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Biomedical subjects

A L Hall

Publications and source records attributed to A L Hall.

At least 19 recordsLinked to original sources
PubMed1997

Cooperation between the Fc epsilonR1 and formyl peptide receptor signaling pathways in RBL(FPR) cells: the contribution of receptor-specific Ca2+ mobilization responses.

RBL(FPR) mast cells express the tyrosine kinase-coupled IgE receptor, Fc epsilonR1, and the G-protein-coupled formyl peptide receptor, FPR. Fc epsilonR1 crosslinking causes Ca2+ stores release, Ca2+ influx, Ins(1,4,5)P3 production and secretion. FPR ligation also mobilizes Ca2+, but without measurable Ins(1,4,5)P3 production or secretion. Co-stimulating the FPR and Fc epsilonR1 induces more Ins(1,4,5)P3 production and secretion than Fc epsilonR1 cross-linking alone. Costimulation also produces more rapid and sustained Ca2+ responses than are generated by Fc epsilonR1 activation alone. We identified multiple differences between the FPR- and Fc epsilonR1-coupled Ca2+ responses, including a more rapid Ca2+ spike response to FPR ligation; intracellular Ca2+ stores that are empty following Fc epsilonR1 crosslinking but partially full following FPR activation; a more sustained Ca2+ influx response to Fc epsilonR1 crosslinking; and the immediate inhibition of stimulated Ca2+ influx by FPR antagonists but not by monovalent ligand that terminates Fc epsilonR1 crosslinking. We hypothesize that the interaction of receptor-specific Ca2+ mobilization pathways contributes to the FPR-mediated potentiation of Fc epsilonR1-coupled secretion.

Animals↗
PubMed1997

Relationship of ligand-receptor dynamics to actin polymerization in RBL-2H3 cells transfected with the human formyl peptide receptor.

The human formyl peptide receptor (FPR) expressed in RBL-2H3 transfectants (RBL[FPR]) behaves qualitatively like the FPR expressed by neutrophils except that it causes sustained F-actin accumulation and cell shape change responses on formyl peptide stimulation. These sustained responses were not accounted for by changes in the transfected receptor's ability to interact with ligand or by receptor density. Signal transduction pathways of transfected and neutrophil FPRs are apparently similar. In transfected cells, dissociation of ligand is sensitive to guanine nucleotide, the G protein is pertussis toxin-sensitive, FPR and G protein appear to be precoupled, the F-actin response is stimulated with the same dose-response profile as in neutrophils, and the F-actin accumulation response is directly regulated by the FPR, even long after initial stimulation. Potentially significant differences between neutrophil and transfected FPR were found when receptor processing was measured. In neutrophils, practically 100% of the FPR is converted to forms that dissociate slowly from ligand and are inactive in signal transduction within 2 min of ligand stimulation. By contrast, 20% or more of transfected FPR remains rapidly dissociating even 5 min after stimulation. Although 80% of neutrophil FPR is internalized by 5 min after stimulation, transfected FPR appears to plateau at 50-60% internalized. Because actin responses in neutrophils are regulated by a small number of active receptors, the inefficiency of receptor inactivation in RBL(FPR) transfectants may account for the prolonged F-actin accumulation response.

Actins↗
PubMed1997

Elution and partial characterization of immunoglobulins bound to ovine placenta.

Immunoglobulins were eluted from ovine placentae and characterized by immunoprecipitation, electrophoresis, western blotting and ELISA. IgG was shown to comprise the bulk of placental-bound immunoglobulins while smaller amounts of IgM and only trace amounts of IgA were demonstrated. Results suggest that ovine placental IgG eluted by surgical cannulation of the uterine blood vessels in situ is similar to that eluted from postpartum placentae in vitro, implying that there may be some transfer of antibodies across the maternal side of the placental barrier to the trophoblast. These antibodies are rich in IgG1 and IgG2, have a relative molecular weight of 158 kDa, and bind to an 80 kDa peptide prepared from pre-acidified ovine placental cotyledons. We propose that the binding of placental IgG to the 80 kDa antigen may prevent immunological rejection of the foetus by competitively excluding cytotoxic cells of maternal origin such as NK cells. Also, given that a similar antigen (80 kDa) has been reported in humans and equines, and shown to be saturated with IgG in term placentae, we propose that this antigen may be conserved in several mammalian species for reproductive purpose. Consequently, we suggest that the ovine placental IgG and the 80 kDa antigen may be suitable as models for the study of maternal-foetal interactions in mammalian pregnancies.

