Evaluational Language Processes in the Deaf

Locus of Control and Evaluation Scales were administered to 137 deaf Ss at the Tennessee School for the Deaf and to 302 control Ss from the public schools of Williamson County, Tennessee. The results strongly supported the hypothesis that the deaf rely very heavily on others for evaluative judgments as well as behavioral decisions. The data were consistent with the frequently made observation that the deaf adolescent is more immature and dependent both in educational level and social-emotional growth. The problem of the importance of evaluational vocabulary for evaluational judgments was discussed.

Cryofixation methods for ultrastructural studies of Dictyostelium discoideum

Cryopreservation methods, including rapid freezing, freeze-substitution, and low-temperature embedment, lead to superior ultrastructural preservation compared with traditional fixation procedures. This is particularly true for the multicellular stages of Dictyostelium discoideum, in which the hydrophobic sheath that surrounds the structures causes delayed penetration by the already slow-acting aqueous chemical fixatives, resulting in cell shape changes, loss of cell-cell contacts, and changes in cell-matrix interactions. The surface tension effects of traditional fixation methods can also result in disruption of the delicate structures. Depth of freezing is often greater than expected because of the relatively dehydrated state of the multicellular structures. Variations in freeze-substitution solvents and embedment media can be employed to allow for antigenic preservation. Commercial instruments exist for most of the procedures, but excellent results can be obtained using inexpensive hand-crafted apparatus.

Characterization of a novel cellulose synthesis inhibitor

The physiological effects of an experimental herbicide and cellulose synthesis inhibitor, N2-(1-ethyl-3-phenylpropyl)-6-(1-fluoro-1-methylethyl)-1,3,5-triazine-2,4-diamine, called AE F150944, are described. In the aminotriazine molecular class, AE F150944 is structurally distinct from other known cellulose synthesis inhibitors. It specifically inhibits crystalline cellulose synthesis in plants without affecting other processes that were tested. The effects of AE F150944 on dicotyledonous plants were tested on cultured mesophyll cells of Zinnia elegans L. cv. Envy, which can be selectively induced to expand via primary wall synthesis or to differentiate into tracheary elements via secondary wall synthesis. The IC50 values during primary and secondary wall synthesis in Z. elegans were 3.91 x 10(-8) M and 3.67 x 10(-9) M, respectively. The IC50 in suspension cultures of the monocot Sorghum halapense (L.) Pers., which were dividing and synthesizing primary walls, was 1.67 x 10(-10) M. At maximally inhibitory concentrations, 18-33% residual crystalline cellulose synthesis activity remained, with the most residual activity observed during primary wall synthesis in Z. elegans. Addition to Z. elegans cells of two other cellulose synthesis inhibitors, 1 microM 2,6-dichlorobenzonitrile and isoxaben, along with AE F150944 did not eliminate the residual cellulose synthesis, indicating little synergy between the three inhibitors. In differentiating tracheary elements, AE F150944 inhibited the deposition of detectable cellulose into patterned secondary wall thickenings, which was correlated with delocalization of lignin as described previously for 2, 6-dichlorobenzonitrile. Freeze-fracture electron microscopy showed that the plasma membrane below the patterned thickenings of AE F150944-treated tracheary elements was depleted of cellulose-synthase-containing rosettes, which appeared to be inserted intact into the plasma membrane followed by their rapid disaggregation. AE F150944 also inhibited cellulose-dependent growth in the rosette-containing alga, Spirogyra pratensis, but it did not inhibit cellulose synthesis in Acetobacter xylinum or Dictyostelium discoideum, both of which synthesize cellulose via linear terminal complexes. Therefore, AE F150944 may inhibit crystalline cellulose synthesis by destabilizing plasma membrane rosettes.

Dictyostelium cell death: early emergence and demise of highly polarized paddle cells

Cell death in the stalk of Dictyostelium discoideum, a prototypic vacuolar cell death, can be studied in vitro using cells differentiating as a monolayer. To identify early events, we examined potentially dying cells at a time when the classical signs of Dictyostelium cell death, such as heavy vacuolization and membrane lesions, were not yet apparent. We observed that most cells proceeded through a stereotyped series of differentiation stages, including the emergence of "paddle" cells showing high motility and strikingly marked subcellular compartmentalization with actin segregation. Paddle cell emergence and subsequent demise with paddle-to-round cell transition may be critical to the cell death process, as they were contemporary with irreversibility assessed through time-lapse videos and clonogenicity tests. Paddle cell demise was not related to formation of the cellulose shell because cells where the cellulose-synthase gene had been inactivated underwent death indistinguishable from that of parental cells. A major subcellular alteration at the paddle-to-round cell transition was the disappearance of F-actin. The Dictyostelium vacuolar cell death pathway thus does not require cellulose synthesis and includes early actin rearrangements (F-actin segregation, then depolymerization), contemporary with irreversibility, corresponding to the emergence and demise of highly polarized paddle cells.

