performance on the Whitehead task. These results suggest that the Schandry task is influenced by external variables (expectations, beliefs) beyond pure awareness of "discrete" visceral sensations and, thus, may not be as powerful a method for determining awareness of individual heartbeats as some other paradigms.

Adult↗
PubMed1999

Rho family proteins and cell migration.

The GTP-binding proteins Rho, Rac and Cdc42 are known to regulate actin organization: Rho induces the assembly of contractile actin-based filaments such as stress fibres, Rac regulates the formation of lamellipodia and membrane ruffles, while Cdc42 is required for filopodium extension. All three proteins can also regulate the assembly of integrin-containing focal adhesion complexes. Cell migration involves co-ordinated and dynamic changes in the actin cytoskeleton and cell adhesion, and we have therefore investigated the roles of Rho family proteins in migration, using two model cell systems. First, in the macrophage cell line Bac1, Rho and Rac were found to be required for colony-stimulating factor-1 (CSF-1)-induced cell migration. In contrast, inhibition of Cdc42 does not prevent macrophages migrating in response to CSF-1, but does prevent recognition of a CSF-1 concentration gradient, so that cells now migrate randomly rather than up the gradient. This implies that Cdc42, and probably filopodia, are required for gradient sensing and cell polarization. Secondly, in the Madin-Darby canine kidney (MDCK) epithelial cell line, Rho and Rac are also essential for migration induced by hepatocyte growth factor/scatter factor. Rac is required for lamellipodium formation and is apparently activated via Ras. Interestingly, however, Rac does not induce lamellipodium formation in unstimulated MDCK cells, indicating that Rac signals differently in epithelial cells compared with fibroblasts or macrophages. Our results point to central roles for Rho, Rac and Cdc42 in co-ordinating cell migration.

Animals↗
PubMed1998

A role for Cdc42 in macrophage chemotaxis.

Three members of the Rho family, Cdc42, Rac, and Rho are known to regulate the organization of actin-based cytoskeletal structures. In Bac1.2F5 macrophages, we have shown that Rho regulates cell contraction, whereas Rac and Cdc42 regulate the formation of lamellipodia and filopodia, respectively. We have now tested the roles of Cdc42, Rac, and Rho in colony stimulating factor-1 (CSF-1)-induced macrophage migration and chemotaxis using the Dunn chemotaxis chamber. Microinjection of constitutively activated RhoA, Rac1, or Cdc42 inhibited cell migration, presumably because the cells were unable to polarize significantly in response to CSF-1. Both Rho and Rac were required for CSF-1-induced migration, since migration speed was reduced to background levels in cells injected with C3 transferase, an inhibitor of Rho, or with the dominant-negative Rac mutant, N17Rac1. In contrast, cells injected with the dominant-negative Cdc42 mutant, N17Cdc42, were able to migrate but did not polarize in the direction of the gradient, and chemotaxis towards CSF-1 was abolished. We conclude that Rho and Rac are required for the process of cell migration, whereas Cdc42 is required for cells to respond to a gradient of CSF-1 but is not essential for cell locomotion.

Animals↗
PubMed1998

Novel and selective 5-HT2C/2B receptor antagonists as potential anxiolytic agents: synthesis, quantitative structure-activity relationships, and molecular modeling of substituted 1-(3-pyridylcarbamoyl)indolines.

The synthesis, biological activity, and molecular modeling of a novel series of substituted 1-(3-pyridylcarbamoyl)indolines are reported. These compounds are isosteres of the previously published indole urea 1 (SB-206553) and illustrate the use of aromatic disubstitution as a replacement for fused five-membered rings in the context of 5-HT2C/2B receptor antagonists. By targeting a region of space previously identified as sterically allowed at the 5-HT2C receptor but disallowed at the 5-HT2A receptor, we have identified a number of compounds which are the most potent and selective 5-HT2C/2B receptor antagonists yet reported. 46 (SB-221284) was selected on the basis of its overall biological profile for further evaluation as a novel, potential nonsedating anxiolytic agent. A CoMFA analysis of these compounds produced a model with good predictive value and in addition good qualitative agreement with both our 5-HT2C receptor model and our proposed binding mode for this class of ligands within that model.

Animals↗
PubMed1998

Intrinsic dendritic cell abnormalities in Wiskott-Aldrich syndrome.

