<i>Sd</i> phenotypes are caused by the ETn insertion.

<p>A. Strategy for creation of the knock-in (ki)ETn allele. The targeting vector was first used to create a targeted allele containing a neomycin resistance (<i>neo</i>) gene flanked by <i>loxP</i> and <i>lox2272</i>. Then, a replacement vector was used to replace <i>neo</i> with ETn by Cre-mediated recombination. Exons are shown as gray or black boxes. Black arrows indicate the direction of gene transcription. The red arrowhead indicates the insertion point of the ETn. The probe used for genotyping is shown as a black box. B. Morphology of the tails of E18.5 embryos. The kiETn/+ and the kiETn/kiETn embryos showed a kinked (arrow) and truncated tail, respectively. C. Hematoxylin and eosin staining of the intervertebral discs (IVDs), anorectum, and kidney of E18.5 embryos. The kiETn/+ embryos showed hypoplasia of the nucleus pulposus of the IVDs (white arrows). The kiETn/kiETn embryos showed a nucleus pulposus defect (white arrow) in the IVD, an anorectal malformation that was classified as fistulas of the urogenital tract (yellow arrow), and hypoplasia of the kidney (black arrow). Bars: 1 mm.