HAIR DEFECTS AND PUP LOSS IN MICE WITH TARGETED DELETION OF THE FIRSTCUT REPEAT DOMAIN OF THE CUX CDP HOMEOPROTEIN GENE/

CDP, a ubiquitous homeoprotein homologous to Drosophila cut, is implic ated as a transcriptional repressor in several developmental systems. It contains four independent DNA binding domains: three ''cut repeats' ' plus the homeodomain. The murine Cux/CDP gene spans more than 200 kb and is composed of at least 21 exons. We designed a targeting constru ct to replace the first cut repeat with a neomycin resistance cassette , introducing a nonsense mutation after position 1319 of the 4.5-kb re ading frame of Cux/CDP. We expected to generate a truncated product of approximate to 60 kDa with this construct, but instead rye obtained m ice expressing a mutant form of the protein, with an internal deletion of 246 amino acids encompassing cut repeat 1, but intact in the C-ter minal region. Ribonuclease protection assays and direct sequencing of mutant cDNA obtained by RT-PCR demonstrate skipping of exons 10 and 11 in the mutant. Homozygous mutant mice, designated Cux/CDP Delta CR1, display a phenotype characterized by curly vibrissae and wavy hair. We also observed a high degree of pup loss in litters born to mutant fem ales, most likely on a nutritional basis. The mutant protein is presen t at levels slightly greater than wild-type, but exhibits the same tis sue distribution as wild-type protein, and has approximately normal af finity for known target sequences (though no DNA targets identified to date require the first cut repeat for binding). These results support the hypothesis that the different DNA binding domains of the ubiquito us Cux/CDP protein are responsible for regulation of different genes i n diverse tissues during development. (C) 1998 Academic Press.