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. 2022 Apr 20;11:e72599. doi: 10.7554/eLife.72599

Figure 1. The standard view of olfactory receptor expression in Drosophila melanogaster.

Figure 1.

(A) The adult fly head (left) has two olfactory organs: the antennae and the maxillary palps (arrows). Olfactory neurons from these organs project to the fly brain (D), to the first center involved in processing of olfactory information, the antennal lobes (E). (B) The olfactory organs are covered by sensory hairs called sensilla (left). Each sensillum contains between one and four olfactory sensory neurons (two example neurons are shown in gray). The dendrites of these neurons extend into the sensilla, and the axons target discrete regions of the antennal lobes called glomeruli (E). Neuronal compartments (dendrites, cell body, axon, axon terminals) are labeled in (C). ( C) Left: in the periphery, each olfactory sensory neuron is traditionally thought to express chemosensory receptors from only one of three gene families on its dendrites: ionotropic receptors (IRs, pink and purple), odorant receptors (ORs, teal and green), or gustatory receptors (GRs, light and dark blue). IRs and ORs require obligate co-receptors (dotted box outline) to form functional ion channels. All ORs utilize a single co-receptor, Orco (teal), while IRs can utilize one (or a combination) of three possible co-receptors (purple): Ir8a, Ir25a, or Ir76b. The two GRs form a functional carbon dioxide detecting channel expressed in only one class of neurons. All other olfactory neurons express one of the four co-receptors. Right: olfactory sensory neurons expressing ORs, IRs, and GRs are thought to project to mutually exclusive glomeruli in the antennal lobe (AL) of the central brain, forming the olfactory map shown in (E). (D) Fly brain stained with anti-brp synaptic marker (nc82), with left AL outlined by the dotted white box. (E) AL map with glomeruli color-coded by the chemosensory receptors (ORs, IRs, or GRs) expressed in the olfactory sensory neurons projecting to them. Only one glomerulus (VC3, striped) receives inputs from neurons expressing chemoreceptors from multiple gene families (ORs and IRs). Compass: D = dorsal, L = lateral, P = posterior.