Takahiro Yamagata

Nucleotide diversity of mitochondrial DNAs between the swamp and the river types of domestic water buffaloes,Bubalus bubalis, based on restriction endonuclease cleavage patterns

Cleavage patterns of mitochondrial DNAs (mtDNAs) by 15 restriction endonucleases were analyzed for 10 swamp and 13 river types of domestic water buffaloes. Digestions with nine enzymes exhibited polymorphisms giving two or three kinds of cleavage patterns. Five mtDNA types were identified, three types in the swamp buffaloes of the Philippines, Vietnam, and Indonesia (S-types) and two types in the river buffaloes of Bangladesh and Pakistan (R-types). Nucleotide diversities ranged from 0.2 to 0.6% within the S- and R-types and from 1.9 to 2.4% between the R-types and the S-types. These values indicated that R-type and S-type mtDNAs differentiated at thesubspecific level of other mammalianspecies reported. The possibility of polyphyletic domestication in different places is discussed for the origin of two distinct types of domestic water buffaloes.

Genetic differentiation between laboratory lines of the musk shrew (Suncus murinus, insectivora) based on restriction endonuclease cleavage patterns of mitochondrial DNA

The cleavage patterns of mitochondrial DNA (mtDNA) by 17 restriction endonucleases were compared between eight lines of musk shrews derived from different wild-caught stocks. Enzymatic digestion byBamHI,PvuII,XbaI, andXhoI showed a cleavage pattern common to all lines that were from five Japanese islands (Nag, Ize, OKI, TKU, and Tr), Bangladesh (BAN), Sri Lanka (SRI), and Java (Bog), and every line lacked cleavage sites forSalI andSmaI. Different cleavage patterns were detected by the remaining 11 enzymes. Within the BAN line, the presence of at least two types of mtDNAs was proved by six enzymes and was not contradictory to the maternal pedigrees going up to the wild ancestors of the stock. More than 30 cleavage sites of the shrew mtDNA were mapped by double-digestion methods. Nucleotide diversities of mtDNA were calculated from these maps and were estimated to be less than 0.5% among Japanese and Bog lines but to be 3.8% between BAN and the other seven lines and 2.3% within the BAN line. These results indicate that BAN shrews differentiate from the other lines to the intersubspecific extent reported in mice previously.

Genetic relationship among the musk shrews,Suncus murinus insectivora, inhabiting islands and the continent based on mitochondrial DNA types

Cleavage patterns of mitochondrial DNA (mtDNA) by restriction endonucleases were examined in musk shrews collected at six trapping sites on two Japanese and two Indonesian islands, on Sri Lanka, situated close to the Indian subcontinent, and on the mainland of East Bengal in Bangladesh. No variation of mtDNAs was found among the Japanese and Indonesian shrews, despite their geographical isolation by the sea. In contrast, at least six mtDNA types were present in the Sri Lanka and the Bangladesh populations (three types for each), and these two populations seemed to be differentiated to the extent, which could be compared to the “mice-intersubspecific” differences. These populations were also differentiated from the Japanese-Indonesian type. Furthermore, a similar level of differentiation was also estimated between two mtDNA types within these respective populations. This feral species might be considered unique because of its high emigration rate caused by human movements and its high rate of subspecific hybridization.

Virological Properties and Nucleotide Sequences of Cas-E-Type Endogenous Ecotropic Murine Leukemia Viruses in South Asian Wild Mice, Mus musculus castaneus

ABSTRACT Two types of endogenous ecotropic murine leukemia viruses (MuLVs), termed AKV- and Cas-E-type MuLVs, differ in nucleotide sequence and distribution in wild mouse subspecies. In contrast to AKV-type MuLV, Cas-E-type MuLV is not carried by common laboratory mice. Wild mice ofMus musculus (M. m.) castaneus carry multiple copies of Cas-E-type endogenous MuLV, including the Fv-4r gene that is a truncated form of integrated MuLV and functions as a hosts resistance gene against ecotropic MuLV infection. Our genetic cross experiments showed that only the Fv-4r gene was associated with resistance to ecotropic F-MuLV infection. Because the spontaneous expression of infectious virus was not detected in M. m. castaneus, we generated mice that did not carry the Fv-4r gene but did carry a single or a few endogenous MuLV loci. In mice not carrying theFv-4r gene, infectious MuLVs were isolated in association with three of six Cas-E-type endogenous MuLV loci. The isolated viruses showed a weak syncytium-forming activity for XC cells, an interfering property of ecotropic MuLV, and a slight antigenic variation. Two genomic DNAs containing endogenous Cas-E-type MuLV were cloned and partially sequenced. All of the Cas-E-type endogenous MuLVs were closely related, hybrid-type viruses with an ecotropicenv gene and a xenotropic long terminal repeat. Duplications and a deletion were found in a restricted region of the hypervariable proline-rich region of Env glycoprotein.

