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Environmental Signals (environmental + signal)
Selected AbstractsEnvironmental signals for seed germination reflect habitat adaptations in four temperate CaryophyllaceaeFUNCTIONAL ECOLOGY, Issue 3 2008F. Vandelook Summary 1Requirements for dormancy break and seed germination are specific for all species and depend chiefly on phylogeny, geographical distribution, habitat preference and life cycle. Studying germination requirements of closely related species with a similar geographic distribution allows one to attribute variation in germination requirements to differences in habitat preference between the species. 2We investigated requirements for dormancy break and the effect of environmental signals on induction of germination in seeds of four closely related Caryophyllaceae species growing in a variety of habitats (Moehringia trinervia, Stellaria holostea, S. nemorum and S. graminea). The species studied depend on disturbances in the vegetation for seed germination and subsequent seedling establishment. 3Seedlings of all four species emerged both in summer and spring. Stellaria nemorum and M. trinervia, both growing in temperate forests, emerged mainly in summer under a closed forest canopy. Seeds of S. graminea, occurring in grasslands, did germinate in summer at an open site, but could not germinate under a closed forest canopy. Seedlings of S. holostea were observed in late summer when buried at an open site or in early spring when sown in a forest patch. 4Seeds of S. holostea and M. trinervia were completely dormant at dispersal in early summer, while germination was low in fresh seeds of S. graminea and S. nemorum. Dormancy was broken, to a certain extent, during all three after-ripening treatments applied (dry storage, cold and warm stratification). 5The effect of three gap-detection signals (light, fluctuating temperatures, nitrates) on germination of fresh and dry stored seeds was tested. Seeds of S. holostea only germinated in response to daily fluctuating temperatures. Although light was the most important signal affecting germination of S. graminea and M. trinervia, we also observed a positive effect of fluctuating temperatures and nitrates on germination. The effect of fluctuating temperatures on germination of S. nemorum was small in both light and dark incubated seeds. Seed germination in this species generally occurred in response to addition of light and nitrates. 6This study on dormancy breaking and germination requirements of the four species enabled us to expose, sometimes subtle, differences in germination requirements. These contrasting germination patterns were related to differences in the species' habitat preferences. [source] Commitment and response to inductive signals of primary mesenchyme cells of the sea urchin embryoDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 1 2004Masato Kiyomoto In the sea urchin embryo, primary mesenchyme cells (PMC) are committed to produce the larval skeleton, although their behavior and skeleton production are influenced by signals from the embryonic environment. Results from our recent studies showed that perturbation of skeleton development, by interfering with ectoderm,extracellular matrix (ECM) interactions, is linked to a reduction in the gene expression of a transforming growth factor (TGF)-beta growth factor, Pl-univin, suggesting a reduction in the blastocoelic amounts of the protein and its putative involvement in signaling events. In the present study, we examined PMC competence to respond to environmental signals in a validated skeleton perturbation model in Paracentrotus lividus. We found that injection of blastocoelic fluid (BcF), obtained from normal embryos, into the blastocoelic cavity of skeleton-defective embryos rescues skeleton development. In addition, PMC from skeleton-defective embryos transplanted into normal or PMC-less blastula embryos are able to position in correct regions of the blastocoel and to engage spicule elongation and patterning. Taken together, these results demonstrate that PMC commitment to direct skeletogenesis is maintained in skeleton perturbed embryos and confirm the role played by inductive signals in regulating skeleton growth and shape. [source] Symbolic dynamics for identifying similarity between rhythms of ecological time seriesECOLOGY LETTERS, Issue 9 2004Bernard Cazelles Abstract Explaining the associations between animal populations or between population and environmental signals is an important challenge. The time series that quantify animal populations are often complex, nonlinear, noisy and non-stationary. These characteristics may make it inappropriate to use traditional techniques when analysing these time series and their mutual dependencies. Here I propose to use symbolic dynamics and techniques from Information Theory to evaluate the degree of dynamic cohesion between time series fluctuations. The main idea is to check whether two (or more) signals tend to oscillate simultaneously, rising and falling together with the same rhythm. Based on synthetic and real time series, I demonstrate that this method is robust to the presence of noise and to the short length of the analysed time series and gives relevant information about the weak relationships between different series. Furthermore, this method appears as simple as classical cross-correlation and outperforms it in the analysed examples. [source] Regulation of virulence determinants in Staphylococcus aureus: complexity and applicationsFEMS MICROBIOLOGY REVIEWS, Issue 2 2004Stéphane Bronner Abstract The virulence