QTL analyses of spontaneous activity by using mouse strains from Mishima battery.

We reported previously that spontaneous activity in the home cage is highly variable among the Mishima battery of mouse strains. In that study, NJL and KJR were found to be hyperactive strains in contrast to BLG2, which showed one of the lowest activity levels. To unravel the genetic loci involved in this behavioral phenotype, we conducted QTL analyses on backcross populations of crosses between either NJL or KJR and BLG2 strains. In the backcross of NJL to BLG2, no single locus was associated with increased spontaneous activity. In the backcross of KJR to BLG2, linkage analysis showed that a locus on the most telomeric region of Chromosome (Chr) 3 was involved in the spontaneous activity, thus named Loco1. Further linkage analysis using selected progeny carrying the allele from KJR at the Loco1 locus suggested the presence of another locus, Loco2, on Chr 17. An analysis showed that Loco1 and Loco2 interacted epistatically.