Biological responses of cells and tissues within an organism are mostly elicited through the function of molecular signal cascades within cells in response to extra- and intra-cellular changes. These pathways are engaged with specificity and fidelity and carry out physiological programs. Proliferation or differentiation, directional migration, survival or secretion, for example, are regulated by signal transduction pathways. Altered or aberrant signaling pathways, in contrast, can lead to diseases. Our goal is to understand signaling cascades and utilize this knowledge to identify novel molecular targets for therapeutic interventions. We use molecular and biochemical tools including embryonic stem cells, genetically engineered mice and viral vector mediated gene delivery to study cell signaling during development and in diseases such as cancer.