Biomedical subjects

Yoshi Kawamoto

Publications and source records attributed to Yoshi Kawamoto.

5 recordsLinked to original sources

PubMed2003

Frequent segmental sequence exchanges and rapid gene duplication characterize the MHC class I genes in lemurs.

Major histocompatibility complex (MHC) class I genes have complicated and profound evolutionary histories. To reconstruct and better understand their histories, partial class I genes (exon 2-intron 2-exon 3) were sequenced in a sampling of prosimians (Strepsirhini, Primates). In total, we detected 117 different sequences from 36 Malagasy prosimians (lemurs) and 1 non-Malagasy prosimian (galago) representing 4 families, 7 genera, and 13 species. Unlike the MHC class II genes ( MHC-DRB), MHC class I genes show a generally genus-specific mode of evolution in lemurs. Additionally, no prosimian class I loci were found to be orthologous to HLA genes, even at highly conserved loci (such as HLA-E, HLA-F). Phylogenetic analysis indicates that nucleotide diversity among loci was very small and the persistence time of the polymorphisms was short, suggesting that the origin of the lemur MHC class I genes detected in this study was relatively recent. The evolutionary mode of these genes is similar to that of classic HLA genes, HLA-A, HLA-B, and HLA-C, in terms of their recent origin and rarity of pseudogenes, and differs from them with respect to the degree of gene duplications. From the viewpoint of MHC genes evolution, some interlocus sequence exchanges were apparently observed in the lemur lineage upon phylogenetic and amino acid motif analyses. This is also in contrast to the evolutionary mode of HLA genes, where intralocus exchanges have certainly occurred but few interlocus exchanges have taken place. Consequently, the gene conversion model for explaining the generation of the MHC diversity among different loci can be thought to play more important roles in the evolution of lemur MHC class I genes than in that of HLA genes.

Animals↗

PubMed2003

Evolution of the cystatin B gene: implications for the origin of its variable dodecamer tandem repeat in humans.

The human cystatin B gene contains a variable number of 12-bp tandem repeats in its promoter region, of which the common alleles contain two or three copies and unusual expansion causes progressive myoclonus epilepsy of the Unverricht-Lundborg type. We undertook a comprehensive analysis of the genomic sequence to address the evolutionary events of this variable repeat. By examination of a contiguous genome sequence spanning 5.0 kb and linkage analysis of detected polymorphic changes, we identified six major intragenic haplotypes in unrelated Japanese subjects. The number of normal repeats was closely correlated with these alleles, indicating that changes in the array should be comparatively rare events during human evolution. To examine the origin of the repeat array further, we also analyzed five primate genomes. Repetitive polymorphism was unlikely in hominoids, and the array originated with the dodecamer itself in the course of primate evolution. The variability conceivably developed after the separation to humans.

Cystatin B↗

PubMed2002

Mhc-DRB genes evolution in lemurs.

Partial exon 2 sequences (202 bp) of the lemur Mhc-DRB genes were sequenced. A total of 137 novel sequences were detected in 66 lemurs, representing four out of the five extant families. Trans-species polymorphisms and even identical sequences were observed not only among genera but also among families. Based on the time-scale of lemur evolution, these findings suggest that some identical sequences have been maintained for more than 40 million years. This is in contrast to the evolutionary mode of simian DRB genes, where such identical sequences have been retained for at most several million years. To explore the reasons behind these unexpected findings, the degree of recombination and the synonymous substitution rate in lemurs and simians were examined. We found that (1) little difference existed in the extent of recombination, (2) frequent recombination occurred within the alpha-helix as well as between the beta-pleated sheet and the alpha-helix, and (3) the synonymous substitution rate was significantly reduced in lemur lineages. Upon phylogenetic analysis, lemur DRB genes were clustered by themselves and separated from the other primate DRB genes (simians and non-Malagasy prosimians). This result suggests that the DRB variations in extant lemur populations have been generated after the divergence of the lemurs from the remaining primates. This mode of substitution accumulation is also supported by a pattern of mismatch distribution among lemur DRB genes. These observations correspond with the postulation that a severe bottleneck occurred when the ancestors of lemurs settled into Madagascar from the African continent.

Amino Acid Motifs↗

PubMed2002

Molecular evolution of IgG subclass among nonhuman primates: implication of differences in antigenic determinants among Apes.

The cross-reactivity of five different rabbit polyclonal antibodies to human IgG and IgG subclass (IgG1, IgG2, IgG3, and IgG4) was determined by competitive ELISA with nine nonhuman primate species including five apes, three Old World monkeys, and one New World monkey. As similar to those previously reported, the reactivity of anti-human IgG antibody with plasma from different primate species was closely related with phylogenic distance from human. Every anti-human IgG subclass antibody showed low cross-reactivity with plasma from Old World and New World monkeys. The plasma from all apes except for gibbons (Hylobates spp.) showed 60 to 100% of cross-reactivity with anti-human IgG2 and IgG3 antibodies. On the other hand, chimpanzee (Pan troglodytes and Pan paniscus) and orangutan (Pongo pygmaeus) plasma showed 100% cross-reactivity with anti-human IgG1 antibody, but gorilla (Gorilla gorilla) and gibbon plasma showed no cross-reactivity. The chimpanzee and gorilla plasma cross-reacted with anti-human IgG4 antibody at different reactivity, 100% in chimpanzee and 50% in gorilla, but no cross-reactivity was observed in orangutan and gibbon plasma. These results suggest the possibilities that the divergence of "human-type" IgG subclasses might occur at the time of divergence of Homo sapience from Hylobatidae, and that the molecular evolution of IgG1 as well as IgG4 is different from that of IgG2 and IgG3 in great apes, this is probably caused by different in development of immune function in apes during the course of evolution.

Animals↗

PubMed2002

Cytogenetic differentiation of two sympatric tree shrew taxa found in the southern part of the Isthmus of Kra.

Sympatric populations of the genus Tupaia encompassing two cytotypes (cyt60, 2n = 60 and cyt62, 2n = 62) were found in the southern part of the Isthmus of Kra (the middle region of the Malay Peninsula, Thailand). C-bands, location of rDNA, and location of non-essential telomeric repeats (TRs) were investigated in detail for 23 animals captured in the area. Such chromosomal traits definitely reveal that two distinct cytotypes exist in the sympatric population, though the external morphological traits are similar. Hybrid cytotypes were not observed; thus, these two cytotypes appear to be genetically isolated sibling species. Chromosomal results compared with previous data, geographic distribution and morphological data observed with new insight suggest that, in the sympatric population, 'cyt60' represents members of Tupaia glis, while 'cyt62' identifies individuals of Tupaia belangeri. The cytogenetic information discovered in the present study offers new insight to morphological classification and, further, may provide substantial diagnostic characteristics for the distinction of tree shrew species.

Animals↗