Research over the past several years has shown that pathways regulating processes such as cell fate decision and organ size control also play pivotal roles during tumorigenesis. While many of the individual signal transduction pathways have been outlined, a major ongoing challenge has been to integrate these findings into a comprehensive map of cellular signaling networks and understand the interactions between the various pathways. This information is critical to our understanding of the mechanisms underlying normal physiological function and the consequences of dysregulation under pathological conditions. Our group employs a host of molecular and model-based approaches to studying signaling pathways regulated by small GTP-binding proteins from the Ras and Rac families and how these pathways crosstalk with pathways controlling cell fate and organ size control, such as the Notch, Wnt and Hpo/YAP pathways.