Cre recombinase tool; Nkx2.5 acts as a key transcription factor and plays essential roles for heart formation. By mating the reporter mice with Cre-expressing mice, Nkx2-5 positive cells derived from double-positive mice were permanently labeled by fluorescent protein. When crossed with mice carrying a targeted floxed alleles, this strain is useful in eliminating tissue-specific conditional expression of the gene.