Environmental Sensing and Signal Transduction Pathways Regulating Morphopathogenic Determinants of Candida albicans

Candida albicans is an opportunistic fungal pathogen that is found in the normal gastrointestinal flora of most healthy humans. However, under certain environmental conditions, it can become a life-threatening pathogen. The shift from commensal organism to pathogen is often correlated with the capacity to undergo morphogenesis. Indeed, under certain conditions, including growth at ambient temperature, the presence of serum or N-acetylglucosamine, neutral pH, and nutrient starvation, C. albicans can undergo reversible transitions from the yeast form to the mycelial form. This morphological plasticity reflects the interplay of various signal transduction pathways, either stimulating or repressing hyphal formation. In this review, we provide an overview of the different sensing and signaling pathways involved in the morphogenesis and pathogenesis of C. albicans. Where appropriate, we compare the analogous pathways/genes in Saccharomyces cerevisiae in an attempt to highlight the evolution of the different components of the two organisms. The downstream components of these pathways, some of which may be interesting antifungal targets, are also discussed.     

Association of GM3 with Zap-70 induced by T cell activation in plasma membrane microdomains: GM3 as a marker of microdomains in human lymphocytes.

Recent evidence demonstrated that T cell activation leads to the redistribution of membrane and intracellular kinase-rich raft microdomains at the site of TCR engagement. In this investigation we demonstrated by high performance thin layer chromatography, gas chromatographic, and mass spectrometric analyses that GM3 is the main ganglioside constituent of these microdomains in human lymphocytes. Then we analyzed GM3 distribution and its interaction with the phosphorylation protein Zap-70. Human T lymphocytes were stimulated with anti-CD3 and anti-CD28. Immunofluorescence microscopy analysis revealed a clustered GM3 distribution over the cell surface and an intracellular localization resembling specific cytoplasmic compartment(s). Scanning confocal microscopy showed that T cell activation induced a significant association between GM3 and Zap-70, as revealed by nearly complete colocalization areas; very few colocalization areas were detected in unstimulated cells. Coimmunoprecipitation experiments revealed that GM3 was immunoprecipitated by anti-Zap-70 only after co-stimulation through CD3 and CD28 as detected by both thin layer chromatography and immunoblotting. Therefore, T cell activation does not promote a redistribution of glycosphingolipid-enriched microdomains but induces Zap-70 translocation in selective membrane domains in which Zap-70 may interact with GM3. These findings suggest that GM3 is a component of a multimolecular signaling complex involved in T cell activation.     

The Actinomyces oris type 2 fimbrial shaft FimA mediates co‐aggregation with oral streptococci,adherence to red blood cells and biofilm development

Interbacterial interactions between oral streptococci and actinomyces and their adherence to tooth surface and the associated host cells are key early events that promote development of the complex oral biofilm referred to as dental plaque. These interactions depend largely on a lectin‐like activity associated with the Actinomyces oris type 2 fimbria, a surface structure assembled by sortase (SrtC2)‐dependent polymerization of the shaft and tip fimbrillins, FimA and FimB respectively. To dissect the function of specific fimbrillins in various adherence processes, we have developed a convenient new technology for generating unmarked deletion mutants of A. oris. Here, we show that the fimB mutant, which produced type 2 fimbriae composed only of FimA, like the wild type co‐aggregated strongly with receptor‐bearing streptococci, agglutinated with sialidase‐treated red blood cells, and formed monospecies biofilm. In contrast, the fimA and srtC2 mutants lacked type 2 fimbriae and were non‐adherent in each of these assays. Plasmid‐based expression of the deleted gene in respective mutants restored adherence to wild‐type levels. These findings uncover the importance of the lectin‐like activity of the polymeric FimA shaft rather than the tip. The multivalent adhesive function of FimA makes it an ideal molecule for exploring novel intervention strategies to control plaque biofilm formation.     

Differential modulation of vascular cell integrin and extracellular matrix expression in vitro by TGF-beta 1 correlates with reciprocal effects on cell migration.

In vitro, BAEC and BASMC migratory phenotypes are known to be reciprocally modulated by both soluble factors and extracellular matrix proteins. In addition, integrin matrix receptors mediate endothelial and smooth muscle cell attachment and migration. To further elucidate these phenomena, we studied the effects of TGF-beta 1 on integrin expression by vascular BASMC and BAEC in tissue culture. TGF-beta 1 upregulated mRNA levels and surface pools of BASMC beta 3 integrin classes without modulating beta 1 integrin mRNA levels or expression of beta 1 integrin organization. In contrast to its effects on BASMC, TGF-beta 1 increased BAEC mRNA levels and surface expression of beta 1 and beta 3 integrins without altering their organization. Conversely, extracellular matrix components (fibronectin, laminin, and fibrinogen) organized cell surface integrins in both BASMC and BAEC without affecting the size of their cell surface pools. These data are consistent with the hypothesis that SMC and EC behavior in neointimal lesions may be modulated, in part, through a coordination of soluble factor and extracellular matrix protein regulation of integrin surface expression and organization.     

