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Search Results: 1 - 10 of 714842 matches for " Fritz A. Mühlschlegel "
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Communication in Fungi
Fabien Cottier,Fritz A. Mühlschlegel
International Journal of Microbiology , 2012, DOI: 10.1155/2012/351832
Abstract: We will discuss fungal communication in the context of fundamental biological functions including mating, growth, morphogenesis, and the regulation of fungal virulence determinants. We will address intraspecies but also interkingdom signaling by systematically discussing the sender of the message, the molecular message, and receiver. Analyzing communication shows the close coevolution of fungi with organisms present in their environment giving insights into multispecies communication. A better understanding of the molecular mechanisms underlying microbial communication will promote our understanding of the “fungal communicome.”
Communication in Fungi
Fabien Cottier,Fritz A. Mühlschlegel
International Journal of Microbiology , 2012, DOI: 10.1155/2012/351832
Abstract: We will discuss fungal communication in the context of fundamental biological functions including mating, growth, morphogenesis, and the regulation of fungal virulence determinants. We will address intraspecies but also interkingdom signaling by systematically discussing the sender of the message, the molecular message, and receiver. Analyzing communication shows the close coevolution of fungi with organisms present in their environment giving insights into multispecies communication. A better understanding of the molecular mechanisms underlying microbial communication will promote our understanding of the “fungal communicome.” 1. Introduction Any form of communication requires the existence of three obligatory components: a sender, a message, and a receiver. The process starts with the release of a message by a sender and ends with the understanding of the message by a receiver. This type of cycle has been developed with different degrees of complexity from prokaryote to higher eukaryotes optimizing fitness and adaptation for individual members and populations. The nature and mode of action of communication is as diverse as the response to the information it carries. Inter- and intraspecies communication has been widely studied analyzing the exchange of information between fungi and bacteria or fungi and plant cells [1, 2]. This review will focus predominantly on intraspecies fungal communication addressing key biological functions including mating, growth, morphological switching, or the regulation of virulence factor expression (Figure 1). We will show that in the fungal kingdom most of these mechanisms are controlled by a variety of messengers including small peptides, alcohols, lipids, and volatile compounds. Figure 1: Schematic representation of fungal intra and interspecies communication. The “sender” is an organism from the fungal kingdom and the “receiver” can be from any kingdom. Genes involved in messenger synthesis are represented as brown hexagons. Proteins involved in secretion or receiving the message are in orange and blue. 2. Peptides: Pheromones Pheromones have been known to act as an informative molecule since 1959 [3] and were reported to be involved in the sexual cycle of fungi in 1974 [4]. In the fungal kingdom, they are involved in the reconnaissance of compatible sexual partner to promote plasmogamy and karyogamy between two opposite mating types followed by meiosis. Taking the example of the extensively described sexual cycle of Saccharomyces cerevisiae, pheromones are diffusible peptides called a-factor (12 aa) when produced by
Functional Characterization of the Small Heat Shock Protein Hsp12p from Candida albicans
Man-Shun Fu, Luisa De Sordi, Fritz A. Mühlschlegel
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0042894
Abstract: Hsp12p is considered to be a small heat shock protein and conserved among fungal species. To investigate the expression of this heat shock protein in the fungal pathogen Candida albicans we developed an anti-CaHsp12p antibody. We show that this protein is induced during stationary phase growth and under stress conditions including heat shock, osmotic, oxidative and heavy metal stress. Furthermore, we find that CaHsp12p expression is influenced by the quorum sensing molecule farnesol, the change of CO2 concentration and pH. Notably we show that the key transcription factor Efg1p acts as a positive regulator of CaHsp12p in response to heat shock and oxidative stress and demonstrate that CaHsp12p expression is additionally modulated by Hog1p and the cAMP-PKA signaling pathway. To study the function of Hsp12p in C. albicans we generated a null mutant, in which all four CaHSP12 genes have been deleted. Phenotypic analysis of the strain shows that CaHSP12 is not essential for stress resistance, morphogenesis or virulence when tested in a Drosophila model of infection. However, when overexpressed, CaHSP12 significantly enhanced cell-cell adhesion, germ tube formation and susceptibility to azole antifungal agents whilst desensitizing C. albicans to the quorum sensing molecule farnesol.
