Independent nuclear motility and hyphal tip growth

1995 ◽  
Vol 73 (S1) ◽  
pp. 122-125 ◽  
Author(s):  
James R. Aist
Keyword(s):  
Tip Growth ◽  
Spindle Pole ◽  
Life Cycles ◽  
Microtubule Organizing Center ◽  
Hyphal Tip Growth ◽  
Spindle Pole Bodies ◽  
Organizing Center ◽  
Key Words Actin ◽  
Tip Cells ◽  
Hyphal Tip

Independent nuclear motility is involved in many important aspects of fungal life cycles, including the following: nuclear division; population of hyphal tip cells, branches, and spores with nuclei; dikaryotization; and karyogamy. Spindle pole bodies are almost constantly in motion during all phases of the nuclear cycle, and they have been linked to most instances of independent nuclear motility. A role for microtubules in this process is now well established, and research is being focused on which set of them, astral or cytoplasmic, is utilized as well as on the microtubule-associated motor proteins that may generate the force. In some cases, F-actin may interact with the microtubules or even provide an alternative cytoskeleton supporting nuclear migration. Hyphal tip growth and independent nuclear motility are coordinated and interrelated processes, making the elucidation of the signals, processes, and structures involved an attractive area for further research. Key words: actin, microtubule, microtubule associated protein, microtubule organizing center, motility, nucleus.

Hyphal tip growth and cytoplasmic characters of Conidiobolus coronatus (Zoopagomycota, Entomophthoromycotina)

Mycologia ◽  
2018 ◽  
Vol 110 (1) ◽  
pp. 31-38 ◽  
Author(s):  
Fisher ◽  
Romberger ◽  
Lowry ◽  
Shange ◽  
Roberson
Keyword(s):  
Tip Growth ◽  
Spindle Pole ◽  
Evolutionary Relationships ◽  
Polarized Growth ◽  
Conidiobolus Coronatus ◽  
Hyphal Tip Growth ◽  
Spindle Pole Bodies ◽  
Transmission Electron ◽  
Tem Microscopy ◽  
Hyphal Tip

Characteristics of hyphal structure and growth can provide insights into the mechanisms of polarized growth and support investigations of fungal phylogeny. To assist with the resolution of evolutionary relationships of the zygomycetes, the authors used comparative bioimaging methods (light [LM] and transmission electron [TEM] microscopy) to describe selected subcellular characters of hyphal tips of Conidiobolus coronatus. Growing hyphae of C. coronatus contain Spitzenkörper (Spk). Spk are most commonly present in hyphae of Dikarya (Ascomycota and Basidiomycota) and are rarely reported in zygomycete hyphae, which possess an apical vesicle crescent (AVC). Such findings raise questions regarding the evolution of the Spk and its relationship with the AVC. Descriptions of additional subcellular characters (e.g., mitotic-phase spindle pole bodies, cytoplasmic behavior, organelle structure) are also presented.

The dynamic behaviour of microtubules and their contributions to hyphal tip growth in Aspergillus nidulans

Microbiology ◽  
2005 ◽  
Vol 151 (5) ◽  
pp. 1543-1555 ◽  
Author(s):  
Karina Sampson ◽  
I. Brent Heath
Keyword(s):  
Aspergillus Nidulans ◽  
Tip Growth ◽  
Spindle Pole ◽  
Hyphal Tip Growth ◽  
Complex Processes ◽  
Spindle Pole Bodies ◽  
Tubulin Subunit ◽  
Apical Cells ◽  
Tip Extension ◽  
Hyphal Tip

