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.
Go
Yasuhiro
Y
Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan.
Satta
Yoko
Y
Kawamoto
Yoshi
Y
Rakotoarisoa
Gilbert
G
Randrianjafy
Albert
A
Koyama
Naoki
N
Hirai
Hirohisa
H
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D020137:Base Pair Mismatch; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D019143:Evolution, Molecular; D005802:Genes, MHC Class II; D014644:Genetic Variation; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000235:genetics; D007900:Lemur / Q000235:genetics* / Q000276:immunology*; D008270:Madagascar; D008969:Molecular Sequence Data; D010802:Phylogeny; D011323:Primates / Q000235:genetics / Q000276:immunology; D012641:Selection, Genetic; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013997:Time Factors
D000949:Histocompatibility Antigens Class II; D004247:DNA