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The spindle checkpoint, also known as the metaphase-to-anaphase transition, the spindle assembly checkpoint (SAC), the metaphase checkpoint, or the mitotic checkpoint, is a cell cycle checkpoint during metaphase of mitosis or meiosis that prevents the separation of the duplicated chromosomes until each chromosome is properly attached to the ...
The mitotic spindle checkpoint occurs at the point in metaphase where all the chromosomes should/have aligned at the mitotic plate and be under bipolar tension. The tension created by this bipolar attachment is what is sensed, which initiates the anaphase entry.
The mitotic spindle checkpoint verifies that all the chromosomes are aligned properly on the metaphase plate and prevents premature entry into anaphase. Chromosomes lined up on the metaphase plate. Two views with the metaphase plate rotated 60°. Stages of early mitosis in a vertebrate cell with micrographs of chromatids
The metaphase checkpoint is a fairly minor checkpoint, in that once a cell is in metaphase, it has committed to undergoing mitosis. However that's not to say it isn't important. In this checkpoint, the cell checks to ensure that the spindle has formed and that all of the chromosomes are aligned at the spindle equator before anaphase begins. [49]
The G1/S checkpoint, G2/M checkpoint, and the checkpoint between metaphase and anaphase all monitor for DNA damage and halt cell division by inhibiting different cyclin-CDK complexes. The p53 tumor-suppressor protein plays a crucial role at the G1/S checkpoint and the G2/M checkpoint. Activated p53 proteins result in the expression of many ...
As metaphase begins, the spindle checkpoint inhibits the APC/C until all sister-kinetochores are attached to opposite poles of the mitotic spindle, a process known as chromosome biorientation. When all kinetochores are properly attached, the spindle checkpoint is silenced and the APC/C can become active.
The spindle checkpoint system is a regulatory system that restrains progression through the metaphase-to-anaphase transition. The Mad2 gene was first identified in the yeast S. cerevisiae in a screen for genes which when mutated would confer sensitivity to microtubule poisons. [ 1 ]
Colchicine arrests cells in metaphase and is a microtubule poison preventing mitotic spindle formation, much like nocodazole. It works by depolymerizing tubulin in microtubules, blocking progression to anaphase through sustained arrest at the spindle assembly checkpoint.