RELATIONSHIPS BETWEEN COMPLEX DELTA-EXPRESSION AND THE SPECIFICATION OF RETINAL CELL FATES DURING DROSOPHILA EYE DEVELOPMENT

Analysis of retinal development in Delta (Dl) temperature-sensitive mu tants reveals requirements for Delta function in the specification of all retinal cells, including photoreceptors, cone cells, pigment cells and cells that make up interommatidial bristles. In situ hybridizatio n and immunohistochemistry indicate that Delta is expressed dynamicall y during the specification of different cell types. Comparisons of Del ta expression patterns with developmental defects in Dl mutants implie s that Delta functions in a cell-nonautonomous manner in the specifica tion of photoreceptors. Delta protein resides predominantly in subcell ular vesicles located primarily at the apical ends of developing retin al cells. Localization of Delta protein in Dl and shibire(isl) mutants implies that Delta is targeted to the cell surface, but is efficientl y removed via endocytosis, resulting in vesicular accumulation.