pGT1Lxf was inserted into intron 4 of the gene and contains the mouse En2 intron 1 sequence, an En2 exon/splice acceptor (SA) sequence, the ORF for beta-geo (a fusion gene composed of beta-galactosidase and neomycin genes) as selective maker, and a polyadenylation (pA) signal sequence. (J:310028)