| Summary: | In order to respond rapidly and appropriately to their environment, cells activate internal signalling pathways, such as the mitogen-activated protein kinase (MAPK) pathways, which elicit appropriate responses through quantitative modulation of gene expression. Conceptually, gene expression may be regulated by a bistable switch or a continuously variable switch. The bistable switch considers the gene in either a stable 'on' state, where transcription happens at a constant rate intrinsic to the system, or a stable 'off' state, where transcription is not permitted. By contrast, the continuously variable switch considers gene transcription as a dynamic process, where the rate of transcription initiation varies with the intensity of the signal perceived. The work in this thesis focuses on the interface between the well-understood MAPK pathways and immediate-early (IE) genes and shows that a continuously variable switch would be more appropriate to convey quantitative regulation. Immunoblotting analyses of MAPK pathways after treatment of synchronised C3H 10T½ cells with the specific PP1 and PP2A protein phosphatase inhibitor, okadaic acid, revealed the presence of turnover of phosphorylation of transcription factor (TF) in the stress-activated MAPK pathways, suggesting dynamic regulation of these MAPK pathways. Analyses of the induction of IE genes c-fos and c-jun after perturbations of the turnover of phosphorylation by phosphatase or kinase inhibitors suggest that rather than static phosphorylation state dynamic turnover of phosphorylation may regulate IE gene induction. Finally, a simplified computational model of the interface is presented, which confirms that dynamic regulation linking rate of initiation to the turnover of phosphorylation of TFs would better convey quantitative responses.
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