of Staphylococcus aureus is essentially determined by cell wall associated proteins and secreted toxins that are regulated and expressed according to growth phases and/or growth conditions. Gene expression is regulated by specific and sensitive mechanisms, most of which act at the transcriptional level. Regulatory factors constitute numerous complex networks, driving specific interactions with target gene promoters. These factors are largely regulated by two-component regulatory systems, such as the agr, saeRS, srrAB, arlSR and lytRS systems. These systems are sensitive to environmental signals and consist of a sensor histidine kinase and a response regulator protein. DNA-binding proteins, such as SarA and the recently identified SarA homologues (SarR, Rot, SarS, SarT, SarU), also regulate virulence factor expression. These homologues might be intermediates in the regulatory networks. The multiple pathways generated by these factors allow the bacterium to adapt to environmental conditions rapidly and specifically, and to develop infection. Precise knowledge of these regulatory mechanisms and how they control virulence factor expression would open up new perspectives for antimicrobial chemotherapy using key inhibitors of these systems. [source] Two-component signal transduction in human fungal pathogensFEMS YEAST RESEARCH, Issue 2 2006Michael Kruppa Abstract Signal transduction pathways provide mechanisms for adaptation to stress conditions. One of the most studied of these pathways is the HOG1 MAP kinase pathway that in Saccharomyces cerevisiae is used to adapt cells to osmostress. The HOG1 MAPK has also been studied in Candida albicans, and more recently observations on the Hog1p functions have been described in two other human pathogens, Aspergillus fumigatus and Cryptococcus neoformans. The important, but not surprising, concept is that this pathway is used for different yet similar functions in each of these fungi, given their need to adapt to different environmental signals. Current studies of C. albicans focus upon the identification of two-component signal proteins that, in both C. albicans and S. cerevisiae, regulate the HOG1 MAPK. In C. albicans, these proteins regulate cell wall biosynthesis (and, therefore, adherence to host cells), osmotic and oxidant adaptation, white-opaque switching, morphogenesis, and virulence of the organism. [source] Role of laccase in the biology and virulence of Cryptococcus neoformansFEMS YEAST RESEARCH, Issue 1 2004Xudong Zhu Abstract Laccase is an important virulence factor for the human pathogen, Cryptococcus neoformans. In this review, we examine the structural, biological and genetic features of the enzyme and its role in the pathogenesis of cryptococcosis. Laccase is expressed in C. neoformans as a cell wall enzyme that possesses a broad spectrum of activity oxidizing both polyphenolic compounds and iron. Two paralogs, CNLAC1 and CNLAC2, are present in the fungus, of which the first one expresses the dominant enzyme activity under glucose starvation conditions. Regulation of the enzyme is in response to various environmental signals including nutrient starvation, the presence of multivalent cations and temperature stress, and is mediated through multiple signal transduction pathways. Study of the function and regulation of this important virulence factor has led to further understanding of mechanisms of fungal pathogenesis and the regulation of stress response in the host cell environment. [source] Synchronicity in southern hemisphere squid stocks and the influence of the Southern Oscillation and Trans Polar IndexFISHERIES OCEANOGRAPHY, Issue 4 2004C. M. Waluda Abstract Squid are short lived, with highly labile populations that respond rapidly to changes in environmental conditions. This makes them a good model for studying the response of recruitment processes to environmental signals. This study examines the influence of the Southern Oscillation Index (SOI) and Trans Polar Index (TPI) on the environment and abundance of six species of commercially important squid from the southern hemisphere, all linked to major current systems connected by the Antarctic Circumpolar Current: Dosidicus gigas (Southeast Pacific), Loligo vulgaris reynaudii (Southeast Atlantic), Nototodarus sloanii, N. gouldi (Southwest Pacific), Illex argentinus and L. gahi (Southwest Atlantic). All fisheries displayed a high level of inter-annual variability and a degree of synchronicity was seen to occur in the abundance of the three Pacific species. The SOI signal was reflected in the environment of each fishery, particularly in Pacific regions. Both indices are correlated with squid abundance, particularly during the early life history stages (SOI) and adult stages (TPI), suggesting some degree of latitudinal separation, with juveniles potentially influenced by environmental variability at lower latitudes and adults at higher latitudes. [source] Environmental signals for seed germination reflect habitat adaptations in four temperate CaryophyllaceaeFUNCTIONAL ECOLOGY, Issue 3 2008F. Vandelook Summary 1Requirements for dormancy break and seed germination are specific for all species and depend chiefly on phylogeny, geographical distribution, habitat preference and life cycle. Studying germination requirements of closely related species with a similar geographic distribution allows one to attribute variation in germination requirements to differences in habitat preference between the species. 