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Mobility, microtubule nucleation and structure of microtubule-organizing centers in multinucleated hyphae of Ashbya gossypii.

Lang C, Grava S, van den Hoorn T, Trimble R, Philippsen P, Jaspersen SL - Mol. Biol. Cell (2009)

Bottom Line: This latter mode is sufficient to support wild-type-like hyphal growth speeds. cMT-dependent nuclear movements were led by a nuclear-associated microtubule-organizing center, the spindle pole body (SPB), which is the sole site of microtubule nucleation in A. gossypii.Analysis of A. gossypii SPBs by electron microscopy revealed an overall laminar structure similar to the budding yeast SPB but with distinct differences at the cytoplasmic side.Each SPB nucleates its own array of cMTs, and the lack of overlapping cMT arrays between neighboring nuclei explains the autonomous nuclear oscillations and bypassing observed in A. gossypii hyphae.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Microbiology, Biozentrum University of Basel, 4056 Basel, Switzerland.

ABSTRACT
We investigated the migration of multiple nuclei in hyphae of the filamentous fungus Ashbya gossypii. Three types of cytoplasmic microtubule (cMT)-dependent nuclear movements were characterized using live cell imaging: short-range oscillations (up to 4.5 microm/min), rotations (up to 180 degrees in 30 s), and long-range nuclear bypassing (up to 9 microm/min). These movements were superimposed on a cMT-independent mode of nuclear migration, cotransport with the cytoplasmic stream. This latter mode is sufficient to support wild-type-like hyphal growth speeds. cMT-dependent nuclear movements were led by a nuclear-associated microtubule-organizing center, the spindle pole body (SPB), which is the sole site of microtubule nucleation in A. gossypii. Analysis of A. gossypii SPBs by electron microscopy revealed an overall laminar structure similar to the budding yeast SPB but with distinct differences at the cytoplasmic side. Up to six perpendicular and tangential cMTs emanated from a more spherical outer plaque. The perpendicular and tangential cMTs most likely correspond to short, often cortex-associated cMTs and to long, hyphal growth-axis-oriented cMTs, respectively, seen by in vivo imaging. Each SPB nucleates its own array of cMTs, and the lack of overlapping cMT arrays between neighboring nuclei explains the autonomous nuclear oscillations and bypassing observed in A. gossypii hyphae.

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Two types of cMTs in A. gossypii. (A) EM micrograph of a hyphal thin section showing a nucleus with its SPB near the cell cortex. (B) Magnified view of the cortex region with a perpendicular cMT (arrows) ending at the cell cortex and two cMTs (asterisks) tangential to the nucleus and parallel to the hyphal axis (center). (C) Graphic presentation of the SPB and the emanating cMTs shown in B. Bars, 500 nm.
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Figure 8: Two types of cMTs in A. gossypii. (A) EM micrograph of a hyphal thin section showing a nucleus with its SPB near the cell cortex. (B) Magnified view of the cortex region with a perpendicular cMT (arrows) ending at the cell cortex and two cMTs (asterisks) tangential to the nucleus and parallel to the hyphal axis (center). (C) Graphic presentation of the SPB and the emanating cMTs shown in B. Bars, 500 nm.

Mentions: We observed cMTs that are nucleated perpendicularly to the SPB OP. At least some of these perpendicular cMTs could be tracked to a region near the cell cortex (Figure 8). We suspect that these microtubules correspond to the short microtubules we observed by live cell imaging of GFP-AgTub1–labeled cells. In addition we also observed tangential microtubules extending into the hyphal cytoplasm parallel to the growth axis (Figure 8). This later class of microtubules has not been observed in S. cerevisiae and might account for some of the differences in nuclear dynamics and cytoskeletal organization between the two organisms. The observation that tangential cMTs run in parallel to the hyphal cortex is consistent with the idea that they correspond to the long microtubules that elongate along the polarity-axis as observed by GFP-AgTub1-labeled strains.


