Revisiting the role of the Himalayas in peopling Nepal: insights from mitochondrial genomes

Abstract

Himalayas was believed to be a formidably geographical barrier between South and East Asia. The observed high frequency of the East Eurasian paternal lineages in Nepal led some researchers to suggest that these lineages were introduced into Nepal from Tibet directly; however, it is also possible that the East Eurasian genetic components might trace their origins to northeast India where abundant East Eurasian maternal lineages have been detected. To trace the origin of the Nepalese maternal genetic components, especially those of East Eurasian ancestry, and then to better understand the role of the Himalayas in peopling Nepal, we have studied the matenal genetic composition extensively, especially the East Eurasian lineages, in Nepalese and its surrounding populations. Our results revealed the closer affinity between the Nepalese and the Tibetans, specifically, the Nepalese lineages of the East Eurasian ancestry generally are phylogenetically closer with the ones from Tibet, albeit a few mitochondrial DNA haplotypes, likely resulted from recent gene flow, were shared between the Nepalese and northeast Indians. It seems that Tibet was most likely to be the homeland for most of the East Eurasian in the Nepalese. Taking into account the previous observation on Y chromosome, now it is convincing that bearer of the East Eurasian genetic components had entered Nepal across the Himalayas around 6 kilo years ago (kya), a scenario in good agreement with the previous results from linguistics and archeology.

Unravelling the distinct strains of Tharu ancestry

“…The latter is consistent with previous observations showing that to a large extent the East Asianspecific genetic component among the Nepali and the Tharu groups has entered the region from the north over the Himalayas. 14,34,35 Consistent with the autosomal analysis, we found that the Tharu groups differ substantially in the overall proportions of East and South Asian-specific hgs in both haploid loci. However, it is clear that notable part (15-50%) of the maternal and paternal lineages among the Tharu trace back to East Asian populations (Table 2).…”

“…The ancestral form of this lineage occurs widely throughout East and Southeast Asia, 37 consistent with dispersal from Tibet and Southeast Asia to northern India via Nepal. 34,35,38 Gene flow in the opposite direction is equally likely for some of the lineages (eg, hgs C, H, J, L and R). An infrequent hg O2a-M95 is also shared among all the groups, although it is uncertain whether this marker arrived in northern India by way of the Tharu or through the Austroasiatic expansion, or both.…”

“…This is indeed the case considering both haploid loci and can be explained by extensive admixture of the Tharu with local populations, which would increase the diversity of South Asian but not East Asian-specific lineages. 35 Because hgs specific to South Asia are found in many different ethnic groups other than the Tharu, we focused our search further on mtDNA lineages presenting all the Tharu groups (Supplementary Table 8). The rare hg M43 is notably found among all the Tharu groups (Table 3).…”

Analysis of mitochondrial genome diversity identifies new and ancient maternal lineages in Cambodian aborigines

“…To determine the phylogenetic positions of the newly discovered Cambodian haplogroups, we employed ARTICLE 133 complete mtDNA genome sequences (including the 98 newly sequenced mitogenomes in the present study and the 35 previously reported mitogenomes from Asia 14,17,[22][23][24][25][28][29][30]32,42,43,48,52 ) to construct the phylogenetic tree. From the NCBI nucleotide database (http://www.ncbi.nlm.nih.gov), we selected 35 mitogenomes, including 10 reported but unclassified mitogenomes related with the newly defined haplogroups in Cambodians.…”

“…Eleven Lao sequences in Cambodians turned out to belong to a sub-branch of haplogroup M3, designated M3d (defined by T11827C-C16344T), to which also four previously published sequences, JF742206 (Nepal) 28 , FJ770946 (India) 29 , DQ112779 (Brahui, Pakistan) 30 and JF742212 (Nepal) 29 belong. The sequences JF742206 and FJ770946, together with the eleven Cambodian Lao samples, form a M3d sub-branch, designated M3d1 (defined by T10238C-T13820C).…”