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Rhodopsins in Drosophila Color Vision

David Jukam, Preet Lidder, and Claude Desplan

CONTENTS

INTRODUCTION

ANATOMY AND MOLECULAR ASPECTS OF COLOR-SENSITIVE OPSINS

IN THE DROSOPHILA EYE

DEVELOPMENT AND PATTERNING OF RHODOPSINS

FOR DROSOPHILA COLOR VISION

COMPARISON BETWEEN MAMMALIAN AND DROSOPHILA COLOR

VISION RHODOPSINS

CONCLUSION

REFERENCES

INTRODUCTION

Color vision relies on an organism’s ability to detect color contrasts independently of intensity. This requires a sensory system that can detect and discriminate between different wavelengths of light. The opsin visual pigments collect light and initiate the conversion of photon energy into an electric signal sent by photoreceptor neurons to the brain, where this information is integrated into a perception. Opsins are photosensitive, seven-transmembrane G protein-coupled receptors of the same protein superfamily as many neurotransmitter, hormone, and sensory receptors that respond to molecular ligands [1, 2]. Different opsins exhibit different spectral sensitivities, and each is maximally sensitive to a particular wavelength of light, depending on its protein structure. Opsins are covalently linked to a retinal chromophore via a protonated Schiff base bond to a lysine residue in the seventh transmembrane domain of the protein [3, 4]. When light hits the opsin–chromophore complex (called rhodopsin), the 11-cis retinal chromophore isomerizes to all-trans retinal, leading to the activation of a G protein and downstream effectors. For example, in Drosophila melanogaster, a Gqα protein mediates the light-dependent activation of phospholipase C and opening of Transient Receptor Potential-Like (TRP/ TRPL) channels, resulting in the depolarization of the cell membrane [5–10]. Vertebrate and invertebrate rhodopsins act on different signal transduction cascades: Light depolarizes photoreceptors in insects and hyperpolarizes photoreceptors in vertebrates, but the

From: Ophthalmology Research: Visual Transduction and Non-Visual Light Perception

Edited by: J. Tombran-Tink and C. J. Barnstable © Humana Press, Totowa, NJ

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