A control transgene in which a sequence cassette encoding a fusion protein composed of 1. a Tag:HA epitope, 2. the complete Mayo extracellular region, including the autoproteolytically active GAIN domain, but with a His to Ala amino acid replacement at the -2 position of 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 Mayo locus, resulting in expression of the fusion protein under the control of endogenous Mayo regulatory sequences. The mutation in the GPS site prevents release of the lexA::VP16 driver upon activation of Mayo.