Microtubules Are Required for Motility and Positioning of Vesicles and Mitochondria in Hyphal Tip Cells of Allomyces macrogynus

The ultrastructure of freeze-substituted tip cells of Fusarium acuminatum was analysed by conventional and high-voltage transmission electron microscopy (HVEM). At least 2 morphologically distinct types of Golgi-like endomembrane cisternae were observed, each existing as single, fenestrated sheets and tubular elements that were often very closely associated with mitochondria. From HVEM observations of thick (0.25 and 0.5 micron) sections, the Spitzenkorper appeared to correspond to an apical mass of vesicles. A network of microfilaments was identified among component vesicles of the Spitzenkorper and adjacent to developing septa. Microtubules were oriented primarily parallel to the direction of hyphal growth and were located in all areas of the cytoplasm, including the tip cell apex. Cytoplasmic vesicles were closely associated with these microtubules. From these observations it is suggested that cytoskeletal elements play important roles in localized cell wall formation. The filasome, a previously unreported type of coated vesicle in fungi, might also be involved in wall synthesis.

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DNA Synthesis in Relation to Hyphal Branching and Wall Composition in Allomyces macrogynus

Australian Journal of Biological Sciences ◽

10.1071/bi9850067 ◽

1985 ◽

Vol 38 (1) ◽

pp. 67 ◽

Cited By ~ 4

Author(s):

Jean Youatt

Keyword(s):

Dna Synthesis ◽

Sodium Sulfide ◽

Methionine Sulfoxide ◽

Cylindrical Shape ◽

Sulfur Amino Acids ◽

Hyphal Branching ◽

The Third ◽

Methionine Sulfone ◽

Allomyces Macrogynus ◽

Hyphal Tip

In A. macrogynus the first replication of DNA occurred after germination, at the time of the first branching of rhizoids. Before the second replication galactan in the wall exceeded the glucan content and was not firmly attached. After the second DNA replication hyphallengthening commenced with an increase in the content of glucan but the walls lacked rigidity. At the time of the third replication walls underwent a change which commenced at the hyphal tip and worked back to the rhizoids, converting the hyphae to a rigid, cylindrical shape. Branching commenced after the fourth replication of DNA. Multiple branching occurred when mature plants were transferred to glucose-histidine-methionine solution without further DNA synthesis. Hyphal branching was used to show that A. macrogynus was able to use methionine, methionine sulfoxide, methionine sulfone, sodium sulfide, cysteine, cystathionine and homocysteine but not cystine. Thioacetamide supported growth through many subcultures showing that A. macrogynus can synthesize its sulfur amino acids.

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MesA, a Novel Fungal Protein Required for the Stabilization of Polarity Axes inAspergillus nidulans

Molecular Biology of the Cell ◽

10.1091/mbc.e03-11-0803 ◽

2004 ◽

Vol 15 (8) ◽

pp. 3658-3672 ◽

Cited By ~ 68

Author(s):

Claire L. Pearson ◽

Kaimei Xu ◽

Kathryn E. Sharpless ◽

Steven D. Harris

Keyword(s):

Molecular Characterization ◽

Regulatory Mechanisms ◽

Membrane Domains ◽

Wild Type ◽

Actin Ring ◽

Fungal Protein ◽

Hyphal Morphogenesis ◽

Actin Cables ◽

Tip Cells ◽

Hyphal Tip

The Aspergillus nidulans proteome possesses a single formin, SepA, which is required for actin ring formation at septation sites and also plays a role in polarized morphogenesis. Previous observations imply that complex regulatory mechanisms control the function of SepA and ensure its correct localization within hyphal tip cells. To characterize these mechanisms, we undertook a screen for mutations that enhance sepA defects. Of the mutants recovered, mesA1 causes the most dramatic defect in polarity establishment when SepA function is compromised. In a wild-type background, mesA1 mutants undergo aberrant hyphal morphogenesis, whereas septum formation remains unaffected. Molecular characterization revealed that MesA is a novel fungal protein that contains predicted transmembrane domains and localizes to hyphal tips. We show that MesA promotes the localized assembly of actin cables at polarization sites by facilitating the stable recruitment of SepA. We also provide evidence that MesA may regulate the formation or distribution of sterol-rich membrane domains. Our results suggest that these domains may be part of novel mechanism that directs SepA to hyphal tips.

