The development of complex metazoans depends on the integration of a handful of signalling pathways that eventually modulate precise patterns of gene expression. The fact that just a few pathways are involved in the generation of such complexity in different organisms, suggests that these are highly regulated and conserved processes. The accurate spatio-temporal coordination of the signalling pathways controls the assignation of different cell fates and their patterning into tissues and organs. The source of diversity relies on the different possible interactions between signalling pathways, such as, the combination of signals and the order in which they are received by the cell or crosstalk. Due to their importance in development, abnormal signalling through these pathways has been strongly associated with developmental disorders, cancers and other diseases. The Notch and Wnt signalling pathways are key components of the intricate network that controls gene expression during development, and genetic analysis in Drosophila has highlighted that interactions between these two signalling pathways are important during this process.This thesis investigates the cross-regulatory interactions between Notch and Wnt signalling pathways in mammals. Using transcriptional reporter assays and biochemical analysis, I have found two molecular mechanisms underlying the inhibitory crosstalk between Notch and β-catenin, the effector of Wnt signalling pathway, in mammalian cells. At the membrane Notch inhibits β-catenin transcriptional activity through Deltex mediated endocytosis of Notch and a component required for β-catenin activation. This is similar to results observed in Drosophila. In the nucleus, I have identified a novel mechanism by which NICD-dependent transcription of Hes/Hey family of transcription factors prevents the activation of Wnt signalling pathway. This mechanism involves the formation of a physical complex between Hey1 and β-catenin/TCF, which allows Hey to block Wnt transcriptional activation. Additionally, I have found that these two mechanisms are conserved across vertebrates.Together the findings of this thesis improve our understanding of the molecular mechanism underlying the Notch/Wnt crosstalk. In turn, this will give an insight into unravelling how a handful of signalling pathways can generate sufficient diversity in signalling output to specify the hundreds of different cell fates generated to make a mammal. Elucidating these signalling networks will also contribute to our understanding of diseases, both their aetiology, by knowing how changes in one signal can influence another, and their treatment as mimicking points of crosstalk is likely to generate very specific therapeutic agents.
|Date of Award||31 Dec 2012|
- The University of Manchester
|Supervisor||Keith Brennan (Supervisor)|