CO2 Acts as a Signalling Molecule in Populations of the Fungal Pathogen Candida albicans
Rebecca A. Hall,Luisa De Sordi,Donna M. MacCallum,Hüsnü Topal,Rebecca Eaton,James W. Bloor,Gary K. Robinson,Lonny R. Levin,Jochen Buck,Yue Wang,Neil A. R. Gow,Clemens Steegborn,Fritz A. Mühlschlegel
PLOS Pathogens , 2010, DOI: 10.1371/journal.ppat.1001193
Abstract: When colonising host-niches or non-animated medical devices, individual cells of the fungal pathogen Candida albicans expand into significant biomasses. Here we show that within such biomasses, fungal metabolically generated CO2 acts as a communication molecule promoting the switch from yeast to filamentous growth essential for C. albicans pathology. We find that CO2-mediated intra-colony signalling involves the adenylyl cyclase protein (Cyr1p), a multi-sensor recently found to coordinate fungal responses to serum and bacterial peptidoglycan. We further identify Lys 1373 as essential for CO2/bicarbonate regulation of Cyr1p. Disruption of the CO2/bicarbonate receptor-site interferes selectively with C. albicans filamentation within fungal biomasses. Comparisons between the Drosophila melanogaster infection model and the mouse model of disseminated candidiasis, suggest that metabolic CO2 sensing may be important for initial colonisation and epithelial invasion. Our results reveal the existence of a gaseous Candida signalling pathway and its molecular mechanism and provide insights into an evolutionary conserved CO2-signalling system.
The bZIP Transcription Factor Rca1p Is a Central Regulator of a Novel CO2 Sensing Pathway in Yeast
Fabien Cottier,Martine Raymond,Oliver Kurzai,Marianne Bolstad,Worraanong Leewattanapasuk,Claudia Jiménez-López,Michael C. Lorenz,Dominique Sanglard,Libu?e Váchová,Norman Pavelka,Zdena Palková,Fritz A. Mühlschlegel
PLOS Pathogens , 2012, DOI: 10.1371/journal.ppat.1002485
Abstract: Like many organisms the fungal pathogen Candida albicans senses changes in the environmental CO2 concentration. This response involves two major proteins: adenylyl cyclase and carbonic anhydrase (CA). Here, we demonstrate that CA expression is tightly controlled by the availability of CO2 and identify the bZIP transcription factor Rca1p as the first CO2 regulator of CA expression in yeast. We show that Rca1p upregulates CA expression during contact with mammalian phagocytes and demonstrate that serine 124 is critical for Rca1p signaling, which occurs independently of adenylyl cyclase. ChIP-chip analysis and the identification of Rca1p orthologs in the model yeast Saccharomyces cerevisiae (Cst6p) point to the broad significance of this novel pathway in fungi. By using advanced microscopy we visualize for the first time the impact of CO2 build-up on gene expression in entire fungal populations with an exceptional level of detail. Our results present the bZIP protein Rca1p as the first fungal regulator of carbonic anhydrase, and reveal the existence of an adenylyl cyclase independent CO2 sensing pathway in yeast. Rca1p appears to regulate cellular metabolism in response to CO2 availability in environments as diverse as the phagosome, yeast communities or liquid culture.
The Earth's magnetopause as a source and sink for equatorial nightside energetic charged particles
M. M. Klida ,T. A. Fritz
Annales Geophysicae (ANGEO) , 2009,
Abstract: The Imaging Proton Spectrometer (IPS) and the Imaging Electron Spectrometer (IES) on the Polar satellite have measured temporary deviations in the isotropy of the pitch angle distributions (PADs) of charged particles in the inner magnetosphere. As Polar passes through the nightside equatorial region, the IPS and IES observe dropouts of charged particles with pitch angles near 90°, known as butterfly distributions caused by the shadowing of the magnetopause. Additionally, Polar observes a lower energy (<60 keV) intensification of locally mirroring ions while simultaneously detecting butterfly PADs in both higher energy ions and electrons. While it is accepted that charged particles can be lost to the magnetopause due to shadowing effects, the modeling here can suggest that the magnetopause can also be a direct source for particles observed in magnetosphere, with a strong dependence upon both pitch angle and particle energy.
