Novel signaling from the peripodial membrane is essential for eye disc patterning in Drosophila

The Drosophila eye disc is a sac of single layer epithelium with two opposi ng sides, the peripodial membrane (PM) and the disc proper (DP). Retinal mo rphogenesis is organized by Notch signaling at the dorsoventral (DV) bounda ry in the DP. Functions of the PM in coordinating growth and patterning of the DP are unknown. We show that the secreted proteins, Hedgehog, Wingless, and Decapentaplegic, are expressed in the PM, yet they control DP expressi on of Notch ligands, Delta and Serrate. Peripodial clones expressing Hedgeh og induce Serrate in the DP while loss of peripodial Hedgehog disrupts disc growth. Furthermore, PM cells extend cellular processes to the DP. Therefo re, peripodial signaling is critical for eye pattern formation and may be m ediated by peripodial processes.