2We investigated requirements for dormancy break and the effect of environmental signals on induction of germination in seeds of four closely related Caryophyllaceae species growing in a variety of habitats (Moehringia trinervia, Stellaria holostea, S. nemorum and S. graminea). The species studied depend on disturbances in the vegetation for seed germination and subsequent seedling establishment. 3Seedlings of all four species emerged both in summer and spring. Stellaria nemorum and M. trinervia, both growing in temperate forests, emerged mainly in summer under a closed forest canopy. Seeds of S. graminea, occurring in grasslands, did germinate in summer at an open site, but could not germinate under a closed forest canopy. Seedlings of S. holostea were observed in late summer when buried at an open site or in early spring when sown in a forest patch. 4Seeds of S. holostea and M. trinervia were completely dormant at dispersal in early summer, while germination was low in fresh seeds of S. graminea and S. nemorum. Dormancy was broken, to a certain extent, during all three after-ripening treatments applied (dry storage, cold and warm stratification). 5The effect of three gap-detection signals (light, fluctuating temperatures, nitrates) on germination of fresh and dry stored seeds was tested. Seeds of S. holostea only germinated in response to daily fluctuating temperatures. Although light was the most important signal affecting germination of S. graminea and M. trinervia, we also observed a positive effect of fluctuating temperatures and nitrates on germination. The effect of fluctuating temperatures on germination of S. nemorum was small in both light and dark incubated seeds. Seed germination in this species generally occurred in response to addition of light and nitrates. 6This study on dormancy breaking and germination requirements of the four species enabled us to expose, sometimes subtle, differences in germination requirements. These contrasting germination patterns were related to differences in the species' habitat preferences. [source] T-cell receptor proximal signaling via the Src-family kinases, Lck and Fyn, influences T-cell activation, differentiation, and toleranceIMMUNOLOGICAL REVIEWS, Issue 1 2009Robert J. Salmond Summary:, T-cell development in the thymus and activation of mature T cells in secondary lymphoid organs requires the ability of cells to respond appropriately to environmental signals at multiple stages of their development. The process of thymocyte selection insures a functional T-cell repertoire, while activation of naive peripheral T cells induces proliferation, gain of effector function, and, ultimately, long-lived T-cell memory. The T-cell immune response is initiated upon engagement of the T-cell receptor (TCR) and coreceptor, CD4 or CD8, by cognate antigen/major histocompatibility complexes presented by antigen-presenting cells. TCR/coreceptor engagement induces the activation of biochemical signaling pathways that, in combination with signals from costimulator molecules and cytokine receptors, direct the outcome of the response. Activation of the src- family kinases p56lck (Lck) and p59fyn (Fyn) is central to the initiation of TCR signaling pathways. This review focuses on our current understanding of the mechanisms by which these two proteins orchestrate T-cell function. [source] Neuropeptide and neurohormone precursors in the pea aphid, Acyrthosiphon pisumINSECT MOLECULAR BIOLOGY, Issue 2010J. Huybrechts Abstract Aphids respond to environmental changes by developing alternative phenotypes with differing reproductive modes. Parthenogenetic reproduction occurs in spring and summer, whereas decreasing day lengths in autumn provoke the production of sexual forms. Changing environmental signals are relayed by brain neuroendocrine signals to the ovarioles. We combined bioinformatic analyses with brain peptidomics and cDNA analyses to establish a catalogue of pea aphid neuropeptides and neurohormones. 42 genes encoding neuropeptides and neurohormones were identified, of which several were supported by expressed sequence tags and/or peptide mass analyses. Interesting features of the pea aphid peptidome are the absence of genes coding for corazonin, vasopressin and sulfakinin and the presence of 10 different genes coding insulin related peptides, one of which appears to be very abundantly expressed. [source] Anatomical perspectives on adult neural stem cellsJOURNAL OF ANATOMY, Issue 3 2005C. Watts Abstract The concept of stem cells within the adult brain is not new. However, only recently have scientific techniques become sufficiently advanced to identify them although this remains problematic and the technology is still developing. Nevertheless, it is now generally recognized that stem cells are restricted to two germinal regions within the intact brain. From here they can migrate to specific destinations where they integrate with existing circuitry. Their identity remains controversial but a growing body of evidence suggests it may have an astrocytic phenotype. Within the germinal regions the stem cells are confined to a niche environment and are capable of responding to environmental signals generated locally in an autocrine or paracrine fashion. The niche environment is also modulated by more generalized systemic and physiological activity. These observations are exciting in their own right and form the basis of this review. They are also beginning to alter how we think about neural injury and disease and to impact on the development of novel therapies. [source] Skeletal Cell Fate Decisions Within Periosteum and Bone Marrow During Bone Regeneration,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2009Céline Colnot Abstract