Mechanics informed fluoroscopy of esophageal transport

Biomechanics and Modeling in Mechanobiology - Fluoroscopy is a radiographic procedure for evaluating esophageal disorders such as achalasia, dysphasia and gastroesophageal reflux disease. It...     

Signaling role of nitric oxide in the induction of plant defense by exogenous application of abiotic inducers

The objective of this work was to search out the probable molecule behind the activation of broad spectrum resistance during abiotic elicitors such as arachidonic acid, cupric chloride, chitosan, isonicotinic acid and salicylic acid mediated induced systemic resistance (ISR) in Raphanus sativus L. The elicitor compounds were sprayed on the radish leaves of healthy plant and after 24 h incubation a significant increase of β-1,3 glucanase, peroxidase, polyphenol oxidase and phenolics as well as a remarkable increase of nitric oxide (NO), a probable potent defense-signaling molecule in plant, was observed. Furthermore, treatment of the host with NO donor, sodium nitroprusside, also induced the same defense molecules. The results suggests that NO might be the signaling molecule during abiotic elicitor mediated ISR induction in the host system.     

Elemental stoichiometry of basal resources and benthic macroinvertebrates along a land use gradient in a Great Basin watershed

The effects of land use on the elemental stoichiometry of aquatic organisms have rarely been studied in semi-arid watersheds. In eight semi-arid sub-watersheds differing in land use, we determined which predictor variable(s) best explains the elemental variability in two basal food resources and benthic macroinvertebrates (BMI). The elemental composition of periphyton and seston was best explained by percentage of urban and agricultural areas, forested land and associated differences in SRP, DOC, and stream water N:P ratios. In contrast, consumer elemental stoichiometry was related to taxonomic identity and feeding mode. Elemental imbalances were higher for collector-gatherer than for scraper and collector-filterer. However, high spatial and temporal variability in the elemental composition of basal food resources obscured clear spatial patterns of imbalances between nutrient-poor upstream and nutrient-rich downstream sites. Results from this study suggest that land use can affect BMI due to alteration in stoichiometry of their food resources. However, taxonomy and allometry must be taken into account to better understand spatial and temporal changes in the elemental composition of BMI. Our results indicate the importance of considering multiple effects to accurately assess land use effects on producer and consumer stoichiometry, particularly the in highly variable Great Basin watersheds.     

alphavbeta5 integrin sustains growth of human pre-B cells through an RGD-independent interaction with a basic domain of the CD23 protein

CD23 is a type II transmembrane glycoprotein synthesized by hematopoietic cells that has biological activity in both membrane-bound and freely soluble forms, acting via a number of receptors, including integrins. We demonstrate here that soluble CD23 (sCD23) sustains growth of human B cell precursors via an RGD-independent interaction with the alphavbeta5 integrin. The integrin recognizes a tripeptide motif in a small disulfide-bonded loop at the N terminus of the lectin head region of CD23, centered around Arg(172), Lys(173), and Cys(174) (RKC). This RKC motif is present in all forms of sCD23 with cytokine-like activity, and cytokine activity is independent of the lectin head, an "inverse RGD" motif, and the CD21 and IgE binding sites. RKC-containing peptides derived from this region of CD23 bind alphavbeta5 and are biologically active. The binding and activity of these peptides is unaffected by inclusion of a short peptide containing the classic RGD sequence recognized by integrins, and, in far-Western analyses, RKC-containing peptides bind to the beta subunit of the alphavbeta5 integrin. The interaction between alphavbeta5 and sCD23 indicates that integrins deliver to cells important signals initiated by soluble ligands without the requirement for interactions with RGD motifs in their common ligands. This mode of integrin signaling may not be restricted to alphavbeta5.     

