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NuMA assembles into an extensive filamentous structure when expressed in the cell cytoplasm
A Saredi1, L Howard, D A Compton
1Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA.
Journal of Cell Science
|March 1, 1996
Summary
Nuclear protein NuMA (NuMA) can form extensive filamentous structures in the cytoplasm, even when its nuclear localization sequence is deleted. This suggests NuMA plays a structural role in both interphase and mitosis.
Area of Science:
- Cell Biology
- Molecular Biology
- Cytoskeleton Dynamics
Background:
- Nuclear protein NuMA (NuMA) is crucial for mitotic spindle organization.
- NuMA typically localizes to the nucleus during interphase.
Purpose of the Study:
- To investigate the consequences of mislocalizing NuMA to the cytoplasm during mitosis.
- To determine if NuMA can form structures outside the nucleus.
Main Methods:
- Site-directed mutagenesis to delete NuMA's nuclear localization sequence (NuMA-DeltaNLS).
- Transient expression of NuMA-DeltaNLS in BHK-21 cells.
- Transmission electron microscopy (TEM) and flow cytometry for structural analysis.
Main Results:
- NuMA-DeltaNLS accumulated in the cytoplasm as a large mass.
- This cytoplasmic NuMA associated with the mitotic spindle without impairing mitosis.
- TEM revealed NuMA-DeltaNLS formed extensive 5 nm filaments organized into 23 nm cables by microtubules.
- Isolated structures were composed solely of NuMA filaments.
Conclusions:
- NuMA can self-assemble into extensive filamentous structures outside the nucleus.
- These findings support a potential structural role for NuMA in interphase or at the mitotic spindle poles.