A Flag-HA-Shox2a-DsRed-polyA cassette and an FRT flanked neo cassette were inserted at the start site in exon 1 via homologous recombination. Flp mediated recombination removed the neo cassette. The Shox2a cDNA encodes an N-terminal FLAG-HA- tagged full length Shox2 gene. The Shox2a cDNA has a heterologous 3'UTR releasing the gene from endogenous miRNA control. Immunofluorescence analysis indicates aberrant elevated expression of the mutant protein at E16.5 in the atrial septum. (J:212095)