Longli Kang

A Mitochondrial Revelation of Early Human Migrations to the Tibetan Plateau Before and After the Last Glacial Maximum

As the highest plateau surrounded by towering mountain ranges, the Tibetan Plateau was once considered to be one of the last populated areas of modern humans. However, this view has been tremendously changed by archeological, linguistic, and genetic findings in the past 60 years. Nevertheless, the timing and routes of entry of modern humans into the Tibetan Plateau is still unclear. To make these problems clear, we carried out high-resolution mitochondrial-DNA (mtDNA) analyses on 562 Tibeto-Burman inhabitants from nine different regions across the plateau. By examining the mtDNA haplogroup distributions and their principal components, we demonstrated that maternal diversity on the plateau reflects mostly a northern East Asian ancestry. Furthermore, phylogeographic analysis of plateau-specific sublineages based on 31 complete mtDNA sequences revealed two primary components: pre-last glacial maximum (LGM) inhabitants and post-LGM immigrants. Also, the analysis of one major pre-LGM sublineage A10 showed a strong signal of post-LGM population expansion (about 15,000 years ago) and greater diversity in the southern part of the Tibetan Plateau, indicating the southern plateau as a refuge place when climate dramatically changed during LGM.

A Map of Copy Number Variations in Chinese Populations

It has been shown that the human genome contains extensive copy number variations (CNVs). Investigating the medical and evolutionary impacts of CNVs requires the knowledge of locations, sizes and frequency distribution of them within and between populations. However, CNV study of Chinese minorities, which harbor the majority of genetic diversity of Chinese populations, has been underrepresented considering the same efforts in other populations. Here we constructed, to our knowledge, a first CNV map in seven Chinese populations representing the major linguistic groups in China with 1,440 CNV regions identified using Affymetrix SNP 6.0 Array. Considerable differences in distributions of CNV regions between populations and substantial population structures were observed. We showed that ∼35% of CNV regions identified in minority ethnic groups are not shared by Han Chinese population, indicating that the contribution of the minorities to genetic architecture of Chinese population could not be ignored. We further identified highly differentiated CNV regions between populations. For example, a common deletion in Dong and Zhuang (44.4% and 50%), which overlaps two keratin-associated protein genes contributing to the structure of hair fibers, was not observed in Han Chinese. Interestingly, the most differentiated CNV deletion between HapMap CEU and YRI containing CCL3L1 gene reported in previous studies was also the highest differentiated regions between Tibetan and other populations. Besides, by jointly analyzing CNVs and SNPs, we found a CNV region containing gene CTDSPL were in almost perfect linkage disequilibrium between flanking SNPs in Tibetan while not in other populations except HapMap CHD. Furthermore, we found the SNP taggability of CNVs in Chinese populations was much lower than that in European populations. Our results suggest the necessity of a full characterization of CNVs in Chinese populations, and the CNV map we constructed serves as a useful resource in further evolutionary and medical studies.

mtDNA Lineage Expansions in Sherpa Population Suggest Adaptive Evolution in Tibetan Highlands

Sherpa population is an ethnic group living in south mountainside of Himalayas for hundreds of years. They are famous as extraordinary mountaineers and guides, considered as a good example for successful adaptation to low oxygen environment in Tibetan highlands. Mitochondrial DNA (mtDNA) variations might be important in the highland adaption given its role in coding core subunits of oxidative phosphorylation in mitochondria. In this study, we sequenced the complete mtDNA genomes of 76 unrelated Sherpa individuals. Generally, Sherpa mtDNA haplogroup constitution was close to Tibetan populations. However, we found three lineage expansions in Sherpas, two of which (C4a3b1 and A4e3a) were Sherpa-specific. Both lineage expansions might begin within the past hundreds of years. Especially, nine individuals carry identical Haplogroup C4a3b1. According to the history of Sherpas and Bayesian skyline plot, we constructed various demographic models and found out that it is unlikely for these lineage expansions to occur in neutral models especially for C4a3b1. Nonsynonymous mutations harbored in C4a3b1 (G3745A) and A4e3a (T4216C) are both ND1 mutants (A147T and Y304H, respectively). Secondary structure predictions showed that G3745A were structurally closing to other pathogenic mutants, whereas T4216C itself was reported as the primary mutation for Lebers hereditary optic neuropathy. Thus, we propose that these mutations had certain effect on Complex I function and might be important in the high altitude adaptation for Sherpa people.