Creating and maintaining cell polarity are complex processes that are not fully understood. Fungal hyphal tip growth is a highly polarized and dynamic process involving both F-actin and microtubules (MTs), but the behaviour and roles of the latter are unclear. To address this issue, MT dynamics and subunit distribution were analysed in a strain of Aspergillus nidulans expressing GFP–α-tubulin. Apical MTs are the most dynamic, the bulk of which move tipwards from multiple subapical spindle pole bodies, the only clear region of microtubule nucleation detected. MTs populate the apex predominantly by elongation at rates about three times faster than tip extension. This polymerization was facilitated by the tipward migration of MT subunits, which generated a tip-high gradient. Subapical regions of apical cells showed variable tubulin subunit distributions, without tipward flow, while subapical cells showed even tubulin subunit distribution and low MT dynamics. Short MTs, of a similar size to those reported in axons, also occasionally slid into the apex. During mitosis in apical cells, MT populations at the tip varied. Cells with less distance between the tip and the first nucleus were more likely to loose normal MT populations and dynamics. Reduced MTs in the tip, during mitosis or after exposure to the MT inhibitor carbendazim (MBC), generally correlated with reduced, but continuing growth and near-normal tip morphology. In contrast, the actin-disrupting agent latrunculin B reduced growth rates much more severely and dramatically distorted tip morphology. These results suggest substantial independence between MTs and hyphal tip growth and a more essential role for F-actin. Among MT-dependent processes possibly contributing to tip growth is the transportation of vesicles. However, preliminary ultrastructural data indicated a lack of direct MT–organelle interactions. It is suggested that the population of dynamic apical MTs enhance migration of the ‘cytomatrix’, thus ensuring that organelles and proteins maintain proximity to the constantly elongating tip.

scholarly journals The role of Aspergillus nidulans polo-like kinase PlkA in microtubule-organizing center control

2021 ◽  
Author(s):  
Xiaolei Gao ◽  
Saturnino Herrero ◽  
Valentin Wernet ◽  
Sylvia Erhardt ◽  
Oliver Valerius ◽  
...  
Keyword(s):  
Aspergillus Nidulans ◽  
Cell Types ◽  
Spindle Pole ◽  
Receptor Protein ◽  
Animal Cells ◽  
Microtubule Organizing Center ◽  
Spindle Pole Bodies ◽  
Organizing Center ◽  
Ring Complex ◽  
Core Components

Centrosomes are important microtubule-organizing centers (MTOC) in animal cells. In addition, non-centrosomal MTOCs (ncMTOCs) were described in many cell types. Functional analogs of centrosomes in fungi are the spindle pole bodies (SPBs). In Aspergillus nidulans additional MTOCs were discovered at septa (sMTOC). Although the core components are conserved in both MTOCs, their composition and organization are different and dynamic. Here, we show that the polo-like kinase PlkA binds the γ-tubulin ring complex (γ-TuRC) receptor protein ApsB and contributes to targeting ApsB to both MTOCs. PlkA coordinates SPB outer plaque with sMTOC activities. PlkA kinase activity was required for astral MT formation involving ApsB recruitment. PlkA also interacted with the γ-TuRC inner plaque receptor protein PcpA. Mitosis was delayed without PlkA, and the PlkA protein was required for proper mitotic spindle morphology, although this function was independent of its catalytic activity. Our results suggest polo-like kinase as a regulator of MTOC activities and as a scaffolding unit through interaction with γ-tubulin ring complex receptors.

scholarly journals Cytoplasmic microtubules and fungal morphogenesis: ultrastructural effects of methyl benzimidazole-2-ylcarbamate determined by freeze-substitution of hyphal tip cells.

1980 ◽  
Vol 87 (1) ◽  
pp. 55-64 ◽  
Author(s):  
R J Howard ◽  
J R Aist
Keyword(s):  
Intracellular Transport ◽  
Freeze Substitution ◽  
Ultrastructural Level ◽  
Spindle Pole ◽  
Voltage Electron ◽  
Spindle Pole Bodies ◽  
Fungal Morphogenesis ◽  
Cytoplasmic Microtubules ◽  
Tip Cells ◽  
Hyphal Tip

The effects of methyl benzimidazole-2-ylcarbamate (MBC), one of only a few agents that are active against microtubules of fungi, were analyzed at the ultrastructural level in freeze-substituted hyphal tip cells of Fusarium acuminatum. Nontreated and control cells had numerous microtubules throughout. After just 10 min of exposure to MBC, almost no cytoplasmic microtubules were present, except near spindle pole bodies. After 45 min of exposure to MBC, no microtubules were present in hyphal tip cells, but they were present in the relatively quiescent subapical cells. These observations suggested that there are different rates of turnover for cytoplasmic microtubules in apical and subapical cells and for microtubules near spindle pole bodies and that MBC acts by inhibiting microtubules assembly. A statistical analysis of the distribution of intracytoplasmic vesicles in thick sections of cells treated with MBC, D2O or MBC + D2O was obtained by use of a high-voltage electron microscope. More than 50% of the vesicles in the apical 30 micrometers of control cells were found to lie within 2 micrometers of the tip cell apex. MBC treatment caused this vesicle distribution to become uniform, resulting in a substantial increase in the number of vesicles in subapical regions. The reduction in the number of cytoplasmic microtubules, induced by MBC, apparently inhibited intracellular transport of these vesicles and rendered random the longitudinal orientation of mitochondria. In most cases, D2O appeared capable of preventing these MBC-effects through stabilization of microtubules. These observations support the "vesicle hypothesis" of tip growth and establish a transport role for cytoplasmic microtubules in fungal morphogenesis.

