Exon 2 was replaced with a floxed lacZ gene with a polyadenylation sequence, diphtheria toxin A (DTA) gene, and frt flanked neo cassette. Germ-line flp-mediated recombination removed the neo cassette leaving the floxed lacZ-polyadenylation sequence upstream of the DTA gene. Cre mediated recombination is necessary to achieve expression of the DTA gene. (J:152390)