Animals↗
PubMed1993

The role of the cyclic nucleotide phosphodiesterase of Dictyostelium discoideum during growth, aggregation, and morphogenesis: overexpression and localization studies with the separate promoters of the pde.

cAMP acts as a primary signal and is regulated by a secreted cyclic nucleotide phosphodiesterase (PDE) throughout development in Dictyostelium discoideum. Expression of the PDE gene (pde) is controlled by promoters specific to vegetative growth (prV), aggregation (prA), or late development (prL). Promoter-containing regions were individually fused to the pde coding sequence. After transformation multiple copies of each construct led to overexpression of PDE mRNA and enzyme activity with the temporal profile expected of each promoter. Overexpression of PDE from prV and prA altered the timing of aggregation compared to control transformants, but the final morphology was normal. Control transformants showed delayed aggregation compared to nontransformed cells. Cells that overexpressed PDE from prL aggregated like the control transformants, but no fruiting bodies were formed. Individual promoter regions were fused to the beta-galactosidase gene (lacZ). Cells that expressed prA-lacZ were dispersed throughout aggregation fields and mounds. Cells that expressed prL-lacZ were first seen distributed homogeneously throughout tight and tipped mounds. In slugs most of these cells are localized in the anterior region. During culmination, cells that expressed the prL-lacZ construct became incorporated into the stalk and were seen in the upper and lower cups surrounding the spore mass.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1991

Purification and characterization of aginactin, a newly identified agonist-regulated actin-capping protein from Dictyostelium amoebae.

Amoeboid chemotaxis involves a regulated increase in actin nucleation activity that is correlated with an increase in actin polymerization occurring seconds after chemotactic stimulation (Carson, M., Weber, A., and Zigmond, S. H. (1986) J. Cell Biol. 103, 2707-2714; Hall, A. L., Warren, V., Dharmawardhane, S., and Condeelis, J. (1989) J. Cell Biol. 109, 2207-2213). We report the isolation and characterization of an agonist-regulated capping protein, aginactin, from Dictyostelium that may regulate these changes in actin nucleation activity. Aginactin is isolated from low speed supernatants of starved amoebae by sequential anion exchange, hydrophobic interaction, fast protein liquid chromatography anion exchange, and hydroxyapatite chromatography. Aginactin migrates with an apparent molecular weight of 70,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels and gel filtration columns, suggesting that it is a globular monomer. Aginactin is a barbed-end capping protein by several criteria. It inhibits the rate and final extent of actin polymerization and increases the apparent critical concentration at substoichiometric ratios to actin. It also inhibits depolymerization of F-actin and inhibits polymerization at the barbed end of Limulus acrosomal bundles. Aginactin is unaffected by micromolar Ca2+, and it neither severs F-actin nor nucleates actin polymerization in either the presence or absence of Ca2+. Aginactin binds to and cosediments with F-actin and has an apparent Kd for capping F-actin of 2.7 nM.

Actin Capping Proteins↗
PubMed1991

Cyclic nucleotide phosphodiesterase of Dictyostelium discoideum and its glycoprotein inhibitor: structure and expression of their genes.

The genes coding for the cyclic nucleotide phosphodiesterase (PD) and the PD inhibitory glycoprotein (PDI) have been cloned and characterized. The PDI gene was isolated as a 1.6 kb genomic fragment, which included the coding sequence containing two small introns and 510 nucleotides of non-translated 5' sequence. From the deduced amino acid sequence we predict a protein with a molecular weight (MW) of 26,000 that, in agreement with previous data, contains 15% cysteine residues. Genomic Southern blot analysis indicates that only one gene encodes the inhibitor. Northern blot analysis shows a single transcript of 0.95 kb. The PDI gene is expressed early in development with little transcript remaining following aggregation. The appearance of PDI mRNA is prevented by the presence of cAMP, but when cAMP is removed the transcript appears within 30 minutes. When cAMP is applied to cells expressing PDI the transcript disappears with a half-life of less than 30 minutes. The PD gene of D. discoideum is transcribed into three mRNAs: a 1.9 kb mRNA specific for growth, a 2.4 kb mRNA specific for aggregation, and a 2.2 kb mRNA specific for late development. The 2.2 kb mRNA is also specific for prestalk cells, and is induced by differentiation-inducing factor. All three mRNAs contain the same coding sequence, and differ only in their 5' non-coding sequences. Each mRNA is transcribed from a different promoter, and by using the chloramphenicol acyltransferase gene as a reporter, we have shown that each promoter displays the same regulation as its cognate mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