Genetic structures of the Tibetans and the Deng people in the Himalayas viewed from autosomal STRs

In the previous studies, the populations in Tibet exhibited a complicated genetic structure, indicating that those populations might be the admixture of East Asian and South/Central Asian populations, or have a North Asian origin. However, there have not been sufficient genetic data to support this hypothesis. In this study, we analyzed 15 autosomal polymorphic tetranucleotide short tandem repeat loci (D5S818, FGA, D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, vWA, TPOX, D18S51) for three populations from Tibet, namely, Deng/Mishmi (n=114), Qamdo Tibetan (n=78) and Lhasa Tibetan (n=101). The total number of observed alleles and the average heterozygosity for all samples were 394 and 0.7574, respectively. Analysis of molecular variance and estimated GST (0.0198) for these allele frequency data suggested the genetic divergence among Tibetan populations was significant. Furthermore, our new allele frequency data for 13 loci were compared with those of 41 world populations previously reported. Results from phylogenetic and multidimensional scaling analyses indicated that: (1) the Deng in Tibet has unique genetic characteristics different from the Tibetans; (2) populations living in the Himalayas area (Deng, Luoba/Adi) composed of a distinct cluster and are closely related to each other than to any other ethnic groups in East Asia; (3) the Tibetans are most similar to the North Asians. This genetic structure is consistent with the geographical barriers and linguistic classifications.

A 3.4-kb Copy-Number Deletion near EPAS1 Is Significantly Enriched in High-Altitude Tibetans but Absent from the Denisovan Sequence

Tibetan high-altitude adaptation (HAA) has been studied extensively, and many candidate genes have been reported. Subsequent efforts targeting HAA functional variants, however, have not been that successful (e.g., no functional variant has been suggested for the top candidate HAA gene, EPAS1). With WinXPCNVer, a method developed in this study, we detected in microarray data a Tibetan-enriched deletion (TED) carried by 90% of Tibetans; 50% were homozygous for the deletion, whereas only 3% carried the TED and 0% carried the homozygous deletion in 2,792 worldwide samples (p < 10(-15)). We employed long PCR and Sanger sequencing technologies to determine the exact copy number and breakpoints of the TED in 70 additional Tibetan and 182 diverse samples. The TED had identical boundaries (chr2: 46,694,276-46,697,683; hg19) and was 80 kb downstream of EPAS1. Notably, the TED was in strong linkage disequilibrium (LD; r(2) = 0.8) with EPAS1 variants associated with reduced blood concentrations of hemoglobin. It was also in complete LD with the 5-SNP motif, which was suspected to be introgressed from Denisovans, but the deletion itself was absent from the Denisovan sequence. Correspondingly, we detected that footprints of positive selection for the TED occurred 12,803 (95% confidence interval = 12,075-14,725) years ago. We further whole-genome deep sequenced (>60×) seven Tibetans and verified the TED but failed to identify any other copy-number variations with comparable patterns, giving this TED top priority for further study. We speculate that the specific patterns of the TED resulted from its own functionality in HAA of Tibetans or LD with a functional variant of EPAS1.

Y-chromosome O3 Haplogroup diversity in Sino-Tibetan populations reveals two migration routes into the Eastern Himalayas

The eastern Himalayas are located near the southern entrance through which early modern humans expanded into East Asia. The genetic structure in this region is therefore of great importance in the study of East Asian origins. However, few genetic studies have been performed on the Sino‐Tibetan populations (Luoba and Deng) in this region. Here, we analyzed the Y‐chromosome diversity of the two populations. The Luoba possessed haplogroups D, N, O, J, Q, and R, indicating gene flow from Tibetans, as well as the western and northern Eurasians. The Deng exhibited haplogroups O, D, N, and C, similar to most Sino‐Tibetan populations in the east. Short tandem repeat (STR) diversity within the dominant haplogroup O3 in Sino‐Tibetan populations showed that the Luoba are genetically close to Tibetans and the Deng are close to the Qiang. The Qiang had the greatest diversity of Sino‐Tibetan populations, supporting the view of this population being the oldest in the family. The lowest diversity occurred in the eastern Himalayas, suggesting that this area was an endpoint for the expansion of Sino‐Tibetan people. Thus, we have shown that populations with haplogroup O3 moved into the eastern Himalayas through at least two routes.

