An Act5C promoter is fused upstream of a loxP cassette containing GAL80. The loxP cassette is followed by the tdTomato coding region that is tagged with Tag:Myr(Unk). In the absence of P1cre recombinase, GAL80 is expressed under the control of the Act5C promoter. The Tag:Myr(Unk)-tagged tdTomato reporter is only expressed after excision of the loxP cassette using P1cre recombinase.