A neural network model of speech acquisition and motor equivalent speech production

This article describes a neural network model that addresses the acquisition of speaking skills by infants and subsequent motor equivalent production of speech sounds. The model learns two mappings during a babbling phase. A phonetic-to-orosensory mapping specifies a vocal tract target for each speech sound; these targets take the form of convex regions in orosensory coordinates defining the shape of the vocal tract. The babbling process wherein these convex region targets are formed explains how an infant can learn phoneme-specific and language-specific limits on acceptable variability of articulator movements. The model also learns an orosensory-to-articulatory mapping wherein cells coding desired movement directions in orosensory space learn articulator movements that achieve these orosensory movement directions. The resulting mapping provides a natural explanation for the formation of coordinative structures. This mapping also makes efficient use of redundancy in the articulator system, thereby providing the model with motor equivalent capabilities. Simulations verify the model's ability to compensate for constraints or perturbations applied to the articulators automatically and without new learning and to explain contextual variability seen in human speech production.Supported in part by AFOSR F49620-92-J-0499     

Fatty acid oxidation in bone tissue and bone cells in culture. Characterization and hormonal influences.

Fatty acid oxidation and its hormonal modulation were investigated in cultured rat calvaria and in cultivated cell populations. The latter were obtained from calvaria of newborn rats by sequential time-dependent digestion with collagenase, yielding eight cell populations: the early ones containing mainly fibroblasts, the middle ones being osteoblast-like, and late ones osteoblast-osteocyte-like. In calvaria, fatty acid oxidation was increased by adding 0.1 mM- and 1.0 mM-palmitate to the medium, containing 10% (v/v) fetal-calf serum. No effect was found after parathyrin addition in vitro or when injected in vivo. All cell populations obtained by sequential digestion were found to oxidize palmitate, whereby the osteoblast-like cells showed a lower oxidation rate than the other populations. Both parathyrin and calcitonin had no effect on fatty acid oxidation. 1,25-Dihydroxycholecalciferol at 1-100 nM and 24,25-dihydroxycholecalciferol at 100 nM increased oxidation primarily in the population enriched with osteoblast-like cells. Insulin at 1.6 microM diminished it in the cell populations enriched with osteoblast-like cells and in the late bone-cell fraction. However, glucagon had no effect. The energy provided by fatty acid oxidation in this system is approx. 40-80% of glucose metabolism, suggesting that this event may be of importance in the energy metabolism of bone.     

A glia-derived neurite-promoting factor with protease inhibitory activity.

Brain cells and glioma cells in culture release a protein which induces neurite outgrowth in neuroblastoma cells. This neurite-promoting factor (NPF), which has been purified from serum-free glioma conditioned medium, has an apparent mol. wt. of 43 000. NPF inhibits urokinase as well as plasminogen activator-dependent caseinolysis or fibrinolysis. NPF and urokinase form an SDS-resistant complex. The fact that this glia-derived NPF is a potent protease inhibitor indicates that glial cells modulate the proteolytic activity associated with neuronal cells and suggests that this phenomenon is one of the biochemical events involved in the regulation of neurite growth.     

Development of Photosystem II in dark grown Chlamydomonas reinhardtii. A light-dependent conversion of PS IIβ, QB-nonreducing centers to the PS IIα, QB-reducing form

The green alga Chlamydomonas reinhardtii is a facultative heterotroph and, when cultured in the presence of acetate, will synthesize chlorophyll (Chl) and photosystem (PS) components in the dark. Analysis of the thylakoid membrane composition and function in dark grown C. reinhardtii revealed that photochemically competent PS II complexes were synthesized and assembled in the thylakoid membrane. These PS II centers were impaired in the electron-transport reaction from the primary-quinone electron acceptor, Q_A, to the secondary-quinone electron acceptor, Q_B (Q_B-nonreducing centers). Both complements of the PS II Chl a–b light harvesting antenna (LHC II-inner and LHC II-peripheral) were synthesized and assembled in the thylakoid membrane of dark grown C. reinhardtii cells. However, the LHC II-peripheral was energetically uncoupled from the PS II reaction center. Thus, PS II units in dark grown cells had a -type Chl antenna size with only 130 Chl (a and b) molecules (by definition, PS II units lack LHC II-peripheral). Illumination of dark grown C. reinhardtii caused pronounced changes in the organization and function of PS II. With a half-time of about 30 min, PS II centers were converted froma Q_B-nonreducing form in the dark, to a Q_B-reducing form in the light. Concomitant with this change, PS II units were energetically coupled with the LHC II-peripheral complement in the thylakoid membrane and were converted to a PS II form. The functional antenna of the latter contained more than 250 Chl(a+b) molecules. The results are discussed in terms of a light-dependent activation of the Q_A-Q_B electron-transfer reaction which is followed by association of the PS II unit with a LHC II-peripheral antenna and by inclusion of the mature form of PS II (PS II) in the membrane of the grana partition region.Abbreviations Chl chlorophyll - PS photosystem - Q_A primary quinone electron acceptor of PS II - Q_B secondary quinone electron acceptor of PS II - LHC light harvesting complex - F₀ non-variable fluorescence yield - F_plf intermediate fluorescence yield plateau leyel - F_max maximum fluorescence yield - F_i initial fluorescence yield increase from F₀ to F_pl (F_pl–F₀) - F_v total variable fluorescence yield (F_m–F0) - DCMU dichlorophenyl-dimethylurea     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

