In search of the ancestors of Native American mitochondrial DNA (mtDNA) haplogroups, we analyzed the mtDNA of 531 individuals from nine indigenous populations in Siberia. All mtDNAs were subjected to high-resolution RFLP analysis, sequencing of the control-region hypervariable segment I (HVS-I), and surveyed for additional polymorphic markers in the coding region. Furthermore, the mtDNAs selected according to haplogroup/subhaplogroup status were completely sequenced. Phylogenetic analyses of the resulting data, combined with those from previously published Siberian arctic and sub-arctic populations, revealed that remnants of the ancient Siberian gene pool are still evident in Siberian populations, suggesting that the founding haplotypes of the Native American A–D branches originated in different parts of Siberia. Thus, lineage A complete sequences revealed in the Mansi of the Lower Ob and the Ket of the Lower Yenisei belong to A1, suggesting that A1 mtDNAs occasionally found in the remnants of hunting-gathering populations of northwestern and northern Siberia belonged to a common gene pool of the Siberian progenitors of Paleoindians. Moreover, lineage B1, which is the most closely related to the American B2, occurred in the Tubalar and Tuvan inhabiting the territory between the upper reaches of the Ob River in the west, to the Upper Yenisei region in the east. Finally, the sequence variants of haplogroups C and D, which are most similar to Native American C1 and D1, were detected in the Ulchi of the Lower Amur. Overall, our data suggest that the immediate ancestors of the Siberian/Beringian migrants who gave rise to ancient (pre-Clovis) Paleoindians have a common origin with aboriginal people of the area now designated the Altai-Sayan Upland, as well as the Lower Amur/Sea of Okhotsk region.
mtDNA variation; native Siberians; Native Americans
Population isolates are a valuable resource for medical genetics because of their reduced genetic, phenotypic and environmental heterogeneity. Further, extended linkage disequilibrium (LD) allows accurate haplotyping and imputation. In this study, we use nuclear and mitochondrial DNA data to determine to what extent the geographically isolated population of the Val Borbera valley also presents features of genetic isolation. We performed a comparative analysis of population structure and estimated effective population size exploiting LD data. We also evaluated haplotype sharing through the analysis of segments of autozygosity. Our findings reveal that the valley has features characteristic of a genetic isolate, including reduced genetic heterogeneity and reduced effective population size. We show that this population has been subject to prolonged genetic drift and thus we expect many variants that are rare in the general population to reach significant frequency values in the valley, making this population suitable for the identification of rare variants underlying complex traits.
genetic isolates; effective population size; linkage disequilibrium; mitochondrial DNA variation
Recent progress in the phylogenetic resolution of the Y-chromosome phylogeny permits the male demographic dynamics and migratory events that occurred in Central and Southern America after the initial human spread into the Americas to be investigated at the regional level. To delve further into this issue, we examined more than 400 Native American Y chromosomes (collected in the region ranging from Mexico to South America) belonging to haplogroup Q – virtually the only branch of the Y phylogeny observed in modern-day Amerindians of Central and South America – together with 27 from Mongolia and Kamchatka. Two main founding lineages, Q1a3a1a-M3 and Q1a3a1-L54(xM3), were detected along with novel sub-clades of younger age and more restricted geographic distributions. The first was also observed in Far East Asia while no Q1a3a1-L54(xM3) Y chromosome was found in Asia except the southern Siberian-specific sub-clade Q1a3a1c-L330. Our data not only confirm a southern Siberian origin of ancestral populations that gave rise to Paleo-Indians and the differentiation of both Native American Q founding lineages in Beringia, but support their concomitant arrival in Mesoamerica, where Mexico acted as recipient for the first wave of migration, followed by a rapid southward migration, along the Pacific coast, into the Andean region. Although Q1a3a1a-M3 and Q1a3a1-L54(xM3) display overlapping general distributions, they show different patterns of evolution in the Mexican plateau and the Andean area, which can be explained by local differentiations due to demographic events triggered by the introduction of agriculture and associated with the flourishing of the Great Empires.
The current human mitochondrial (mtDNA) phylogeny does not equally represent all human populations but is biased in favour of representatives originally from north and central Europe. This especially affects the phylogeny of some uncommon West Eurasian haplogroups, including I and W, whose southern European and Near Eastern components are very poorly represented, suggesting that extensive hidden phylogenetic substructure remains to be uncovered. This study expanded and re-analysed the available datasets of I and W complete mtDNA genomes, reaching a comprehensive 419 mitogenomes, and searched for precise correlations between the ages and geographical distributions of their numerous newly identified subclades with events of human dispersal which contributed to the genetic formation of modern Europeans. Our results showed that haplogroups I (within N1a1b) and W originated in the Near East during the Last Glacial Maximum or pre-warming period (the period of gradual warming between the end of the LGM, ∼19 ky ago, and the beginning of the first main warming phase, ∼15 ky ago) and, like the much more common haplogroups J and T, may have been involved in Late Glacial expansions starting from the Near East. Thus our data contribute to a better definition of the Late and postglacial re-peopling of Europe, providing further evidence for the scenario that major population expansions started after the Last Glacial Maximum but before Neolithic times, but also evidencing traces of diffusion events in several I and W subclades dating to the European Neolithic and restricted to Europe.
