RESUMO
Human leukocyte antigen (HLA) plays a critical role in innate and adaptive immunity and is a well-known example of genes under natural selection. However, the genetic aspect of receptors recognizing HLA molecules has not yet been fully elucidated. Leukocyte immunoglobulin (Ig)-like receptors (LILRs) are a family of HLA class I-recognizing receptors comprising activating and inhibitory forms. We previously reported that the allele frequency of the 6.7 kb LILRA3 deletion is extremely high (71%) in the Japanese population, and we identified premature termination codon (PTC)-containing alleles. In this study, we observed a wide distribution of the high deletion frequency in Northeast Asians (84% in Korean Chinese, 79% in Man Chinese, 56% in Mongolian, and 76% in Buryat populations). Genotyping of the four HapMap populations revealed that LILRA3 alleles were in strong linkage disequilibrium with LILRB2 alleles in Northeast Asians. In addition, PTC-containing LILRA3 alleles were detected in Northeast Asians but not in non-Northeast Asians. Furthermore, flow-cytometric analysis revealed that the LILRB2 allele frequent in Northeast Asians was significantly associated with low levels of expression. F(ST) and extended-haplotype-homozygosity analysis for the HapMap populations provided evidence of positive selection acting on the LILRA3 and LILRB2 loci. Taken together, our results suggest that both the nonfunctional LILRA3 alleles and the low-expressing LILRB2 alleles identified in our study have increased in Northeast Asians because of natural selection. Our findings, therefore, lead us to speculate that not only HLA class I ligands but also their receptors might be sensitive to the local environment.
Assuntos
Povo Asiático , Antígenos de Histocompatibilidade Classe I/genética , Desequilíbrio de Ligação , Glicoproteínas de Membrana/genética , Receptores Imunológicos/genética , Seleção Genética , Feminino , Frequência do Gene , Haplótipos , Humanos , MasculinoRESUMO
The Khoton Mongolian population is a small and relatively isolated ethnic group residing predominantly in the northwestern part of Mongolia. A recent genetic study of the Y chromosome revealed that the major Mongolian ethnic groups have a relatively close genetic affinity to populations in the northern part of East Asia, while the Khoton population reflected an apparent genetic differentiation from the other Mongolian populations. To further investigate the genetic features of the Khoton and the other Mongolian populations, we analyzed the single nucleotide polymorphisms (SNPs) in the Xq13.3 region, which is thought to have an extremely low level of recombination in the human X chromosome. We found that the frequency distribution of Xq13.3 haplotypes in the Khoton population was substantially different from those in three other Mongolian populations (Khalkh, Uriankhai, and Zakhchin). The same relationship was also revealed by the results from the population tree and principal-component (PC) analysis based on the allele frequencies. These results are largely consistent with the hypothesis that the Khoton population descended from a nomadic tribe of Turkish origin, which has been supported by previous anthropological, historical, and Y-chromosome studies. However, the population structure analysis produced an additional finding, namely, that the Khoton population is likely to be an admixed population.
Assuntos
Alelos , Cromossomos Humanos X/genética , Haplótipos/genética , Povo Asiático , Cromossomos Humanos Y/genética , Frequência do Gene , Genética Populacional/métodos , Humanos , Mongólia , Polimorfismo de Nucleotídeo Único , Recombinação Genética/genéticaRESUMO
About 20 ethnic groups reside in Mongolia. On the basis of genetic and anthropological studies, it is believed that Mongolians have played a pivotal role in the peopling of Central and East Asia. However, the genetic relationships among these ethnic groups have remained obscure, as have their detailed relationships with adjacent populations. We analyzed 16 binary and 17 STR polymorphisms of human Y chromosome in 669 individuals from nine populations, including four indigenous ethnic groups in Mongolia (Khalkh, Uriankhai, Zakhchin, and Khoton). Among these four Mongolian populations, the Khalkh, Uriankhai, and Zakhchin populations showed relatively close genetic affinities to each other and to Siberian populations, while the Khoton population showed a closer relationship to Central Asian populations than to even the other Mongolian populations. These findings suggest that the major Mongolian ethnic groups have a close genetic affinity to populations in northern East Asia, although the genetic link between Mongolia and Central Asia is not negligible.
