A Novel Gγ Isolated from Drosophila Constitutes a Visual G Protein γ Subunit of the Fly Compound Eye

Simone Schulz,Armin Huber,Karin Schwab,Reinhard Paulsen

doi:10.1074/jbc.274.53.37605

Simone Schulz, Armin Huber + Show 2 more

Open Access

https://doi.org/10.1074/jbc.274.53.37605

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Abstract

Visual transduction in the compound eye of flies is a well established model system for the study of G protein-coupled transduction pathways. To characterize key components of the phototransduction cascade we performed substractive hybridization screening. We cloned the cDNA coding for the visual Ggamma (Ggamma(e)) subunit from Drosophila which had so far eluded identification at the molecular level. Northern blot analysis revealed the presence of a major, 1.4-kilobase(kb) Ggamma(e) transcript and two minor transcripts of 1.8 and 6 kb in size. The major 1.4-kb mRNA is expressed preferentially in the eye. The spatial expression pattern determined for Ggamma(e) as well as co-immunoprecipitation experiments demonstrated that Ggamma(e) dimerizes with Gbeta(e) to form the heterodimeric Gbetagamma subunit which functions in visual transduction in the Drosophila compound eye. Ggamma(e) shares common characteristics with the visual Ggamma subunits of human rod and cone photoreceptors although different classes of Galpha subunits are employed in vertebrate and invertebrate phototransduction. By the molecular cloning and characterization of the visual gamma subunit of Drosophila one of the few missing links in the well studied Drosophila phototransduction cascade has been characterized to complete our knowledge about the Drosophila visual transduction pathway.

Highlights

The visual cascade in the microvillar photoreceptors of the Drosophila compound eye is activated by light absorption of five rhodopsins which are differentially expressed in a distinct pattern within an ordered array of eight photoreceptor cells [1]
In the absence of any information on the existence of a distinct visual G␥ subunit, it has been suggested that Drosophila G␥1, the only G␥ subunit cloned from Drosophila so far, might associate with diverse G proteins, including the visual G protein [20]
DmG␥e Is Predominantly Expressed in Photoreceptor Cells and Forms the Visual G␤␥ Complex with G␤e— the novel G␥e subunit was isolated by a differential hybridization screen designed to isolate clones which are preferentially expressed in the eye, it is not certain that G␥e codes for the ␥ subunit of the visual G protein

Summary

Introduction

The visual cascade in the microvillar photoreceptors of the Drosophila compound eye is activated by light absorption of five rhodopsins which are differentially expressed in a distinct pattern within an ordered array of eight photoreceptor cells [1]. Photoreceptor- expressed genes encoding the G␣ (G␣q) and G␤ (G␤e) subunits of the visual G protein have been isolated [15,16,17], whereas the visual G␥ (G␥e) subunit had eluded identification at the molecular level.

Results

Conclusion