(A) Domain structures of the subunits of kainate ionotropic glutamate receptors in vertebrates (GluK1-5) and Drosophila (Clumsy, CG9935, CG11155, DKaiRIC, DKaiRID). The Drosophila kainate iGluR subunits share the same domain organization as those of vertebrates. Clumsy has a long cytoplasmic terminal domain (CTD), which shares limited sequence homology with that of the vertebrate receptor subunit GluK5. ATD: amino-terminal domain; S1 and S2: two parts of ligand binding domain; TMD: transmembrane domain; CTD: cytoplasmic terminal domain.
(B) Wild-type and various iGluR RNAi-knockdown flies were tested for spectral preference to UV over green light as described in . Tm5c-Gal4 was used to drive RNAi expression of four kainate iGluRs subunits that are normally expressed in Tm5c neurons. RNAi-mediated knockdown of the Clumsy iGluR subunit (Tm5c-G4>Clumsy-RNAi [1X]), but not DKaiRIC, DKaiRID, or CG11155, caused a significant reduction of UV preference. The performance of wild-type flies and matched controls is shown for comparison. Increasing the copy number of UAS-Clumsy RNAi transgenes (Tm5c-G4>Clumsy-RNAi [2X]) further reduced flies’ UV preference. n.s.: not significant (p>0.05); *: significant (p<0.05).
(C) RNAi-knockdown any of the three subunits (i.e. DKaiRIC, DKaiRID and CG11155), in addition to Clumsy, caused no further reduction of UV preference, as compared with Clumsy RNAi knockdown. n.s.: not significant (p>0.05); *: significant (p<0.05). RNAi-knockdown of the three subunits, DKaiRIC, DKaiRID and CG11155, reduced UV preference close to the level caused by RNAi clumsy alone, suggesting these subunits are functionally redundant. n.s.: not significant (p>0.05); *: significant (p<0.05).