Bone repair requires the mobilization of adult skeletal stem cells/progenitors to allow deposition of cartilage and bone at the injury site. These stem cells/progenitors are believed to come from multiple sources including the bone marrow and the periosteum. The goal of this study was to establish the cellular contributions of bone marrow and periosteum to bone healing in vivo and to assess the effect of the tissue environment on cell differentiation within bone marrow and periosteum. Results show that periosteal injuries heal by endochondral ossification, whereas bone marrow injuries heal by intramembranous ossification, indicating that distinct cellular responses occur within these tissues during repair. Next, lineage analyses were used to track the fate of cells derived from periosteum, bone marrow, and endosteum, a subcompartment of the bone marrow. Skeletal progenitor cells were found to be recruited locally and concurrently from periosteum and/or bone marrow/endosteum during bone repair. Periosteum and bone marrow/endosteum both gave rise to osteoblasts, whereas the periosteum was the major source of chondrocytes. Finally, results show that intrinsic and environmental signals modulate cell fate decisions within these tissues. In conclusion, this study sheds light into the origins of skeletal stem cells/progenitors during bone regeneration and indicates that periosteum, endosteum, and bone marrow contain pools of stem cells/progenitors with distinct osteogenic and chondrogenic potentials that vary with the tissue environment. [source] The Actin Cytoskeleton and Signaling Network during Pollen Tube Tip GrowthJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 2 2010Ying Fu The organization and dynamics of the actin cytoskeleton play key roles in many aspects of plant cell development. The actin cytoskeleton responds to internal developmental cues and environmental signals and is involved in cell division, subcellular organelle movement, cell polarity and polar cell growth. The tip-growing pollen tubes provide an ideal model system to investigate fundamental mechanisms of underlying polarized cell growth. In this system, most signaling cascades required for tip growth, such as Ca2+ -, small GTPases- and lipid-mediated signaling have been found to be involved in transmitting signals to a large group of actin-binding proteins. These actin-binding proteins subsequently regulate the structure of the actin network, as well as the rapid turnover of actin filaments (F-actin), thereby eventually controlling tip growth. The actin cytoskeleton acts as an integrator in which multiple signaling pathways converge, providing a general growth and regulatory mechanism that applies not only for tip growth but also for polarized diffuse growth in plants. [source] Conserved fate and function of ferumoxides-labeled neural precursor cells in vitro and in vivoJOURNAL OF NEUROSCIENCE RESEARCH, Issue 5 2010Mikhal E. Cohen Abstract Recent progress in cell therapy research for brain diseases has raised the need for non-invasive monitoring of transplanted cells. For therapeutic application in multiple sclerosis, transplanted cells need to be tracked both spatially and temporally, in order to assess their migration and survival in the host tissue. Magnetic resonance imaging (MRI) of superparamagnetic iron oxide-(SPIO)-labeled cells has been widely used for high resolution monitoring of the biodistribution of cells after transplantation into the central nervous system (CNS). Here we labeled mouse glial-committed neural precursor cells (NPCs) with the clinically approved SPIO contrast agent ferumoxides and examined their survival and differentiation in vitro, as well as their functional response to environmental signals present within the inflamed brain of experimental autoimmune encephalomyelitis (EAE) mice in vivo. We show that ferumoxides labeling does not affect NPC survival and pluripotency in vitro. Following intracerebroventricular (ICV) transplantation in EAE mice, ferumoxides-labeled NPCs responded to inflammatory cues in a similar fashion as unlabeled cells. Ferumoxides-labeled NPCs migrated over comparable distances in white matter tracts and differentiated equally into the glial lineages. Furthermore, ferumoxides-labeled NPCs inhibited lymph node cell proliferation in vitro, similarly to non-labeled cells, suggesting a preserved immunomodulatory function. These results demonstrate that ferumoxides-based MRI cell tracking is well suited for non-invasive monitoring of NPC transplantation. © 2009 Wiley-Liss, Inc. [source] Human embryonic stem cell-derived neural precursors develop into neurons and integrate into the host brainJOURNAL OF NEUROSCIENCE RESEARCH, Issue 6 2006Daniel J. Guillaume Abstract Whether and how in-vitro-produced human neural precursors mature and integrate into the brain are crucial to the utility of human embryonic stem (hES) cells in treating neurological disorders. After transplantation into the ventricles of neonatal immune-deficient mice, hES-cell-derived neural precursors stopped expressing the cell division marker Ki67, except in neurogenic areas, and differentiated into neurons and then glia in a temporal course intrinsic to that of human cells regardless of location. The human cells located in the gray matter became neurons in the olfactory bulb and striatum, whereas those in the white matter produced exclusively glia. Importantly, the grafted human cells formed synapses. Thus, the in-vitro-produced human neural precursors follow their intrinsic temporal program to produce neurons and glia and, in response to