Genetic dissection of bread wheat diversity and identification of adaptive loci in response to elevated tropospheric ozone

Rising tropospheric ozone affects the performance of important cereal crops thus threatening global food security. In this study, genetic variation of wheat regarding its physiological and yield responses to ozone was explored by exposing a diversity panel of 150 wheat genotypes to elevated ozone and control conditions throughout the growing season. Differential responses to ozone were observed for foliar symptom formation quantified as leaf bronzing score (LBS), vegetation indices and yield components. Vegetation indices representing the carotenoid to chlorophyll pigment ratio (such as Lic2) were particularly ozone-responsive and were thus considered suitable for the non-invasive diagnosing of ozone stress. Genetic variation in ozone-responsive traits was dissected by a genome-wide association study (GWAS). Significant marker-trait associations were identified for LBS on chromosome 5A and for vegetation indices (NDVI and Lic2) on chromosomes 6B and 6D. Analysis of linkage disequilibrium (LD) in these chromosomal regions revealed distinct LD blocks containing genes with a putative function in plant redox biology such as cytochrome P450 proteins and peroxidases. This study gives novel insight into the natural genetic variation in wheat ozone response, and lays the foundation for the molecular breeding of tolerant wheat varieties.     

The biphasic increase of PIP2 in the fertilized eggs of starfish: new roles in actin polymerization and Ca2+ signaling

Background

Fertilization of echinoderm eggs is accompanied by dynamic changes of the actin cytoskeleton and by a drastic increase of cytosolic Ca²⁺. Since the plasma membrane-enriched phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) serves as the precursor of inositol 1,4,5 trisphosphate (InsP₃) and also regulates actin-binding proteins, PIP2 might be involved in these two processes.

Methodology/Principal Findings

In this report, we have studied the roles of PIP2 at fertilization of starfish eggs by using fluorescently tagged pleckstrin homology (PH) domain of PLC-δ1, which has specific binding affinity to PIP2, in combination with Ca²⁺ and F-actin imaging techniques and transmission electron microscopy. During fertilization, PIP2 increased at the plasma membrane in two phases rather than continually decreasing. The first increase was quickly followed by a decrease about 40 seconds after sperm-egg contact. However, these changes took place only after the Ca²⁺ wave had already initiated and propagated. The fertilized eggs then displayed a prolonged increase of PIP2 that was accompanied by the appearance of numerous spikes in the perivitelline space during the elevation of the fertilization envelope (FE). These spikes, protruding from the plasma membrane, were filled with microfilaments. Sequestration of PIP2 by RFP-PH at higher doses resulted in changes of subplasmalemmal actin networks which significantly delayed the intracellular Ca²⁺ signaling, impaired elevation of FE, and increased occurrences of polyspermic fertilization.

Conclusions/Significance

Our results suggest that PIP2 plays comprehensive roles in shaping Ca²⁺ waves and guiding structural and functional changes required for successful fertilization. We propose that the PIP2 increase and the subsequent formation of actin spikes not only provide the mechanical supports for the elevating FE, but also accommodate increased membrane surfaces during cortical granule exocytosis.     

Mapping Cold-Water Coral Habitats at Different Scales within the Northern Ionian Sea (Central Mediterranean): An Assessment of Coral Coverage and Associated Vulnerability

In this study, we mapped the distribution of Cold-Water Coral (CWC) habitats on the northern Ionian Margin (Mediterranean Sea), with an emphasis on assessing coral coverage at various spatial scales over an area of 2,000 km² between 120 and 1,400 m of water depth. Our work made use of a set of data obtained from ship-based research surveys. Multi-scale seafloor mapping data, video inspections, and previous results from sediment samples were integrated and analyzed using Geographic Information System (GIS)-based tools. Results obtained from the application of spatial and textural analytical techniques to acoustic meso-scale maps (i.e. a Digital Terrain Model (DTM) of the seafloor at a 40 m grid cell size and associated terrain parameters) and large-scale maps (i.e. Side-Scan Sonar (SSS) mosaics of 1 m in resolution ground-truthed using underwater video observations) were integrated and revealed that, at the meso-scale level, the main morphological pattern (i.e. the aggregation of mound-like features) associated with CWC habitat occurrences was widespread over a total area of 600 km². Single coral mounds were isolated from the DTM and represented the geomorphic proxies used to model coral distributions within the investigated area. Coral mounds spanned a total area of 68 km² where different coral facies (characterized using video analyses and mapped on SSS mosaics) represent the dominant macro-habitat. We also mapped and classified anthropogenic threats that were identifiable within the examined videos, and, here, discuss their relationship to the mapped distribution of coral habitats and mounds. The combined results (from multi-scale habitat mapping and observations of the distribution of anthropogenic threats) provide the first quantitative assessment of CWC coverage for a Mediterranean province and document the relevant role of seafloor geomorphology in influencing habitat vulnerability to different types of human pressures.     

Sequestering miR165/166 enhances seed germination in Arabidopsis thaliana under normal condition and ABA treatment

Journal of Plant Biochemistry and Biotechnology - Seed germination is a dynamic process involving imbibition, increased metabolic activity and protrusion of a tiny plantlet rupturing the seed coat....