Mask, a Component of the Hippo Pathway, is Required For Drosophila Eye Morphogenesis

Hippo Signaling is a regulator of tissue growth, but we show that the Yki and its cofactor Maskalso have a critical role in the morphogenesis of the post-mitotic Drosophila pupal eye. Mask is required for the correct distribution and accumulation of adherens junctions and appropriate organization of the cytoskeleton. Accordingly, disrupting mask expression led to severe patterning defects. Similar phenotypes were observed when yki was reduced or in response to ectopic wts and mis-patterning phenotypes observed when mask expression was reduced were modified by Hippo pathway activity, supporting our hypothesis that Mask’s function in fly eye patterning is within the context of Hippo signaling. RNA-sequencing analyses revealed that Mask regulates the transcription of numerous genes associated with cytoskeletal organization and cell adhesion, including FER kinase that phosphorylates β-Catenin and Vinculin. Similar trends in FER and Vincexpression were observed when yki was reduced, suggesting that Mask:Yki complexes contribute to the adhesive properties and architecture of retinal cells. Since it is well-established that Hippo pathway activity is responsive to changes in cell adhesion and the cytoskeleton, our data support that a feedback loop utilizes Hippo signaling to both sense and regulate adhesion and the cytoskeleton to fine-tune morphogenesis.