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Fine structural studies of early mitotic stages in untreated and nocodazole-treated HeLa cells
1Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg, Federal Republic of Germany.
Abstract:
When cells in mitosis are treated with nocodazole, a microtubule-disrupting drug, it can be shown in comparison to untreated cells that microtubules are responsible for the polarized formation of indentations, folds, tubes, and crypts of the nuclear envelope in prophase nuclei. No translocation of chromosomes within the nucleus takes place. Microtubules are not necessary for chromosome condensation, nuclear envelope breakdown, the formation of trilaminar kinetochores, and the orientation of sister-kinetochores within one chromosome in relation to each other. The orientation of kinetochores in relation to the mitotic poles, however, is mediated by microtubules. The data shown here support the working hypothesis about chromosome translocation in prophase nuclei which was presented in an earlier paper.
Insights
Microtubules are crucial for shaping the nuclear envelope during cell division (mitosis) but do not move chromosomes. They guide kinetochore orientation towards mitotic poles, supporting prior hypotheses.
Area of Science:
- Cell Biology
- Molecular Biology
- Cytoskeleton Dynamics
Background:
- The role of microtubules in nuclear envelope dynamics during mitosis is not fully understood.
- Nocodazole, a microtubule-disrupting agent, provides a tool to investigate microtubule functions.
Purpose of the Study:
- To elucidate the specific roles of microtubules in nuclear envelope morphogenesis during prophase.
- To determine the necessity of microtubules for various stages of mitosis, including chromosome condensation and kinetochore organization.
Main Methods:
- Comparative analysis of cellular structures in mitotic cells treated with nocodazole versus untreated control cells.
- Microscopic observation to assess nuclear envelope morphology and chromosome behavior.
Main Results:
- Microtubules are essential for the polarized formation of nuclear envelope indentations, folds, tubes, and crypts in prophase.
- Microtubules are not required for chromosome condensation, nuclear envelope breakdown, or trilaminar kinetochore formation.
- Microtubules mediate the orientation of kinetochores relative to mitotic poles, but not sister-kinetochore orientation within a chromosome.
- Chromosome translocation within the nucleus does not occur under these experimental conditions.
Conclusions:
- Microtubules play a critical role in establishing the complex architecture of the nuclear envelope during early mitosis.
- Microtubule-dependent kinetochore orientation is vital for proper mitotic spindle alignment.
- Findings support a previously proposed hypothesis regarding chromosome translocation in prophase nuclei.