What is repeated in a repetition? Effects of practice conditions on motor skill acquisition.

The nature of repetition and its contribution to the acquisition of motor skills in neurologically healthy subjects are examined in this article. We argue that cognitive processing is a key component of practice, which is undermined by repetitive performances. The effects on motor learning of contextual interference, knowledge-of-results delivery schedules, and observation of models are examined, with particular reference to the nature of practice. The role of repetition in learning with respect to physical therapy is also discussed.

Cognition↗
PubMed1990

Mechanisms of amoeboid chemotaxis: an evaluation of the cortical expansion model.

In this work we evaluate the cortical expansion model for amoeboid chemotaxis with regard to new information about molecular events in the cytoskeleton following chemotactic stimulation of Dictyostelium amoebae. A rapid upshift in the concentration of chemoattractant can be used to synchronize the motile behavior of a large population of cells. This synchrony presents an opportunity to study the biochemical basis of morphological changes such as pseudopod extension that are required for amoeboid chemotaxis. Changes in the composition and activity of the cytoskeleton following stimulation can be measured with precision and correlated with important morphological changes. Such studies demonstrate that activation of actin nucleation is one of the first and most crucial events in the actin cytoskeleton following stimulation. This activation is followed by incorporation of specific actin cross-linking proteins into the cytoskeleton, which are implicated in the extension of pseudopods and filopods. These results, as well as those from studies with mutants deficient in myosin, indicate that cortical expansion, driven by focal actin polymerization, cross-linking and gel osmotic swelling, is an important force for pseudopod extension. It is concluded that whereas three forces, frontal sliding, tail contraction, and cortical expansion may cooperate to produce amoeboid movement, the cortical expansion model offers the simplest explanation of how focal stimulation with a chemoattractant causes polarized pseudopod extension.

Actins↗
PubMed1990

The cyclic nucleotide phosphodiesterase gene of Dictyostelium discoideum contains three promoters specific for growth, aggregation, and late development.

The cyclic nucleotide phosphodiesterase (phosphodiesterase) plays essential roles throughout the development of Dictyostelium discoideum. It is crucial to cellular aggregation and to postaggregation morphogenesis. The phosphodiesterase gene is transcribed into three mRNAs, containing the same coding sequence connected to different 5' untranslated sequences, that accumulate at different times during the life cycle. A 1.9-kilobase (kb) mRNA is specific for growth, a 2.4-kb mRNA is specific for aggregation, and a 2.2-kb mRNA is specific for late development and is only expressed in prestalk cells. Hybridization of RNA isolated from cells at various stages of development with different upstream regions of the gene indicated separate promoters for each of the three mRNAs. The existence of specific promoters was confirmed by fusing the three putative promoter regions to the chloramphenicol acetyltransferase reporter gene, and the analysis of transformants containing these constructs. The three promoters are scattered within a 4.1-kilobase pair (kbp) region upstream of the initiation codon. The late promoter is proximal to the coding sequence, the growth-specific promoter has an initiation site that is 1.9 kbp upstream of the ATG codon, and the aggregation-specific promoter has an initiation site 3 kbp upstream.

Amino Acid Sequence↗
PubMed1990

The utility and generality of Mini-Mental State Examination scores in Alzheimer's disease.

The present study sought to evaluate the validity and generality of the Mini-Mental State Examination (MMSE) and its subsection scores. We gave the MMSE and other neuropsychological tests to 51 patients with probable Alzheimer's disease. On the basis of correlational and factor analyses, overall performance on the MMSE proved to have good concurrent validity with other comprehensive neuropsychological assessment instruments. However, the MMSE subsections should not be viewed as highly specific measures of cognition or memory.

