During the development and maintenance of tissues and organs, cells must decide whether, when, where and how much to proliferate. Improper control of cell proliferation can lead to developmental defects and cancer. We are focusing on the relatively unexplored area of the control of pattern and extent of germline proliferation as a model for this process. In particular, we are interested in signaling between somatic cells and the germ line that influences germline proliferation during development. Our entry into this area is aided by our identification and analysis of C. elegans mutants that have germline tumors. We are using our detailed knowledge of germline tumor formation to design and carry out large-scale genetic screens - including RNAi-based screens - to identify genes that affect tumor formation. These approaches have identified candidate genes including genes involved in the insulin signaling pathway.