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Chromosome mal-orientation and reorientation during mitosis
1Wadsworth Center for Labs and Research, Albany, New York 12201-0509.
Abstract:
We argue that mal-orientation of mitotic chromosomes is not as rare as once believed. However, unlike bivalents during meiosis I, the reorientation of a mal-oriented mitotic chromosome has yet to be observed. This appears to be due, in part, to the difficulty in differentiating mal-oriented chromosomes from mono-oriented ones which are common during spindle formation in living mitotic cells. We assume that mitotic cells possess mechanisms for correcting chromosome mal-orientations that are similar to those operating during meiosis. However, unlike meiosis, where reorientation appears to be triggered when tension on a K-fiber is relieved or reduced, other factors related to the close proximity of sister kinetochores may also induce reorientation in mal-oriented mitotic chromosomes. We favor a model in which the reorientation of a mitotic kinetochore depends on, and is initiated by, the kinetochore capturing MTs from the pole to which it is reorienting.
Insights
Chromosome mal-orientation in mitosis is more common than previously thought. While reorientation mechanisms are assumed to exist, they are difficult to observe and may involve sister kinetochore proximity.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- Chromosome mal-orientation during mitosis is considered rare.
- Reorientation of mal-oriented mitotic chromosomes has not been directly observed.
- Distinguishing mal-oriented from mono-oriented chromosomes in live cells is challenging.
Purpose of the Study:
- To investigate the frequency and mechanisms of chromosome mal-orientation correction in mitosis.
- To propose a model for mitotic chromosome reorientation.
Main Methods:
- Observational studies of chromosome behavior during mitosis.
- Analysis of kinetochore-microtubule interactions.
- Comparison with mechanisms of chromosome reorientation during meiosis.
Main Results:
- Mitotic chromosome mal-orientation is likely more frequent than previously assumed.
- Reorientation of mal-oriented mitotic chromosomes is difficult to observe due to challenges in distinguishing them from mono-oriented chromosomes.
- Proposed model suggests reorientation is dependent on and initiated by kinetochore capture of microtubules from the reorienting pole.
Conclusions:
- Mitotic cells likely possess mechanisms to correct chromosome mal-orientations, potentially similar to meiotic processes.
- Factors beyond tension relief, such as sister kinetochore proximity, may influence mitotic reorientation.
- The proposed model highlights the role of microtubule capture in initiating mitotic kinetochore reorientation.