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Loss of mitotic centrosomal microtubule initiation capacity at the metaphase-anaphase transition
Abstract:
The microtubule initiation capacity of the mitotic centrosome was studied in PtK1 cells by using the highly reversible microtubule inhibitor nocodazole. Cells blocked with nocodazole at any stage prior to onset of anaphase completed mitosis by reforming the spindle following release from the drug. Cells treated with nocodazole immediately upon onset of sister chromatid separation and then released did not complete mitosis, but instead progressed directly to an interphase state. This anaphase-linked transition in response to treatment was clearly evident as a change in centrosomal microtubule initiation capacity coincident with commencement of sister chromatid separation. Cells blocked in very late metaphase and then released were found to have retained the enhanced centrosomal microtubule initiation capacity characteristic of early mitosis. Cells blocked after the beginning of anaphase and then released, however, displayed dramatically reduced centrosomal microtubule initiation capacity. Mitotic cells blocked with colcemid or nocodazole and lysed into microtubule protein containing buffers also exhibited stage-specific differences in their ability to initiate microtubule in the centrosomal region. Cells blocked prior to anaphase onset and lysed into microtubule protein nucleated a number of microtubules typical of that found in a metaphase aster; anaphase cells nucleated substantially fewer microtubules.
Insights
The study reveals that the centrosome
Area of Science:
- Cell Biology
- Molecular Biology
- Cytoskeleton Dynamics
Background:
- The centrosome acts as the primary microtubule-organizing center during mitosis.
- Centrosome microtubule initiation capacity is crucial for proper spindle formation and chromosome segregation.
- Understanding stage-specific changes in centrosome function is key to comprehending cell cycle regulation.
Purpose of the Study:
- To investigate the dynamic changes in microtubule initiation capacity of the mitotic centrosome in PtK1 cells.
- To determine the relationship between cell cycle stage, particularly anaphase onset, and centrosome function.
- To elucidate the molecular mechanisms underlying the regulation of centrosomal microtubule nucleation.
Main Methods:
- Utilized the reversible microtubule inhibitor nocodazole to block PtK1 cells at specific mitotic stages.
- Observed cell cycle progression and spindle reformation upon release from nocodazole treatment.
- Assessed centrosomal microtubule initiation capacity by lysing cells in microtubule protein-rich buffers and quantifying microtubule nucleation.
Main Results:
- Cells released from nocodazole block before anaphase completed mitosis and reformed spindles.
- Cells treated at anaphase onset and released failed to complete mitosis, entering an interphase state.
- Centrosomal microtubule initiation capacity decreased significantly after the onset of anaphase, as evidenced by reduced microtubule nucleation in lysed cells.
Conclusions:
- Centrosome microtubule initiation capacity undergoes a significant, anaphase-linked reduction.
- This reduction in nucleation ability is a critical factor influencing cell cycle progression after sister chromatid separation.
- The findings highlight stage-specific regulation of centrosome function during mitosis.