Septins AspA and AspC Are Important for Normal Development and Limit the Emergence of New Growth Foci in the Multicellular Fungus
            <i>Aspergillus nidulans</i>

Lindsey, Rebecca L.; Cowden, Susan; Hernández-Rodríguez, Yainitza; Momany, Michelle

doi:10.1128/ec.00269-09

Cited by 73 publications

(98 citation statements)

References 44 publications

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“…However, since yeast septin mutants do not display the simultaneous emergence of multiple buds, AspB also appears to have a role in restricting new growth foci not seen in S. cerevisiae. A. nidulans ⌬aspA and ⌬aspC strains also show the emergence of extra germ tubes and branches, as does a septin deletion mutant in another filamentous fungus, U. maydis (1,38). Thus, the restriction of new growth foci might be a common function for septins in other filamentous fungi.…”

Section: Discussionmentioning

confidence: 93%

“…We recently showed that in A. nidulans septins AspA and AspC interact as AspA-GFP forms small, abnormal structures in ⌬aspC strains, while AspC-GFP does not localize in ⌬aspA strains (38). To determine whether AspB interacts with other septins, we crossed the aspB-gfp strain to ⌬aspA, ⌬aspC, ⌬aspA ⌬aspC, ⌬aspD, and ⌬aspE strains and selected progeny carrying aspB-gfp and the appropriate septin deletion.…”

Section: Resultsmentioning

confidence: 99%

“…We previously showed that deletions of aspA, aspC, or both aspA and aspC result in early and increased germ tube and branch emergence, abnormal septation, and disorganized conidiophores and that AspA and AspC localization is codependent, suggesting that these septins interact (38). Both AspA and AspC localized as spots and bars in dormant and expanding conidia, rings at forming septa and the bases of emerging germ tubes, branches, and conidiophore layers, and as spots and filaments in the cytoplasm and cell cortex (38). aspB was previously reported to be an essential gene and immunofluorescence showed that AspB localizes to sites of septation and branching and to emerging conidiophore layers (47,64).…”

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The Septin AspB in Aspergillus nidulans Forms Bars and Filaments and Plays Roles in Growth Emergence and Conidiation

2012

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In yeast, septins form rings at the mother-bud neck and function as diffusion barriers. In animals, septins form filaments that can colocalize with other cytoskeletal elements. In the filamentous fungus Aspergillus nidulans there are five septin genes, aspA (an ortholog of Saccharomyces cerevisiae CDC11), aspB (an ortholog of S. cerevisiae CDC3), aspC (an ortholog of S. cerevisiae CDC12), aspD (an ortholog of S. cerevisiae CDC10), and aspE (found only in filamentous fungi). The aspB gene was previously reported to be the most highly expressed Aspergillus nidulans septin and to be essential. Using improved gene targeting techniques, we found that deletion of aspB is not lethal but results in delayed septation, increased emergence of germ tubes and branches, and greatly reduced conidiation. We also found that AspB-green fluorescent protein (GFP) localizes as rings and collars at septa, branches, and emerging layers of the conidiophore and as bars and filaments in conidia and hyphae. Bars are found in dormant and isotropically expanding conidia and in subapical nongrowing regions of hyphae and display fast movements. Filaments form as the germ tube emerges, localize to hyphal and branch tips, and display slower movements. All visible AspB-GFP structures are retained in ⌬aspD and lost in ⌬aspA and ⌬aspC strains. Interestingly, in the ⌬aspE mutant, AspB-GFP rings, bars, and filaments are visible in early growth, but AspB-GFP rods and filaments disappear after septum formation. AspE orthologs are only found in filamentous fungi, suggesting that this class of septins might be required for stability of septin bars and filaments in highly polar cells. Septins are evolutionarily conserved GTP binding proteins that form complexes and are increasingly viewed as cytoskeletal elements (62). Septins are found in all eukaryotes except higher plants (20,52) and are involved in a variety of cellular processes including cytokinesis, vesicle trafficking, cytoskeleton organization, polarity, and formation of diffusion barriers (35,39,44,53,62). Perhaps, not surprisingly given their roles in such critical processes, septin defects have been associated with many human diseases (29).The septins were first discovered in the budding yeast Saccharomyces cerevisiae as temperature-sensitive cell cycle mutants defective in cytokinesis (31, 41). Early in the yeast cell cycle, septins localize as a cap at the future site of bud emergence. As the bud emerges, septins localize first as a ring at the mother/bud neck and later as an hourglass structure as the bud develops (25,26,37). At cytokinesis, the hourglass structure converts into two rings. Septins at the neck form diffusion barriers that keep the cellular machinery necessary for growth and cytokinesis properly localized (16,18,22,49,50,60). In addition, septins are part of the morphogenesis checkpoint that coordinates nuclear division with bud formation (37).In S. cerevisiae septins organize into hetero-oligomeric octamers that associate end to end to form nonpolar filaments (6). Electron ...

