The Molecular Function of Ase1p: Evidence for a MAP-Dependent Midzone-Specific Spindle Matrix

The midzone is the domain of the mitotic spindle that maintains spindle bipolarity during anaphase and generates forces required for spindle elongation (anaphase B). Although there is a clear role for microtubule (MT) motor proteins at the spindle midzone, less is known about how microtubule-associa...

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Bibliographic Details
Published in:The Journal of cell biology 2003-02, Vol.160 (4), p.517-528
Main Authors: Schuyler, Scott C., Liu, Jenny Y., Pellman, David
Format: Article
Language:English
Subjects:
Anaphase
Cell cycle
Cells
Fluorescence
Matrix
Microtubules
Mitosis
Mitotic spindle apparatus
Molecules
Saccharomycetales
Spindle pole body
Yeasts
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Summary:The midzone is the domain of the mitotic spindle that maintains spindle bipolarity during anaphase and generates forces required for spindle elongation (anaphase B). Although there is a clear role for microtubule (MT) motor proteins at the spindle midzone, less is known about how microtubule-associated proteins (MAPs) contribute to midzone organization and function. Here, we report that budding yeast Ase1p is a member of a conserved family of midzone-specific MAPs. By size exclusion chromatography and velocity sedimentation, both Ase1p in extracts and purified Ase1p behaved as a homodimer. Ase1p bound and bundled MTs in vitro. By live cell microscopy, loss of Ase1p resulted in a specific defect: premature spindle disassembly in mid-anaphase. Furthermore, when overexpressed, Ase1p was sufficient to trigger spindle elongation in S phase-arrested cells. FRAP revealed that Ase1p has both a very slow rate of turnover within the midzone and limited lateral diffusion along spindle MTs. We propose that Ase1p functions as an MT cross-bridge that imparts matrix-like characteristics to the midzone. MT-dependent networks of spindle midzone MAPs may be one molecular basis for the postulated spindle matrix.
ISSN:0021-9525
1540-8140
DOI:10.1083/jcb.200210021