VITAMIN-A, VISUAL PIGMENTS, AND VISUAL RECEPTORS IN DROSOPHILA

The fly visual system has served for decades as a model for receptor s pectral multiplicity and vitamin A utilization. A diverse armamentariu m of structural techniques has dovetailed with convenient electrophysi ology, photochemistry, genetics, and molecular biology in Drosophila t o facilitate recent progress, which is reviewed here. New data are als o presented. Ultrastructure of retinula cells of carotenoid-deprived f lies shows that organelles associated with protein biosynthesis, i.e., rough endoplasmic reticulum and Golgi apparatus, are present, while o rganelles associated with rhabdomere turnover, i.e., multivesicular bo dies (MVBs), are rare. Ultrastructure and morphometry suggest that ret inoic acid-rearing stimulates membrane export and rhabdomere buildup, even though functional rhodopsin is missing. Confocal microscopy sugge sts that RH4, one of the ultraviolet rhodopsins, may reside in the pre viously-described pale fluorescent R7 cells with RH3 in the yellow flu orescent R7 cells. (C) 1996 Wiley-Liss, Inc.