Gene targeting
A targeted allele of Tbx15 was constructed using the same approach described in Russ et al. (2000). In brief, an IRES-LacZ-neo cassette with 5′ and 3′ homology arms of 3.5 kb and 1.8 kb was inserted into a unique BamHI site that lies 479 nucleotides downstream of the transcriptional initiation site (relative to the mRNA sequence) in exon 3. Positive ES clones were injected into B6 blastocysts, and chimeric founders crossed to either B6 mice or to deH/+ animals.