The Hippo signaling pathway, also known as the Salvador/Warts/Hippo (SWH) pathway, controls organ size in animals by regulating cell proliferation and apoptosis. The Hippo pathway consists of a cascade of core kinases, of which Hpo phosphorylated protein kinase (Wts) and Hpo (MST1/2 in mammals) are members of the STE-20 protein kinase family. This highly conserved serine/threonine kinase group regulates several cellular processes, including cell proliferation, apoptosis, and various stress responses.