NIPBL’s role in building cohesion

Thesis

Cohesin is integral to life through its ability to organise our duplicated DNA until it is segregated between two daughter cells. Equal segregation is ensured through a process called sister chromatid cohesion, which is essential to all eukaryotic life. The process of building sister chromatid cohesion, however, is not well understood. In this thesis, we explore the role of one of cohesin’s main regulatory proteins, NIPBL, in facilitating this process. NIPBL associates cohesin with DNA, a process which underpins all of cohesin’s activities. It also stimulates cohesin’s ATPase activity which underpins some of its DNA organising abilities. To explore NIPBL’s role in cohesin regulation, we develop the first internal NIPBL degron that allows acute depletion of all known isoforms of the protein. We find that NIPBL is essential and required for cohesion. We use this tool to explore the dependency of cohesion on NIPBL throughout the cell cycle to learn how NIPBL aids cohesin. We find that NIPBL is required for the establishment of cohesion, predominantly through its role as a cohesin loader, but not the maintenance of cohesion once it is built. We identify the critical window in the cell cycle where NIPBL first associates cohesin with DNA, and hence when NIPBL is essential for cohesion. In this thesis, we reveal a simple but powerful idea, that once NIPBL has fulfilled its task before S-phase of associating cohesin with DNA, it is no longer required for cohesion establishment or maintenance.

Authors: Johns, IG

• DOI: 10.5287/ora-14oraa0k5
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: chromosome dynamics; SMC proteins; establishment of sister chromatid cohesion; cohesin; conversion pathway; regulation by NIPBL
• Subjects: Sister chromatid cohesion; Chromosome dynamics; Regulation of cohesin; 3D genome organisation