Vitamin A, visual pigments, and visual receptors inDrosophila

Abstract

The fly visual system has served for decades as a model for receptor spectral multiplicity and vitamin A utilization. A diverse armamentarium of structural techniques has dovetailed with convenient electrophysiology, photochemistry, genetics, and molecular biology in Drosophila to facilitate recent progress, which is reviewed here. New data are also presented. Ultrastructure of retinula cells of carotenoid‐deprived flies shows that organelles associated with protein biosynthesis, i.e., rough endoplasmic reticulum and Golgi apparatus, are present, while organelles associated with rhabdomere turnover, i.e., multivesicular bodies (MVBs), are rare. Ultrastructure and morphometry suggest that retinoic acid‐rearing stimulates membrane export and rhabdomere buildup, even though functional rhodopsin is missing. Confocal microscopy suggests that RH4, one of the ultraviolet rhodopsins, may reside in the previously‐described pale fluorescent R7 cells with RH3 in the yellow fluorescent R7 cells. © 1996 Wiley‐Liss, Inc.

Hydroxylated sphingolipid biosynthesis regulates photoreceptor apical domain morphogenesis

“…In addition, the overall levels of Rhodopsin as well as rhabdomeric Rh1 (revealed by immuno-EM) are reduced ( Huber et al, 1994 ; Sapp et al, 1991 ). We confirmed the development of thinner rhabdomeres ( Lee et al, 1996 ) in wild-type PRCs upon carotenoid depletion ( Fig. 5 G vs. 5 E ).…”

The sense of smell, its signalling pathways, and the dichotomy of cilia and microvilli in olfactory sensory cells

“…Therefore, photoreceptor cells increase their quantum efficiency by forming multilayered stacks of membranes that are tightly packed with photosensitive rhodopsin molecules. This functional cytoarchitecture can likewise be observed in vertebrate [86] and invertebrate eyes [87], where stacks of membrane discs or rhabdomeric microvilli ensure high quantum efficiency of each photosensitive cell. In the case of olfactory sensory neurons, however, the situation is slightly different.…”

Photoreceptor responses of fruitflies with normal and reduced arrestin content studied by simultaneous measurements of visual pigment fluorescence and ERG

“…Whereas the fluorescence of Drosophila rhodopsin is negligible, the metarhodopsin strongly fluoresces, with a high emission in the red wavelength range (Stavenga 1983 ; Stavenga et al 1984 ). The fluorescence measurements are preferably applied in white-eyed mutants and are performed with a microspectrophotometer where a diaphragm isolates the fluorescence from the deep pseudopupil (Lee et al 1996 ; Stark and Thomas 2004 ). Other pigments than Rh1 metarhodopsin contribute to the emission signal, especially with blue excitation light.…”