The relationship between pathogenic fungal metabolities (fusaric and picolinic acid), endogenous ethylene evolution and the development of ethylene-like symptoms

Summary The effects of fusaric acid (5-n-butylpicolinic acid), picolinic acid (2-pyridine carboxylic acid), and picloram (4-amino-3, 5, 6-trichloropicolinic acid) on endogenous ethylene production by tomato cuttings and elongation growth of oat coleoptile sections were measured. Ethylene production by tomato cuttings was substantially stimulated by treatment with 1×10⁻³ and 1×10⁻⁵ M picoloram and to a lesser extent by 1×10⁻³ M fusaric acid; picolinic acid had little effect. The ethylene levels produced in response to fusaric acid are not high enough to account for the ethylene injury observed in Fusarium wilt. Fusaric acid inhibited oat coleoptile extension, picolinic acid had little effect, and picloram promoted growth.     

Geomorphology variables predict fish assemblages for forested and endorheic rivers of two continents

Stream fishes are restricted to specific environments with appropriate habitats for feeding and reproduction. Interactions between streams and surrounding landscapes influence the availability and type of fish habitat, nutrient concentrations, suspended solids, and substrate composition. Valley width and gradient are geomorphological variables that influence the frequency and intensity that a stream interacts with the surrounding landscape. For example, in constrained valleys, canyon walls are steeply sloped and valleys are narrow, limiting the movement of water into riparian zones. Wide valleys have long, flat floodplains that are inundated with high discharge. We tested for differences in fish assemblages with geomorphology variation among stream sites. We selected rivers in similar forested and endorheic ecoregion types of the United States and Mongolia. Sites where we collected were defined as geomorphologically unique river segments (i.e., functional process zones; FPZs) using an automated ArcGIS‐based tool. This tool extracts geomorphic variables at the valley and catchment scales and uses them to cluster stream segments based on their similarity. We collected a representative fish sample from replicates of FPZs. Then, we used constrained ordinations to determine whether river geomorphology could predict fish assemblage variation. Our constrained ordination approach using geomorphology to predict fish assemblages resulted in significance using fish taxonomy and traits in several watersheds. The watersheds where constrained ordinations were not successful were next analyzed with unconstrained ordinations to examine patterns among fish taxonomy and traits with geomorphology variables. Common geomorphology variables as predictors for taxonomic fish assemblages were river gradient, valley width, and valley slope. Significant geomorphology predictors of functional traits were valley width‐to‐floor width ratio, elevation, gradient, and channel sinuosity. These results provide evidence that fish assemblages respond similarly and strongly to geomorphic variables on two continents.     

Structural Changes and Aluminium Distribution in Maize Root Tissues

Growth and structural responses of primary roots of Zea mays L. to aluminium chloride were studied. The treatment of seedlings with 50 μM AlCl₃ resulted in high accumulation of Al, partial inhibition of root growth, occurrence of surface lesions in peripheral tissues, root thickening caused by expansion of inner cortical cells, reduced root cap length, extensive vacuolation, cell distortion, and increased synthesis of callose within 24 h. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mathematical modeling of the formation of apoptosome in intrinsic pathway of apoptosis

Caspase-9 is the protease that mediates the intrinsic pathway of apoptosis, a type of cell death. Activation of caspase-9 is a multi-step process that requires dATP or ATP and involves at least two proteins, cytochrome c and Apaf-1. In this study, we mathematically model caspase-9 activation by using a system of ordinary differential equations (an ODE model) generated by a systems biology tool Simpathica—a simulation and reasoning system, developed to study biological pathways. A rudimentary version of “model checking” based on comparing simulation data with that obtained from a recombinant system of caspase-9 activation, provided several new insights into regulation of this protease. The model predicts that the activation begins with binding of dATP to Apaf-1, which initiates the interaction between Apaf-1 and cytochrome c, thus forming a complex that oligomerizes into an active caspase-9 holoenzyme via a linear binding model with cooperative interaction rather than through network formation.     

