Recombinase-mediated cassette exchange (RMCE) replaced the selection cassette in Gt(ROSA)26Sortm1(CAG-flpe)Arte with a 5' deleted neomycin resistance cassette, the CAG promoter, loxP flanked strong transcriptional termination site (LSL), the mouse Lin28b gene, IRES, and the firefly luciferase gene. Cre-mediated recombination can be utilized to remove the STOP cassette and get expression of the Lin28b gene.