Fig. 2.

The catweasel mutation maps to chromosome 12 and catweasel mice have a mutation in the Six1 gene. (A) Genome scan of 30 Cwe/+ animals. The percentage of animals with two C3H loci is displayed on the Y axis and alternating autosomes in white and grey on the X-axis with each bar representing one marker. (B) Schematical representation of the critical region on chromosome 12 between D12Mit36 and D12Mit274 (61.6–73.6 Mb). The two columns represent the genotypes of two mice with recombination breakpoints that defined the critical region (C) Partial sequencing of genomic DNA of wildtype, Cwe/+ and Cwe/Cwe mice using primers spanning exon 1 of the Six1 gene. Between residue 220 and 230 of the sequenced PCR product, we identified an A to G substitution (red arrow) corresponding to position 411 of the Six1 open reading frame. (D) A schematical representation of the Six1 protein, with its amino-terminal end (red), Six domain (yellow), DNA binding homeobox domain (purple) and putative transactivation domain (green). The amino-terminal region (between residues 87 and 146) of the homeobox domain is conserved between various species. The identified mutation in catweasel mice (red arrow) and residues mutated in branchio-oto-renal syndrome (⁎; Ruf et al., 2004) are indicated. (E–G) Wildtype (E), Cwe/+ (F) and Cwe/Cwe (G) embryos (E9.5) were analysed for Six1 expression by whole mount RNA in situ hybridisation. Six1 is expressed widely with high levels in somites and the otic cup (arrowhead). No significant difference between control and mutant embryos was found. Scale bar = 1 mm. aa, amino acid; ba, branchial arch; dmSine, Drosophila melanogaster Sine oculis; drSix1, Danio rerio Six1; hsSIX1, Homo sapiens SIX1; Mb, mega basepairs; mmSix1-Cwe, Mus musculus Six1 with the catweasel mutation; mmSix1-WT, wildtype Mus musculus Six1; lb, limb bud; so, somites.