Figure 3. IR93a is co-expressed with IR25a and IR40a in sacculus neurons.
(a) Left: schematic of the adult Drosophila antenna, illustrating the location of the sacculus (red) in the interior of this appendage. Right: the sacculus is composed of three main chambers (I, II, III), which are lined with sensilla of various morphologies (cartoon adapted from [Shanbhag et al., 1995]). (b) Top: immunofluorescence on a whole-mount wild-type antenna showing expression of IR93a protein (green) in two groups of soma (arrows) around sacculus chambers I and II; these chambers are visualized by cuticle autofluorescence shown in the images on the right. The arrowhead marks the concentration of IR93a in the dendritic endings that innervate the sensilla in chamber I. Note that the dendrites of chamber II neurons are not visible in this image; sensilla localization of IR93a in these cells is more easily detected in antennal sections; see panel (d). Bottom: Ir93aMI05555 mutants lack detectable IR93a protein. Scale bar is 20 µm. (c–e) Double immunofluorescence with the indicated antibodies on antennal cryosections revealing co-expression of these IRs in sacculus neurons; the arrows point to the cluster of neurons innervating chamber II. Scale bar is 10 µm. IR25a is expressed in additional neurons that do not express IR93a or IR40a because of IR25a’s broader role as an olfactory IR co-receptor (Abuin et al., 2011).