environmental signals, generate cells appropriate to their target regions and integrate into the brain. © 2006 Wiley-Liss, Inc. [source] NepA is a structural cell wall protein involved in maintenance of spore dormancy in Streptomyces coelicolorMOLECULAR MICROBIOLOGY, Issue 6 2009Wouter De Jong Summary Streptomycetes have a complex morphogenetic programme culminating in the formation of aerial hyphae that develop into chains of spores. After spore dispersal, environmental signals trigger dormant spores to germinate to establish a new colony. We here compared whole genome expression of a wild-type colony of Streptomyces coelicolor forming aerial hyphae and spores with that of the chp null mutant that forms few aerial structures. This revealed that expression of 244 genes was significantly altered, among which genes known to be involved in development. One of the genes that was no longer expressed in the ,chpABCDEFGH mutant was nepA, which was previously shown to be expressed in a compartment connecting the substrate mycelium with the sporulating parts of the aerial mycelium. We here show that expression is also detected in developing spore chains, where NepA is secreted to end up as a highly insoluble protein in the cell wall. Germination of spores of a nepA deletion mutant was faster and more synchronous, resulting in colonies with an accelerated morphogenetic programme. Crucially, spores of the ,nepA mutant also germinated in water, unlike those of the wild-type strain. Taken together, NepA is the first bacterial structural cell wall protein that is important for maintenance of spore dormancy under unfavourable environmental conditions. [source] Looking inside the box: bacterial transistor arraysMOLECULAR MICROBIOLOGY, Issue 1 2008Thomas S. Shimizu Summary One often compares cells to computers, and signalling proteins to transistors. Location and wiring of those molecular transistors is paramount in defining the function of the subcellular chips. The bacterial chemotactic sensing apparatus is a large, stable assembly consisting of thousands of receptors, signal transducing kinases and linking proteins, and is responsible for the motile response of the bacterium to environmental signals, whether chemical, mechanical, or thermal. Because of its rich functional repertoire despite its relative simplicity, this chemosome has attracted much attention from both experimentalists and theoreticians, and the bacterial chemotaxis response becoming a benchmark in Systems Biology. Structural and functional models of the chemotactic device have been developed, often based on particular assumptions regarding the topology of the receptor lattice. In this issue of Molecular Microbiology, Briegel et al. provide a detailed view of the receptor arrangement, unravelling the wiring of the molecular signal processors. [source] A Csr-type regulatory system, including small non-coding RNAs, regulates the global virulence regulator RovA of Yersinia pseudotuberculosis through RovMMOLECULAR MICROBIOLOGY, Issue 5 2008Ann Kathrin Heroven Summary The MarR-type regulator RovA controls expression of virulence genes of Yersinia pseudotuberculosis in response to environmental signals. Using a genetic strategy to discover components that influence rovA expression, we identified new regulatory factors with homology to components of the carbon storage regulator system (Csr). We showed that overexpression of a CsrB- or a CsrC-type RNA activates rovA, whereas a CsrA-like protein represses RovA synthesis. We further demonstrate that influence of the Csr system on rovA is indirect and occurs through control of the LysR regulator RovM, which inhibits rovA transcription. The CsrA protein had also a major influence on the motility of Yersinia, which was independent of RovM. The CsrB and CsrC RNAs are differentially expressed in Yersinia. CsrC is highly induced in complex but not in minimal media, indicating that medium-dependent rovM expression is mediated through CsrC. CsrB synthesis is generally very low. However, overexpression of the response regulator UvrY was found to activate CsrB production, which in turn represses CsrC synthesis independent of the growth medium. In summary, the post-transcriptional Csr-type components were shown to be key regulators in the co-ordinated environmental control of physiological processes and virulence factors, which are crucial for the initiation of Yersinia infections. [source] Looking through the eyes of fungi: molecular genetics of photoreceptionMOLECULAR MICROBIOLOGY, Issue 1 2007Alfredo Herrera-Estrella Summary Filamentous fungi respond to a variety of environmental signals. One of them is light, providing critical information about orientation, or impending stress. Cells of filamentous fungi appear to sense blue light through a unique transcription factor that has a flavin chromophore and activates its targets in a light-dependent manner, the white collar (WC) complex. Fungal photophysiology, though, predicted a greater complexity of responses to the whole visible spectrum. The rapidly growing fungal genome database provides candidates to explain how fungi see not only blue, but also near-UV, green and red light. At the same time, there are surprises in the genomes, including photoreceptors for which there are no obvious photoresponses. Linking these genes and their functions will help understand how a list of only a few biological chromophores accounts for such a diversity of responses. At the same time, deeper mechanistic understanding of how the WC complex functions will lead to fundamental insights at the point where the environment