A sequence cassette has been introduced into the attP site present in TI{TI}5-HT2BattP, restoring the deleted 5-HT2B sequence and tagging isoform D with Tag:V5. The tag is followed by a 2A-lexA::p65 cassette, resulting in the lexA::p65 driver being expressed as a separate protein under the control of the endogenous 5-HT2B regulatory sequences (only the expression of isoform D is trapped by lexA::p65). 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).