Drosophila Schip1 Links Expanded and Tao-1 to Regulate Hippo Signaling

Regulation of organ size is essential in animal development, and Hippo (Hpo) signaling is a major conserved mechanism for controlling organ growth. In Drosophila, Hpo and Warts kinases are core components of this pathway and function as tumor suppressors by inhibiting Yorkie (Yki). Expanded (Ex) is a regulator of the Hpo activity, but how they are linked is unknown. Here, we show that Schip1, a Drosophila homolog of the mammalian Schwannomin interacting protein 1 (SCHIP1), provides a link between Ex and Hpo. Ex is required for apical localization of Schip1 in imaginal discs. Schip1 is necessary for promoting membrane localization and phosphorylation of Hpo by recruiting the Hpo kinase Tao-1. Taking these findings together, we conclude that Schip1 directly links Ex to Hpo signaling by recruiting Tao-1. This study provides insights into the mechanism of Tao-1 regulation and a potential growth control function for SCHIP1 in mammals.