Yki-Mitf-ECM regulation of eye progenitor epithelium morphology. - Project Summary: Form is inextricably linked with function in the eye, where the topology of the retina in part determines what incident light can be detected; this is true for both the camera eye of vertebrates and for the compound eyes of invertebrates, such as the fly, Drosophila melanogaster. In both cases, retinal development and function is promoted through its association with a support tissue – retinal pigmented epithelium (RPE, vertebrates) or peripodial epithelium (PE, fly). While much study has been focused on the molecular mechanisms underlying retinal specification, photoreceptor differentiation and on vision-associated diseases, the contribution of support tissues to the development and morphogenesis of the adult eye structure has received significantly less attention. Mutations in YAP1 and MITF are associated with congenital malformation of the human eye, resulting in the optic fissure closure defect coloboma (YAP1 and MITF) or microphthalmia (MITF). In neither context are the factors or processes upstream or downstream of YAP1 or MITF known or understood. I have recently described a Retinal Displacement (RDis) paradigm in fly, where developmental misalignment of Retina and PE tissues leads to congenital malformation of the compound eye. This powerful genetic model has led us to identify the conserved fly orthologs of YAP1 (Yki) and MITF (Mitf) as critical regulators of ocular epithelial topology. Furthermore, this model has allowed us to discover how the Hippo signaling cascade regulates Yki in the developing eye. Our preliminary data suggest that another critical factor in fly eye morphogenesis is the attachment of support tissue cells to the extracellular matrix (ECM), and recent work in vertebrate models has highlighted the importance of ECM in maintaining the Retina-RPE tissue boundary. The proposed research will explore the relationships among ECM, Yki and Mitf, in the genetically tractable fly model. In Aim 1 of this proposal, we will perform the first systematic investigation into how ECM factors contribute to ocular tissue morphogenesis, and we will investigate how ECM and PE-ECM connectivity are disrupted in RDis. In Aim 2, we will uncover the transcriptional targets of Yki and Mitf in the developing eye and test the hypothesis that they directly regulate ECM factor expression to maintain ocular epithelium topology. Our enhanced understanding of PE-ECM attachment and its molecular regulation will serve as a springboard for future detailed studies of the interplay among cell and epithelial properties that control eye organogenesis.