Mobility, microtubule nucleation and structure of microtubule-organizing centers in multinucleated hyphae of Ashbya gossypii.

Lang C, Grava S, van den Hoorn T, Trimble R, Philippsen P, Jaspersen SL - Mol. Biol. Cell (2009)

Two types of cMTs in A. gossypii. (A) EM micrograph of a hyphal thin section showing a nucleus with its SPB near the cell cortex. (B) Magnified view of the cortex region with a perpendicular cMT (arrows) ending at the cell cortex and two cMTs (asterisks) tangential to the nucleus and parallel to the hyphal axis (center). (C) Graphic presentation of the SPB and the emanating cMTs shown in B. Bars, 500 nm.
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Related In: Results  -  Collection

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Figure 8: Two types of cMTs in A. gossypii. (A) EM micrograph of a hyphal thin section showing a nucleus with its SPB near the cell cortex. (B) Magnified view of the cortex region with a perpendicular cMT (arrows) ending at the cell cortex and two cMTs (asterisks) tangential to the nucleus and parallel to the hyphal axis (center). (C) Graphic presentation of the SPB and the emanating cMTs shown in B. Bars, 500 nm.
Mentions: We observed cMTs that are nucleated perpendicularly to the SPB OP. At least some of these perpendicular cMTs could be tracked to a region near the cell cortex (Figure 8). We suspect that these microtubules correspond to the short microtubules we observed by live cell imaging of GFP-AgTub1–labeled cells. In addition we also observed tangential microtubules extending into the hyphal cytoplasm parallel to the growth axis (Figure 8). This later class of microtubules has not been observed in S. cerevisiae and might account for some of the differences in nuclear dynamics and cytoskeletal organization between the two organisms. The observation that tangential cMTs run in parallel to the hyphal cortex is consistent with the idea that they correspond to the long microtubules that elongate along the polarity-axis as observed by GFP-AgTub1-labeled strains.

Bottom Line: This latter mode is sufficient to support wild-type-like hyphal growth speeds. cMT-dependent nuclear movements were led by a nuclear-associated microtubule-organizing center, the spindle pole body (SPB), which is the sole site of microtubule nucleation in A. gossypii.Analysis of A. gossypii SPBs by electron microscopy revealed an overall laminar structure similar to the budding yeast SPB but with distinct differences at the cytoplasmic side.Each SPB nucleates its own array of cMTs, and the lack of overlapping cMT arrays between neighboring nuclei explains the autonomous nuclear oscillations and bypassing observed in A. gossypii hyphae.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Microbiology, Biozentrum University of Basel, 4056 Basel, Switzerland.

ABSTRACT
We investigated the migration of multiple nuclei in hyphae of the filamentous fungus Ashbya gossypii. Three types of cytoplasmic microtubule (cMT)-dependent nuclear movements were characterized using live cell imaging: short-range oscillations (up to 4.5 microm/min), rotations (up to 180 degrees in 30 s), and long-range nuclear bypassing (up to 9 microm/min). These movements were superimposed on a cMT-independent mode of nuclear migration, cotransport with the cytoplasmic stream. This latter mode is sufficient to support wild-type-like hyphal growth speeds. cMT-dependent nuclear movements were led by a nuclear-associated microtubule-organizing center, the spindle pole body (SPB), which is the sole site of microtubule nucleation in A. gossypii. Analysis of A. gossypii SPBs by electron microscopy revealed an overall laminar structure similar to the budding yeast SPB but with distinct differences at the cytoplasmic side. Up to six perpendicular and tangential cMTs emanated from a more spherical outer plaque. The perpendicular and tangential cMTs most likely correspond to short, often cortex-associated cMTs and to long, hyphal growth-axis-oriented cMTs, respectively, seen by in vivo imaging. Each SPB nucleates its own array of cMTs, and the lack of overlapping cMT arrays between neighboring nuclei explains the autonomous nuclear oscillations and bypassing observed in A. gossypii hyphae.

Show MeSH
Related in: MedlinePlus