A panel of 74 AISNPs: Improved ancestry inference within Eastern Asia

Many ancestry informative SNP (AISNP) panels have been published. Ancestry resolution in them varies from three to eight continental clusters of populations depending on the panel used. However, none of these panels differentiates well among East Asian populations. To meet this need, we have developed a 74 AISNP panel after analyzing a much larger number of SNPs for Fst and allele frequency differences between two geographically close population groups within East Asia. The 74 AISNP panel can now distinguish at least 10 biogeographic groups of populations globally: Sub-Saharan Africa, North Africa, Europe, Southwest Asia, South Asia, North Asia, East Asia, Southeast Asia, Pacific and Americas. Compared with our previous 55-AISNP panel, Southeast Asia and North Asia are two newly assignable clusters. For individual ancestry assignment, the likelihood ratio and ancestry components were analyzed on a different set of 500 test individuals from 11 populations. All individuals from five of the test populations - Yoruba (YRI), European (CEU), Han Chinese in Henan (CHNH), Rondonian Surui (SUR) and Ticuna (TIC) - were assigned to their appropriate geographical regions unambiguously. For the other test populations, most of the individuals were assigned to their self-identified geographical regions with a certain degree of overlap with adjacent populations. These alternative ancestry components for each individual thus help give a clearer picture of the possible group origins of the individual. We have demonstrated that the new AISNP panel can achieve a deeper resolution of global ancestry.

Increasing the reference populations for the 55 AISNP panel: the need and benefits

Ancestry inference for an individual can only be as good as the reference populations with allele frequency data on the SNPs being used. If the most relevant ancestral population(s) does not have data available for the SNPs studied, then analyses based on DNA evidence may indicate a quite distantly related population, albeit one among the more closely related of the existing reference populations. We have added reference population allele frequencies for 14 additional population samples (with >1100 individuals studied) to the 125 population samples previously published for the Kidd Lab 55 AISNP panel. Allele frequencies are now publicly available for all 55 SNPs in ALFRED and FROG-kb for a total of 139 population samples. This Kidd Lab panel of 55 ancestry informative SNPs has been incorporated in commercial kits by both ThermoFisher Scientific and Illumina for massively parallel sequencing. Researchers employing those kits will find the enhanced set of reference populations useful.

Genetic evidence for an East Asian origin of Chinese Muslim populations Dongxiang and Hui

There is a long-going debate on the genetic origin of Chinese Muslim populations, such as Uygur, Dongxiang, and Hui. However, genetic information for those Muslim populations except Uygur is extremely limited. In this study, we investigated the genetic structure and ancestry of Chinese Muslims by analyzing 15 autosomal short tandem repeats in 652 individuals from Dongxiang, Hui, and Han Chinese populations in Gansu province. Both genetic distance and Bayesian-clustering methods showed significant genetic homogeneity between the two Muslim populations and East Asian populations, suggesting a common genetic ancestry. Our analysis found no evidence of substantial gene flow from Middle East or Europe into Dongxiang and Hui people during their Islamization. The dataset generated in present study are also valuable for forensic identification and paternity tests in China.

Northward genetic penetration across the Himalayas viewed from Sherpa people

Abstract The Himalayas have been suggested as a natural barrier for human migrations, especially the northward dispersals from the Indian Subcontinent to Tibetan Plateau. However, although the majority of Sherpa have a Tibeto-Burman origin, considerable genetic components from Indian Subcontinent have been observed in Sherpa people living in Tibet. The western Y chromosomal haplogroups R1a1a-M17, J-M304, and F*-M89 comprise almost 17% of Sherpa paternal gene pool. In the maternal side, M5c2, M21d, and U from the west also count up to 8% of Sherpa people. Those lineages with South Asian origin indicate that the Himalayas have been permeable to bidirectional gene flow.