Abstract
Microtubules are filaments composed of dimers of alpha- and beta-tubulins, which have a variety of functions in living cells. In fungi, the spindle pole bodies usually have been considered to be microtubule-organizing centers. We used the antimicrotubule drug Benomyl in block/release experiments to depolymerize and repolymerize microtubules in Aspergillus nidulans germlings to learn more about the microtubule nucleation process in this filamentous fungus. Twenty seconds after release from Benomyl short microtubules were formed from several bright (immunofluorescent) dots distributed along the germlings, suggesting that microtubule nucleation is randomly distributed in A. nidulans germlings. Since nuclear movement is dependent on microtubules in A. nidulans we analyzed whether mutants defective in nuclear distribution along the growing hyphae (nud mutants) have some obvious microtubule defect. Cytoplasmic, astral and spindle microtubules were present and appeared to be normal in all nud mutants. However, significant changes in the percentage of short versus long mitotic spindles were observed in nud mutants. This suggests that some of the nuclei of nud mutants do not reach the late stage of cell division at normal temperatures.
Highlights
Aspergillus nidulans is a filamentous fungus of considerable biological interest and importance that provides an excellent model system for genetic and biochemical analysis of microtubule-associated functions (MartinezRossi and Azevedo, 1989a,b; Andrade-Monteiro et al, 1994), among them mitosis and nuclear migration
Since nuclear movement has been shown to be dependent on microtubules in A. nidulans, we analyzed whether mutants defective in nuclear distribution along the growing hyphae had some obvious microtubule defect
To allow microtubule repolymerization and to observe regions of microtubule nucleation in A. nidulans, germlings previously exposed to Benomyl for 90 min were transferred to Benomyl-free YG medium
Summary
Aspergillus nidulans is a filamentous fungus of considerable biological interest and importance that provides an excellent model system for genetic and biochemical analysis of microtubule-associated functions (MartinezRossi and Azevedo, 1989a,b; Andrade-Monteiro et al, 1994), among them mitosis and nuclear migration.Microtubules are filaments composed of dimers of alpha- and beta-tubulins implicated in a variety of functions, including ciliary and flagellar movements, cell motility and cytoplasmic streaming, nucleus and chromosome movement, maintenance of cell shape, intracellular and axoplasmic transport, and anchorage of cell surface receptors (Mandelkow and Mandelkow, 1994). Xiang et al (1994) have shown that a microtubule-associated mechanochemical ATPase protein, cytoplasmic dynein, is involved in nuclear movement in A. nidulans. We carried out block/release experiments to depolymerize and repolymerize microtubules by using the antimicrotubule drug Benomyl in order to understand the microtubule nucleation process in A. nidulans germlings.
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