impinges, in this case in the form of photons, on the transcriptional machinery of the cell. [source] Leaving on the lights: host-specific derepression of Mycobacterium tuberculosis gene expression by anti-sigma factor gene mutationsMOLECULAR MICROBIOLOGY, Issue 5 2006Robert N. Husson Summary Regulation of transcription by alternative sigma factors is a strategy widely used by bacteria to adapt to changes in environmental conditions. For several pathogenic bacteria, alternative sigma factor-regulated gene expression is critical for virulence. The activity of many alternative sigma factors is in turn controlled by regulatory proteins that transduce and integrate environmental signals. In this issue of Molecular Microbiology, Said-Salim et al. demonstrate high-level expression of genes encoding major protein antigens in the bovine subspecies of Mycobacterium tuberculosis, in contrast to low-level expression in the human subspecies. Having previously suggested that SigK regulates the expression of these genes, the authors found that the high-expressers have point mutations in Rv0444c, a gene adjacent to sigK, and provided evidence that this gene encodes an anti-sigma factor whose function is abrogated by these mutations. These findings not only demonstrate an adaptive mechanism of potential importance in tuberculosis immunity and pathogenesis, but also raise interesting questions regarding the origin of these mutations and their effects on anti-sigma factor function. [source] A novel sensor kinase,response regulator hybrid regulates type III secretion and is required for virulence in Pseudomonas aeruginosaMOLECULAR MICROBIOLOGY, Issue 4 2004Michelle A. Laskowski Summary The type III secretion system (TTSS) of Pseudomonas aeruginosa is induced by contact with eukaryotic cells and by growth in low-calcium media. We have identified a protein, RtsM, that is necessary for expression of the TTSS genes in P. aeruginosa. RtsM possesses both histidine kinase and response regulator domains common to two-component signalling proteins, as well as a large predicted periplasmic domain and seven transmembrane domains. Deletion of rtsM resulted in a defect in production and secretion of the type III effectors. Northern blot analysis revealed that mRNAs encoding the effectors ExoT and ExoU are absent in the ,rtsM strain under TTSS-inducing conditions. Using transcriptional fusions, we demonstrated that RtsM is required for transcription of the operons encoding the TTSS effectors and apparatus in response to calcium limitation or to host cell contact. The operon encoding the TTSS regulator ExsA does not respond to calcium limitation, but the basal transcription rate of this operon was lower in ,rtsM than in the wild-type parent, PA103. The defect in TTSS effector production and secretion of ,rtsM could be complemented by overexpressing ExsA or Vfr, two transcriptional activators involved in TTSS regulation. ,rtsM was markedly less virulent than PA103 in a murine model of acute pneumonia, demonstrating that RtsM is required in vivo. We propose that RtsM is a sensor protein at the start of a signalling cascade that induces expression of the TTSS in response to environmental signals. [source] Environmental regulation of recA gene expression in Porphyromonas gingivalisMOLECULAR ORAL MICROBIOLOGY, Issue 3 2001Y. Liu The recA gene product in Porphyromonas gingivalis is involved in DNA repair. Further, disruption of this gene can affect the proteolytic activity and expression of other virulence factors in this organism. Since several known environmental factors can influence virulence gene expression in P. gingivalis, we investigated the influence of these signals on the expression of the recA gene in this organism. A heterodiploid strain of P. gingivalis (designated FLL118) containing a transcriptional fusion of the recA promoter region and the promoterless tetracycline-resistant gene [tetA(Q)2] and xylosidase/arabinosidase (xa) gene cassette was constructed. The recA promoter activity was assessed by measurement of xylosidase activity in FLL118. The expression remained relatively constant during different growth phases, at different pH levels and in the presence of DNA-damaging agents. In response to hemin limitation and in the presence of calcium there was a moderate increase in recA promoter activity. Temperature also affected the expression. The highest level of xylosidase activity was observed in cultures at 32°C with a decline of approximately 46% as growth temperature increased to 41°C. Reverse transcriptase polymerase chain reaction analysis revealed that this regulation may be occurring at the transcriptional level. These results suggest that expression of the recA gene in P. gingivalis W83 is responsive to several environmental signals but is not regulated by a DNA damage,inducible SOS-like regulatory system. [source] Chlamydospore formation in Candida albicans and Candida dubliniensis, an enigmatic developmental programmeMYCOSES, Issue 1 2007Peter Staib Summary Chlamydospore formation has served for a long time for identification of the human fungal pathogen Candida albicans, but the biological function of these structures still remains a secret. They have been proposed to allow survival in harsh environmental conditions, but this assumption remains to be proven. Chlamydospores are produced only by the two closely related species C. albicans and Candida dubliniensis, whose natural habitats are humans and warm-blooded animals, but not by other Candida species that are also found outside animal hosts. However, no role in the pathogenesis of Candida