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Biomedical subjects

R L Blanton

Publications and source records attributed to R L Blanton.

At least 19 recordsLinked to original sources
PubMed2001

Spore coat formation and timely sporulation depend on cellulose in Dictyostelium.

Cellulose is a major component of the extracellular coat that surrounds the terminally-differentiated spore of Dictyostelium. It is sandwiched between two layers of proteins that derive from prespore vesicles by exocytosis. Strains unable to synthesize cellulose due to null mutations in the gene encoding the catalytic subunit of cellulose synthase (dcsA) failed to make detergent-resistant spores but produced small, highly refractile, round spore-like cells up to a day late. Although these cells resembled spores in appearance, they were unstable, only transiently ellipsoid in shape, and sensitive to hypo-osmotic shock, drying, or detergents. Differentiation of these pseudo-spores was induced in the normal time frame by activation of the cAMP-dependent protein kinase or co-development with wild type cells, and coat proteins were secreted by the dcsA-null cells at the same time as wild type cells. A substantial fraction of secreted coat proteins was loosely associated with the surface of the mutant cells, resembling the precoat posited to form early during normal sporulation. Transmission electron microscopy revealed that the precoat had little ultrastructural organization in the absence of cellulose. Thus, cellulose in the coat appears to be required for the organization of the pre-coat precursors as well as the stability, dormancy, and shape of the spore.

Animals↗
PubMed2000

Adherens junctions and beta-catenin-mediated cell signalling in a non-metazoan organism.

Mechanical forces between cells have a principal role in the organization of animal tissues. Adherens junctions are an important component of these tissues, connecting cells through their actin cytoskeleton and allowing the assembly of tensile structures. At least one adherens junction protein, beta-catenin, also acts as a signalling molecule, directly regulating gene expression. To date, adherens junctions have only been detected in metazoa, and therefore we looked for them outside the animal kingdom to examine their evolutionary origins. The non-metazoan Dictyostelium discoideum forms a multicellular, differentiated structure. Here we describe the discovery of actin-associated intercellular junctions in Dictyostelium. We have isolated a gene encoding a beta-catenin homologue, aardvark, which is a component of the junctional complex, and, independently, is required for cell signalling. Our discovery of adherens junctions outside the animal kingdom shows that the dual role of beta-catenin in cell-cell adhesion and cell signalling evolved before the origins of metazoa.

Actins↗
PubMed2000

The cellulose synthase gene of Dictyostelium.

Cellulose is a major component of the extracellular matrices formed during development of the social amoeba, Dictyostelium discoideum. We isolated insertional mutants that failed to accumulate cellulose and had no cellulose synthase activity at any stage of development. Development proceeded normally in the null mutants up to the beginning of stalk formation, at which point the culminating structures collapsed onto themselves, then proceeded to attempt culmination again. No spores or stalk cells were ever made in the mutants, with all cells eventually lysing. The predicted product of the disrupted gene (dcsA) showed significant similarity to the catalytic subunit of cellulose synthases found in bacteria. Enzyme activity and normal development were recovered in strains transformed with a construct expressing the intact dcsA gene. Growing amoebae carrying the construct accumulated the protein product of dcsA, but did not make cellulose until they had developed for at least 10 hr. These studies show directly that the product of dcsA is necessary, but not sufficient, for synthesis of cellulose.

Amino Acid Sequence↗
PubMed1996

Cellulose microfibrils, cell motility, and plasma membrane protein organization change in parallel during culmination in Dictyostelium discoideum.

Prestalk cells of Dictyostelium discoideum contribute cellulose to two distinct structures, the stalk tube and the stalk cell wall, during culmination. This paper demonstrates by freeze fracture electron microscopy that two distinct types of intramembrane particle aggregates, which can be characterized as cellulose microfibril terminal complexes, occur in the plasma membranes of cells synthesizing these different forms of cellulose. The same terminal complexes were observed in situ in developing culminants and in vitro in monolayer cells induced to synthesize the two types of cellulose. We propose that cessation of cell motility is associated with a change in packing and intramembrane mobility of the particle aggregates, which cause a change in the nature of the cellulose synthesized. The terminal complexes are compared to those described in other organisms and related to the previous hypothesis of two modes of cellulose synthesis in Dictyostelium.

Animals↗
PubMed1996

Detection of cellulose with improved specificity using laser-based instruments.

