A 2A-GAL4 cassette followed by a Disc\RFP3xP3.cUa marker has been inserted into the endogenous Octβ2R locus, at the 3' end of the open reading frame of the RA isoform. This results in the GAL4 driver being expressed as a separate protein under the control of endogenous Octβ2R regulatory sequences (the expression of only the RA isoform is expected to be trapped by GAL4).