A loxP site was inserted in between exons 4 and 5. A floxed neomycin resistance cassette was inserted downstream of exon 8 and also replaced the codons of the last 4 amino acids of Tbx6. Cre-mediated recombination removed the selection cassette. Northern blot analysis confirmed normal Ppp4c transcript expression in embryo. RT-PCR confirmed normal Tbx6 transcript expression. Cre-mediated recombination removed the selection cassette and exons 5 through 8.