Publications (6)25.97 Total impact
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Article: The Paxillin-like protein AgPxl1 is required for apical branching and maximal hyphal growth in A.gossypii.
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ABSTRACT: The development from young, slowly growing hyphae to fast growing hyphae in filamentous fungi is referred to as hyphal maturation. We have identified the Paxillin-like protein AgPxl1 in Ashbyagossypii as a developmental protein that is specifically required for hyphal maturation. The early development of A.gossypii strains lacking AgPxl1 is indistinguishable from wild-type. However, at later developmental stages the maximal hyphal extension rate is less than half compared to wild-type and apical branching is affected. Apical branching is characterised as the symmetric division of fast growing hyphal tips resulting in two sister hyphae. In Agpxl1Delta strains two thirds of the apical branching events lead to asymmetric sister hyphae where growth of one branch is either completely aborted or slowed down while extension of the other branch is not affected. This suggests that AgPxl1 plays a role in the organisation of growth and efficient division of growth upon apical branching in mature mycelia. The conserved C-terminal LIM domains are necessary for AgPxl1 function and also contribute to tip localisation. AgCLA4, a PAK-like kinase, is epistatic to AgPXL1 and robust localisation of AgPxl1 depends on AgCla4. This suggests that AgCla4 acts upstream of AgPxl1.Fungal Genetics and Biology 07/2008; 45(6):829-38. · 3.74 Impact Factor -
Article: The Yak1 kinase is involved in the initiation and maintenance of hyphal growth in Candida albicans.
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ABSTRACT: Members of the dual-specificity tyrosine-phosphorylated and regulated kinase (DYRK) family perform a variety of functions in eukaryotes. We used gene disruption, targeted pharmacologic inhibition, and genome-wide transcriptional profiling to dissect the function of the Yak1 DYRK in the human fungal pathogen Candida albicans. C. albicans strains with mutant yak1 alleles showed defects in the yeast-to-hypha transition and in maintaining hyphal growth. They also could not form biofilms. Despite their in vitro filamentation defect, C. albicans yak1Delta/yak1Delta mutants remained virulent in animal models of systemic and oropharyngeal candidiasis. Transcriptional profiling showed that Yak1 was necessary for the up-regulation of only a subset of hypha-induced genes. Although downstream targets of the Tec1 and Bcr1 transcription factors were down-regulated in the yak1Delta/yak1Delta mutant, TEC1 and BCR1 were not. Furthermore, 63% of Yak1-dependent, hypha-specific genes have been reported to be negatively regulated by the transcriptional repressor Tup1 and inactivation of TUP1 in the yak1Delta/yak1Delta mutant restored filamentation, suggesting that Yak1 may function upstream of Tup1 in governing hyphal emergence and maintenance.Molecular biology of the cell 06/2008; 19(5):2251-66. · 5.98 Impact Factor -
Article: The SH3/PH domain protein AgBoi1/2 collaborates with the Rho-type GTPase AgRho3 to prevent nonpolar growth at hyphal tips of Ashbya gossypii.
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ABSTRACT: Unlike most other cells, hyphae of filamentous fungi permanently elongate and lack nonpolar growth phases. We identified AgBoi1/2p in the filamentous ascomycete Ashbya gossypii as a component required to prevent nonpolar growth at hyphal tips. Strains lacking AgBoi1/2p frequently show spherical enlargement at hyphal tips with concomitant depolarization of actin patches and loss of tip-located actin cables. These enlarged tips can repolarize and resume hyphal tip extension in the previous polarity axis. AgBoi1/2p permanently localizes to hyphal tips and transiently to sites of septation. Only the tip localization is important for sustained elongation of hyphae. In a yeast two-hybrid experiment, we identified the Rho-type GTPase AgRho3p as an interactor of AgBoi1/2p. AgRho3p is also required to prevent nonpolar growth at hyphal tips, and strains deleted for both AgBOI1/2 and AgRHO3 phenocopied the respective single-deletion strains, demonstrating that AgBoi1/2p and AgRho3p function in a common pathway. Monitoring the polarisome of growing hyphae using AgSpa2p fused to the green fluorescent protein as a marker, we found that polarisome disassembly precedes the onset of nonpolar growth in strains lacking AgBoi1/2p or AgRho3p. AgRho3p locked in its GTP-bound form interacts with the Rho-binding domain of the polarisome-associated formin AgBni1p, implying that AgRho3p has the capacity to directly activate formin-driven actin cable nucleation. We conclude that AgBoi1/2p and AgRho3p support polarisome-mediated actin cable formation at hyphal tips, thereby ensuring permanent polar tip growth.Eukaryotic Cell 11/2006; 5(10):1635-47. · 3.60 Impact Factor -
Article: Phosphatidylinositol-dependent phospholipases C Plc2 and Plc3 of Candida albicans are dispensable for morphogenesis and host-pathogen interaction.
