Mechanical load-bearing mechanisms in the human kinetochore

Programme overview:
This MRC-funded doctoral training partnership (DTP) brings together cutting-edge molecular and analytical sciences with innovative computational approaches in data analysis to enable students to address hypothesis-led biomedical research questions. This is a 4-year programme whose first year involves a series of taught modules and two laboratory-based research projects that lead to an MSc in Interdisciplinary Biomedical Research. The first two terms consist of a selection of taught modules that allow students to gain a solid grounding in multidisciplinary science. Students also attend a series of masterclasses led by academic and industry experts in areas of molecular, cellular and tissue dynamics, microbiology and infection, applied biomedical technologies and artificial intelligence and data science. During the third and summer terms students conduct two eleven-week research projects in labs of their choice.

Project:
Equal segregation of duplicated chromosomes (sister chromatids) in mitosis is essential for all living organisms. Errors in this process can be detrimental as they are a cause of chromosomal instability, aneuploidy and tumorigenesis. In order to accomplish segregation, chromosomes need to first align at the cell equator, a process termed congression. However, the mechanisms underlying chromosome motions in mitosis remain poorly understood.

Congression is achieved by 'depolymerisation-coupled pulling' (DCP) of chromosomes by the interaction of a multi-protein complex assembled on each chromatid - the kinetochore, with dynamic microtubules of the mitotic spindle. The spindle and kinetochore-associated (Ska) complex provides mechanical load-bearing support in this process and its loss causes attachment failure at high microtubule pulling forces (event named flipping). Flipping is also observed in normal cells, suggesting that it acts as a mechanical self-check. Furthermore, modulation of the microtubule-binding affinity of Ska by the error-correction machinery is important for formation of correct attachments (attachment of the kinetochores in a sister pair to microtubules from opposite spindle poles). Moreover, Ska is targeted to the kinetochore by Ndc80, which is also important for establishment of attachments and modulated in error-correction.

An open question remains how the two complexes cooperate to mediate microtubule attachment and load bearing, and how error correction and mechanical self-check processes are coordinated. This PhD project will tackle this problem using high spatiotemporal resolution imaging of congressing kinetochores with fluorescently labelled endogenous Ska to investigate the relation between Ska kinetochore recruitment and kinetochore flipping. In addition, to further understand the mechanical and chemical signals that govern Ska and Ndc80 action, we use a combination of multi-channel imaging and computational analysis to reveal the in vivo nano-scale architecture of the Ska complex and Ndc80 in response to force, attachment and modulation (phosphorylation).