A cometabilic kinetics model incorporating enzyme inhbition, inactivation, and recovery: I. Model development, analysis, and testing

Cometabolic biodegradation prcesses are important for bioremediation of hazardous waste sites. However, these proceeses are not well understood and have not been modeled thoroughly. Traditional Michaelis-Menten kinetics models often are used, but toxic effects and bacterial responses to toxicity may cause changes in enzyme levels, rendering such models inappropriate. In this article, a conceptual and mathematical model of cometabolic enzyme kinetics i described. Model derivation is based on enzyme/growth-substrate/nongrowth-substrate interaction and incorporates enzyme inhibition (caused by the presence of a cometabolic compound), inactivation (resulting from toxicity of a cometabolic product), and recovery (associated with bacterial synthesis of new enbzyme in response to inactivation). The mathematical model consists of a system of two, nonlinear ordinary differential equations that can be solved implicitly using numerical methods, providing estimates of model parameters. Model analysis shows that growth substraate adn nongrowth substrate oxidation rates are related by a dimensionless constant. Reliability of tehy model solution prcedure is verifiedl by abnalyzing data ses, containing random error, from simulated experimentss with trichhloroethyylene (TCE) degradation by ammonia-oxidizing bacterialunder various conditions. Estimation of the recovery rate contant is deterimined to be sensitive to intial TCE concentration. Model assumptions are evaluated in a companion article using data from TCE degradation experiments with amoniaoxidizing bacteria. (c) 1995 John Wiley & Sons, Inc.     

Trace gas exchange over terrestrial ecosystems: methods and perspectives in micrometeorology

Quantification of the surface-atmosphere exchange of trace gasesis recognized as an essential prerequisite to understandingthe role of the biosphere in the global climate system. Amongthe micrometeorological methods available to measure surface-atmospherefluxes, the aerodynamic gradient, the energy balance/Bowen ratio,the eddy covariance and the eddy accumulation methods are themost widely employed. This brief review describes the theoreticalbackground and the practical applications of these methodologiesand is particularly directed to plant ecophysiologists, ecologistsand botanists who may be interested in scaling biological processesto the canopy level. Key words: Trace gas exchange, biosphere, surface-atmosphere fluxes, aerodynamic gradient, Bowen ratio, eddy covariance, eddy accumulation, micrometeorology     

Rapid intracellular degradation of newly synthesized collagen by bone cells. Effect of dichloromethylenebisphosphonate

Experiments were carried out to determine whether bone cells isolated from rat calvaria degrade newly synthesized collagen intracellularly prior to secretion and to assess the effect of dichloromethylenebisphosphonate, a compound shown to stimulate collagen synthesis during this event. The findings indicate that isolated bone cells grown in culture degraded a proportion (average 16%) of newly synthesized collagen prior to secretion. This process was markedly reduced by exposure to dichloromethylenebisphosphonate in a dose-related manner. Concomitantly with the observed decrease of degradation, an increase of collagen synthesis was detected as determined by the incorporation of [3H]proline into collagenase-digestible proteins or by the conversion of [3H]proline into [3H]hydroxyproline. No similar enhancement on total non-collagenous protein synthesis was evident. Dichloromethylenebisphosphonate did not influence the extracellular degradation of collagen. Although the reduction in intracellular degradation accounted only for part of the bisphosphonate mediated increase in net collagen synthesis, it is conceivable that the rate of collagen synthesis is regulated, at least in part, by mechanisms that modulate the level of intracellular degradation.     

Plant DNA topoisomerase I is recognized and inhibited by human Scl-70 sera autoantibodies

Type I topoisomerases (EC 5.99.1.2) are those enzymes capable of relaxing negatively supercoiled DNA without the need for ATP. The central role played by these enzymes in cell function suggests that the structure of type I topoisomerases may be highly conserved in eukaryotic cells. However, the extent of the conservation among eukaryotes is unknown. Human DNA topoisomerase I is an autoimmune antigen (Scl-70) of scleroderma patients. We have found that the autoimmune antibodies in human Scl-70 sera recognize protein from various plants, and these proteins display DNA relaxation function. In addition, Scl-70 antibodies were able to inhibit enzymatic activity of plant topoisomerase I. Therefore, the immunological cross-reactivity of the plant topoisomerase with human antibodies demonstrates that, despite divergence of eukaryotic organisms, these plant and animal enzymes retain structurally similar enzymatic features.