scholarly journals Role of fungal dynein in hyphal growth, microtubule organization, spindle pole body motility and nuclear migration

1998 ◽  
Vol 111 (11) ◽  
pp. 1555-1566 ◽  
Author(s):  
S. Inoue ◽  
B.G. Turgeon ◽  
O.C. Yoder ◽  
J.R. Aist
Keyword(s):  
Spindle Pole Body ◽  
Nuclear Migration ◽  
Cytoplasmic Dynein ◽  
Spindle Pole ◽  
Wild Type ◽  
Interphase Nuclei ◽  
Spindle Pole Bodies ◽  
Body Motility ◽  
Tip Cells ◽  
Hyphal Tip

Cytoplasmic dynein is a microtubule-associated motor protein with several putative subcellular functions. Sequencing of the gene (DHC1) for cytoplasmic dynein heavy chain of the filamentous ascomycete, Nectria haematococca, revealed a 4,349-codon open reading frame (interrupted by two introns) with four highly conserved P-loop motifs, typical of cytoplasmic dynein heavy chains. The predicted amino acid sequence is 78.0% identical to the cytoplasmic dynein heavy chain of Neurospora crassa, 70.2% identical to that of Aspergillus nidulans and 24.8% identical to that of Saccharomyces cerevisiae. The genomic copy of DHC1 in N. haematococca wild-type strain T213 was disrupted by inserting a selectable marker into the central motor domain. Mutants grew at 33% of the wild-type rate, forming dense compact colonies composed of spiral and highly branched hyphae. Major cytological phenotypes included (1) absence of aster-like arrays of cytoplasmic microtubules focused at the spindle pole bodies of post-mitotic and interphase nuclei, (2) limited post-mitotic nuclear migration, (3) lack of spindle pole body motility at interphase, (4) failure of spindle pole bodies to anchor interphase nuclei, (5) nonuniform distribution of interphase nuclei and (6) small or ephemeral Spitzenkorper at the apices of hyphal tip cells. Microtubule distribution in the apical region of tip cells of the mutant was essentially normal. The nonuniform distribution of nuclei in hyphae resulted primarily from a lack of both post-mitotic nuclear migration and anchoring of interphase nuclei by the spindle pole bodies. The results support the hypothesis that DHC1 is required for the motility and functions of spindle pole bodies, normal secretory vesicle transport to the hyphal apex and normal hyphal tip cell morphogenesis.

γ-Tubulin and the fungal microtubule cytoskeleton

1995 ◽  
Vol 73 (S1) ◽  
pp. 352-358 ◽  
Author(s):  
Berl R. Oakley
Keyword(s):  
Cell Cycle ◽  
Mitotic Spindle ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Microtubule Organizing Center ◽  
Pole Body ◽  
Spindle Pole Bodies ◽  
Key Words Tubulin ◽  
Organizing Center ◽  
Chromosomal Condensation

γ-Tubulin is present in phylogenetically diverse eukaryotes. It is a component of microtubule organizing centers such as the spindle pole bodies of fungi. In Aspergillus nidulans and Schizosaccharomyces pombe, it is essential for nuclear division, and, thus, for viability. In A. nidulans, nuclei carrying a γ-tubulin disruption can be maintained in heterokaryons, and the phenotypes caused by the disruption can be determined in uninucleate spores produced by the heterokaryons. Experiments with heterokaryons created in strains with mutations that allow synchronization of the cell cycle reveal that γ-tubulin is not required for the transition from the G1 phase of the cell cycle through S phase to G2, nor for the entry into mitosis as judged by chromosomal condensation. It is, however, required for the formation of the mitotic spindle and for the successful completion of mitosis. Staining with the MPM-2 monoclonal antibody reveals that spindle pole body replication occurs in the absence of functional γ-tubulin. Finally, human γ-tubulin functions in fission yeast, and this indicates that γ-tubulin has similar functions in widely divergent organisms. Key words: tubulin, microtubule, spindle pole body, microtubule organizing center.

