A sequence cassette has been introduced into the attP site present in TI{TI}OambattP, restoring the deleted Oamb sequence and tagging isoforms C and F with 2xTag:MYC. The tag is followed by a 2A-GAL4 cassette, resulting in the GAL4 driver being expressed as a separate protein under the control of the endogenous Oamb regulatory sequences (only the expression of isoforms C and F is trapped by GAL4). A single loxP site is present downstream of the driver sequence (markers present in the progenitor insertion and donor plasmid have been removed using P1cre).