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Title: Functional analysis of heterochromatin protein 1-driven localisation and activity of the chromosomal passenger complex
Author: Ruppert, Jan Gustav
ISNI:       0000 0004 7654 3124
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2018
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The ultimate goal of mitosis is the equal distribution of chromosomes between the two daughter cells. One of the key players that ensures faithful chromosome segregation is the chromosomal passenger complex (CPC). CPC localisation to mitotic centromeres is complex, involving interactions with Shugoshin and binding to phosphorylated histone H3T3. It was recently reported that Heterochromatin Protein 1 (HP1) has a positive impact on CPC function during mitosis. The interaction between HP1 and the CPC appears to be perturbed in cancer-­‐derived cell lines, resulting in decreased HP1 levels at mitotic centromeres and may be a potential cause for increased chromosome mis-­‐segregation rates. In this study, I tethered HP1α to centromeres via the DNA-­‐binding domain CENP-­‐B. However, instead of improving the rate of chromosome mis-­‐segregation, HP1α tethering resulted in activity of the spindle assembly checkpoint and destabilisation of kinetochore-­‐microtubule attachments, most likely caused by the robust recruitment of the CPC. Tethered HP1α even traps the CPC at centromeres during mitotic exit, resulting in a catalytically active CPC throughout interphase. However, it was not clear whether endogenous HP1 contributes to CPC localisation and function prior to mitosis. Here I also describe a substantial interaction between endogenous HP1 and the CPC during the G2 stage of the cell cycle. The two isoforms HP1α and HP1γ contribute to the clustering of the CPC into active foci in G2 cells, a process that is independent of CDK1 kinase activity. Furthermore, the H3S10ph focus formation in the G2 phase appears to be independent of H3T3ph and H2AT120ph, the two histone marks that determine the CPC localisation in early mitosis. Together, my results indicate that HP1 contributes to CPC concentration and activation at pericentromeric heterochromatin in G2. This novel mode of CPC localisation occurs before the Aurora B-­‐driven methyl/phos switch releases HP1 from chromatin, which possibly enables the H3T3ph and H2AT120ph driven localisation of the CPC during mitosis.
Supervisor: Earnshaw, Bill ; Heun, Patrick Sponsor: European Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chromosome Passenger Complex ; CPC ; Heterochromatin Protein 1 ; HP1 ; centromeres ; HP1-­-driven CPC clustering ; CPC localisation