Fig. 1. Structure of knock-in vectors for Oct3/4 and Rex1. Structure of knock-in vector for Oct3/4 constructed to replace the coding region of the mouse Oct3/4 gene with Oct3/4- ECFP (or YFP) fusion gene and IRES-puromycin resistance gene to express Oct3/4-ECFP (or YFP) fusion protein from the recombinant allele, and structure of knock-in vector for Rex1 for insertion of an EGFP (or herpes simplex virus 2 thymidine kinase gene) and IRES-blasticidin resistance gene into exon 4 of the mouse Rex1 gene. Black boxes represent coding regions. Southern blotting analyses of the Oct3/4 locus and the Rex1 locus are shown at the bottom. Genomic DNA was digested with EcoRI for analyses of the Oct3/4 locus; a 300 bp probe from intron 5 produced an 11.6 kb band from the wild-type locus and a 10.3 kb band from the targeted locus. For analyses of the Rex1 locus, genomic DNA was digested with EcoRI, and hybridization with a 300 bp probe produced a 7.9 kb band from the wild-type locus and a 5.7 kb (5.9 kb for tk2 vector) band from the targeted locus. BSD, blasticidin S deaminase; E, EcoRI; P, positions of probes; Puro, puromycin-N-acetyltransferase; S, SpeI; tk2, herpes simplex virus 2 thymidine kinase (HSVtk2).