Specific detection of cellulose has not been possible using laser based instruments such as laser scanning confocal microscopes (LSCM) and fluorescently activated cell sorters (FACS). Common cellulose dyes are nonspecific and/or nonexcitable with common lasers. Furthermore, many lasers emit wavelengths that overlap with autofluorescence from chlorophyll and other plant molecules. We demonstrate that a cellulase and an isolated bacterial cellulose binding domain (CBD) conjugated to fluorescent dyes can be used for laser detection of cellulose with improved specificity. Cell walls of differentiating tracheary elements and spores of Dictyostelium discoideum were tested in this study. For double labeling, autofluorescence interfering with the rhodamine signal was eliminated by collecting each excitation channel separately followed by computer recombination or by using a narrow band pass barrier filter allowing simultaneous channel collection. Using these methods, cellulose and microtubules tagged with a monoclonal antibody to alpha-tubulin were effectively colocalized in chlorophyll-containing tracheary elements using a LSCM. Also, Dictyostelium discoideum spores labeled or unlabeled with CBD-FITC were separated into two populations by FACS indicating that this tag should be useful in future mutagenesis experiments. Therefore, the presence or absence of cellulose can now be analyzed using common lasers.

Animals↗
PubMed1995

The phosphodiesterase secreted by prestalk cells is necessary for Dictyostelium morphogenesis.

Dictyostelium discoideum secretes a cyclic nucleotide phosphodiesterase to control cAMP levels during development. Three promoters control expression of the gene--one during vegetative growth, one during aggregation, and one which constrains phosphodiesterase synthesis to prestalk cells. In this report we show that the expression of phosphodiesterase (PDE) in prestalk cells is necessary for morphogenesis. A gene that codes for a specific glycoprotein inhibitor of the phosphodiesterase (Kd = 0.1 nM) was fused to the prestalk-specific promoter of the PDE gene. Transformants carrying multiple copies of this construct secreted inhibitor in 100-fold excess after the aggregation process had occurred. The first effect seen was an elongated tip, followed by a block in slug formation and an inability to culminate. Stalk and spores cells are produced but morphogenesis is uncoupled from cellular differentiation. Overproduction of inhibitor during earlier stages delayed aggregation, but did not affect fruiting body formation. A phosphodiesterase mutant was transformed with a plasmid that expresses PDE only during aggregation and not in prestalk cells. The defect in aggregation was rescued, but the defect in later development was not. The combined results indicate that PDE expression in prestalk cells is critical to morphogenesis. To ask whether the inhibitor gene under its normal regulation had a role in aggregation or later morphogenesis, it was destroyed by homologous recombination. The loss of the gene did not prevent development under the conditions used.

Amino Acid Sequence↗
PubMed1994

Disruption of the gene encoding the EcmA, extracellular matrix protein of Dictyostelium alters slug morphology.

The ecmA and ecmB genes of Dictyostelium are expressed in prestalk and stalk cells. They encode components of the slime sheath, the extracellular matrix that surrounds the migrating slug, and the stalk tube, the matrix that encases stalk cells. We have generated, by homologous gene disruption, a mutant in which the ecmB gene is inactivated but the strain develops normally. In contrast, ecmA null mutant strains develop to form abnormally long and thin standing slugs. While the slime sheath of mutant slugs appears to be normal in electron microscopic observations, the sheath material remaining on the substratum after the slug travels through it is abnormally susceptible to breakage. After a short period of migration the axial ratio of mutant slugs decreases to that of normal slugs and, at culmination, normal fruiting bodies are produced. These data suggest that the EcmA protein has its primary role during slug formation, where it contributes to the strength of the slime sheath, and that the function of the EcmB protein is dispensible.

Animals↗
PubMed1991

Motivational processes and behavioral inhibition in breath holding.

Large individual differences in breathing performance have made it difficult to investigate the effects of psychological variables on respiratory parameters. This study uses an experimental approach to investigating the effects of attentional and motivational factors on breath-holding span in humans. The effects of shock threat (negative incentive), monetary reward (positive incentive), and mantra meditation (attentional control) on breath-holding span at functional residual capacity (FRC) were compared. Based on Jeffrey Gray's (1975, 1987) theory of behavioral inhibition, it was predicted that shock threat would extend FRC breath holding. Breath holding was increased under the shock threat condition but not under the monetary reward or mantra meditation conditions.

Adult↗
PubMed1988

Oddity learning in developmentally delayed children: facilitation by means of familiar stimuli.

Four of 8 low-functioning, developmentally delayed children initially failed to demonstrate oddity responding under conditions in which ostensibly similar children did show oddity responding (e.g., Soraci et al., 1987). In the context of a multiple baseline across-subjects design, each of the 4 previously unsuccessful children demonstrated statistically significant increases in the percentage of correct oddity responses immediately upon introduction of familiar stimuli. These results indicate that perceptual differentiation enhances relational learning of the type required by the oddity task.

