Generation of <i>Gbx1</i> mutant mice.

<p>(A) For the construction of the conditional <i>Gbx1-</i> null, <i>loxP</i> sites were inserted flanking exon 2 and a neomycin expression cassette was inserted 5′ to the flanked region as depicted in the schematic. Deletion of exon 2, thereby rendering the endogenous gene null, is mediated by the mating of a mouse containing the targeted allele with a mouse ubiquitously expressing ß-actin Cre. (B) To identify ES cells that properly underwent homologous recombination, the long and short homology arms were screened by Southern Blot of restriction digested genomic DNA. (C) The presence of the WT and targeted alleles in the progeny derived from targeted ES cells were confirmed by PCR of genomic DNA using specific primer sets. Arrow in (A) represents direction of neo transcription; Arrowheads in (A) represent the location of PCR primers used in (C); Gray box indicates exon 2 (E2), which encodes the <i>Gbx1</i> homeodomain; Purple box indicates the <i>neo</i> cassette flanked by FRT sites (orange circles); White triangles represent the position of <i>loxP</i> sites.