Sakha – an area connecting South and Northeast Siberia – is significant for understanding the history of peopling of Northeast Eurasia and the Americas. Previous studies have shown a genetic contiguity between Siberia and East Asia and the key role of South Siberia in the colonization of Siberia.
We report the results of a high-resolution phylogenetic analysis of 701 mtDNAs and 318 Y chromosomes from five native populations of Sakha (Yakuts, Evenks, Evens, Yukaghirs and Dolgans) and of the analysis of more than 500,000 autosomal SNPs of 758 individuals from 55 populations, including 40 previously unpublished samples from Siberia. Phylogenetically terminal clades of East Asian mtDNA haplogroups C and D and Y-chromosome haplogroups N1c, N1b and C3, constituting the core of the gene pool of the native populations from Sakha, connect Sakha and South Siberia. Analysis of autosomal SNP data confirms the genetic continuity between Sakha and South Siberia. Maternal lineages D5a2a2, C4a1c, C4a2, C5b1b and the Yakut-specific STR sub-clade of Y-chromosome haplogroup N1c can be linked to a migration of Yakut ancestors, while the paternal lineage C3c was most likely carried to Sakha by the expansion of the Tungusic people. MtDNA haplogroups Z1a1b and Z1a3, present in Yukaghirs, Evens and Dolgans, show traces of different and probably more ancient migration(s). Analysis of both haploid loci and autosomal SNP data revealed only minor genetic components shared between Sakha and the extreme Northeast Siberia. Although the major part of West Eurasian maternal and paternal lineages in Sakha could originate from recent admixture with East Europeans, mtDNA haplogroups H8, H20a and HV1a1a, as well as Y-chromosome haplogroup J, more probably reflect an ancient gene flow from West Eurasia through Central Asia and South Siberia.
Our high-resolution phylogenetic dissection of mtDNA and Y-chromosome haplogroups as well as analysis of autosomal SNP data suggests that Sakha was colonized by repeated expansions from South Siberia with minor gene flow from the Lower Amur/Southern Okhotsk region and/or Kamchatka. The minor West Eurasian component in Sakha attests to both recent and ongoing admixture with East Europeans and an ancient gene flow from West Eurasia.
mtDNA; Y chromosome; Autosomal SNPs; Sakha
Ethnic Belarusians make up more than 80% of the nine and half million people inhabiting the Republic of Belarus. Belarusians together with Ukrainians and Russians represent the East Slavic linguistic group, largest both in numbers and territory, inhabiting East Europe alongside Baltic-, Finno-Permic- and Turkic-speaking people. Till date, only a limited number of low resolution genetic studies have been performed on this population. Therefore, with the phylogeographic analysis of 565 Y-chromosomes and 267 mitochondrial DNAs from six well covered geographic sub-regions of Belarus we strove to complement the existing genetic profile of eastern Europeans. Our results reveal that around 80% of the paternal Belarusian gene pool is composed of R1a, I2a and N1c Y-chromosome haplogroups – a profile which is very similar to the two other eastern European populations – Ukrainians and Russians. The maternal Belarusian gene pool encompasses a full range of West Eurasian haplogroups and agrees well with the genetic structure of central-east European populations. Our data attest that latitudinal gradients characterize the variation of the uniparentally transmitted gene pools of modern Belarusians. In particular, the Y-chromosome reflects movements of people in central-east Europe, starting probably as early as the beginning of the Holocene. Furthermore, the matrilineal legacy of Belarusians retains two rare mitochondrial DNA haplogroups, N1a3 and N3, whose phylogeographies were explored in detail after de novo sequencing of 20 and 13 complete mitogenomes, respectively, from all over Eurasia. Our phylogeographic analyses reveal that two mitochondrial DNA lineages, N3 and N1a3, both of Middle Eastern origin, might mark distinct events of matrilineal gene flow to Europe: during the mid-Holocene period and around the Pleistocene-Holocene transition, respectively.
