A floxed and Frted PGK-neo cassette was inserted on one side and a single loxP sites was inserted on the other side of a 410 bp fragment that included exon 3. Cre- and Flp-mediated recombination resulted in removal of exon 3. Immunoblot analysis confirmed the absence of full length protein expression in brains and hearts from homozygous mice. Expression of a short form in the heart is not disrupted in homozygotes.