A high-resolution genetic map of the nervous locus on mouse chromosome 8

The nervous (nr) mutant mouse displays two gross recessive traits: both an exaggeration of juvenile hyperactivity and a pronounced ataxia become apparent during the third and fourth postnatal weeks. Using an intersubspecific intercross, we have established a high-resolution map of a segment of mouse chromosome 8 that places the nr locus in a genomic segment defined by D8Rck1 on the centromeric end and D8Mit3 on the telomeric end. This map position places the nr locus within the BALB/cGr congenic region of the C3HeB/ FeJ-nr strain, confirming the accuracy of our study. We used this map position to identify and evaluate three genes-ankyrin 1, cortexin, and farnesyltransferase-as candidates for the nr gene. These three genes were eliminated from consideration but allowed us to establish the conservation of synteny between the region containing the nr locus and a segment of the short arm of human chromosome 8 (8p21-p11.2). Finally, the incomplete penetrance of the nr phenotype led us to perform a screen for modifier loci, and we present evidence that such a nervous modifier locus may exist on mouse chromosome 5.