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Microtubule rearrangements during mitosis in multinucleate cells
R Armas-Portela1, N Paweletz, H P Zimmermann
1Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg, Federal Republic of Germany.
Abstract:
The peroxidase-antiperoxidase (PAP) method for the detection of polymerized tubulin has been used to study the microtubule rearrangements during mitosis in PtK1 and HeLa multinucleate cells obtained by polyethyleneglycol (PEG)-mediated fusion. We demonstrate here that the transition of the microtubular cytoskeleton from interphase to mitosis is an inducible event and independent of the factor(s) responsible for chromatin condensation and nuclear envelope breakdown. However, for the induction of the microtubule rearrangements nuclear envelope breakdown is required. At midprophase, cytoskeletal microtubule rearrangements start for multinucleate PtK1 cells, whereas in HeLa cells such changes are delayed, and a more abrupt transition is observed here. After complete nuclear envelope breakdown (prometaphase) mitotic asters and spindles but no cytoplasmic (interphase) microtubuli can be observed in both systems. Metaphase is characterized by an interaction between the different mitotic poles which show the form of bipolar spindles, but individual separated mitotic poles far removed from the chromatin can also be seen.
Insights
Microtubule rearrangements during mitosis are inducible and require nuclear envelope breakdown. This study used the peroxidase-antiperoxidase (PAP) method to observe these cytoskeletal changes in fused multinucleate cells.
Area of Science:
- Cell Biology
- Cytoskeleton Dynamics
- Mitotic Processes
Background:
- Microtubules play a crucial role in cell division.
- Understanding microtubule rearrangements during mitosis is key to cell cycle regulation.
Purpose of the Study:
- To investigate microtubule rearrangements during mitosis in multinucleate cells.
- To determine the relationship between microtubule dynamics and nuclear events like envelope breakdown.
Main Methods:
- Utilized the peroxidase-antiperoxidase (PAP) method for detecting polymerized tubulin.
- Studied PtK1 and HeLa cells fused using polyethyleneglycol (PEG) to create multinucleate systems.
- Observed microtubule cytoskeleton changes during the transition from interphase to mitosis.
Main Results:
- Microtubule rearrangement is an inducible event, independent of chromatin condensation or initial nuclear envelope breakdown.
- Nuclear envelope breakdown is essential for initiating microtubule rearrangements.
- Timing of microtubule rearrangement differs between PtK1 and HeLa cells, with PtK1 showing earlier changes.
- Post-nuclear envelope breakdown, only mitotic structures (asters, spindles) are visible, not cytoplasmic microtubules.
- Metaphase displays interactions between mitotic poles forming bipolar spindles, with some poles detached from chromatin.
Conclusions:
- The transition to a mitotic microtubule cytoskeleton is inducible and linked to nuclear envelope breakdown.
- Cell-type specific differences exist in the timing of these mitotic rearrangements.
- The study provides insights into the orchestration of microtubule dynamics during cell division.