A floxed neo cassette was removed from Ebf2tm1Ggc via in vivo cre mediated recombination. The lacZ gene remained in frame and in place of the 5.2 kb fragment containing the coding regions of the first five exons. The deleted region included sequence encoding the majority of the DNA binding domain. The absence of full length transcript was confirmed by RT-PCR analysis of homozygous mutant mice. lacZ expression was determined to be driven by the endogenous promoter.