Cbfa2t3tm1Swh heterozygotes were crossed with transgenic cre mice resulting in excision of exon 8 from the germline. It was predicted to be a null allele because splicing from exon 7 to exon 9 introduces a stop codon and would trigger nonsense-mediated mRNA decay. Gene inactivation in homozygotes was confirmed by a lack of signal in immunoblot assays of splenocyte nuclear extracts. (J:140967)