To better define the structure and origin of the Bulgarian paternal gene pool, we have examined the Y-chromosome variation in 808 Bulgarian males. The analysis was performed by high-resolution genotyping of biallelic markers and by analyzing the STR variation within the most informative haplogroups. We found that the Y-chromosome gene pool in modern Bulgarians is primarily represented by Western Eurasian haplogroups with ∼ 40% belonging to haplogroups E-V13 and I-M423, and 20% to R-M17. Haplogroups common in the Middle East (J and G) and in South Western Asia (R-L23*) occur at frequencies of 19% and 5%, respectively. Haplogroups C, N and Q, distinctive for Altaic and Central Asian Turkic-speaking populations, occur at the negligible frequency of only 1.5%. Principal Component analyses group Bulgarians with European populations, apart from Central Asian Turkic-speaking groups and South Western Asia populations. Within the country, the genetic variation is structured in Western, Central and Eastern Bulgaria indicating that the Balkan Mountains have been permeable to human movements. The lineage analysis provided the following interesting results: (i) R-L23* is present in Eastern Bulgaria since the post glacial period; (ii) haplogroup E-V13 has a Mesolithic age in Bulgaria from where it expanded after the arrival of farming; (iii) haplogroup J-M241 probably reflects the Neolithic westward expansion of farmers from the earliest sites along the Black Sea. On the whole, in light of the most recent historical studies, which indicate a substantial proto-Bulgarian input to the contemporary Bulgarian people, our data suggest that a common paternal ancestry between the proto-Bulgarians and the Altaic and Central Asian Turkic-speaking populations either did not exist or was negligible.
Complex I (CI) deficiency is a frequent cause of mitochondrial disorders and, in most cases, is due to mutations in CI subunit genes encoded by mitochondrial DNA (mtDNA). In this study, we establish the pathogenic role of the heteroplasmic mtDNA m.3890G>A/MT-ND1 (p.R195Q) mutation, which affects an extremely conserved amino acid position in ND1 subunit of CI. This mutation was found in a young-adult male with optic atrophy resembling Leber's hereditary optic neuropathy (LHON) and bilateral brainstem lesions. The only previously reported case with this mutation was a girl with fatal infantile Leigh syndrome with bilateral brainstem lesions. Transfer of the mutant mtDNA in the cybrid cell system resulted in a marked reduction of CI activity and CI-dependent ATP synthesis in the presence of a normally assembled enzyme.
These findings establish the pathogenicity of the m.3890G>A/MT-ND1 mutation and remark the link between CI mutations affecting the mtDNA-encoded ND subunits and LHON-like optic atrophy, which may be complicated by bilateral and symmetric lesions affecting the central nervous system. Peculiar to this mutation is the distribution of the brainstem lesions, with sparing of the striatum in both patients.
► Heteroplasmic m.3890G>A/MT-ND1 mutation causes optic atrophy and bilateral brainstem lesions ► This mutation affects a conserved amino acid in a functional domain of ND1 subunit ► This mutation significantly affects CI redox activity and function
CI, Complex I; CII, Complex II; CIII, Complex III; CIV, Complex IV; LHON, Leber's hereditary optic neuropathy; mtDNA, mitochondrial DNA; nDNA, nuclear DNA; OS, Oculus Sinister (left eye); OD, Oculus Dexter (right eye); Mitochondrial disorder; Vision loss; MT-ND1; Complex I
With analyses of entire mitogenomes, studies of Native American mitochondrial DNA (mtDNA) variation have entered the final phase of phylogenetic refinement: the dissection of the founding haplogroups into clades that arose in America during and after human arrival and spread. Ages and geographic distributions of these clades could provide novel clues on the colonization processes of the different regions of the double continent. As for the Southern Cone of South America, this approach has recently allowed the identification of two local clades (D1g and D1j) whose age estimates agree with the dating of the earliest archaeological sites in South America, indicating that Paleo-Indians might have reached that region from Beringia in less than 2000 years. In this study, we sequenced 46 mitogenomes belonging to two additional clades, termed B2i2 (former B2l) and C1b13, which were recently identified on the basis of mtDNA control-region data and whose geographical distributions appear to be restricted to Chile and Argentina. We confirm that their mutational motifs most likely arose in the Southern Cone region. However, the age estimate for B2i2 and C1b13 (11–13,000 years) appears to be younger than those of other local clades. The difference could reflect the different evolutionary origins of the distinct South American-specific sub-haplogroups, with some being already present, at different times and locations, at the very front of the expansion wave in South America, and others originating later in situ, when the tribalization process had already begun. A delayed origin of a few thousand years in one of the locally derived populations, possibly in the central part of Chile, would have limited the geographical and ethnic diffusion of B2i2 and explain the present-day occurrence that appears to be mainly confined to the Tehuelche and Araucanian-speaking groups.
Leber’s hereditary optic neuropathy (LHON) is a maternally inherited blinding disorder, which in over 90% of cases is due to one of three primary mitochondrial DNA (mtDNA) point mutations (m.11778G>A, m.3460G>A and m.14484T>C, respectively in MT-ND4, MT-ND1 and MT-ND6 genes). However, the spectrum of mtDNA mutations causing the remaining 10% of cases is only partially and often poorly defined.