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Section: Discussionmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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The Septin AspB in Aspergillus nidulans Forms Bars and Filaments and Plays Roles in Growth Emergence and Conidiation

2012

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“…Effectors likely to be immediately downstream of RasA signaling are the conserved GTPase proteins ModA (Aspergillus Cdc42 homolog) and RacA, for activation of mitogen-activated protein kinase or p21-activated kinase pathways (18,24,47). Other interesting candidates that may physically or genetically interact with RasA at the plasma membrane or endomembranes are the septins and Rho proteins, both of which play roles in germination and branch formation of A. nidulans (16,26,48). Future work in this area will focus on the identification of RasA effectors to construct improved molecular models of fungal growth and morphogenesis.…”

Section: Discussionmentioning

confidence: 99%

Plasma Membrane Localization Is Required for RasA-Mediated Polarized Morphogenesis and Virulence of Aspergillus fumigatus

et al. 2012

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f Ras is a highly conserved GTPase protein that is essential for proper polarized morphogenesis of filamentous fungi. Localization of Ras proteins to the plasma membrane and endomembranes through posttranslational addition of farnesyl and palmitoyl residues is an important mechanism through which cells provide specificity to Ras signal output. Although the Aspergillus fumigatus RasA protein is known to be a major regulator of growth and development, the membrane distribution of RasA during polarized morphogenesis and the role of properly localized Ras signaling in virulence of a pathogenic mold remain unknown. Here we demonstrate that Aspergillus fumigatus RasA localizes primarily to the plasma membrane of actively growing hyphae. We show that treatment with the palmitoylation inhibitor 2-bromopalmitate disrupts normal RasA plasma membrane association and decreases hyphal growth. Targeted mutations of the highly conserved RasA palmitoylation motif also mislocalized RasA from the plasma membrane and led to severe hyphal abnormalities, cell wall structural changes, and reduced virulence in murine invasive aspergillosis. Finally, we provide evidence that proper RasA localization is independent of the Ras palmitoyltransferase homolog, encoded by erfB, but requires the palmitoyltransferase complex subunit, encoded by erfD. Our results demonstrate that plasma membrane-associated RasA is critical for polarized morphogenesis, cell wall stability, and virulence in A. fumigatus.

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“…In S. cerevisiae, septins form scaffolds that are essential for normal polarized growth, septation, and cytokinesis (Oh and Bi 2011). In filamentous fungi, septins are needed for normal septum formation and appear to delimit growth sites (DeMay et al 2009;Lindsey et al 2010;Ryder et al 2013). For example, the absence of septins in A. nidulans leads to the simultaneous emergence of multiple germ tubes and hyperbranching.…”

Section: The Cytoskeletonmentioning

confidence: 99%

Fungal Morphogenesis

Lin

Alspaugh

Liu

et al. 2014

Cold Spring Harbor Perspectives in Medicine

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Morphogenesis in fungi is often induced by extracellular factors and executed by fungal genetic factors. Cell surface changes and alterations of the microenvironment often accompany morphogenetic changes in fungi. In this review, we will first discuss the general traits of yeast and hyphal morphotypes and how morphogenesis affects development and adaptation by fungi to their native niches, including host niches. Then we will focus on the molecular machinery responsible for the two most fundamental growth forms, yeast and hyphae. Last, we will describe how fungi incorporate exogenous environmental and host signals together with genetic factors to determine their morphotype and how morphogenesis, in turn, shapes the fungal microenvironment. PROPERTIES OF MORPHOGENESIS IN FUNGAL CELLS

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Septins AspA and AspC Are Important for Normal Development and Limit the Emergence of New Growth Foci in the Multicellular Fungus Aspergillus nidulans

Cited by 73 publications

References 44 publications

The Septin AspB in Aspergillus nidulans Forms Bars and Filaments and Plays Roles in Growth Emergence and Conidiation

The Septin AspB in Aspergillus nidulans Forms Bars and Filaments and Plays Roles in Growth Emergence and Conidiation

Plasma Membrane Localization Is Required for RasA-Mediated Polarized Morphogenesis and Virulence of Aspergillus fumigatus

Fungal Morphogenesis

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