infections has been assigned to these unusual cells and only a limited number of studies have been conducted in the past to unravel their function. The development of new molecular tools and the recent discovery of mating in C. albicans have also restimulated investigations to understand the morphogenesis and function of chlamydospores. The finding that chlamydospore formation is differentially controlled by certain environmental signals in C. albicans and C. dubliniensis has opened new approaches to study the regulation of this morphogenetic programme. These studies have already identified genes and signalling pathways that are required for chlamydospore production and should lead to a detailed understanding of this fascinating developmental process. [source] Identifying environmental signals from population abundance data using multivariate time-series analysisOIKOS, Issue 11 2009Masami Fujiwara Individual organisms are affected by various natural and anthropogenic environmental factors throughout their life history. This is reflected in the way population abundance fluctuates. Consequently, observed population dynamics are often produced by the superimposition of multiple environmental signals. This complicates the analysis of population time-series. Here, a multivariate time-series method called maximum autocorrelation factor analysis (MAFA) was used to extract underlying signals from multiple population time series data. The extracted signals were compared with environmental variables that were suspected to affect the populations. Finally, a simple multiple regression analysis was applied to the same data set, and the results from the regression analysis were compared with those from MAFA. The extracted signals with MAFA were strongly associated with the environmental variables, suggesting that they represent environmental factors. On the other hand, with the multiple regression analysis, one of the important signals was not identifiable, revealing the shortcoming of the conventional approach. MAFA summarizes data based on their lag-one autocorrelation. This allows the identification of underlying signals with a small effect size on population abundance during the observation. It also uses multiple time series collected in parallel; this enables us to effectively analyze short time series. In this study, annual spawning adult counts of Chinook salmon at various locations within the Klamath Basin, California, were analyzed. [source] The role of abscisic acid and auxin in the response of poplar to abiotic stressPLANT BIOLOGY, Issue 2 2010J. Popko Abstract The plant hormones auxin and abscisic acid may at first sight appear to be a conflicting pair of plant regulators. Abscisic acid content increases during stress and protects plant water status. The content of free auxin in the developing xylem of poplar declines during stress, while auxin conjugates increase. This indicates that specific down-regulation of a signal transduction chain is important in plant adaptation to stress. Diminished auxin content may be a factor that adapts growth and wood development of poplar during adverse environmental conditions. To allow integration of environmental signals, abscisic acid and auxin must interact. Data are accumulating that abscisic acid,auxin cross-talk exists in plants. However, knowledge of the role of plant hormones in the response of trees to stress is scarce. Our data show that differences in the localisation of ABA synthesis exist between the annual, herbaceous plant Arabidopsis and the perennial woody species, poplar. [source] Moss Systems Biology en Route: Phytohormones in Physcomitrella DevelopmentPLANT BIOLOGY, Issue 3 2006E. L. Decker Abstract: The moss Physcomitrella patens has become a powerful model system in modern plant biology. Highly standardized cell culture techniques, as well as the necessary tools for computational biology, functional genomics and proteomics have been established. Large EST collections are available and the complete moss genome will be released soon. A simple body plan and the small number of different cell types in Physcomitrella facilitate the study of developmental processes. In the filamentous juvenile moss tissue, developmental decisions rely on the differentiation of single cells. Developmental steps are controlled by distinct phytohormones and integration of environmental signals. Especially the phytohormones auxin, cytokinin, and abscisic acid have distinct effects on early moss development. In this article, we review current knowledge about phytohormone influences on early moss development in an attempt to fully unravel the complex regulatory signal transduction networks underlying the developmental decisions of single plant cells in a holistic systems biology approach. [source] A physiological overview of the genetics of flowering time controlPLANT BIOTECHNOLOGY JOURNAL, Issue 1 2005Georges Bernier Summary Physiological studies on flowering time control have shown that plants integrate several environmental signals. Predictable factors, such as day length and vernalization, are regarded as ,primary', but clearly interfere with, or can even be substituted by, less predictable factors. All plant parts participate in the sensing of these interacting factors. In the case of floral induction by photoperiod, long-distance signalling is known to occur between the leaves and the shoot apical meristem (SAM) via the phloem. In the long-day plant, Sinapis alba, this long-distance signalling has also been shown to involve the root system and to include sucrose, nitrate, glutamine and cytokinins, but