In order to improve such a list of pathological variants, we completely sequenced the mitochondrial genomes of suspected LHON patients from Italy, France and Germany, lacking the three primary common mutations. Phylogenetic and conservation analyses were performed. Sixteen mitochondrial genomes were found to harbor at least one of the following nine rare LHON pathogenic mutations in genes MT-ND1 (m.3700G>A/p.A132T, m.3733G>A-C/p.E143K-Q, m.4171C>A/p.L289M), MT-ND4L (m.10663T>C/p.V65A) and MT-ND6 (m.14459G>A/p.A72V, m.14495A>G/p.M64I, m.14482C>A/p.L60S, and m.14568C>T/p.G36S). Phylogenetic analyses revealed that these substitutions were due to independent events on different haplogroups, whereas interspecies comparisons showed that they affected conserved amino acid residues or domains in the ND subunit genes of complex I.
Our findings indicate that these nine substitutions are all primary LHON mutations. Therefore, despite their relative low frequency, they should be routinely tested for in all LHON patients lacking the three common mutations. Moreover, our sequence analysis confirms the major role of haplogroups J1c and J2b (over 35% in our probands versus 6% in the general population of Western Europe) and other putative synergistic mtDNA variants in LHON expression.
Knowledge of high resolution Y-chromosome haplogroup diversification within Iran provides important geographic context regarding the spread and compartmentalization of male lineages in the Middle East and southwestern Asia. At present, the Iranian population is characterized by an extraordinary mix of different ethnic groups speaking a variety of Indo-Iranian, Semitic and Turkic languages. Despite these features, only few studies have investigated the multiethnic components of the Iranian gene pool. In this survey 938 Iranian male DNAs belonging to 15 ethnic groups from 14 Iranian provinces were analyzed for 84 Y-chromosome biallelic markers and 10 STRs. The results show an autochthonous but non-homogeneous ancient background mainly composed by J2a sub-clades with different external contributions. The phylogeography of the main haplogroups allowed identifying post-glacial and Neolithic expansions toward western Eurasia but also recent movements towards the Iranian region from western Eurasia (R1b-L23), Central Asia (Q-M25), Asia Minor (J2a-M92) and southern Mesopotamia (J1-Page08). In spite of the presence of important geographic barriers (Zagros and Alborz mountain ranges, and the Dasht-e Kavir and Dash-e Lut deserts) which may have limited gene flow, AMOVA analysis revealed that language, in addition to geography, has played an important role in shaping the nowadays Iranian gene pool. Overall, this study provides a portrait of the Y-chromosomal variation in Iran, useful for depicting a more comprehensive history of the peoples of this area as well as for reconstructing ancient migration routes. In addition, our results evidence the important role of the Iranian plateau as source and recipient of gene flow between culturally and genetically distinct populations.
Most genetic studies on modern cattle have established a common origin for all taurine breeds in the Near East, during the Neolithic transition about 10 thousand years (ka) ago. Yet, the possibility of independent and/or secondary domestication events is still debated and is fostered by the finding of rare mitochondrial DNA (mtDNA) haplogroups like P, Q and R. Haplogroup T1, because of its geographic distribution, has been the subject of several investigations pointing to a possible independent domestication event in Africa and suggesting a genetic contribution of African cattle to the formation of Iberian and Creole cattle. Whole mitochondrial genome sequence analysis, with its proven effectiveness in improving the resolution of phylogeographic studies, is the most appropriate tool to investigate the origin and structure of haplogroup T1.
A survey of >2200 bovine mtDNA control regions representing 28 breeds (15 European, 10 African, 3 American) identified 281 subjects belonging to haplogroup T1. Fifty-four were selected for whole mtDNA genome sequencing, and combined with ten T1 complete sequences from previous studies into the most detailed T1 phylogenetic tree available to date.
Phylogenetic analysis of the 64 T1 mitochondrial complete genomes revealed six distinct sub-haplogroups (T1a–T1f). Our data support the overall scenario of a Near Eastern origin of the T1 sub-haplogroups from as much as eight founding T1 haplotypes. However, the possibility that one sub-haplogroup (T1d) arose in North Africa, in domesticated stocks, shortly after their arrival from the Near East, can not be ruled out. Finally, the previously identified “African-derived American" (AA) haplotype turned out to be a sub-clade of T1c (T1c1a1). This haplotype was found here for the first time in Africa (Egypt), indicating that it probably originated in North Africa, reached the Iberian Peninsula and sailed to America, with the first European settlers.