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ABSTRACT: Phospholipases play an important role as virulence factors in human pathogens. Candida albicans, the major fungal pathogen of humans, encodes phospholipases of type A, B, C and D. Type B Plb2 and type D Pld1 phospholipases have been shown to contribute to virulence in this organism. We analyzed, in C. albicans, PLC2 and PLC3, two highly conserved genes coding for phosphatidylinositol-dependent phospholipases C with homology to the known virulence factor PlcA in the human pathogen Listeria monocytogenes. We show that expression of PLC2 and PLC3 is upregulated under different filament-inducing conditions and in the constitutive filamentous mutant tup1Delta. In order to analyze PLC2 and PLC3 function in C. albicans, we constructed strains that carry PLC2 or PLC3 under a constitutive promoter and strains that lack all four PLC2/3 alleles. These strains were not affected in their ability to produce filaments under non-inducing conditions, nor was filamentation modified under inducing conditions, suggesting that PLC2/3 are not critical determinants of the yeast-to-hypha switch. In a cell culture model for macrophage interaction, phagocytosis of C. albicans and subsequent killing were not influenced by PLC2/3. These results demonstrate that C. albicans PLC2 and PLC3 are dispensable for virulence; moreover, they underline the sharp contrast with the function of plcA in L. monocytogenes.Research in Microbiology 09/2005; 156(7):822-9. · 2.76 Impact Factor -
Article: A Ras-like GTPase is involved in hyphal growth guidance in the filamentous fungus Ashbya gossypii.
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ABSTRACT: Characteristic features of morphogenesis in filamentous fungi are sustained polar growth at tips of hyphae and frequent initiation of novel growth sites (branches) along the extending hyphae. We have begun to study regulation of this process on the molecular level by using the model fungus Ashbya gossypii. We found that the A. gossypii Ras-like GTPase Rsr1p/Bud1p localizes to the tip region and that it is involved in apical polarization of the actin cytoskeleton, a determinant of growth direction. In the absence of RSR1/BUD1, hyphal growth was severely slowed down due to frequent phases of pausing of growth at the hyphal tip. During pausing events a hyphal tip marker, encoded by the polarisome component AgSPA2, disappeared from the tip as was shown by in vivo time-lapse fluorescence microscopy of green fluorescent protein-labeled AgSpa2p. Reoccurrence of AgSpa2p was required for the resumption of hyphal growth. In the Agrsr1/bud1Delta deletion mutant, resumption of growth occurred at the hyphal tip in a frequently uncoordinated manner to the previous axis of polarity. Additionally, hyphal filaments in the mutant developed aberrant branching sites by mislocalizing AgSpa2p thus distorting hyphal morphology. These results define AgRsr1p/Bud1p as a key regulator of hyphal growth guidance.Molecular Biology of the Cell 11/2004; 15(10):4622-32. · 4.94 Impact Factor -
Article: Maximal polar growth potential depends on the polarisome component AgSpa2 in the filamentous fungus Ashbya gossypii.
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ABSTRACT: We used actin staining and videomicroscopy to analyze the development from a spore to a young mycelium in the filamentous ascomycete Ashbya gossypii. The development starts with an initial isotropic growth phase followed by the emergence of germ tubes. The initial tip growth speed of 6-10 microm/h increases during early stages of development. This increase is transiently interrupted in response to the establishment of lateral branches or septa. The hyphal tip growth speed finally reaches a maximum of up to 200 micro/h, and the tips of these mature hyphae have the ability to split into two equally fast-growing hyphae. A search for A. gossypii homologs of polarisome components of the yeast Saccharomyces cerevisiae revealed a remarkable size difference between Spa2p of both organisms, with AgSpa2p being double as long as ScSpa2p due to an extended internal domain. AgSpa2 colocalizes with sites of polarized actin. Using time-lapse videomicroscopy, we show that AgSpa2p-GFP polarization is established at sites of branch initiation and then permanently maintained at hyphal tips. Polarization at sites of septation is transient. During apical branching the existing AgSpa2p-GFP polarization is symmetrically divided. To investigate the function of AgSpa2p, we generated two AgSPA2 mutants, a partial deletion of the internal domain alone, and a complete deletion. The mutations had an impact on the maximal hyphal tip growth speed, on the hyphal diameter, and on the branching pattern. We suggest that AgSpa2p is required for the determination of the area of growth at the hyphal tip and that the extended internal domain plays an important role in this process.Molecular Biology of the Cell 11/2003; 14(10):4140-54. · 4.94 Impact Factor
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Institutions
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2003–2008
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Universität Basel
Basel, BS, Switzerland
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