The DNA construct was made by replacing ZsGreen with TdTomato in plasmid pCAG-loxP-STOP-loxP-ZsGreen (Addgene plasmid #51269, donated by Pawel Pelczar). CRISPR/Cas9 genome editing technology was used to knock in the DNA construct into the rat ROSA26 locus in the embryos from outbred BluHsd:LE. Reporter line that can be crossed with Cre-expressing strains. In presence of Cre, the floxed "STOP" upstream of the TdTomato gene is deleted allowing expression of the red fluorescent TdTomato protein. ROSA26 is a synonym for rat Thumpd3-as1 (RGD:6491660) and is used as an official symbol for rat strain nomenclature.