Characterising electron butterfly pitch angle distributions in the magnetosphere through observations and simulations
M. M. Klida ,T. A. Fritz
Annales Geophysicae (ANGEO) , 2013,
Abstract: The Imaging Electron Spectrometer (IES) on the Polar satellite has measured the average characteristics of the equatorial electron pitch angle distributions (PADs) in the midnight sector as a function of radial distance out to the 9 RE apogee of the Polar satellite. Depressions in the observed fluxes of electrons occur with pitch angles around 90° in the equatorial zone, while the more field-aligned electrons remain largely unchanged. The orbital precessions of the satellite have allowed much of the inner equatorial magnetosphere to be observed. Statistically, butterfly PADs with different shapes are observed selectively in different regions, which can provide insight to their source and possible history. Electron paths of varied pitch angles were modelled using Runge-Kutta approximations of the Lorentz force in a Tsyganenko (T96) simulated magnetosphere. The resulting drift paths suggest that the process of magnetopause shadowing plays a significant role in the loss of these electrons. Case studies of the drifting patterns of electrons with varied pitch angles were simulated from Polar's orbit when a butterfly PAD was observed on 3 October 2002 at an altitude near 9 RE and on 12 September 2000 at an altitude near 6 RE. These two locations represent regions on each side of the boundary of stable trapping. The modelling effort strongly suggests that magnetopause shadowing does play a significant role in the loss of equatorially drifting electrons from the outer regions of the inner magnetosphere.
On the Momentum Dependence of the Nucleon - Nucleus Optical Potential
M. Kleinmann,R. Fritz,H. Müther,A. Ramos
Physics , 1994, DOI: 10.1016/0375-9474(94)90795-1
Abstract: The momentum dependence of the mean-field contribution to the real part of the optical model potential is investigated employing realistic nucleon-nucleon interactions. Within a non-relativistic approach a momentum dependence originates from the non-locality of the Fock exchange term. Deducing the real part of the optical model from a relativistic Dirac Brueckner Hartree Fock approximation for the self-energy of the nucleons yields an additional momentum dependence originating from the non-relativistic reduction of the self-energy. It is demonstrated that large Fock terms are required in the non-relativistic approach to simulate these relativistic features. A comparison is made between a local density approximation for the optical model and a direct evaluation in finite nuclei.
Colorectal cancer screening of high-risk populations: A national survey of physicians
Pascale M White, Malini Sahu, Michael A Poles, Fritz Francois
BMC Research Notes , 2012, DOI: 10.1186/1756-0500-5-64
Abstract: The average knowledge score was 37 ± 18% among the 512 respondents. Gastroenterologists averaged higher scores compared to internists, and family physicians, p = 0.001. Only 28% of physicians correctly identified the screening initiation point for African-Americans while only 12% of physicians correctly identified the screening initiation point and interval for a patient with a family history of CRC. The most commonly cited barriers to referring high-risk patients for CRC screening were "patient refusal" and "lack of insurance reimbursement."There is a lack of knowledge amongst physicians of the screening guidelines for high-risk populations, based on family history and ethnicity. Educational programs to improve physician knowledge and to reduce perceived barriers to CRC screening are warranted to address health disparities in colorectal cancer.As the third leading cause of malignancy-related death in the United States, colorectal cancer (CRC) is expected to be responsible for over 50,000 deaths in 2011 [1,2]. While various CRC screening efforts have been implemented [3], notable disparities in screening prevalence exist among minorities, those with low incomes, lower education, as well as among individuals without health insurance [3].While some of the barriers that influence CRC screening rates include patient factors, as delineated above [4-6], there are also physician-related factors that should be considered, such as failure to recommend screening to patients [7-9]. The decision whether or not to adopt a screening strategy might be driven by both physician-perceived as well as real barriers such as patient co-morbidities, prior patient refusal of screening and lack of patient compliance, physician forgetfulness, time restrictions, and a lack of reminder systems and test tracking systems [10,11]. In addition, physician knowledge of current CRC screening guidelines may be an important contributing factor to screening referral practices.Primary care physician reco
Properties of a cusp diamagnetic cavity boundary
B. M. Walsh, T. A. Fritz,J. Chen
Annales Geophysicae (ANGEO) , 2008,
Abstract: While crossing through the high-altitude dayside cusp on 29 September 1978 and again on 30 October 1978, the ISEE-1 spacecraft observed enhanced energetic particle flux and a depressed and turbulent magnetic field, the signature characteristics of a cusp diamagnetic cavity. As ISEE-1 approached the cavity during each event, a boundary sounding technique was used to measure properties of an emitting boundary. Sounding over multiple energy channels reveals an energy dependent boundary with lower energy particles filling a larger cavity than higher energy particles. Relative motion of the boundary as well as boundary orientation are also measured. The two cusp events were measured at different locations and during different geomagnetic and solar wind conditions; however, they show similar results.
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