Loss of the beta-catenin homologue aardvark causes ectopic stalk formation in Dictyostelium

Aardvark (Aar) is a Dictyostelium beta-catenin homologue with both cytoskeletal and signal transduction roles during development. Here, we show that loss of aar causes a novel phenotype where multiple stalks appear during late development. Ectopic stalks are preceded by misexpression of the stalk marker ST-lacZ in the surrounding tissue. This process does not involve the kinase GSK-3. Mixing experiments show that ectopic ST-lacZ expression and stalk formation are cell non-autonomous. The protein-cellulose matrix surrounding the stalk of aar mutant fruiting bodies is defective, and damage to the stalk of wild-type fruiting bodies leads to ectopic ST-lacZ expression. We postulate that poor synthesis of the stalk tube matrix allows diffusion of a stalk cell-inducing factor into the surrounding tissue.

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.

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.

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.

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.

New hope for old dreams: evidence that plant cellulose synthase genes have finally been identified

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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.

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.

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.

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.

A 1,4-β-D-glucan-synthase system from Dictyostelium discoideum

Particulate membrane preparations have been isolated from culminating Dictyostelium discoideum cells. The preparations incorporated glucose from uridine 5'-diphosphate-glucose into a glucose polymer or polymers. These have been shown to be homopolymers of β-linked glucose. A high percentage (78% by methylation analysis) of the linkages formed are 1,4-linkages and a lower percentage (12%) are 1,3-linkages. The glucan-synthase complex present in the particulate membrane preparation has an apparent Km of 0.28 mM and a Vmax of 1.59 nmol·min(-1)·(mg protein)(-1). The enzyme system is dependent upon Mg(2+) and cellobiose for maximal activity, but is inhibited by millimolar levels of Ca(2+). Particulate membrane preparations were made from cells at various times during a synchronous developmental time course and demonstrated that the glucan-synthase activity appeared at the tight-aggregate stage of development.

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.

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.

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.

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.

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.

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.

Coding medium and word recall by deaf and hearing subjects

Forty deaf subjects were compared with 40 fifth graders with normal hearing on the learning of 16 English words. Eight of the words had sign equivalents; eight did not. The task consisted of eight study-test trials. Analysis of the mean number of correct responses showed higher recall of signable than unsignable words. The deaf recalled all words better than the hearing, but this advantage was due primarily to the deaf’s superior recall of the signable words. It was concluded that having a single sign equivalent for a word facilitated its recall.

Some "cloze" technique studies of language capability in the deaf

The performances of 40 deaf adolescents (18 year olds) and 40 sixth-grade hearing students were compared on a multiple-choice sentence completion test. The deaf subjects' scores were significantly lower than the hearing subjects' scores, particularly for adjectives, prepositions, and conjunctions.

A variation of the “cloze” procedure was administered to 63 deaf subjects from the Pennsylvania School for the Deaf, 93 deaf subjects from the Tennessee School for the Deaf, 95 fifth-grade hearing subjects, and 76 twelfth-grade hearing subjects. Three conditions were used: a printed story with either every third word, every fourth word, or every fifth word deleted. The results indicated that the two deaf groups performed similarly but much lower than either of the hearing groups. There was no general effect of span between deleted words; only the deaf increased in ability to predict the correct form class of function words with increasing span between deleted words. It was suggested that the deaf use quite different types of rules in constructing a sentence than hearing subjects, particularly with regard to function words.

Phrase-learning in deaf and hearing subjects

Two groups each containing 24 deaf subjects were compared with 24 fifth graders and 24 twelfth graders with normal hearing on the learning of segments of written English. Eight subjects from each group learned phrasally defined segments such as “paid the tall lady,” eight more learned the same words in nonphrases having acceptable English word order such as “lady paid the tall,” and the remaining eight in each group learned the same words scrambled, “lady tall the paid.” The task consisted of 12 study-test trials. Analyses of the mean number of words recalled correctly and the probability of recalling the whole phrase correctly, given that one word of it was recalled, indicated that both ages of hearing subjects showed facilitation on the phrasally defined segments, interference on the scrambled segments. The deaf groups showed no differential recall as a function of phrasal structure. It was concluded that the deaf do not possess the same perceptual or memory processes with regard to English as do the hearing subjects.

Patterns of word association in the deaf

Comparisons were made of the word associations of normal Ss and two groups of deaf Ss. A special set of coding categories was used in a content analysis of the responses. The results suggest that in comparison to normal Ss, the deaf give relatively more associations that could have been learned from visual experience and from reading simple material, and they give fewer associations that supposedly are learned from subtle uses of language. Also, it was found that deaf Ss frequently are unable to give associates, suggesting that, as a group, words are less meaningful to deaf than normals.