The spectral sensitivity of Drosophila photoreceptors

Camilla R Sharkey,Jorge Blanco,Trevor J Wardill,Maya M Leibowitz,Daniel Pinto-Benito

doi:10.1038/s41598-020-74742-1

Camilla R Sharkey, Jorge Blanco + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-74742-1

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Abstract

Drosophila melanogaster has long been a popular model insect species, due in large part to the availability of genetic tools and is fast becoming the model for insect colour vision. Key to understanding colour reception in Drosophila is in-depth knowledge of spectral inputs and downstream neural processing. While recent studies have sparked renewed interest in colour processing in Drosophila, photoreceptor spectral sensitivity measurements have yet to be carried out in vivo. We have fully characterised the spectral input to the motion and colour vision pathways, and directly measured the effects of spectral modulating factors, screening pigment density and carotenoid-based ocular pigments. All receptor sensitivities had significant shifts in spectral sensitivity compared to previous measurements. Notably, the spectral range of the Rh6 visual pigment is substantially broadened and its peak sensitivity is shifted by 92 nm from 508 to 600 nm. We show that this deviation can be explained by transmission of long wavelengths through the red screening pigment and by the presence of the blue-absorbing filter in the R7y receptors. Further, we tested direct interactions between inner and outer photoreceptors using selective recovery of activity in photoreceptor pairs.

Highlights

Drosophila melanogaster has long been a popular model insect species, due in large part to the availability of genetic tools and is fast becoming the model for insect colour vision
Sensitivity of the photoreceptors is largely determined by the underlying visual pigment and ommatidia can be subdivided into two major classes, ‘pale’ (p) or ‘yellow’ (y), owing to the appearance of the inner pair of photoreceptors in transmitted light, with the latter possessing a blue-absorbing yellow filter in the R7y receptor alongside the UVsensitive Rh4 visual pigment[5]
We reveal significant shifts in spectral sensitivity for all receptor sensitivities and a large 92 nm shift in sensitivity of the Rh6 visual pigment when measured in its native photoreceptor (R8y) from 508 to 600 nm

Summary

Introduction

Drosophila melanogaster has long been a popular model insect species, due in large part to the availability of genetic tools and is fast becoming the model for insect colour vision. The spectral range of the Rh6 visual pigment is substantially broadened and its peak sensitivity is shifted by 92 nm from 508 to 600 nm We show that this deviation can be explained by transmission of long wavelengths through the red screening pigment and by the presence of the blue-absorbing filter in the R7y receptors. Peak sensitivities for Rh3–Rh6 have been estimated from microspectrophotometery (MSP), visual pigment extracts and electroretinography (ERG) with ectopic expression of inner receptor opsin in the more numerous outer receptors, using white-eyed Drosophila[3,4] This enabled the underlying visual pigment sensitivities to be measured (Rh3–Rh6 λmax: 345, 375, 437, 508 nm; Fig. 1b), these studies were unable to quantify the sensitivity of each when measured in vivo, in the photoreceptor cells where the opsins are normally expressed along with their naturally associated ocular screening pigment and photoreceptor filtering pigments (Fig. 1c–e). The effect of light leakage on the Drosophila Rh6 visual pigment has yet to be tested in vivo

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