The Late Glacial Maximum (LGM), ∼20 thousand years ago (kya), is thought to have forced the people inhabiting vast areas of northern and central Europe to retreat to southern regions characterized by milder climatic conditions. Archaeological records indicate that Franco-Cantabria might have been the major source for the re-peopling of Europe at the beginning of the Holocene (11.5 kya). However, genetic evidence is still scarce and has been the focus of an intense debate.
Based on a survey of more than 345,000 partial control region sequences and the analysis of 53 mitochondrial DNA (mtDNA) genomes, we identified an mtDNA lineage, HV4a1a, which most likely arose in the Franco-Cantabrian area about 5.4 kya and remained confined to northern Iberia.
The HV4a1a lineage and several of its younger branches reveal for the first time genetic continuity in this region and long-term episodes of isolation. This, in turn, could at least in part explain the unique linguistic and cultural features of the Basque region.
For millennia, the southern part of the Mesopotamia has been a wetland region generated by the Tigris and Euphrates rivers before flowing into the Gulf. This area has been occupied by human communities since ancient times and the present-day inhabitants, the Marsh Arabs, are considered the population with the strongest link to ancient Sumerians. Popular tradition, however, considers the Marsh Arabs as a foreign group, of unknown origin, which arrived in the marshlands when the rearing of water buffalo was introduced to the region.
To shed some light on the paternal and maternal origin of this population, Y chromosome and mitochondrial DNA (mtDNA) variation was surveyed in 143 Marsh Arabs and in a large sample of Iraqi controls. Analyses of the haplogroups and sub-haplogroups observed in the Marsh Arabs revealed a prevalent autochthonous Middle Eastern component for both male and female gene pools, with weak South-West Asian and African contributions, more evident in mtDNA. A higher male than female homogeneity is characteristic of the Marsh Arab gene pool, likely due to a strong male genetic drift determined by socio-cultural factors (patrilocality, polygamy, unequal male and female migration rates).
Evidence of genetic stratification ascribable to the Sumerian development was provided by the Y-chromosome data where the J1-Page08 branch reveals a local expansion, almost contemporary with the Sumerian City State period that characterized Southern Mesopotamia. On the other hand, a more ancient background shared with Northern Mesopotamia is revealed by the less represented Y-chromosome lineage J1-M267*. Overall our results indicate that the introduction of water buffalo breeding and rice farming, most likely from the Indian sub-continent, only marginally affected the gene pool of autochthonous people of the region. Furthermore, a prevalent Middle Eastern ancestry of the modern population of the marshes of southern Iraq implies that if the Marsh Arabs are descendants of the ancient Sumerians, also the Sumerians were most likely autochthonous and not of Indian or South Asian ancestry.
Mitochondrial dysfunction has been implicated in rare and common forms of type 2 diabetes (T2DM). Additionally, rare mitochondrial DNA (mtDNA) mutations have been shown to be causal for T2DM pathogenesis. So far, many studies have investigated the possibility that mtDNA variation might affect the risk of T2DM, however, when found, haplogroup association has been rarely replicated, even in related populations, possibly due to an inadequate level of haplogroup resolution. Effects of mtDNA variation on diabetes complications have also been proposed. However, additional studies evaluating the mitochondrial role on both T2DM and related complications are badly needed. To test the hypothesis of a mitochondrial genome effect on diabetes and its complications, we genotyped the mtDNAs of 466 T2DM patients and 438 controls from a regional population of central Italy (Marche). Based on the most updated mtDNA phylogeny, all 904 samples were classified into 57 different mitochondrial sub-haplogroups, thus reaching an unprecedented level of resolution. We then evaluated whether the susceptibility of developing T2DM or its complications differed among the identified haplogroups, considering also the potential effects of phenotypical and clinical variables. MtDNA backgrounds, even when based on a refined haplogroup classification, do not appear to play a role in developing T2DM despite a possible protective effect for the common European haplogroup H1, which harbors the G3010A transition in the MTRNR2 gene. In contrast, our data indicate that different mitochondrial haplogroups are significantly associated with an increased risk of specific diabetes complications: H (the most frequent European haplogroup) with retinopathy, H3 with neuropathy, U3 with nephropathy, and V with renal failure.
