Generation of uniform fly retinas

The compound eye of Drosophila melanogaster is composed of about 800 ommatidial units, each containing eight photoreceptor cells (R1-R8). Based on their spectral sensitivities, three subtypes can be distinguished [1]: The 'pale' (p) and 'yellow' (y) ommatidia [2] are distributed randomly throughout the main part of the eye (Figure 1A). They show different spectral sensitivity, at shorter and longer wavelengths, respectively. The third subtype, consisting of morphologically distinct ommatidia with monochromatic inner photoreceptors, is found in a narrow stripe at the dorsal rim (DRA) of the adult eye and probably detects polarized light [3]. Here, we completely re-designed the stochastic p/y mosaic by manipulating only three genes: spineless [4], the growth regulator melted, and the tumor suppressor warts/lats [5]. By enforcing unambiguous cell fate decisions independently in both R7 and R8 cells, completely homogeneous retinas consisting of only one ommatidial subtype can be created, including unusual opsin combinations that never occur in the wild type.