Fig. 3. The targeting strategy used for the Ripply2 gene and the external morphology of the resulting knockout mouse. (A) The top line shows the genomic organization of the Ripply2 gene, the second line represents the structure of the targeting vector, and the bottom two lines show the predicted structure of the Ripply2 locus following homologous recombination. The first exon of Ripply2 was partially deleted and replaced with a floxed neo cassette (the arrowheads on the line represent loxP sites). A germline chimeric mouse was then generated from recombinant ES cells containing the targeted allele and crossed with a CAG-Cre mouse to remove the neo cassette and establish the Ripply2-knockout mouse line. Ssp, SspI; E, EcoRI; B, BamHI; H, HindIII; N, NcoI; K, KpnI; X, XhoI. (B) The Ripply2-null mouse dies soon after birth and the external morphology at E17.5 is similar to those of segmentation-defective mutants, featuring a short trunk with rudimental tails.