A sequence cassette has been introduced into the attP site present in TI{TI}5-HT1BattP, restoring the deleted 5-HT1B sequence and tagging isoforms A and D 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 5-HT1B regulatory sequences (only the expression of isoforms A and D 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).