Identification of an N-ethyl-N-nitrosourea–induced mutation in Wdr1 causing spontaneous inflammation and thrombocytopenia. (A) Typical ear lesion observed in mice homozygous for the redears mutation at 6 months of age. A full histopathologic survey of major organs detected no other gross abnormalities. (B) Haplotype panel summarizing 521 meiotic events generated by outcrossing rd to 129S6/SvEv and collecting progeny from subsequent intercross and backcross matings. The final candidate interval for rd, defined by D5RD47 and D5RD51, was 1.81 Mb. (C) Electropherograms of DNA sequence from the Wdr1 exon 9/intron 9 splice boundary showing the presence of a T-to-A transversion in the second nucleotide of the splice donor in homozygous rd mice. (D) Schematic of the Wdr1 locus, with splicing of intron 9 indicated by dashed lines. The mutated nucleotide in intron 9 is underlined. Wdr1 intron 9 is a noncanonical AT–AC intron, a rare (0.036%) class of intron whose intron splice donor and acceptor dinucleotide sequences are AT and AC, respectively. AT–AC intron splice donors possess a highly conserved consensus sequence, ATATCCT, and the rd mutation affects the second nucleotide of this consensus. This causes activation of a cryptic AT–AC splice donor consensus, ATATCAA, present 6 bp upstream in exon 9, producing a transcript containing a 6-bp in-frame deletion. This transcript was identified in the bone marrow and spleen of Wdr1^rd/rd mice. (E) Domain structure of Wdr1. The protein comprises 11 WD40 repeats, which, from studies of Aip1 in yeast and C. elegans, are predicted to form 2 beta-propellers. The location of the 2 residues deleted in the mutant rd Wdr1 protein is indicated. (F) Amino acid sequence of Wdr1/Aip1 at the carboxy terminus of the sixth WD40 repeat. The sequence of the mutant rd Wdr1 protein, which lacks the highly conserved isoleucine and asparagine residues, is shown.