Mapping tumor-suppressor genes with multipoint statistics from copy-number-variation data

Array-based comparative genomic hybridization (arrayCGH) is a microarray-based comparative genomic hybridization technique that has been used to compare tumor genomes with normal genomes, thus providing rapid genomic assays of tumor genomes in terms of copy-number variations of those chromosomal segments that have been gained or lost. When properly interpreted, these assays are likely to shed important light on genes and mechanisms involved in the initiation and progression of cancer. Specifically, chromosomal segments, deleted in one or both copies of the diploid genomes of a group of patients with cancer, point to locations of tumor-suppressor genes (TSGs) implicated in the cancer. In this study, we focused on automatic methods for reliable detection of such genes and their locations, and we devised an efficient statistical algorithm to map TSGs, using a novel multipoint statistical score function. The proposed algorithm estimates the location of TSGs by analyzing segmental deletions (hemi- or homozygous) in the genomes of patients with cancer and the spatial relation of the deleted segments to any specific genomic interval. The algorithm assigns, to an interval of consecutive probes, a multipoint score that parsimoniously captures the underlying biology. It also computes a P value for every putative TSG by using concepts from the theory of scan statistics. Furthermore, it can identify smaller sets of predictive probes that can be used as biomarkers for diagnosis and therapeutics. We validated our method using different simulated artificial data sets and one real data set, and we report encouraging results. We discuss how, with suitable modifications to the underlying statistical model, this algorithm can be applied generally to a wider class of problems (e.g., detection of oncogenes).     

Quantitative analysis of germline mitosis in adult C. elegans

Certain aspects of the distal gonad of C. elegans are comparable to niche/stem cell systems in other organisms. The distal tip cell (DTC) caps a blind-ended tube; only the distal germ cells maintain proliferation in response to signaling from the DTC via the GLP-1/Notch signaling pathway in the germ line. Fruitful comparison between this system and other stem cell systems is limited by a lack of basic information regarding germ cell division behavior in C. elegans. Here, we explore the spatial pattern of cell division frequency in the adult C. elegans germ line relative to distance from the distal tip. We mapped the positions of actively dividing germline nuclei in over 600 fixed gonad preparations including the wild type and a gain-of-function ligand-responsive GLP-1 receptor mutant with an extended mitotic zone. One particularly surprising observation from these data is that the frequency of cell divisions is lower in distal-most cells-cells that directly contact the distal tip cell body-relative to cells further proximal, a difference that persists in the gain-of-function GLP-1 mutant. These results suggest that cell division frequency in the distal-most cells may be suppressed or otherwise controlled in a complex manner. Further, our data suggest that the presence of an active cell division influences the probability of observing simultaneous cell divisions in the same gonad arm, and that simultaneous divisions tend to cluster spatially. We speculate that this system behaves similarly to niche/stem cell/transit amplifying cell systems in other organisms.     

Cadmium-induced stimulation of stress-protein hsp70 in lichen photobiont Trebouxia erici

The expression of stress protein 70 (hsp70) was studied in lichen photobiont Trebouxia erici during short-term exposition to cadmium and copper (0.0, 1.0, 5.0 and 10.0 μM). We found two isoforms of hsp70 in the untreated as well as in heavy metal-treated cells due to the maintenance of protein homeostasis. Cu-treated cells had a relatively constant amount of hsp70 over all the tested concentrations. However, Cd caused an increase in hsp70 expression, especially at the lowest concentration (1.0 μM). Higher Cd concentrations were associated with acute toxicity and a reduced expression of hsp70 in the cells.     

IgG-recognizing shed tumor-associated antigens can promote tumor invasion and metastasis

Tumors secreting glycoproteins that act as tumor-associated antigens have been described as highly invasive and metastatic. In this study, the consequences of the humoral immune response (HIR) against these antigens were investigated. Using an in vitro model of tumor cell invasion, results indicated that the invasiveness of tumor cells secreting antigenic secreted/shed tumor glycoproteins (STGP) increases in the presence of specific anti-STGP IgG, polymorphonuclear cells and monocytes. This in vitro model showed that the coincidental presence in the matrix of both STGP and specific anti-STGP IgG increases the local release of IL-1beta, IL-6 and vascular endothelial growth factor (VEGF) by stromal cells, but not by tumor cells. Using an in vivo model, the experiments show that immune-competent mice develop an anti-tumor HIR with anti-STGP IgG production. In this model, tumor growth was increased in parallel with the serum concentration of specific anti-STGP IgG. In athymic nude (nu/nu)-beige mice the same trend was observed, suggesting a T-cell-independent tumor-promoting effect induced by anti-STGP IgG. Tumor histology showed intense infiltration of IgG-positive plasma cells and lymphocytes. A severe combined immunodeficient-beige mouse-based in vivo model of tumors, experimentally infiltrated with monoclonal IgG plasmocytoma cells, showed that only specific anti-STGP-IgG-secreting cells could exacerbate tumor invasion, angiogenesis and metastasis. These results suggest that tumors shedding/secreting antigenic STGP can induce a host IgG immune response that can promote invasion and metastasis by inducing tumor infiltrating stromal cells to release proinflammatory cytokines and VEGF.