Wiskott-Aldrich syndrome (WAS) is an X-linked disorder characterized by immune deficiency, eczema, and microthrombocytopenia. Biochemical evidence indicates that the Wiskott-Aldrich syndrome protein (WASp) is involved in regulating the actin cytoskeleton. Here we report that WAS dendritic cells (DC) have an immunophenotype very similar to normal DC. However, as a consequence of an intrinsically abnormal cytoarchitecture, they are unable to polarize normally and have severely reduced translocational motility in vitro. These findings indicate that WASp is an essential effector for Cdc-42-mediated polarization of primary hematopoietic cells, and suggest that a significant component of the clinical phenotype of WAS could arise from peripheral DC dysmotility and aberrant immune cell trafficking in vivo. Intrinsic dysfunction of the DC population may also have an important role in the pathogenesis of other primary immunodeficiency syndromes, while induced changes in DC cytoskeletal signaling pathways may contribute to the initiation of acquired immunological and inflammatory disorders.

Actins↗
PubMed1998

Retinoic acid as a chemotactic molecule in neuronal development.

We describe the results of experiments on dissociated cultures of embryonic chick neural tissue which were designed to investigate further the role of all-trans-retinoic acid (tRA) on neurite outgrowth and, by inference, on the developing nervous system in vivo. We show that tRA increases both the number of neurites and the length of neurites extending from these chick neural tube cells at nM concentrations. Secondly, using the newly designed Dunn chamber in which stable gradients of compounds can be generated, we show that neurites respond to a gradient of tRA by growing up the gradient. These observations indicate a role for RA in vivo, not only in the initial outgrowth of neurites, but also in their guidance to the appropriate targets.

Animals↗
PubMed1998

Chemotaxis of macrophages is abolished in the Wiskott-Aldrich syndrome.

Wiskott-Aldrich syndrome (WAS) is a rare disease characterized by microthrombocytopenia, eczema and immune deficiency. In this study a direct-viewing chemotaxis chamber was used to analyse chemotactic responses of WAS neutrophils and macrophages in stable linear concentration gradients. In five patients with classic WAS, chemotaxis of macrophages but not of neutrophils was found to be abolished, whereas the speed of random motility of both cell types was found to be indistinguishable from control cells. This supports the existence of an essential functional link, previously suggested by biochemical studies, between Cdc42, WAS protein (WASp) and the actin cytoskeleton in primary human macrophages. Moreover, these data suggest that Cdc42-WASp-mediated filopodial extension is a requirement for chemotaxis but not for chemokinesis in these cells. Abnormal directional cell motility of macrophages and related antigen-presenting cells may play a significant part in the immune deficiency and eczema of WAS.

Chemotaxis↗
PubMed1998

Molecular cloning and characterization of the genes coding for the highly immunogenic cluster of 90-kilodalton envelope proteins from the Chlamydia psittaci subtype that causes abortion in sheep.

Proteins present in the outer membrane of chlamydiae that are involved in mucosal epithelial cell infection must clearly be identified and characterized if we are to understand and modify the pathogenic mechanisms utilized by these organisms. We have identified and isolated a family of four genes encoding putative outer membrane proteins (POMPs), a group of proteins of approximately 90 kDa present in the outer membrane of the subtype of Chlamydia psittaci that causes ovine enzootic abortion (strain S26/3). These proteins, although minor components, are major immunogens, as shown by the immunoblotting of chlamydial outer membrane complexes with postabortion sheep sera, and are therefore potential diagnostic and/or protective antigen candidates. Immunoblotting of the expressed amino- and carboxy-terminal halves of one of the POMPs with postabortion sheep sera showed that the major humoral immune response appeared to be directed solely against the amino-terminal half. This result, in combination with the positive immunofluorescence staining of S26/3-infected cells using POMP-specific (specific to the amino-terminal half of the proteins) monoclonal antibodies, suggests the probable surface localization of the POMPs and, more specifically, the surface exposure of the amino-terminal half of these proteins. The four pomp genes are highly homologous, sharing 82 to 100% similarity with each other (two of the genes are identical). Genes with strong and weak homologies were also detected in C. psittaci avian and feline pneumonitis strains, respectively. No pomp homologs were found in strains of C. trachomatis and C. pneumoniae, but this does not preclude their existence. The absence of homology with various subtypes of C. pecorum, which complicate the diagnosis of the ovine abortion subtype, indicates the possible suitability of the these 90-kDa proteins as serodiagnostic antigens.

