This transgene contains the coding sequence for Cre recombinase, followed by a polyadenylation signal to terminate the fusion transcript immediately after the recombinase gene, inserted into a mouse genomic bacterial artificial chromosome (BAC) at the ATG transcription initiation codon of the solute carrier family 6 (neurotransmitter transporter, serotonin), member 4 gene so that expression of the recombinase is driven by the regulatory sequences of the mouse gene.