Contents I. II. III. IV. V. VI. VII. VIII. IX.
Cytoskeletal microtubules (
Microtubules are severed by katanin at distinct cellular locations to facilitate reorientation or amplification of dynamic microtubule arrays, but katanin targeting mechanisms are poorly understood. Here we show that a centrosomal microtubule-anchoring complex is used to recruit katanin in acentrosomal plant cells. The conserved protein complex of Msd1 (also known as SSX2IP) and Wdr8 is localized at microtubule nucleation sites along the microtubule lattice in interphase Arabidopsis cells. Katanin is recruited to these sites for efficient release of newly formed daughter microtubules. Our cell biological and genetic studies demonstrate that Msd1-Wdr8 acts as a specific katanin recruitment factor to cortical nucleation sites (but not to microtubule crossover sites) and stabilizes the association of daughter microtubule minus ends to their nucleation sites until they become severed by katanin. Molecular coupling of sequential anchoring and severing events by the evolutionarily conserved complex renders microtubule release under tight control of katanin activity.
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Cytoskeletal microtubules (
Pits are regions in the cell walls of plant tracheary elements that lack secondary walls. Each pit consists of a space within the secondary wall called a pit chamber, and a modified primary wall called the pit membrane. The pit membrane facilitates transport of solutions between vessel cells and restricts embolisms during drought. Here we analyzed the role of an angiosperm‐specific TPX2‐like microtubule protein MAP20 in pit formation using Live cell imaging was used to analyze the interaction of MAP20 with microtubules and the impact of MAP20 on microtubule dynamics. MAP20‐specific antibody was used to study expression and localization of MAP20 in different cell types during vascular bundle development. We used an artificial microRNAs (amiRNA) knockdown approach to determine the function of MAP20 is expressed during the late stages of vascular bundle development and localizes around forming pits and under secondary cell wall thickenings in metaxylem cells. MAP20 suppresses microtubule depolymerization; however, unlike the animal TPX2 counterpart, MAP20 does not cooperate with the γ‐tubulin ring complex in microtubule nucleation. Knockdown of We conclude that
A central question in eukaryotic cell biology asks, during cell division, how is the growth and distribution of organelles regulated to ensure each daughter cell receives an appropriate amount. For vacuoles in budding yeast, there are well described organelle-to-cell size scaling trends as well as inheritance mechanisms involving highly coordinated movements. It is unclear whether such mechanisms are necessary in the symmetrically dividing fission yeast,
Microtubule reorganization often results from the loss of polymer induced through breakage or active destruction by energy‐using enzymes. Pre‐existing defects in the microtubule lattice likely lower structural integrity and aid filament destruction. Using large‐scale molecular simulations, we model diverse microtubule fragments under forces generated at specific positions to locally crush the filament. We show that lattices with 2% defects are crushed and severed by forces three times smaller than defect‐free ones. We validate our results with direct comparisons of microtubule kinking angles during severing. We find a high statistical correlation between the angle distributions from experiments and simulations indicating that they sample the same population of structures. Our simulations also indicate that the mechanical environment of the filament affects breaking: local mechanical support inhibits healing after severing, especially in the case of filaments with defects. These results recall reports of microtubule healing after flow‐induced bending and corroborate prior experimental studies that show severing is more likely at locations where microtubules crossover in networks. Our results shed new light on mechanisms underlying the ability of microtubules to be destroyed and healed in the cell, either by external forces or by severing enzymes wedging dimers apart. © 2016 Wiley Periodicals, Inc.