A floxed neo cassette was placed upstream of exon 3 and an additional loxP site was inserted downstream of exon 3. Cre-mediated recombination removed the neo cassette and exon 3, resulting in an out-of-frame transcript of exon 2-4 splicing. qRT-PCR analysis of RNA isolated from the left and right cardiac ventricles confirmed that expression is absent in homozygous and reduced to approximately half in heterozygous mutant mice. (J:226561)