A targeting vector was designed to insert an FRT-flanked PGK-Neo-pA 500 bp downstream of the 3' UTR of the Col1a1 locus. The FRT-flanked PGK-Neo-pA in the 3' UTR of the Col1a1 locus was replaced by co-injection of a tetO-Nanog (Nanog homeobox) plasmid and flpe recombinase. The tetO-Nanog plasmid contained a splice acceptor-double polyA sequence and the tetracycline responsive element (tetO) upstream of the Nanog gene. (J:279984)