Population Structure of Wild Musk Shrews (Suncus murinus) in Asia Based on Mitochondrial DNA Variation, with Research in Cambodia and Bhutan

The musk shrew (Suncus murinus) is a small mammalian species belonging to Insectivora. It is widely distributed in Asia. To identify the genetic relationship among wild musk shrew populations and examine its migration route, we investigated the populations of Cambodia and Bhutan by using mitochondrial DNA restriction fragment length polymorphism analysis and compared them with other Asian populations previously described. Four haplotypes were detected in Cambodia and eight in Bhutan. A total of 53 haplotypes were detected in Asia and were classified largely into two groups, the Continental and Island types, based on a minimum spanning network. From the distribution of mtDNA types in wild musk shrews, three major population groups are identified in Asia: South Asia, Southeast Asia, and Malay. It is suggested that the Malay population group was a mix of South and Southeast Asian population groups and that this was a contact area of the two groups. In addition, other contact areas between the South and Southeast Asian groups exist in Myanmar, but unlike the Malay, the Myanmar area was the border of these groups.

Female mice of DDK strain are fully fertile in the intersubspecific crosses with Mus musculus molossinus and M. m. castaneus

The female mice of DDK strain are almost infertile when mated with males from other strains. This phenomenon is caused by the early death of F1 embryos owing to the incompatibility system attributed to the ovum mutant (Om) locus on Chromosome (Chr) 11 and known as DDK syndrome. In the present study, DDK females were found to be fully fertile in the intersubspecific matings with the males of two wild mouse-derived strains, MOM (originated from Japanese wild mice, Mus musculus molossinus) and Cas (originated from Philippine wild mice, M. m. castaneus), indicating that no incompatibility exists between DDK oocytes and spermatozoa of MOM and Cas strains. Furthermore, this compatibility has been confirmed by the following two findings: (1) Normal fertility was shown by the two types of backcrosses, DDK females x F(1) (DDK female x MOM male) males and DDK females x F(1) (DDK female x Cas male) males; and (2) the offspring from these backcrosses segregated equally into the homozygotes and heterozygotes as genotyped by the microsatellite markers closely linked to Om locus. MOM and Cas strains would be useful for further investigations on the Om locus. On the other hand, the litter size of F(1) [C57BL/6Cr (B6) female x Cas male] females mated with B6 males was about half that of the mating with DDK males. It would be interesting to investigate whether this reduction in fertility is related to the Om locus or not.

Phylogeography of Wild Musk Shrew ( Suncus Murinus ) Populations in Asia Based on Blood Protein/Enzyme Variation

The musk shrew (Suncus murinus) is an insectivore species that inhabits tropical and subtropical Asia widely. To clarify the genetic relationship among wild musk shrew populations, we examined the electrophoretic variants of biparentally inherited genetic markers at 10 loci coding for eight blood proteins/enzymes in a total of 639 animals and compared the results obtained from the mitochondrial DNA data. The principal-component analysis performed using the allele frequency data revealed that the 17 populations could be divided into two major groups, a South Asian group and a Southeast Asian group that includes several island populations bound by Myanmar. The degrees of genetic divergence among populations were higher within the Southeast Asian group than within the South Asian group. This finding was incongruent with the mtDNA diversity. Analysis conducted at the individual level showed that a shrew from the central region in Myanmar that carries a South Asian type of mtDNA showed the electrophoretic variants specific to the Southeast Asian group, suggesting that this region is a contact zone between the two major groups.