Lmf1^{Gt(OST195742)Lex}

A gene-trap cassette containing a splice acceptor sequence, neomycin resistance gene and polyadenylation sequence (SA-neo-pA), was inserted into intron 1. Although RT-PCR analysis revealed transcripts corresponding to exon 1 and the gene-trap cassette in neonatal liver, sequences 3' of exon 1 were undetectable in homozygous mutant mice. qPCR analysis showed absence of exon 6 expression in mutant MEFs, thus confirming absence of transcripts with sequences downstream of the integration site. The gene-trap allele most likely represents a null allele.