The role and dynamics of DNA catenation in sister chromatid cohesion

Thesis

Cohesion is the fundamental activity that tethers eukaryotic sister chromatids from S phase until mitosis. The Structural Maintenance of Chromosomes (SMC) complex, known as cohesin, mediates this process by co-entrapping sister chromatids within its ring-like structure. Sister chromatids are also extensively entangled through DNA catenation, which involves physical interlinks created during DNA replication and protected by cohesin. Unresolved DNA catenation in mitosis leads to anaphase bridges and segregation errors. Nevertheless, the role of DNA catenation and the mechanism by which cohesin safeguards it remain uncertain. Additionally, DNA catenation co-accumulates alongside cohesin at pericentromeres borders under spindle forces in metaphase, but the underlying mechanism has never been investigated. Elucidating whether DNA catenation is implicated in sister chromatid cohesion and what molecular phenomena drive its function and dynamics is critical for fully understanding chromosome segregation. Our lab recently found that cohesin is unable to withstand spindle forces when DNA catenation is artificially removed in metaphase-arrested cells. By measuring cohesion in cells lacking functional cohesin, I find that DNA catenation can noticeably hold sister chromatids without spindle forces but fails to do so when these are present. Moreover, I demonstrate that the ability of cohesin to stably co-entrap sister chromatids is essential for retaining DNA catenation at pericentromeres under spindle forces, but not for protecting DNA catenation from topoisomerase 2. The latter function is antagonised by condensin-directed topoisomerase 2 activity across the cell cycle. The fine balance of topoisomerase 2 activity set by cohesin and condensin is shifted towards decatenation when the protein is truncated at its C-terminus, revealing a key regulatory feature residing in this region. Overall, this project reveals the crucial role of DNA catenation in maintaining sister chromatid cohesion, providing unprecedented insights into its regulation and turnover via a coordinated SMC mechanism.

Authors: Mateos Martín, A

• DOI: 10.5287/ora-yevpqaj2x
• Type of award: MSc by Research
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English