Abstract
The spindle assembly checkpoint (SAC) is a genome surveillance mechanism that protects against aneuploidization. Despite profound progress on understanding mechanisms of its activation, it remains unknown what aspect of chromosome–spindle interactions is monitored by the SAC: kinetochore–microtubule attachment or the force generated by dynamic microtubules that signals stable biorientation of chromosomes? To answer this, we uncoupled these two processes by expressing a non-phosphorylatable version of the main microtubule-binding protein at kinetochores (HEC1-9A), causing stabilization of incorrect kinetochore–microtubule attachments despite persistent activity of the error-correction machinery. The SAC is fully functional in HEC1-9A-expressing cells, yet cells in which chromosomes cannot biorient but are stably attached to microtubules satisfy the SAC and exit mitosis. SAC satisfaction requires neither intra-kinetochore stretching nor dynamic microtubules. Our findings support the hypothesis that in human cells the end-on interactions of microtubules with kinetochores are sufficient to satisfy the SAC without the need for microtubule-based pulling forces.
Highlights
The spindle assembly checkpoint (SAC) is a genome surveillance mechanism that protects against aneuploidization
Despite profound insights into the molecular mechanisms of SAC signalling gained in recent years[3], a fundamental question remains unresolved: what defect in spindle assembly is ‘sensed’ by the SAC? Lack of kinetochore–microtubule attachment, absence of the force generated by dynamic microtubules that signals stable biorientation of chromosomes, or both? various studies have addressed this[4,5,6,7,8,9,10,11,12,13], a consensus has not been reached[14,15,16]
We used our previously published HEC1 reconstitution system in which green fluorescent protein (GFP)-HEC1 variants are expressed from a conditional promoter in an isogenic background of HeLa-FlpIn cells[34]
Summary
The spindle assembly checkpoint (SAC) is a genome surveillance mechanism that protects against aneuploidization. Despite profound progress on understanding mechanisms of its activation, it remains unknown what aspect of chromosome–spindle interactions is monitored by the SAC: kinetochore–microtubule attachment or the force generated by dynamic microtubules that signals stable biorientation of chromosomes? Distance between sister kinetochores (‘tension’) was often used as a proxy for a state of stable biorientation required to satisfy the SAC, but recent findings indicate that this may not be a valid assumption[17,18]. These studies have inspired current models that invoke tension within a kinetochore, generated by microtubule-pulling forces, as the signal that satisfies the SAC. Our findings indicate that stable end-on microtubule attachments are sufficient to silence the SAC
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
