The Sox17 translational stop codon in exon 5 was replaced by a T2A (Thosea asigna virus, TaV) self-cleaving peptide followed by the improved Cre (iCre) for the efficient and equimolar translation of Sox17 and icre. Sox17 and icre are postranslationally cleaved by a 2A-mediated ribosome-skipping mechanism. The FRT-flanked neo selection cassette was subsequently deleted in the germline by FLP-mediated recombination.