A targeting construct was designed to insert a lacZ-puro cassette into exon 1, deleting sequence that encodes transcriptional regulatory regions and for the CUT domain required for DNA binding. In-frame stop codons were included in the vector, following the lacZ sequence to prevent the production of a truncated Onecut2 protein or read-through transcripts initiated in the lacZ or puro cassettes. RT-PCR failed to detect Onecut2 transcript in mutant liver samples. (J:100352)