, 2005). OR35a-dependent responses to γ-hexalactone persisted in both IR8a and IR25a mutants ( Figures 2B and 2C), indicating independent functioning of this selleck chemicals receptor. The ac2 sensilla neurons respond strongly to acetic acid and 1,4-diaminobutane, and these responses are selectively abolished in IR8a and IR25a mutants, respectively ( Figures 2B and 2C). Finally, ac1 sensilla contain three IR-expressing neurons, but only one strong agonist, ammonia, has been identified ( Yao et al., 2005). Responses to this odor were retained in both IR8a and IR25a mutants,

as well as in IR8a/IR25a double mutants ( Figures 2B and 2C). All defects in odor-evoked responses in IR8a and IR25a mutants were rescued by expression of the corresponding cDNA transgenes using IR8a or IR25a promoters via the GAL4/UAS system ( Figures 2B and 2C; see Figure S1 available online) ( Brand and Perrimon, 1993). The sole exception was our failure to restore ac2 1,4-diaminobutane responses in IR25a mutants (data not shown).

We ascribe this lack of rescue activity to the poor recapitulation of endogenous IR25a expression by our IR25a-GAL4 line ( Figure S1B). Expression of IR25a in IR8a mutant neurons did not rescue electrophysiological responses (data not AT13387 research buy shown), indicating selective functional properties of these two receptors beyond their distinct expression patterns ( Figure 1C). Taken together, the loss of multiple distinct ligand-evoked responses in IR8a and IR25a mutants suggests that these proteins function as coreceptors that act with different subsets of odor-specific IRs. To determine the cellular basis for the loss of electrophysiological responses in these IR coreceptor mutant neurons, we initially focused on the role of IR8a in the correct functioning of the phenylacetaldehyde receptor IR84a (Benton et al., 2009). An EGFP-tagged version of IR84a localizes to the sensory cilium in its endogenous neurons (Figure 3A), defined by the distal distribution relative to the cilium base marker 21A6 (Husain et al., 2006 and Zelhof et al., 2006). By contrast, in IR8a mutants, EGFP:IR84a

is restricted to the inner dendritic segment ( Figure 3A). Restoration of IR8a expression under the control of the IR84a promoter rescues this localization defect, defining a cell-autonomous function almost for IR8a in promoting cilia targeting of IR84a ( Figure 3A). We tested the generality of this requirement for IR8a by examining the cilia localization of a second receptor, IR64a, which is coexpressed with IR8a in morphologically distinct grooved peg sensilla in the third chamber of the sacculus (Ai et al., 2010). EGFP:IR64a is abundant in the outer dendrite of these neurons in wild-type sensilla, and this localization is abolished in IR8a mutants ( Figure S2A). We observed more heterogeneous levels of EGFP:IR64a in IR8a mutant neurons, suggesting that this mislocalized protein is destabilized.