Cbfb^tm2.1Spe

This allele contains an extra copy of exon 4, interrupted by the lacZ coding sequence with a polyadenylation signal, inserted in reverse orientation immediately upstream of the endogenous exon 4. A V(D)J recombination signal sequence (RSS) with a 12-bp spacer resides upstream of the reversed exon4-lacZ, and an RSS with a 23-bp spacer lies downstream of the endogenous exon 4. The allele was generated in vivo by crossing mice heterozygous for Cbfbtm2Spe with mice expressing cre recombinase under control of the cytomegalovirus promoter to delete a loxP-flanked neo cassette in the progeny. lacZ is not expressed in cells of mice with this mutation. The exogenous sequences cause aberrant splicing resulting in loss of exon 4 from a significant proportion of transcripts from this allele, so that heterozygous mutant mice express ~65% of the normal level of full-length mRNA and homozygous mutants ~30%. (J:124224)