The role of cohesin in regulating early steps of cellular differentiation and reprogramming

• Main Author: Mello Cintra L. Muller, Thias
• Other Authors: Merkenschlager, Matthias
• Published: Imperial College London 2013
• Subjects: 610
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.631201

The cohesion protein complex is critical for sister chromatid cohesion and proper chromosome segregation in cycling cells and has additional roles in gene regulation and chromatin organisation. Particularly, cohesin has been implicated in regulating genes critical for maintaining pluripotency in embryonic stem (ES) cells. Here I ask whether cohesin regulates gene expression during early stages of ES cell differentiation and the reprogramming of somatic cells towards pluripotency. In order to dissociate the role of cohesin in gene expression from cohesin’s essential functions during the cell cycle I have established genetic approaches to conditionally delete cohesion in ES cells and in somatic cells. By depleting cohesin in ES cells my results reinforce the suggested role of cohesin in pluripotency maintenance, but also show that cohesin removal preferentially leads to mesoderm and neuroectoderm differentiation. In addition, data presented here suggest that cohesin is required for the silencing of X-inactivating genes that occurs during the differentiation of female ES cells. To explore the role of cohesin in reprogramming I used experimental heterokaryons generated by fusing ES cells and somatic cells. In this system, the re-expression of ES-specific genes in somatic cell nuclei occurs in the absence of cell division, thereby obviating the need for cohesin for cell division-related functions. Interestingly, by depleting cohesion in ES cells I found that cohesin is not required for the ability of ES cells to induce reprogramming of somatic cells. Instead, cohesin depletion enhanced their reprogramming ability to re-activate the expression of pluripotency markers in somatic cells, possibly by a mechanism that involves the up-regulation of the reprogramming factor c-Myc. In contrast, somatic cells require cohesin to be reprogrammed. Cohesin-depleted somatic cells were unable to re-activate pluripoency markers and failed to silence lineage-specific somatic genes after fusion. Finally, ongoing experiments to establish a rapid and reversible system for proteolytic cleavage of cohesion in mammalian cells, will contribute to understand the mechanisms by which cohesin regulates gene expression in cellular differentiation and reprogramming.