Amino Acid Sequence↗
PubMed1998

RhoE regulates actin cytoskeleton organization and cell migration.

The actin cytoskeleton is regulated by Rho family proteins: in fibroblasts, Rho mediates the formation of actin stress fibers, whereas Rac regulates lamellipodium formation and Cdc42 controls filopodium formation. We have cloned the mouse RhoE gene, whose product is a member of the Rho family that shares (except in one amino acid) the conserved effector domain of RhoA, RhoB, and RhoC. RhoE is able to bind GTP but does not detectably bind GDP and has low intrinsic GTPase activity compared with Rac. The role of RhoE in regulating actin organization was investigated by microinjection in Bac1.2F5 macrophages and MDCK cells. In macrophages, RhoE induced actin reorganization, leading to the formation of extensions resembling filopodia and pseudopodia. In MDCK cells, RhoE induced the complete disappearance of stress fibers, together with cell spreading. However, RhoE did not detectably affect the actin bundles that run parallel to the outer membranes of cells at the periphery of colonies, which are known to be dependent on RhoA. In addition, RhoE induced an increase in the speed of migration of hepatocyte growth factor/scatter factor-stimulated MDCK cells, in contrast to the previously reported inhibition produced by activated RhoA. The subcellular localization of RhoE at the lateral membranes of MDCK cells suggests a role in cell-cell adhesion, as has been shown for RhoA. These results suggest that RhoE may act to inhibit signalling downstream of RhoA, altering some RhoA-regulated responses, such as stress fiber formation, but not affecting others, such as peripheral actin bundle formation.

Actins↗
PubMed1998

The Rho GTPases in macrophage motility and chemotaxis.

The GTP-binding proteins, Rho, Rac and Cdc42 are known to regulate actin organisation. Rho induces the assembly of contractile actin-based microfilaments such as stress fibres, Rac regulates the formation of membrane ruffles and lamellipodia, and Cdc42 activation is necessary for the formation of filopodia. In addition, all three proteins can also regulate the assembly of integrin-containing focal adhesion complexes. The orchestration of these distinct cytoskeletal changes is thought to form the basis of the coordination of cell motility and we have investigated the roles of Rho family proteins in migration using a model system. We have found that in the macrophage cell line Bac1, the cytokine CSF-1 rapidly induces actin reorganisation: it stimulates the formation of filopodia, lamellipodia and membrane ruffles, as well as the appearance of fine actin cables within the cell. We have shown that Cdc42, Rac and Rho regulate the CSF-1 induced formation of these distinct actin filament-based structures. Using a cell tracking procedure we found that both Rho and Rac were required for CSF-1 stimulated cell translocation. In contrast, inhibition of Cdc42 does not prevent macrophages migrating in response to CSF-1, but does prevent recognition of a CSF-1 concentration gradient, so that cells now migrate randomly rather than up the gradient of this chemotactic cytokine. This implies that Cdc42, and thus probably filopodia, are required for gradient sensing and cell polarisation in macrophages.

Animals↗
PubMed1997

Comparison of five tests for the detection of antibodies against chlamydial (enzootic) abortion of ewes.

Five tests for antibodies against chlamydial (enzootic) abortion of ewes were compared using 255 sera from experimentally (group 1) or naturally (group 2) infected animals, flocks free of the disease (group 3) and individual animals testing positively by the complement fixation test but from flocks with no evidence of chlamydial abortion (group 4). Sera from five specific pathogen-free lambs vaccinated with two different subtypes of Chlamydia pecorum were also included (group 5). All tests used some form of processed culture of C psitiaci as antigen. Specificities, established with group 3 and 4 sera, ranged between 96 per cent (ELISA using lipopolysaccharide antigen) and 59 per cent (Immunocomb). Reactions with group 5 sera suggested that the cause of false positive results in the field might be cross-reactive antibodies against the arthritogenic subtype of C pecorum. Sensitivities, established with groups 1 and 2 sera, ranged between 81 per cent (Immunocomb) and 51 per cent (ELISA using solubilised protein antigen). The minimum sample sizes required to be 95 per cent certain of detecting at least five seropositives in two infected flocks (combined data) were 15 to 48, dependent on the test applied. The Western blot test, applied to a proportion of samples, yielded no false positives with group 3 sera but 31.7 per cent with group 4 sera. Thus, none of the tests in this comparison emerged as sufficiently satisfactory in all respects, suggesting that further improvements in chlamydial serology must come through the use of non-native antigens or in the form of a competitive ELISA.

