Organ growth control in the absence of Hippo signalling

The evolutionarily conserved Hippo signaling pathway is considered a regulator of organ growth and size during development. This conclusion derives from the observation that Hippo pathway kinase mutation, and consequent activation of the transcription coactivator Yorkie in Drosophila, or YAP/TAZ in mouse, yields dramatically overgrown adult structures. However, we discovered that loss of the Hippo pathway effector and Yorkie binding partner Scalloped, does not alter developmental cell proliferation or organ growth in Drosophila, and in mouse liver, proven models for growth control studies. Our data, and results from others, indicate that Hippo pathway activation is constitutively necessary to restrain Yorkie induced overgrowth but is not modulated by upstream signals to regulate organ growth and size. Rather, we show that the Hippo pathway regulates tissue differentiation and regeneration. In conclusion, we show that the Hippo pathway does not transduce instructive signals during development and thus is dispensable for organ growth and size control.status: publishe