We report a sampling strategy based on Mendelian Breeding Units (MBUs), representing an interbreeding group of individuals sharing a common gene pool. The identification of MBUs is crucial for case-control experimental design in association studies. The aim of this work was to evaluate the possible existence of bias in terms of genetic variability and haplogroup frequencies in the MBU sample, due to severe sample selection. In order to reach this goal, the MBU sampling strategy was compared to a standard selection of individuals according to their surname and place of birth. We analysed mitochondrial DNA variation (first hypervariable segment and coding region) in unrelated healthy subjects from two different areas of Sardinia: the area around the town of Cabras and the western Campidano area. No statistically significant differences were observed when the two sampling methods were compared, indicating that the stringent sample selection needed to establish a MBU does not alter original genetic variability and haplogroup distribution. Therefore, the MBU sampling strategy can be considered a useful tool in association studies of complex traits.
breeding units strategy; mtDNA haplogroup distribution; association studies
When domestic taurine cattle diffused from the Fertile Crescent, local wild aurochsen (Bos primigenius) were still numerous. Moreover, aurochsen and introduced cattle often coexisted for millennia, thus providing potential conditions not only for spontaneous interbreeding, but also for pastoralists to create secondary domestication centers involving local aurochs populations. Recent mitochondrial genomes analyses revealed that not all modern taurine mtDNAs belong to the shallow macro-haplogroup T of Near Eastern origin, as demonstrated by the detection of three branches (P, Q and R) radiating prior to the T node in the bovine phylogeny. These uncommon haplogroups represent excellent tools to evaluate if sporadic interbreeding or even additional events of cattle domestication occurred.
The survey of the mitochondrial DNA (mtDNA) control-region variation of 1,747 bovine samples (1,128 new and 619 from previous studies) belonging to 37 European breeds allowed the identification of 16 novel non-T mtDNAs, which after complete genome sequencing were confirmed as members of haplogroups Q and R. These mtDNAs were then integrated in a phylogenetic tree encompassing all available P, Q and R complete mtDNA sequences.
Phylogenetic analyses of 28 mitochondrial genomes belonging to haplogroups P (N = 2), Q (N = 16) and R (N = 10) together with an extensive survey of all previously published mtDNA datasets revealed major similarities between haplogroups Q and T. Therefore, Q most likely represents an additional minor lineage domesticated in the Near East together with the founders of the T subhaplogroups. Whereas, haplogroup R is found, at least for the moment, only in Italy and nowhere else, either in modern or ancient samples, thus supporting an origin from European aurochsen. Haplogroup R could have been acquired through sporadic interbreeding of wild and domestic animals, but our data do not rule out the possibility of a local and secondary event of B. primigenius domestication in Italy.
The Tuareg of the Fezzan region (Libya) are characterized by an extremely high frequency (61%) of haplogroup H1, a mitochondrial DNA (mtDNA) haplogroup that is common in all Western European populations. To define how and when H1 spread from Europe to North Africa up to the Central Sahara, in Fezzan, we investigated the complete mitochondrial genomes of eleven Libyan Tuareg belonging to H1. Coalescence time estimates suggest an arrival of the European H1 mtDNAs at about 8,000–9,000 years ago, while phylogenetic analyses reveal three novel H1 branches, termed H1v, H1w and H1x, which appear to be specific for North African populations, but whose frequencies can be extremely different even in relatively close Tuareg villages. Overall, these findings support the scenario of an arrival of haplogroup H1 in North Africa from Iberia at the beginning of the Holocene, as a consequence of the improvement in climate conditions after the Younger Dryas cold snap, followed by in situ formation of local H1 sub-haplogroups. This process of autochthonous differentiation continues in the Libyan Tuareg who, probably due to isolation and recent founder events, are characterized by village-specific maternal mtDNA lineages.
Alzheimer's Disease (AD) is the most common neurodegenerative disease and the leading cause of dementia among senile subjects. It has been proposed that AD can be caused by defects in mitochondrial oxidative phosphorylation. Given the fundamental contribution of the mitochondrial genome (mtDNA) for the respiratory chain, there have been a number of studies investigating the association between mtDNA inherited variants and multifactorial diseases, however no general consensus has been reached yet on the correlation between mtDNA haplogroups and AD.
We applied for the first time a high resolution analysis (sequencing of displacement loop and restriction analysis of specific markers in the coding region of mtDNA) to investigate the possible association between mtDNA-inherited sequence variation and AD in 936 AD patients and 776 cognitively assessed normal controls from central and northern Italy. Among over 40 mtDNA sub-haplogroups analysed, we found that sub-haplogroup H5 is a risk factor for AD (OR = 1.85, 95% CI:1.04–3.23) in particular for females (OR = 2.19, 95% CI:1.06–4.51) and independently from the APOE genotype. Multivariate logistic regression revealed an interaction between H5 and age. When the whole sample is considered, the H5a subgroup of molecules, harboring the 4336 transition in the tRNAGln gene, already associated to AD in early studies, was about threefold more represented in AD patients than in controls (2.0% vs 0.8%; p = 0.031), and it might account for the increased frequency of H5 in AD patients (4.2% vs 2.3%). The complete re-sequencing of the 56 mtDNAs belonging to H5 revealed that AD patients showed a trend towards a higher number (p = 0.052) of sporadic mutations in tRNA and rRNA genes when compared with controls.