Abortion, Septic↗
PubMed1997

Serological diagnosis of chlamydial abortion in sheep and goats: comparison of the complement fixation test and an enzyme-linked immunosorbent assay employing solubilised proteins as antigen.

A new ELISA for antibodies against chlamydial abortion of ewes which uses detergent solubilised proteins (dsp) of Chlamydia psittaci as antigen (Anderson, I.E., Herring, A.J., Jones, G.E., Low, J.C., Greig, A., 1995. Development and evaluation of an indirect ELISA to detect antibodies to abortion strains of Chlamydia psittaci in sheep sera. Vet. Microbiol., 43, pp. 1-12] was compared with the complement fixation test (CFT) in screening 1000 ovine and caprine sera obtained from selected flocks/herds ('flocks') and submitted to a veterinary diagnostic laboratory. Fifteen of the 17 'flocks' had a history of abortion while the remaining two did not and were classified as 'negative flocks'. Infection with Chlamydia was confirmed during the study period in five 'flocks' using direct immunofluorescence and the modified Ziehl Neelsen stain on pathological material. The dspELISA and CFT identified 37 and 45 positive sera on 158 samples tested from these 'flocks'. Chlamydia antibodies were not detected in one of the two negative flocks, in two other flocks where the cause of abortion was undetermined and in three flocks in which the causes of abortion were diagnosed as Listeriosis and/or Salmonellosis. One of the 'negative flocks' yielded two positive reactors by CFT and five by dspELISA, suggesting infection with a cross-reactive subtype of C. pecorum. Of the five 'flocks' in which a definitive diagnosis from pathological material was not possible, four were positive by both serological tests, suggesting that the abortions were due to Chlamydia. The fifth flock, though negative by dspELISA and marginally positive in two samples by CFT, had experienced confirmed chlamydial abortions in previous lambing seasons, but culling and tetracycline treatment have prevented further abortions in the study period. Overall, the proportions of samples positive by CFT and dspELISA were similar (9.1% and 8.8%). These studies confirmed the value of the dspELISA as a screening test for chlamydial abortion. Furthermore, the dspELISA compared to the CFT is easier to perform, does not require reagent titration at each testing and uses automated assessment of results.

Abortion, Veterinary↗
PubMed1997

Rho, Rac and Cdc42 regulate actin organization and cell adhesion in macrophages.

Rho family proteins are known to regulate actin organization in fibroblasts, but their functions in cells of haematopoietic origin have not been studied in detail. Bac1.2F5 cells are a colony-stimulating factor-1 (CSF-1)-dependent murine macrophage cell line; CSF-1 stimulates their proliferation and motility, and acts as a chemoattractant. CSF-1 rapidly induced actin reorganization in Bac1 cells: it stimulated the formation of filopodia, lamellipodia and membrane ruffles at the plasma membrane, as well as the appearance of fine actin cables within the cell interior. Microinjection of constitutively activated (V12)Rac1 stimulated lamellipodium formation and membrane ruffling. The dominant inhibitory Rac mutant, N17Rac1, inhibited CSF-1-induced lamellipodium formation, and also induced cell rounding. V12Cdc42 induced the formation of long filopodia, while the dominant inhibitory mutant N17Cdc42 prevented CSF-1-induced formation of filopodia but not lamellipodia. V14RhoA stimulated actin cable assembly and cell contraction, while the Rho inhibitor, C3 transferase, induced the loss of actin cables. Bac1 cells had cell-to-substratum adhesion sites containing beta1 integrin, pp125FAK, paxillin, vinculin, and tyrosine phosphorylated proteins. These 'focal complexes' were present in growing and CSF-1-starved cells, but were disassembled in cells injected with N17Cdc42 or N17Rac1. Interestingly, beta1 integrin did not disperse until long after focal phosphotyrosine and vinculin staining had disappeared. We conclude that in Bac1 macrophages Cdc42, Rac and Rho regulate the formation of distinct actin filament-based structures, and that Cdc42 and Rac are also required for the assembly of adhesion sites to the extracellular matrix.

Actins↗