The correct development of multicellular organisms is dependent upon the communication of individual cells by signalling. Negative feedback loops are often key, as once a signalling pathway has been activated, and the resulting changes in gene expression implemented, the pathway must be attenuated. Misregulation of these processes can lead to diseases such as cancer. The Ras pathway is a well-characterised example, being overactive in many types of cancer. In C. elegans, it has been proposed that attenuation of Ras can occur through the action of sumoylation on chromatin factors. To this end, we performed an RNAi screen in a SUMO-sensitised background, in which we targeted predicted C. elegans chromatin factors. We identified BET-1, a double bromodomain protein, and subsequently showed that it interacts genetically and physically with the sumoylation pathway to prevent hyperactivation of Ras signalling. Loss of BET-1 caused phenotypes consistent with excessive Ras signalling in the vulva and germline, and led to increased Ras signalling at a global level in the worm. Loss of both BET-1 and SUMO led to a striking effect on fluid homeostasis, and loss of muscle mass, in adult worms. This synthetic phenotype was found to be caused in part by overexpression of the FGF receptor, EGL-15. To summarise, the RNAi screen successfully identified BET-1 and other candidates as novel regulators of Ras signalling. We have shown that BET-1 alone has a role in preventing excessive Ras signalling in C. elegans, and that BET-1 and SUMO work together to maintain fluid homeostasis and muscle mass. In conclusion, the work presented in this thesis shows that BET-1 and SUMO cooperate to prevent excessive Ras signalling, and is consistent with a model in which BET-1 and SUMO perform this function by acting as part of a negative feedback loop.
|Date of Award
|1 Aug 2012
- The University of Manchester
|Gino Poulin (Supervisor) & Christian Heintzen (Supervisor)