scholarly journals The Msd1–Wdr8–Pkl1 complex anchors microtubule minus ends to fission yeast spindle pole bodies

2015 ◽  
Vol 209 (4) ◽  
pp. 549-562 ◽  
Author(s):  
Masashi Yukawa ◽  
Chiho Ikebe ◽  
Takashi Toda
Keyword(s):  
Fission Yeast ◽  
Critical Role ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Microtubule Organizing Center ◽  
Spatiotemporal Regulation ◽  
Spindle Pole Bodies ◽  
Organizing Center ◽  
Spindle Microtubules ◽  
Insight Into

The minus ends of spindle microtubules are anchored to a microtubule-organizing center. The conserved Msd1/SSX2IP proteins are localized to the spindle pole body (SPB) and the centrosome in fission yeast and humans, respectively, and play a critical role in microtubule anchoring. In this paper, we show that fission yeast Msd1 forms a ternary complex with another conserved protein, Wdr8, and the minus end–directed Pkl1/kinesin-14. Individual deletion mutants displayed the identical spindle-protrusion phenotypes. Msd1 and Wdr8 were delivered by Pkl1 to mitotic SPBs, where Pkl1 was tethered through Msd1–Wdr8. The spindle-anchoring defect imposed by msd1/wdr8/pkl1 deletions was suppressed by a mutation of the plus end–directed Cut7/kinesin-5, which was shown to be mutual. Intriguingly, Pkl1 motor activity was not required for its anchoring role once targeted to the SPB. Therefore, spindle anchoring through Msd1–Wdr8–Pkl1 is crucial for balancing the Cut7/kinesin-5–mediated outward force at the SPB. Our analysis provides mechanistic insight into the spatiotemporal regulation of two opposing kinesins to ensure mitotic spindle bipolarity.

Potent Chitin Synthase Inhibitors from Plants

2020 ◽  
Vol 16 (1) ◽  
pp. 58-63
Author(s):  
Amrutha Vijayakumar ◽  
Ajith Madhavan ◽  
Chinchu Bose ◽  
Pandurangan Nanjan ◽  
Sindhu S. Kokkal ◽  
...  
Keyword(s):  
Cell Wall ◽  
Candida Albicans ◽  
Caenorhabditis Elegans ◽  
Aspergillus Niger ◽  
Small Molecules ◽  
Tip Growth ◽  
Chitin Synthase ◽  
Chitin Synthesis ◽  
Hyphal Tip Growth ◽  
Hyphal Tip

Background: Chitin is the main component of fungal, protozoan and helminth cell wall. They help to maintain the structural and functional characteristics of these organisms. The chitin wall is dynamic and is repaired, rearranged and synthesized as the cells develop. Active synthesis can be noticed during cytokinesis, laying of primary septum, maintenance of lateral cell wall integrity and hyphal tip growth. Chitin synthesis involves coordinated action of two enzymes namely, chitin synthase (that lays new cell wall) and chitinase (that removes the older ones). Since chitin synthase is conserved in different eukaryotic microorganisms that can be a ‘soft target’ for inhibition with small molecules. When chitin synthase is inhibited, it leads to the loss of viability of cells owing to the self- disruption of the cell wall by existing chitinase. Methods: In the described study, small molecules from plant sources were screened for their ability to interfere with hyphal tip growth, by employing Hyphal Tip Burst assay (HTB). Aspergillus niger was used as the model organism. The specific role of these small molecules in interfering with chitin synthesis was established with an in-vitro method. The enzyme required was isolated from Aspergillus niger and its activity was deduced through a novel method involving non-radioactively labelled substrate. The activity of the potential lead molecules were also checked against Candida albicans and Caenorhabditis elegans. The latter was adopted as a surrogate for the pathogenic helminths as it shares similarity with regard to cell wall structure and biochemistry. Moreover, it is widely studied and the methodologies are well established. Results: Out of the 11 compounds and extracts screened, 8 were found to be prospective. They were also found to be effective against Candida albicans and Caenorhabditis elegans. Conclusion: Purified Methyl Ethyl Ketone (MEK) Fraction1 (F1) of Coconut (Cocos nucifera) Shell Extract (COSE) was found to be more effective against Candida albicans with an IC50 value of 3.04 μg/mL and on L4 stage of Caenorhabditis elegans with an IC50 of 77.8 μg/mL.

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