Arabidopsis as a model host for studying plant-pathogen interactions

Because the molecular biology and genetics of Arabidopsis thaliana are so well defined, it is potentially a superb subject for research on plant-pathogen interactions. Viruses, bacteria and fungi that infect Arabidopsis and are representative pathogens of economically important plants have recently been described. The search now is for a pathogenic fungus with tractable genetics to combine with a direct analysis of plant resistance genes.     

Thermodynamic parameters for an expanded nearest-neighbor model for formation of RNA duplexes with Watson-Crick base pairs

Improved thermodynamic parameters for prediction of RNA duplex formation are derived from optical melting studies of 90 oligoribonucleotide duplexes containing only Watson-Crick base pairs. To test end or base composition effects, new sets of duplexes are included that have identical nearest neighbors, but different base compositions and therefore different ends. Duplexes with terminal GC pairs are more stable than duplexes with the same nearest neighbors but terminal AU pairs. Penalizing terminal AU base pairs by 0.45 kcal/mol relative to terminal GC base pairs significantly improves predictions of DeltaG degrees37 from a nearest-neighbor model. A physical model is suggested in which the differential treatment of AU and GC ends accounts for the dependence of the total number of Watson-Crick hydrogen bonds on the base composition of a duplex. On average, the new parameters predict DeltaG degrees37, DeltaH degrees, DeltaS degrees, and TM within 3.2%, 6.0%, 6.8%, and 1.3 degreesC, respectively. These predictions are within the limit of the model, based on experimental results for duplexes predicted to have identical thermodynamic parameters.     

The swine as a model for studying exercise-induced changes in lipid metabolism

The function of cytokines produced during Hymenolepis nana egg infection in mice in protective immunity against re-infection was examined. Treatment of mice with monoclonal antibody (MAb) against mouse interferon (IFN)-gamma caused suppression of protective immunity against H. nana re-infection when the MAb was injected intraperitoneally at a daily dose of 40.0 mg kg-1 during the effector phase of protective immunity. Although high levels of IFN-gamma, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 beta were released into the intestinal tracts of the parasitised mice at challenge infection, there was almost no release of these cytokines in mice treated with the MAb. Daily administration of rolipram failed to suppress the protective immunity, even when 400 micrograms kg-1 of the agent was administered into mice during the effector phase of immunity. Treatment of mice with rolipram completely suppressed both TNF-alpha and IL-1 beta production in intestinal tracts, induced by H. nana challenge infection. However, endogenous IFN-gamma production in the intestine was scarcely affected by rolipram. These results strongly suggest that IFN-gamma is the most important (or essential) cytokine in protective immunity to H. nana re-infection, rather than TNF-alpha and IL-1 beta.     

Yeast as a model organism for studying the actions of DNA topoisomerase-targeted drugs

The budding yeast Saccharomyces cerevisiae has been exploited to investigate the cytotoxic mechanisms of drugs that target DNA topoisomerases. This model organism has been used to establish eukaryotic DNA topoisomerase I or II as the cellular target of specific antineoplastic agents, to define mutations in these enzymes that confer drug resistance and to elucidate the cellular factors that modulate cell sensitivity to DNA topoisomerase-targeted drugs. These findings have provided valuable insights into the critical activities of these enzymes and how perturbing their functions produces DNA damage and cell death.     

Ecological moral realism: An alternative theoretical framework for studying moral psychology.

The authors propose that the empirical study of human moral behavior as undertaken by positive psychologists, psychologists interested in the study of values, and experimental ethicists can be normative at its core, yet also remain truly scientific. To do this, those interested in the empirical study of human moral behavior should consider the concept of affordances, which is central to the Gibsonian ecological psychology tradition, as an approach to studying virtues and strengths. From this perspective, virtues can be better defined as part of moral analogues of affordances (MAAs). Just as the affordance "being-climbable" is a relation between climbing ability and height, so one can similarly define a MAA as an opportunity for moral behavior. Virtues, on this account, would be defined as abilities to behave appropriately in morally relevant situations. If one studies virtues as components of MAAs, virtues are only comprehensible in terms of morally relevant situations. Similarly, morally relevant situations are comprehensible only in terms of abilities to behave appropriately in them, that is, in terms of virtues. We believe that such an approach holds many advantages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amphibian metamorphosis as a model for studying the developmental actions of thyroid hormone

The thyroid hormones L-thyroxine and triiodo-L-thyronine have profound effects on postembryonic development of most vertebrates. Analysis of their action in mammals is vitiated by the exposure of the developing foetus to a number of maternal factors which do not allow one to specifically define the role of thyroid hormone (TH) or that of other hormones and factors that modulate its action. Amphibian metamorphosis is obligatorily dependent on TH which can initiate all the diverse physiological manifestations of this postembryonic developmental process (morphogenesis, cell death, re-structuring, etc.) in free-living embryos and larvae of most anurans. This article will first describe the salient features of metamorphosis and its control by TH and other hormones. Emphasis will be laid on the key role played by TH receptor (TR), in particular the phenomenon of TR gene autoinduction, in initiating the developmental action of TH. Finally, it will be argued that the findings on the control of amphibian metamorphosis enhance our understanding of the regulation of postembryonic development by TH in other vertebrate species.     

