Atypical Membrane Topology and Heteromeric Function of Drosophila Odorant Receptors In Vivo
(A) Representative stimulus-evoked calcium signals recorded from the axon terminals of Gr21a neurons in the antennal lobe V glomerulus of a control animal (UAS-G-CaMP/UAS-G-CaMP;Gr21a-Gal4/Gr21a-Gal4; left column) and an animal misexpressing OR83b and GFP:OR43a in Gr21a neurons (UAS-G-CaMP/+;Gr21a-Gal4/UAS-GFP:Or43a;UAS-G-CaMP/UAS-Or83b; right column). Top row: intrinsic G-CaMP fluorescence of the V glomerulus. Dotted lines mark the antennal lobe border, and the black squares mark the area of the V glomerulus evaluated for stimulus-evoked changes in fluorescence. Middle row: false-color–coded images during stimulation with CO2 (5%) or cyclohexanol (10−2) represent ΔF/F (%) according to the scales on the right panel. Bottom row: time traces of stimulus-evoked signals of the V glomerulus. Black bars indicate odor stimulation time. The diminished responses to CO2 in animals expressing GFP:OR43a/OR83b may reflect competition between the resident and ectopic receptors in engaging the ciliary trafficking pathway or downstream signaling components.
(B) Normalized odor-evoked calcium responses of control (blue) and GFP:OR43a/OR83b-misexpressing (red) animals [genotypes as in (A)] expressed as a percentage of the CO2 response in each genotype. GFP:OR43a/OR83b-misexpressing animals show stronger responses than control animals for the odor stimuli (all at 10−2) marked with an asterisk (p < 0.05; two-tailed unpaired t-test; n = 4 animals per genotype and stimulus). Chemical Abstracts Service (CAS) registry numbers: cyclohexanol (108–93–0), cyclohexanone (108–94–1), hexanol (111–27–3), benzaldehyde (100–52–7), isoamyl acetate (123–92–2), geranyl acetate (105–87–3), octanol (111–87–5), linalool (126–91–0), caproic acid (142–62–1).