Aged↗
PubMed1989

Changes in the association of actin-binding proteins with the actin cytoskeleton during chemotactic stimulation of Dictyostelium discoideum.

Triton-insoluble cytoskeletons were isolated from Dictyostelium discoideum AX3 cells prior to and following stimulation with 2'deoxy cyclic adenosine monophosphate (cAMP). Temporal changes in the content of actin and a 120,000 dalton actin-binding protein (ABP-120) in cytoskeletons following stimulation were monitored. Both actin and ABP-120 were incorporated into the cytoskeleton at 30-40 seconds following stimulation, which is cotemporal with the onset of pseudopod extension during stimulation of amoebae with chemoattractants. Changes in the content of total cytoskeletal protein and cytoskeletal myosin were determined under the same experimental conditions as controls. These proteins exhibited different kinetics from those of cytoskeletal ABP-120 and actin following the addition of 2'deoxy cAMP. The authors concluded that the association of ABP-120 with the cytoskeleton is regulated during cAMP signalling. Furthermore, these results indicate that ABP-120 is involved in cross-linking newly assembled actin filaments into the cytoskeleton during chemoattractant-stimulated pseudopod extension.

Actins↗
PubMed1989

Transduction of the chemotactic signal to the actin cytoskeleton of Dictyostelium discoideum.

Dictyostelium discoideum amebae chemotax toward folate during vegetative growth and toward extracellular cAMP during the aggregation phase that follows starvation. Stimulation of starving amebae with extracellular cAMP leads to both actin polymerization and pseudopod extension (Hall et al., 1988, J. Cell. Biochem. 37, 285-299). We have identified an actin nucleation activity (NA) from starving amebae that is regulated by cAMP receptors and controls actin polymerization (Hall et al., 1989, J. Cell Biol., in press). We show here that NA from vegetative cells is also regulated by chemotactic receptors for folate. Our studies indicate that NA is an essential effector in control of the actin cytoskeleton by chemotactic receptors. Guided by a recently proposed model for signal transduction from the cAMP receptor (Snaar-Jagalska et al., 1988, Dev. Genet. 9, 215-225), we investigated which of three signaling pathways activates the NA effector. Treatment of whole cells with a commercial pertussis toxin preparation (PT) inhibited cAMP-stimulated NA. However, endotoxin contamination of the PT appears to account for this effect. The synag7 mutation and caffeine treatment do not inhibit activation of NA by cAMP. Thus, neither activation of adenylate cyclase nor a G protein sensitive to PT treatment of whole cells is necessary for the NA response. Actin nucleation activity stimulated with folate is normal in vegetative fgdA cells. However, cAMP suppresses rather than activates NA in starving fgdA cells. This indicates that the components of the actin nucleation effector are present and that a pathway regulating the inhibitor(s) of nucleation remains functional in starving fgdA cells. The locus of the fgdA defect, a G protein implicated in phospholipase C activation, is directly or indirectly responsible for transduction of the stimulatory chemotactic signal from cAMP receptors to the nucleation effector in Dictyostelium.

Actins↗
PubMed1989

Identification of actin nucleation activity and polymerization inhibitor in ameboid cells: their regulation by chemotactic stimulation.

Actin polymerization occurs in amebae of Dictyostelium discoideum after chemotactic stimulation (Hall, A. L., A. Schlein, and J. Condeelis. 1988. J. Cell. Biochem. 37:285-299). When cells are lysed with Triton X-100 during stimulation, an actin nucleation activity is detected in lysates by measuring the rate of pyrene-labeled actin polymerization. This stimulated nucleation activity is closely correlated with actin polymerization observed in vivo in its kinetics, developmental regulation, and cytochalasin D sensitivity. Actin polymerization is coordinate with pseudopod extension in synchronized populations of cells and is correlated with the accumulation of F actin in pseudopods. The stimulated actin nucleation activity is present in low-speed pellets from Triton lysates (cytoskeletons) within 3 s of stimulation and is stable compared with the nucleation activity of whole cell lysates. Low-speed supernatants contain a reversible inhibitor of the actin nucleation activity that is itself regulated by chemotactic stimulation. Neither activity requires Ca2+ and both are fully expressed in 10 mM EGTA. Fractions containing the inhibitor do not sever actin filaments but do inhibit actin polymerization that is seeded by fragments of purified F actin. These results indicate that chemotactic stimulation of Dictyostelium discoideum generates both an actin-nucleating activity and an actin-polymerization inhibitor, and suggest that the parallel regulation of these two activities leads to the transient phases of actin polymerization observed in vivo. The different compartmentation of these two activities may account for polarized pseudopod extension in gradients of chemoattractant.

