Fig. 3. Targeted disruption of the Disp gene. (A) Schematic diagram showing the Disp genomic locus, the targeting vector and the mutant allele. The top line shows a partial restriction map of the Disp genomic locus. The Disp genomic locus consists of eight exons (E1-E8). The second exon (E2) contains the translation start ATG and is followed by a 50 kb intron. A large Disp genomic locus suggests that Disp may be subject to intricate transcriptional regulation. The regions between the broken lines represent the 5' and 3' regions of homology and X indicates events of homologous recombination. The location of the fragments used as the 5' or 3' external probes in Southern blotting are shown, as well as the sizes of the fragments detected for wild-type and targeted alleles. (B) Southern blot analysis of targeted Disp E8 allele. Southern blot analysis of genomic DNA from 9.5 dpc embryos generated from matings between Disp E8^+/- heterozygous animals. DNA was digested with EcoRI and hybridized with the 3' probe. The resulting 4.5 kb and 5.2 kb bands correspond to the wild-type and targeted allele, respectively.