YAP1 and neoplasm: Here, we identify the protocadherins Fat (Ft) and Dachsous (Ds), the Warts-Hippo tumor suppressor pathway, and the transcriptional co-activator Yorkie (Yki, a YES associated protein, or YAP) as components of the feed-forward signaling mechanism, and we show how this mechanism promotes wing growth in response to Wg.