This strain is a conditional red fluorescent reporter rat strain carrying the expression cassette of the red fluorescent protein reporter gene (tdTomato). In the absence of Cre recombinase, the expression termination element (loxP-Stop-loxP, LSL) upstream of the tdTomato gene expression cassette blocks tdTomato expression. When this rat is crossed with a rat expressing Cre recombinase, Cre-positive cells, and their downstream differentiated lineages in the offspring undergo Cre recombinase-mediated deletion of the expression termination element between loxP sites, thereby achieving conditional expression of tdTomato protein. Strong tdTomato red fluorescent signals can then be observed in the relevant tissues or cells using a fluorescent microscope.