Functional Genomics in the Mouse: Phenotype-Based Mutagenesis Screens

Region-specific mutagenesis screen for novel mutations in the proximal portion of mouse chromosome 5. (A) Schematic representation of the wild-type chromosome 5 and the two marker chromosomes Rwand W^19H. The approximate position of four loci that serve as starting points for the generation of deletion complexes (dipeptidyl amino peptidase like protein 6, Dpp6; mouse homolog of the Huntington disease gene, Hdh; quininoid dihydropteridine reductase, Qdpr; and GABA_Areceptor, β-1 subunit, Gabrb1) are indicated. Atleft chromosomal locations of these four loci in the human genome are indicated. The Rw chromosome is associated with a 30-cM chromosomal inversion (Stephenson et al. 1994; R.B. Hough, A. Lengeling, and M. Bucan, unpubl.). The W^19H mutation is associated with a 4-Mb chromosomal deletion, which includes several known genes, such as a cluster of receptor tyrosine kinases, Kit, Pdgfra, and Flk1, cytoplasmic kinases Txk andTec, and the Clock gene (King et al. 1997a,b). (B) The breeding scheme of the pilot screen usingW^19H. In this screen, ENU-treated males are crossed to Rw/+ females and the Rw/+ G₁progeny are used for matings with the W^19H /+ mice to generate G₂ families that are screened for novel (recessive) mutations within the chromosomal region uncovered by theW^19H deletion. Four classes of (G₂) progeny are generated in this cross. (1) Mice with theW^19H deletion in trans to the mutagenized chromosome; (2) mice compound heterozygous for W^19H deletion and Rw chromosome; (3) normally pigmented mice that are heterozygous for mutagenized chromosome; and (4) mice heterozygous for the Rw chromosome. W^19H /+* mice are observed for novel recessive mutations; failure to recoverW^9H /+* mice in this cross implies that a recessive lethal mutation exists in this region.