Attention↗
PubMed1987

Oddity performance in preschool children at risk for mental retardation: transfer and maintenance.

The oddity performance of five preschool children at risk for mental retardation was facilitated by increasing the number of nonodd elements in a visual array. A combination intrasubject reversal and multiple baseline across subjects design indicated the internal validity of interventions designed to enhance the perceptual salience and consequent stimulus control of the odd stimulus. Results demonstrate that transfer and maintenance of oddity learning can be obtained even with individuals for whom correct oddity responding is uncommon. The typically poor performance of young and developmentally delayed children as compared to nondelayed children on tasks such as the oddity task may be attributable to a lower sensitivity to relational information.

Attention↗
PubMed1986

Effects of cognitive and psychomotor tasks on breath-holding span.

Bartlett (J. Appl. Physiol. 42: 717-721, 1977) demonstrated that a psychomotor task (hand dynamometer) extended breath holds at functional residual capacity (FRC) in a manner comparable to Valsalva and Mueller maneuvers. This led us to the hypothesis that distraction of a subject's attention from dyspneic sensations accounted for Bartlett's findings. This hypothesis was tested by comparing a hand dynamometer task (rubber-bulb squeeze) with a mental performance task (mental arithmetic). Results for tasks performed separately and concurrently in a within-subjects design showed comparable effects, without reaching a FRC breath-hold performance ceiling. Implications of results for effects of nonmechanical and nonchemical factors on respiratory drive are discussed.

Adolescent↗
PubMed1982

Sustained responding under intermittent reinforcement in psychotic children.

A procedure is described that classifies abnormal children with respect to their capacity to sustain adaptive responding without consistent, extrinsic reinforcement. The procedure was used to assess individual differences in tolerance for intermittent reinforcement among a group of 21 psychotic children. The procedure was found to correlate with three variables established by previous research to be important prognostically--i.e., measures of intelligence, social competence, and language functioning. Findings are discussed with respect to the construct of motivation as distinguished from the construct of ability. It is suggested that whether or not the experimental measure is regarded as relevant to the global construct of motivation, it has clear relevance to potential deficits in the important capacity to sustain adaptive responding.

Adaptation, Psychological↗
PubMed1981

Consistency among commonly used procedures for assessment of abnormal children.

Administered the Stanford-Binet and/or its downward extension the Cattell Infant Intelligence Scale to 22 children in a school for severely behaviorally disordered boys and girls. Assessments also were made with the Vineland Social Maturity Scale and with a scale of language development. A subgroup of 17 children were assessed with Rimland's E-2 Scale, which is designed to assess the presence and degree of the condition of autism. Correlations among these commonly used assessment procedures are reported. Findings are discussed with respect to the construct validity of the tests and with respect to practical problems of implementation. Issues that concern the distinctiveness of specific classification dimensions and the heterogeneity of the syndrome of autism also are discussed.

Autistic Disorder↗
PubMed1980

Autoshaping of abnormal children.

Three experimentally naive abnormal children were exposed to a terminal operant contingency, i.e., reinforcement was delivered only if the children pressed a panel during intervals when it was lighted. Despite the absence of both successive approximation and manual shaping, it was found that each child began to respond discriminatively within a small number of trials. These data replicated previous animal studies concerned with the phenomena of autoshaping and signal-controlled responding. It was also found, however, that one type of autoshaping, the classical conditioning procedure, had a powerful suppressive effect on the discriminative responding. An experimental analysis that consisted procedure, had a powerful suppressive effect on discriminative responding. An experimental analysis that consisted of intrasubject reversal an multiple baseline designs established the internal validity of the findings. The finding of rapid acquisition of signal-controlled responding obtained with the initial procedure is suggessted to have practical significance. The disruptive effects of the classical form of autoshaping are discussed in terms of negative behavioral contrast.

Adolescent↗
PubMed1980

Classification of abnormal children: discrimination learning ability.

Large individual differences exist among psychotic and retarded children, and a procedure that would enable classification of discrimination learning ability would be of value. A procedure designed to assess the discrimination learning thresholds of low-functioning children is described. A performance index (PI) that reflects accuracy of discriminative responding, difficulty of the discriminations attained, and learning rate was found to correlate significantly with mental age, intelligence quotient, Vineland Social Age, Vineland Social Quotient, and language functioning, but not with chronological age. The question of the optimal magnitude of correlation between a new measure and existing measures is discussed.

Autistic Disorder↗