Our results indicate that high resolution analysis of inherited mtDNA sequence variation can help in identifying both ancient polymorphisms defining sub-haplogroups and the accumulation of sporadic mutations associated with complex traits such as AD.
Leber's hereditary optic neuropathy (LHON) is a maternally inherited blinding disease due to mitochondrial DNA (mtDNA) point mutations in complex I subunit genes, whose incomplete penetrance has been attributed to both genetic and environmental factors. Indeed, the mtDNA background defined as haplogroup J is known to increase the penetrance of the 11778/ND4 and 14484/ND6 mutations. Recently it was also documented that the professional exposure to n-hexane might act as an exogenous trigger for LHON. Therefore, we here investigate the effect of the n-hexane neurotoxic metabolite 2,5-hexanedione (2,5-HD) on cell viability and mitochondrial function of different cell models (cybrids and fibroblasts) carrying the LHON mutations on different mtDNA haplogroups. The viability of control and LHON cybrids and fibroblasts, whose mtDNAs were completely sequenced, was assessed using the MTT assay. Mitochondrial ATP synthesis rate driven by complex I substrates was determined with the luciferine/luciferase method. Incubation with 2,5-HD caused the maximal loss of viability in control and LHON cells. The toxic effect of this compound was similar in control cells irrespective of the mtDNA background. On the contrary, sensitivity to 2,5-HD induced cell death was greatly increased in LHON cells carrying the 11778/ND4 or the 14484/ND6 mutation on haplogroup J, whereas the 11778/ND4 mutation in association with haplogroups U and H significantly improved cell survival. The 11778/ND4 mutation on haplogroup U was also more resistant to inhibition of complex I dependent ATP synthesis by 2,5-HD. In conclusion, this study shows that mtDNA haplogroups modulate the response of LHON cells to 2,5-HD. In particular, haplogroup J makes cells more sensitive to its toxic effect. This is the first evidence that an mtDNA background plays a role by interacting with an environmental factor and that 2,5-HD may be a risk element for visual loss in LHON. This proof of principle has broad implications for other neurodegenerative disorders such as Parkinson's disease.
Central Asia and the Indian subcontinent represent an area considered as a source and a reservoir for human genetic diversity, with many markers taking root here, most of which are the ancestral state of eastern and western haplogroups, while others are local. Between these two regions, Terai (Nepal) is a pivotal passageway allowing, in different times, multiple population interactions, although because of its highly malarial environment, it was scarcely inhabited until a few decades ago, when malaria was eradicated. One of the oldest and the largest indigenous people of Terai is represented by the malaria resistant Tharus, whose gene pool could still retain traces of ancient complex interactions. Until now, however, investigations on their genetic structure have been scarce mainly identifying East Asian signatures.
High-resolution analyses of mitochondrial-DNA (including 34 complete sequences) and Y-chromosome (67 SNPs and 12 STRs) variations carried out in 173 Tharus (two groups from Central and one from Eastern Terai), and 104 Indians (Hindus from Terai and New Delhi and tribals from Andhra Pradesh) allowed the identification of three principal components: East Asian, West Eurasian and Indian, the last including both local and inter-regional sub-components, at least for the Y chromosome.
Although remarkable quantitative and qualitative differences appear among the various population groups and also between sexes within the same group, many mitochondrial-DNA and Y-chromosome lineages are shared or derived from ancient Indian haplogroups, thus revealing a deep shared ancestry between Tharus and Indians. Interestingly, the local Y-chromosome Indian component observed in the Andhra-Pradesh tribals is present in all Tharu groups, whereas the inter-regional component strongly prevails in the two Hindu samples and other Nepalese populations.
The complete sequencing of mtDNAs from unresolved haplogroups also provided informative markers that greatly improved the mtDNA phylogeny and allowed the identification of ancient relationships between Tharus and Malaysia, the Andaman Islands and Japan as well as between India and North and East Africa. Overall, this study gives a paradigmatic example of the importance of genetic isolates in revealing variants not easily detectable in the general population.
