Eye color pigment granules in wild-type and mutant Drosophila melanogaster

Abstract

Eye color pigment granules were studied in ultrathin sections of the wild-type fruit fly Drosophila melanogaster and the following eye-color mutants, cinnabar (cn), brown (bw), cinnabar brown (cn bw), and white (w). Ommatin-containing granules of the primary pigment cells are electron lucent in newly emerged flies but are dense in aged flies. The intraretinular granules are of intermediate or high electron density and also contain ommatins. The content of these granules was deduced from comparisons between wild type and cn, which blocks ommatin synthesis. The bw mutant was used to show that drosopterins reside throughout the secondary pigment cells while drosopterin granules monopolize the distal portion. The secondary pigment cell's granules, especially the most distal ones, are electron lucent in our work as well as in most earlier publications. Here we show that these granules are manifested as holes in the section. Both ommatins and drosopterins reside more proximally in the compound eye's pigment cells. We show that white-eyed flies have unusually large granules, and the possible function of these structures is discussed.