Joined at the hip: kinetochores, microtubules, and spindle assembly checkpoint signaling

• The SAC monitors connections between chromosomes and the spindle to ensure faithful chromosome segregation.
• The SAC machinery is directly coupled to the microtubule-binding network on mitotic kinetochores.
• Much knowledge has been gained about the molecular mechanisms and regulation of this coupling.
• These mechanisms provide clues about how the SAC can be extinguished on microtubule capture by kinetochores.

Error-free chromosome segregation relies on stable connections between kinetochores and spindle microtubules. The spindle assembly checkpoint (SAC) monitors such connections and relays their absence to the cell cycle machinery to delay cell division. The molecular network at kinetochores that is responsible for microtubule binding is integrated with the core components of the SAC signaling system. Molecular-mechanistic understanding of how the SAC is coupled to the kinetochore–microtubule interface has advanced significantly in recent years. The latest insights not only provide a striking view of the dynamics and regulation of SAC signaling events at the outer kinetochore but also create a framework for understanding how that signaling may be terminated when kinetochores and microtubules connect.