A theoretical model for creep crack growth

A theory of creep crack growth has been developed with the presumption that the crack growth occurs by the diffusion of vacancies along the grain boundaries. This is consistent with many experimental results that show that creep fracture is generally of intergranular type and the activation energies for crack growth rates fall within the range of grain boundary diffusion energies. The theory is based on the concept that creep crack growth results from a balance of two competing processes-the diffusion of point defects that contributes to the growth and the creep deformation process that retards the growth and causes even its arrest. The present analysis shows that crack growth via grain boundary diffusion occurs within some temperature range. The upper limiting temperature is determined by the bulk diffusion process which disperses the vacancies, that are diffusing to the crack tip, to the plastic zone ahead of the crack front. The lower temperature limit is set by the fact that the grain boundary diffusion rates decrease with the decrease in temperature and thus large stress intensities approaching the fracture toughness value are required to accomplish crack growth by the grain boundary diffusion. Outside these limits creep crack growth occurs via deformation which is significantly slower than growth by the grain boundary diffusion process. The importance of the present analysis rests on the fact that service conditions for many high temperature structural materials fall within the regime wherein creep crack growth occurs via grain boundary diffusion.     

Picture perception: Toward a theoretical model.

Describes J. J. Gibson's new theory of picture perception and a program of research within his framework. An analysis of pictorial information is proposed in which a systematic investigation of the structural components of pictures and their varying effects on perception is seen as preliminary to the postulation of hypothetical pick-up mechanisms. The basic components of pictures are described, and literature is reviewed in the problem areas of distorted and impoverished information, observation from the wrong station point, coexisting flatness and depth information, and the ambiguity of the source of a single projection. The feasibility of the Gibsonian enterprise is demonstrated, and further avenues for research into a structural analysis of pictorial information are noted. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An event count model for studying health services utilization

OBJECTIVES: The purpose of this article is to first conceptualize health services utilization behavior as event counts. Based on this concept and behavioral theory, the author presents the Generalized Event Count model as an alternative modeling tool for studying health services utilization. This model is theory driven and is consistent with behavioral assumptions. METHODS: In presenting the Generalized Event Count model, the author first examines its model assumptions to see whether they conform to elements of behavior theory, assumptions of health services utilization, and the distribution assumption of the nature of the data. To demonstrate the Generalized Event Count model, the author applied this model to an empirical ambulatory care utilization data set from a 1988 household interview of Chinese-Americans in Boston's inner-city community. RESULTS: The Generalized Event Count model analysis suggested that the regular source of medical care and the use of Chinese medicine were strong predictors of physician visits for this population. Further, the Generalized Event Count model was able to test that most of the ambulatory visits within an individual were correlated. CONCLUSIONS: Compared with other models, the Generalized Event Count model is more consistent with health services utilization behavioral assumptions. Moreover, it makes an efficient use of information from the utilization data for model estimation. This model has the potential of having broad applications in studying various types of health services utilization, especially for analyzing cross-sectional utilization data.     

A functional ribosomal RNA tertiary structure involves a base triple interaction

Comparative sequence analysis reveals a coordinated set of nucleotide exchanges between the base pair 1092/1099 and the unpaired position 1072 [(1092/1099)1072] in the L11 binding domain of 23S ribosomal RNA. This set of exchanges has occurred at least 4 times during evolution, suggesting that these positions form a base triple. The analysis further suggests an important role for positions (1065/1073), adjacent to 1072. The covariation at positions (1092/1099)1072 is studied here by analysis of RNA variants using UV melting and binding of ribosomal protein L11 and thiostrepton to assay for tertiary folding of this domain. The tertiary structure of the RNA is eliminated by alteration of the unpaired nucleotide (C1072 to U mutation), and binding of L11 and thiostrepton are reduced 10-fold compared to the wild type. In contrast, substitution of the base pair (CG1092/1099 to UA mutation) allows formation of the tertiary structure but dramatically alters the pH dependence of tertiary folding. The fully compensated set of mutations, (CG)C to (UA)U, restores the tertiary structure of the RNA to a state almost identical to the wild type. The nature of this base triple and its implications for the folding of the RNA and ligand interactions are discussed.