To elucidate the biological functions of mammalian Bptf during mammalian embryonic development we generated two mutant mouse lines. One line, designated as BptfXG023, was derived from an ES cell line carrying an in-frame gene-trap vector insertion between exons 15 and 16 of Bptf (Figure S2A, Figure S2B, S2C, S2D, S2E, S2F) (XG023; http://www.genetrap.org/) [26]. We identified the precise junction of the insertion site of the gene trap by DNA sequence analysis of the corresponding PCR products, and confirmed by RT-PCR that trapping of Bptf mRNA into vector sequences leads to loss of RNA splicing between exons 15 and 16, and reduced expression of Bptf sequences 3′ to the insertion site (Figure S3A, Figure S3B). In addition, we confirmed by 5′-RACE that the insertion resulted in an in-frame fusion between Bptf and β-galactosidase-neomycin phosphotransferase (β-Geo) sequences of the gene-trap vector. (Figure S3C). Consistent with previous findings, Northern blotting of adult tissue RNA showed that both wild-type Bptf and the Bptf–β-Geo fusion alleles are specifically expressed at high levels in the testis and at moderate levels in the lung, spleen, and brain
