Induction of retinal development by the peripodial epithelium in Drosophila

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Project Summary: Induction, the process by which one tissue signals to and influences the development of another, is a central feature of metazoan development. Some of the most famous and best studied examples of inductive interactions include the communication that takes place between the ectoderm, mesoderm, and endoderm during early embryonic development. Other examples include the signaling that leads to proper neural plate, somite, and brain development. Relevant to this proposal are the inductive cues that are sent by the vertebrate lens to ensure proper specification, positioning, and patterning of the adjacent retina. Mutations that either disrupt transcriptional networks within and signaling emanating from the lens lead to catastrophic retinal disorders. As such, there is intense interest in identifying and understanding the mechanisms underlying the induction of retinal development by the adjoining lens. This application is focused on using the eye- antennal disc of the fruit fly, Drosophila melanogaster, as an experimental system for studying inductive events during eye formation. The eye-antennal disc is a sac-like structure that contains three different tissues. The retina develops from a columnar epithelium called the disc proper. Overlying the disc proper is a sheet of squamous cells called the peripodial epithelium. These two layers are stitched together along their edges by a strip of cuboidal cells called the margin (which is itself derived from the peripodial epithelium). As such, the eye-antennal disc resembles a closed pillowcase. Evidence from the published literature indicates that signaling from the peripodial epithelium is important for inducing fate specification, growth, patterning, and cell fate choices within the retina. While the vertebrate lens and fly peripodial epithelium are non-homologous structures it appears that both tissues make use of common regulatory modules to induce developmental changes in the retina. For example, recent studies have shown that Pax6 and BMP4/TGFβ signaling are both required in the lens and peripodial epithelium for retinal development. In this proposal we will address a number of exciting questions that go to the heart understanding how development of the retina is induced by neighboring tissues. Using modern molecular, cellular, and genetic methods we will develop a state-of-the-art contemporary perspective on how the peripodial epithelium influences the development of the eye and directly contributes to formation of the head. As part of these studies we will pursue the identification of transcription factors and signaling pathways that are important in the peripodial epithelium for retinal development. These gene regulatory networks will be relevant to understanding how the vertebrate lens communicates to the adjacent retina. We will test the specific hypotheses that Pax6 and the So-Eya complex regulate the production of ligands for the TGFβ and Notch signaling pathways. From the aims presented here we will acquire new insights into the mechanisms by which transcriptional networks and signaling pathways are integrated to control inductive events during retinal specification and patterning.