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An inner centromere protein that stimulates the microtubule depolymerizing activity of a KinI kinesin
Ryoma Ohi1, Margaret L Coughlin, William S Lane
1Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA. ryoma_ohi@hms.harvard.edu
Abstract:
Mitosis requires precise control of microtubule dynamics. The KinI kinesin MCAK, a microtubule depolymerase, is critical for this regulation. In a screen to discover previously uncharacterized microtubule-associated proteins, we identified ICIS, a protein that stimulates MCAK activity in vitro. Consistent with this biochemical property, blocking ICIS function in Xenopus extracts with antibodies caused excessive microtubule growth and inhibited spindle formation. Prior to anaphase, ICIS localized in an MCAK-dependent manner to inner centromeres, the chromosomal region located in between sister kinetochores. From Xenopus extracts, ICIS coimmunoprecipitated MCAK and the inner centromere proteins INCENP and Aurora B, which are thought to promote chromosome biorientation. By immunoelectron microscopy, we found that ICIS is present on the surface of inner centromeres, placing it in an ideal location to depolymerize microtubules associated laterally with inner centromeres. At inner centromeres, MCAK-ICIS may destabilize these microtubules and provide a mechanism that prevents kinetochore-microtubule attachment errors.
Insights
Researchers discovered ICIS, a protein that enhances microtubule depolymerase MCAK activity. This finding is crucial for regulating cell division (mitosis) and preventing errors in chromosome attachment during cell division.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Precise control of microtubule dynamics is essential for accurate mitosis.
- The KinI kinesin MCAK is a key microtubule depolymerase regulating these dynamics.
Purpose of the Study:
- To identify novel microtubule-associated proteins.
- To investigate the function of the newly identified protein ICIS in mitosis and its interaction with MCAK.
Main Methods:
- Biochemical assays to test ICIS activity on MCAK.
- Xenopus egg extracts to study microtubule dynamics and spindle formation.
- Immunoelectron microscopy to determine protein localization.
Main Results:
- ICIS was identified as a protein that stimulates MCAK activity in vitro.
- Blocking ICIS function in Xenopus extracts led to excessive microtubule growth and impaired spindle formation.
- ICIS localized to inner centromeres in an MCAK-dependent manner and co-immunoprecipitated with MCAK, INCENP, and Aurora B.
Conclusions:
- ICIS is a novel regulator of microtubule depolymerization by MCAK.
- ICIS plays a critical role in preventing kinetochore-microtubule attachment errors during mitosis.
- The MCAK-ICIS complex at inner centromeres likely destabilizes microtubules to ensure proper chromosome segregation.