Colonization and Differentiation Traits of the Japanese House Mouse, Mus musculus (Rodentia, Muridae), Inferred from Mitochondrial Haplotypes and External Body Characteristics.

To evaluate the colonization histories of the Japanese house mice (Mus musculus), phenotypic and genotypic admixtures of the subspecific traits were studied by evaluation of external body characteristics and mitochondrial gene elements. We analyzed mitochondrial Cytb gene and coat colorations and body dimensions as subspecific characteristics in mice from four areas of the Japanese Islands, the Sorachi, Ishikari and Iburi areas of Hokkaido, the Hidaka area of Hokkaido, and northeastern and central Honshu. Three occurrence patterns of the subspecific haplotypes of Cytb-the castaneus type only, the musculus type only, and the castaneus, musculus, and domesticus types together-were observed in the study areas. In central Honshu, the properties of haplotypes were in accord with the external characteristics as reported in previous findings. In contrast, complicated external characteristics were observed in the Hidaka area, where mice showed multiple haplotype properties. In addition, in northeastern Honshu, coat colorations were not in accord with haplotype properties and such discordance was also observed in most mice in the Sorachi, Ishikari and Iburi areas of Hokkaido. These complexities and discordances suggest that the genetic and phenotypic properties have been caused by different processes, not only through founder effects by migrations and subsequent subspecific hybridizations but also through differentiation in each study area.

Molecular analyses of the agouti allele in the Japanese house mouse identify a novel variant of the agouti gene.

It has been thought that the Japanese house mouse carries the Aw allele at the agouti locus causing light-colored bellies, but they do not always show this coloration. Thus, the presence of the Aw allele seems to be doubtful in them. To ascertain whether the Aw allele is present, a two-pronged approach was used. First, we compared lengths of DNA fragments obtained from three PCRs conducted on them to the known fragment sizes generated from mouse strains exhibiting homozygosities of either a/a, A/A, or Aw/Aw. PCR I, PCR II, and PCR III amplify only in the A and Aw alleles, the a and Aw alleles, and the a allele, respectively, and we detected amplifications in strains with A/A and Aw/Aw by PCR I, in those with a/a and the Japanese house mouse by PCR II, and in those with a/a by PCR III. Second, we sequenced the exon 1A region of the agouti gene and obtained sequences corresponding to the above strains and the Japanese house mouse, but their sequences were similar to those of the a allele. We concluded that their agouti allele is not identical to the Aw allele and seems to be a novel type similar to the a allele.