Functional organisation of the human kinetochore and roles of the Ska complex

Accurate chromosome segregation demands that sister kinetochores form force- generating attachments to microtubules nucleated from opposite poles of the mi- totic spindle (Bi-orientation). Kinetochores are assembled form hundreds of protein components with the Ndc80 complex providing the main attachment activity, and auxiliary load bearing provided by the Ska complex. Bi-orientation is monitored by the spindle assembly checkpoint (SAC) and catalysed by error correction processes that detect and eliminate incorrect attachments. However, our understanding of how the kinetochore is organised in vivo, and how this structure adapts to chemical and mechanical stimuli is poorly understood. This will be crucial to understanding how the SAC and error correction systems operate. Here, in collaboration with the Burroughs Lab, we developed a method for measuring the 3D euclidian-corrected distances between kinetochore components (_EC). We have used this approach to map the 3D architecture of the human kinetochore. We also show that the Ndc80 complex jack-knifes at unattached kinetochores and how this is coordinated with SAC signalling. Our data support a model by which jack-knifing initiates after SAC silencing, and completes as the final checkpoint proteins unbind. We further used endogenously labeled Ska to provide evidence of how the Ska complex is flexibly linked to Ndc80 in vivo. These data provide a blueprint for the human kinetochore and new insight into how structural adaption is coupled to checkpoint and error correction processes