HbS-Savaria: The Anti-polymerization Effect of a Single Mutation in Human α-chains

Recombinant α-Savaria globin (α^S49R) was assembled with β^S chains by the alloplex intermediate pathway to generate tetrameric rHbS-Sarvaria (α₂^S49Rβ₂^E6V) that exhibited normal O₂ affinity and co-operatively at pH 7.4. Allosteric effectors, 2,3-DPG, L35, and NaCl increased O₂ affinity by 15%. Bohr effects were similar for rHbS-Savaria and HbS (0.38 ± 0.025 vs. 0.46 ± 0.03, respectively). The C_SAT of HbS increased from 16.7 ± 0.8 to 27.0 ± 1.0 g/dL. Co-polymerization demonstrated inhibition predominantly by the Cis-dimer. Molecular modeling indicated that the positive charge at α-49 generated a strong anion-binding site and reduced flexibility of the CD-region by restricting movement in the E and F helices. The molecular distance between Arg-49 and Asn-78 in the neighboring double strand decreased, and electrostatic repulsion between the inter-double strands increased, resulting in inhibition of polymerization. The Savaria mutation may be useful for the design of super-inhibitory α-chains and gene therapy of sickle cell anemia.     

Seasonal variation of births in rural West Bengal: magnitude, direction and correlates

This paper examines seasonal variation of births in a rural community of West Bengal, India, by exploring data from the 1992-93 National Family Health Survey. Suitable time series analyses were used to determine the seasonal pattern of births and to estimate peaks. The trigonometric regression technique was used to carry out this objective. The study attempted to link the results of the regression analysis to the atmospheric temperature of the region during 1987-91, the distribution of respondents' husbands' occupations and the marriage pattern of the community. It was found that, in the study population, conceptions were numerous in the first quarter of a calendar year and the distribution of conceptions over calendar months was negatively associated with the average monthly temperature. In addition, the marriage pattern of the community and the occupational distribution of the fathers also had a significant effect on the distribution of births over calendar months. It is hoped that the findings will boost the development of needs-based maternal and child health (MCH) and family planning programmes in the community.     

A mini-Tn5-derived transposon with reportable and selectable markers enables rapid generation and screening of insertional mutants in Gram-negative bacteria

We re-engineered a classic tool for mutagenesis and gene expression studies in Gram-negative bacteria. Our modified Tn5-based transposon contains multiple features that allow rapid selection for mutants, direct quantification of gene expression and straightforward cloning of the inactivated gene. The promoter-less gfp-km cassette provides selection and reporter assay depending on the activity of the promoter upstream of the transposon insertion site. The cat gene facilitates positive antibiotic selection for mutants, while the narrow R6Kγ replication origin forces transposition in recipient strains lacking the pir gene and enables cloning of the transposon flanked with the disrupted gene from the chromosome. The suicide vector pCKD100, a plasmid that could be delivered into recipient cells through biparental mating or electroporation, harbours the modified transposon. We used the transposon to mutagenize Pectobacterium versatile KD100, Pseudumonas coronafaciens PC27R and Escherichia coli 35150N. The fluorescence intensities of mutants expressing high GFP could be quantified and detected qualitatively. Transformation efficiency from conjugation ranged from 1600 to 1900 CFU per ml. We sequenced the upstream flanking regions, identified the putative truncated genes and demonstrated the restoration of the GFP phenotype through marker exchange. The mini-Tn5 transposon was also utilized to construct mutant a library of P. versatile for forward genetic screens.     

Functional significance of active site residues in the enzymatic component of the Clostridium difficile binary toxin

Clostridium difficile binary toxin (CDT) is an ADP-ribosyltransferase which is linked to enhanced pathogenesis of C. difficile strains. CDT has dual function: domain a (CDTa) catalyses the ADP-ribosylation of actin (enzymatic component), whereas domain b (CDTb) transports CDTa into the cytosol (transport component). Understanding the molecular mechanism of CDT is necessary to assess its role in C. difficile infection. Identifying amino acids that are essential to CDTa function may aid drug inhibitor design to control the severity of C. difficile infections. Here we report mutations of key catalytic residues within CDTa and their effect on CDT cytotoxicity. Rather than an all-or-nothing response, activity of CDTa mutants vary with the type of amino acid substitution; S345A retains cytotoxicity whereas S345Y was sufficient to render CDT non-cytotoxic. Thus CDTa cytotoxicity levels are directly linked to ADP-ribosyltransferase activity.