A control transgene in which a sequence cassette encoding a fusion protein composed of 1. a Tag:HA epitope, 2. the complete Ktch extracellular region, including the autoproteolytically active GAIN domain, but with a mutation in the GPCR proteolysis site (GPS) that prevents cleavage, 3. the juxta- and transmembrane segment of N (JTS), 4. the lexA::VP16 driver and 5. three copies of the Tag:V5 epitope has been inserted into the Ktch locus, resulting in expression of the fusion protein under the control of endogenous Ktch regulatory sequences. The mutation in the GPS site prevents release of the lexA::VP16 driver upon activation of Ktch.