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Effects of the sterol demethylase inhibitor, cyproconazole, on hyphal tip cells of Sclerotium rolfsii

Pesticide Biochemistry and Physiology ◽

10.1016/0048-3575(90)90003-k ◽

1990 ◽

Vol 36 (2) ◽

pp. 115-126 ◽

Cited By ~ 10

Author(s):

Melvin S. Fuller ◽

Robert W. Roberson ◽

Ulrich Gisi

Keyword(s):

Sclerotium Rolfsii ◽

Tip Cells ◽

Hyphal Tip

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Ash1 Protein, an Asymmetrically Localized Transcriptional Regulator, Controls Filamentous Growth and Virulence of Candida albicans

Molecular and Cellular Biology ◽

10.1128/mcb.22.24.8669-8680.2002 ◽

2002 ◽

Vol 22 (24) ◽

pp. 8669-8680 ◽

Cited By ~ 31

Author(s):

Diane O. Inglis ◽

Alexander D. Johnson

Keyword(s):

Candida Albicans ◽

Mouse Model ◽

Regulatory Protein ◽

Cell Nuclei ◽

Yeast Form ◽

Disseminated Candidiasis ◽

Transcriptional Regulatory ◽

Tip Cells ◽

Hyphal Tip

ABSTRACT In response to a number of distinct environmental conditions, the fungal pathogen Candida albicans undergoes a morphological transition from a round, yeast form to a series of elongated, filamentous forms. This transition is believed to be critical for virulence in a mouse model of disseminated candidiasis. Here we describe the characterization of C. albicans ASH1, a gene that encodes an asymmetrically localized transcriptional regulatory protein involved in this response. We show that C. albicans ash1 mutants are defective in responding to some filament-inducing conditions. We also show that Ash1p is preferentially localized to daughter cell nuclei in the budding-yeast form of C. albicans cell growth and to the hyphal tip cells in growing filaments. Thus, Ash1p “marks” newly formed cells and presumably directs a specialized transcriptional program in these cells. Finally, we show that ASH1 is required for full virulence of C. albicans in a mouse model of disseminated candidiasis.

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Effects of the demethylase inhibitor, cyproconazole, on hyphal tip cells of Sclerotium rolfsii

Pesticide Biochemistry and Physiology ◽

10.1016/0048-3575(89)90151-x ◽

1989 ◽

Vol 34 (2) ◽

pp. 130-142 ◽

Cited By ~ 14

Author(s):

Robert W. Roberson ◽

Melvin S. Fuller ◽

Christian Grabski

Keyword(s):

Sclerotium Rolfsii ◽

Tip Cells ◽

Hyphal Tip

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The Role of Microtubules in Rapid Hyphal Tip Growth of Aspergillus nidulans

Molecular Biology of the Cell ◽

10.1091/mbc.e04-09-0798 ◽

2005 ◽

Vol 16 (2) ◽

pp. 918-926 ◽

Cited By ~ 137

Author(s):

Tetsuya Horio ◽

Berl R. Oakley

Keyword(s):

Growth Rate ◽

Aspergillus Nidulans ◽

Tip Growth ◽

Fluorescent Protein ◽

Time Lapse ◽

Polarized Growth ◽

Green Fluorescent ◽

Tip Cells ◽

Hyphal Tip

The filamentous fungus Aspergillus nidulans grows by polarized extension of hyphal tips. The actin cytoskeleton is essential for polarized growth, but the role of microtubules has been controversial. To define the role of microtubules in tip growth, we used time-lapse microscopy to measure tip growth rates in germlings of A. nidulans and in multinucleate hyphal tip cells, and we used a green fluorescent protein-α-tubulin fusion to observe the effects of the antimicrotubule agent benomyl. Hyphal tip cells grew ≈5 times faster than binucleate germlings. In germlings, cytoplasmic microtubules disassembled completely in mitosis. In hyphal tip cells, however, microtubules disassembled through most of the cytoplasm in mitosis but persisted in a region near the hyphal tip. The growth rate of hyphal tip cells did not change significantly in mitosis. Benomyl caused rapid disassembly of microtubules in tip cells and a 10× reduction in growth rate. When benomyl was washed out, microtubules assembled quickly and rapid tip growth resumed. These results demonstrate that although microtubules are not strictly required for polarized growth, they are rate-limiting for the growth of hyphal tip cells. These data also reveal that A. nidulans exhibits a remarkable spatial regulation of microtubule disassembly within hyphal tip cells.

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