Georgopoulou, D; (2015) Investigating a role for cohesin in genome organisation and gene regulation in post-mitotic astrocytes. Doctoral thesis , UCL (University College London).

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Abstract

The cohesin complex has a conserved and fundamental role in chromosome biology as it is involved in sister chromatid cohesion, DNA repair and gene regulation. Mutations in cohesin and its regulators lead to human developmental disorders and cancer, and it is hypothesised that this is due to cohesin’s roles in gene regulation. Cohesin mediates gene regulation primarily through the formation or stabilisation of long-range chromatin loops from CTCF, a conserved transcriptional regulator, binding sites. Cohesin-anchored chromatin loops were first described at specific loci to physically tether distal regulatory elements to gene promoters. This thesis investigated whether the roles of cohesin in mediating chromatin loops at individual loci in the genome could apply genome wide, and if so, whether such global cohesin-anchored chromatin loops could contribute to chromosomal organisation. To test this, I established a post-mitotic cell system from mouse so that cohesin proteins could be genetically deleted in a manner that did not interfere with their roles in mitosis. Using this system, cohesin was shown to be an anchor point for chromatin loops of all scales throughout the genome which included both gene loops and loops required for chromosome architecture. Cohesin-deficient post-mitotic cells exhibited global chromosomal decompaction and widespread transcriptional deregulation. While the majority of cohesin chromatin pools were depleted, chromatin domain borders were not abolished and residual cohesin complexes were still bound to chromatin in cohesin-deficient cells. To test whether such residual cohesin complexes may still be mediating long-range chromatin loops and thus maintaining chromosome structures, I used RNAi to knock-down cohesin regulators, such as CTCF and Stag proteins, in cohesin-deficient post-mitotic astrocytes. My results highlight a role for CTCF and Stag proteins in the regulation of cohesin-mediated genome organisation in mouse. Thus, it was shown that cohesin proteins have key roles in genome organisation and functions.

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