Actins↗
PubMed1989

cAMP-mediated inhibition of intracellular particle movement and actin reorganization in Dictyostelium.

Before addition of cAMP, Dictyostelum amoebae rapidly translocating in buffer are elongate, exhibit expansion zones primarily at the anterior end and filamentous actin (F-actin) localization primarily in the anterior pseudopodia. Intracellular particle movement is primarily in the anterior direction, and the average rate of particle movement is roughly five times the rate of cellular translocation. Within seconds after the addition of 10(-6)M cAMP, there is a dramatic suppression of cellular translocation, an inhibition of pseudopod formation, a freeze in cellular morphology, a dramatic depression in intracellular particle movement, loss of F-actin localization in pseudopodia concomitant with relocalization of F-actin in the general cytoplasmic cortex under the plasma membrane, and a doubling of F-actin content. After 10 s, expansion zones are again visible at the cell perimeter, but they no longer are localized in the original anterior portion of the cell. There is a slight rebound in particle movement after 10 s, but particles with persistent tracks now show no directionality towards the original anterior portion of the cell, as they did before cAMP addition. Finally, in parallel with the resumption of peripheral expansion and the small rebound in particle movement, there is a decrease in total cellular F-actin to the untreated level. The pattern of microtubule organization is unaffected by the addition of cAMP.

Actins↗
PubMed1988

Relationship of pseudopod extension to chemotactic hormone-induced actin polymerization in amoeboid cells.

Aggregation-competent amoeboid cells of Dictyostelium discoideum are chemotactic toward cAMP. Video microscopy and scanning electron microscopy were used to quantitate changes in cell morphology and locomotion during uniform upshifts in the concentration of cAMP. These studies demonstrate that morphological and motile responses to cAMP are sufficiently synchronous within a cell population to allow relevant biochemical analyses to be performed on large numbers of cells. Changes in cell behavior were correlated with F-actin content by using an NBD-phallacidin binding assay. These studies demonstrate that actin polymerization occurs in two stages in response to stimulation of cells with extracellular cAMP and involves the addition of monomers to the cytochalasin D-sensitive (barbed) ends of actin filaments. The second stage of actin assembly, which peaks at 60 sec following an upshift in cAMP concentration, is temporally correlated with the growth of new pseudopods. The F-actin assembled by 60 sec is localized in these new pseudopods. These results indicate that actin polymerization may constitute one of the driving forces for pseudopod extension in amoeboid cells and that nucleation sites regulating polymerization are under the control of chemotaxis receptors.

Actins↗
PubMed1987

Stroke treatment: comparison of integrated behavioral-physical therapy vs traditional physical therapy programs.

This was a controlled study of the efficacy of two forms of therapy on upper limb functions of hemiparetic patients--one heavily behavioral and the other based on Bobath therapeutic exercises. It arose from an earlier pilot study comparing EMG biofeedback with physical therapy from which it was concluded that both the elapsed time since the acute stroke and the severity of residual disability were particularly important factors. Of 29 patients included and randomly assigned to one or the other heavily systematized therapies, 18 were classified as having early-severe and 11 as late-mild conditions. Multiple function tests by a "blinded" special technician in another location revealed that overall both forms of therapy obtained worthwhile clinical and statistical improvement, which was maintained at nine-month recheck testing; but there was no statistically significant superiority of one therapy over the other under the very specific circumstances of the research design. Ease of delivering care and other socioeconomic considerations become important factors in choosing either or both of these methods.

Adult↗