Spindle Poisons and Cell Fate: A Tale of Two Pathways
Figure 1
The spindle assembly checkpoint (SAC) controls the metaphase to anaphase transition
By inhibiting the degradation of cyclin B by the anaphase promoting complex/cyclosome (APC/C), the SAC arrests the cell in metaphase until all kinetochores are attached to spindle microtubules. A. In the absence of microtubule attachments, unattached kinetochores recruit checkpoint proteins and activate them, allowing Mad2, Bub3, and BubR1 to inhibit Cdc20 activation of APC/C, resulting in high amounts cyclin B and metaphase arrest. B. When all kinetochores have proper microtubule attachments, checkpoint proteins are no longer recruited to kinetochores and Cdc20 activates APC/C, which drives cyclin B degradation. Depletion of cyclin B causes anaphase onset.