A Neolithic domestication of taurine cattle in the Fertile Crescent from local aurochsen (Bos primigenius) is generally accepted, but a genetic contribution from European aurochsen has been proposed. Here we performed a survey of a large number of taurine cattle mitochondrial DNA (mtDNA) control regions from numerous European breeds confirming the overall clustering within haplogroups (T1, T2 and T3) of Near Eastern ancestry, but also identifying eight mtDNAs (1.3%) that did not fit in haplogroup T. Sequencing of the entire mitochondrial genome showed that four mtDNAs formed a novel branch (haplogroup R) which, after the deep bifurcation that gave rise to the taurine and zebuine lineages, constitutes the earliest known split in the mtDNA phylogeny of B. primigenius. The remaining four mtDNAs were members of the recently discovered haplogroup Q. Phylogeographic data indicate that R mtDNAs were derived from female European aurochsen, possibly in the Italian Peninsula, and sporadically included in domestic herds. In contrast, the available data suggest that Q mtDNAs and T subclades were involved in the same Neolithic event of domestication in the Near East. Thus, the existence of novel (and rare) taurine haplogroups highlights a multifaceted genetic legacy from distinct B. primigenius populations. Taking into account that the maternally transmitted mtDNA tends to underestimate the extent of gene flow from European aurochsen, the detection of the R mtDNAs in autochthonous breeds, some of which are endangered, identifies an unexpected reservoir of genetic variation that should be carefully preserved.
The debate concerning the mechanisms underlying the prehistoric spread of farming to Southeast Europe is framed around the opposing roles of population movement and cultural diffusion. To investigate the possible involvement of local people during the transition of agriculture in the Balkans, we analysed patterns of Y-chromosome diversity in 1206 subjects from 17 population samples, mainly from Southeast Europe. Evidence from three Y-chromosome lineages, I-M423, E-V13 and J-M241, make it possible to distinguish between Holocene Mesolithic forager and subsequent Neolithic range expansions from the eastern Sahara and the Near East, respectively. In particular, whereas the Balkan microsatellite variation associated to J-M241 correlates with the Neolithic period, those related to E-V13 and I-M423 Balkan Y chromosomes are consistent with a late Mesolithic time frame. In addition, the low frequency and variance associated to I-M423 and E-V13 in Anatolia and the Middle East, support an European Mesolithic origin of these two clades. Thus, these Balkan Mesolithic foragers with their own autochthonous genetic signatures, were destined to become the earliest to adopt farming, when it was subsequently introduced by a cadre of migrating farmers from the Near East. These initial local converted farmers became the principal agents spreading this economy using maritime leapfrog colonization strategies in the Adriatic and transmitting the Neolithic cultural package to other adjacent Mesolithic populations. The ensuing range expansions of E-V13 and I-M423 parallel in space and time the diffusion of Neolithic Impressed Ware, thereby supporting a case of cultural diffusion using genetic evidence.
Balkan Neolithic; farming transition; peopling of Europe; Y-chromosome haplogroups
Human genetic diversity observed in Indian subcontinent is second only to that of Africa. This implies an early settlement and demographic growth soon after the first 'Out-of-Africa' dispersal of anatomically modern humans in Late Pleistocene. In contrast to this perspective, linguistic diversity in India has been thought to derive from more recent population movements and episodes of contact. With the exception of Dravidian, which origin and relatedness to other language phyla is obscure, all the language families in India can be linked to language families spoken in different regions of Eurasia. Mitochondrial DNA and Y chromosome evidence has supported largely local evolution of the genetic lineages of the majority of Dravidian and Indo-European speaking populations, but there is no consensus yet on the question of whether the Munda (Austro-Asiatic) speaking populations originated in India or derive from a relatively recent migration from further East.
Here, we report the analysis of 35 novel complete mtDNA sequences from India which refine the structure of Indian-specific varieties of haplogroup R. Detailed analysis of haplogroup R7, coupled with a survey of ~12,000 mtDNAs from caste and tribal groups over the entire Indian subcontinent, reveals that one of its more recently derived branches (R7a1), is particularly frequent among Munda-speaking tribal groups. This branch is nested within diverse R7 lineages found among Dravidian and Indo-European speakers of India. We have inferred from this that a subset of Munda-speaking groups have acquired R7 relatively recently. Furthermore, we find that the distribution of R7a1 within the Munda-speakers is largely restricted to one of the sub-branches (Kherwari) of northern Munda languages. This evidence does not support the hypothesis that the Austro-Asiatic speakers are the primary source of the R7 variation. Statistical analyses suggest a significant correlation between genetic variation and geography, rather than between genes and languages.
Our high-resolution phylogeographic study, involving diverse linguistic groups in India, suggests that the high frequency of mtDNA haplogroup R7 among Munda speaking populations of India can be explained best by gene flow from linguistically different populations of Indian subcontinent. The conclusion is based on the observation that among Indo-Europeans, and particularly in Dravidians, the haplogroup is, despite its lower frequency, phylogenetically more divergent, while among the Munda speakers only one sub-clade of R7, i.e. R7a1, can be observed. It is noteworthy that though R7 is autochthonous to India, and arises from the root of hg R, its distribution and phylogeography in India is not uniform. This suggests the more ancient establishment of an autochthonous matrilineal genetic structure, and that isolation in the Pleistocene, lineage loss through drift, and endogamy of prehistoric and historic groups have greatly inhibited genetic homogenization and geographical uniformity.