The Drosophila melanogaster Phospholipid Flippase dATP8B Is Required for Odorant Receptor Function

Yu-Chi Liu,Anupama Dahanukar,Travis K Johnson,Mays Imad,Anandasankar Ray,Konrad E Zinsmaier,Richard E Burke,Kavita R Sharma,Marien De Bruyne,Takahiro Honda,Michelle W Pearce,Sandhya Charlu,Coral G Warr,Robert R H Anholt

doi:10.1371/journal.pgen.1004209

Abstract

The olfactory systems of insects are fundamental to all aspects of their behaviour, and insect olfactory receptor neurons (ORNs) exhibit exquisite specificity and sensitivity to a wide range of environmental cues. In Drosophila melanogaster, ORN responses are determined by three different receptor families, the odorant (Or), ionotropic-like (IR) and gustatory (Gr) receptors. However, the precise mechanisms of signalling by these different receptor families are not fully understood. Here we report the unexpected finding that the type 4 P-type ATPase phospholipid transporter dATP8B, the homologue of a protein associated with intrahepatic cholestasis and hearing loss in humans, is crucial for Drosophila olfactory responses. Mutations in dATP8B severely attenuate sensitivity of odorant detection specifically in Or-expressing ORNs, but do not affect responses mediated by IR or Gr receptors. Accordingly, we find dATP8B to be expressed in ORNs and localised to the dendritic membrane of the olfactory neurons where signal transduction occurs. Localisation of Or proteins to the dendrites is unaffected in dATP8B mutants, as is dendrite morphology, suggesting instead that dATP8B is critical for Or signalling. As dATP8B is a member of the phospholipid flippase family of ATPases, which function to determine asymmetry in phospholipid composition between the outer and inner leaflets of plasma membranes, our findings suggest a requirement for phospholipid asymmetry in the signalling of a specific family of chemoreceptor proteins.

Highlights

In insects such as Drosophila melanogaster the detection of environmental odours is achieved by arrays of olfactory receptor neurons (ORNs) housed in different types of chemosensory hairs on two olfactory organs, the antenna and the maxillary palp
Orco has been suggested to be activated by cAMP [4], and in addition it has been suggested that phosphorylation of Orco by protein kinase C (PKC) is required for its activation [9]
Insects can detect a wide range of environmental cues using three different families of olfactory receptor proteins

Summary

Introduction

In insects such as Drosophila melanogaster the detection of environmental odours is achieved by arrays of olfactory receptor neurons (ORNs) housed in different types of chemosensory hairs (sensilla) on two olfactory organs, the antenna and the maxillary palp. Each class of ORN is tuned to specific chemical signals by expression of different olfactory receptor genes. The responses of most insect ORNs are reliant on members of two large and divergent families of olfactory receptor proteins, the odorant receptor (Or) and Ionotropic glutamate-like receptor (IR) families. Orco is required for Or proteins to be transported to the dendrites [5], and heterologous expression studies suggest Orco is part of the functional receptor and is essential for the initial fast inward current upon ligand binding [6,7]. Heterologous expression experiments demonstrated a slower metabotropic current after Or stimulation, as well as an increase in cAMP [4]. A recent study suggests that metabotropic regulation of Orco regulates Or sensitivity [13]. The mechanism of Or signalling appears to be complex, with both ionotropic and metabotropic pathway involvement, and despite much investigation is not fully understood

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