not gibberellins. In Arabidopsis thaliana, a number of genetic pathways controlling flowering time have been identified. Models now extend beyond ,primary' controlling factors and show an ever-increasing number of cross-talks between pathways triggered or influenced by various environmental factors and hormones (mainly gibberellins). Most of the genes involved are preferentially expressed in meristems (the SAM and the root tip), but, surprisingly, only a few are expressed preferentially or exclusively in leaves. However, long-distance signalling from leaves to SAM has been shown to occur in Arabidopsis during the induction of flowering by long days. In this review, we propose a model integrating physiological data and genes activated by the photoperiodic pathway controlling flowering time in early-flowering accessions of Arabidopsis. This model involves metabolites, hormones and gene products interacting as long- or short-distance signalling molecules. [source] Proteomic strategies to elucidate pathogenic mechanisms of spirochetesPROTEOMICS - CLINICAL APPLICATIONS, Issue 9 2007Jarlath E. Nally Dr. Abstract Spirochetes are a unique group of bacteria that include several motile and highly invasive pathogens that cause a multitude of acute and chronic disease processes. Nine genomes of spirochetes have been completed, which provide significant insights into pathogenic mechanisms of disease and reflect an often complex lifestyle associated with a wide range of environmental and host factors encountered during disease transmission and infection. Characterization of the outer membrane of spirochetes is of particular interest since it interacts directly with the host and environs during disease and likely contains candidate vaccinogens and diagnostics. In concert with appropriate fractionation techniques, the tools of proteomics have rapidly evolved to characterize the proteome of spirochetes. Of greater significance, studies have confirmed the differential expression of many proteins, including those of the outer membrane, in response to environmental signals encountered during disease transmission and infection. Characterization of the proteome in response to such signals provides novel insights to understand pathogenic mechanisms of spirochetes. [source] Wiskott,Aldrich syndrome protein and the cytoskeletal dynamics of dendritic cellsTHE JOURNAL OF PATHOLOGY, Issue 4 2004Yolanda Calle Abstract The regulated migration and spatial localization of dendritic cells in response to environmental signals are critical events during the initiation of physiological immune responses and maintenance of tolerance. Cells deficient in the Wiskott,Aldrich syndrome protein (WASP) have been used to demonstrate the importance of the dynamic remodelling of the actin-based cytoskeleton during the selective adhesion and migration of these cells. Unlike most cell types, macrophages, dendritic cells, and osteoclasts utilize a specialized adhesive array termed the podosome in order to migrate. Podosomes are composed of many of the same structural and regulatory proteins as seen in the more commonly found focal adhesion, but are unique in their requirement for WASP. Without WASP, podosomes cannot form and the affected cells are obliged to use focal adhesions for their migratory activities. Once activated by a series of upstream regulatory proteins, WASP acts as a scaffold for the binding of the potent actin nucleating protein complex known as Arp2/3. This article reviews the available evidence that suggests that failures in the regulation of the actin cytoskeleton may contribute significantly to the immunopathology of the Wiskott,Aldrich syndrome. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [source] GIGANTEA is a component of a regulatory pathway determining wall ingrowth deposition in phloem parenchyma transfer cells of Arabidopsis thalianaTHE PLANT JOURNAL, Issue 4 2010Joshua Edwards Summary Transfer cells are specialised transport cells containing invaginated wall ingrowths that generate an amplified plasma membrane surface area with high densities of transporter proteins. They trans -differentiate from differentiated cells at sites at which enhanced rates of nutrient transport occur across apo/symplasmic boundaries. Despite their physiological importance, little is known of the molecular mechanisms regulating construction of their intricate wall ingrowths. We investigated the genetic control of wall ingrowth formation in phloem parenchyma transfer cells of leaf minor veins in Arabidopsis thaliana. Wall ingrowth development in these cells is substantially enhanced upon exposing plants to high-light or cold treatments. A hierarchical bioinformatic analysis of public microarray datasets derived from the leaves of plants subjected to these treatments identified GIGANTEA (GI) as one of 46 genes that are commonly up-regulated twofold or more under both high-light and cold conditions. Histological analysis of the GI mutants gi-2 and gi-3 showed that the amount of phloem parenchyma containing wall ingrowths was reduced 15-fold compared with wild-type. Discrete papillate wall ingrowths were formed in gi-2 plants but failed to develop into branched networks. Wall ingrowth development in gi-2 was not rescued by exposing these plants to high-light or cold conditions. In contrast, over-expression of GI in the gi-2 background restored wall ingrowth deposition to wild-type levels. These results indicate that GI regulates the ongoing development of wall ingrowth networks at a point downstream of inputs from environmental signals. [source] | ||||||||||||||||||||||||||||