Reconstructing the phylogeny of African mitochondrial DNA lineages in Slavs

To elucidate the origin of African-specific mtDNA lineages, revealed previously in Slavonic populations (at frequency of about 0.4%), we completely sequenced eight African genomes belonging to haplogroups L1b, L2a, L3b, L3d and M1 gathered from Russians, Czechs, Slovaks and Poles. Results of phylogeographic analysis suggest that at least part of the African mtDNA lineages found in Slavs (such as L1b, L3b1, L3d) appears to be of West African origin, testifying to an opportunity of their occurrence as a result of migrations to Eastern Europe through Iberia. However, a prehistoric introgression of African mtDNA lineages into Eastern Europe (approximately 10 000 years ago) seems to be probable only for European-specific subclade L2a1a, defined by coding region mutations at positions 6722 and 12903 and detected in Czechs and Slovaks. Further studies of the nature of African admixture in gene pools of Europeans require the essential enlargement of databases of African complete mitochondrial genomes.European Journal of Human Genetics (2008) 16, 1091-1096; doi:10.1038/ejhg.2008.70; published online 9 April 2008.     

五个母系遗传非综合征性耳聋和药物性耳聋的中国汉族家系

目的 通过对母系遗传非综合征性耳聋家系临床和分子遗传学特征分析,进一步探讨线粒体12S rRNA基因对母系遗传药物性耳聋的影响.方法 收集5个非综合征性耳聋患者家系,提取基因组DNA,然后进行线粒体DNA全序列和间隙连接蛋白β2(gap junction protein beta 2,GJB2)基因扩增并测序分析.结果 5个家系内和家系间的母系成员在听力损失、发病年龄和听力曲线上存在较大差异.5个家系耳聋发生的外显率分别为17.6%、50.0%、66.7%、31.3%和23.1%,平均外显率是37.7%.线粒体全序列显示家系间存在已知的1555A＞G突变和不同的多态性位点,分别属于东亚人群D4b2b、B4c1b1、F3、C1、D5a单倍型.这5个家系没有携带已知的线粒体DNA继发突变,但发现了2个保守性较高的ND1L89T和CO3 A200T突变.而且,GJB2基因上未发现与耳聋相关的突变.结论 这5个母系遗传非综合征性耳聋家系中,线粒体DNA继发突变、GJB2基因可能没有影响1555A＞G的表型表达.然而,氨基糖甙类抗生素、线粒体DNA多态性及其他核修饰基因可能对这5个耳聋家系的表型表达起到修饰作用.     

Association of whole mtDNA,an NADPH G11914A variant,and haplogroups with high physical performance in an elite military troop

Physical performance is a multifactorial and complex trait influenced by environmental and hereditary factors. Environmental factors alone have been insufficient to characterize all outstanding phenotypes. Recent advances in genomic technologies have enabled the investigation of whole nuclear and mitochondrial genome sequences, increasing our ability to understand interindividual variability in physical performance. Our objective was to evaluate the association of mitochondrial polymorphic loci with physical performance in Brazilian elite military personnel. Eighty-eight male military personnel who participated in the Command Actions Course of the Army were selected. Total DNA was obtained from blood samples and a complete mitochondrial genome (mtDNA) was sequenced using Illumina MiSeq platform. Twenty-nine subjects completed the training program (FINISHED, ‘F''), and fifty-nine failed to complete (NOT_FINISHED, ‘NF''). The mtDNA from NF was slightly more similar to genomes from African countries frequently related to endurance level. Twenty-two distinct mtDNA haplogroups were identified corroborating the intense genetic admixture of the Brazilian population, but their distribution was similar between the two groups (F_ST=0.0009). Of 745 polymorphisms detected in the mtDNA, the position G11914A within the NADPH gene component of the electron transport chain, was statistically different between F and NF groups (P=0.011; OR: 4.286; 95%CI: 1.198-16.719), with a higher frequency of the G allele in group F individuals). The high performance of military personnel may be mediated by performance-related genomic traits. Thus, mitochondrial genetic markers such as the ND4 gene may play an important role on physical performance variability.     

An approach to yeast classification by mapping mitochondrial DNA from Dekkera/Brettanomyces and Eeniella genera

Summary Sequences hybridzing to mitochondrial DNA probes from Saccharomyces cerevisiae have been mapped in six mitochondrial genomes from the Dekkera/Brettanomyces yeasts and in mtDNA from the closely related Eeniella nana. Sequence order for the 34.5 kbp mtDNA of E. nana is identical to that for mtDNAs from B. custersianus (28.5 kbp) and B. naardenensis (41.7 kbp) thereby suggesting that the former yeast is affiliated with the latter two species. A closer relationship is suggested for D. intermedia and D. bruxellensis as mtDNAs from these yeasts, 73.2 and 85.0 kbp respectively, have the same sequence order and mostly common restriction endonuclease sites. Differences between the two molecules are reminiscent of those found in mtDNA polymorphisms of S. cerevisiae strains thereby suggesting that the two Dekkera yeasts are variants of a single species. An unusual feature of the Dekkera species mtDNA is an inversion of the cytochrome b hybridizable region relative to the LrRNA sequence. Likewise mtDNA from B. anomalus (57.7 kbp) has an inversion of the cytochrome oxidase subunit 1 sequence with respect to the LrRNA sequence. By contrast the largest mtDNA (101.1 kbp) from B. custersd has the cytochrome b and LrRNA sequences in the same orientation. In addition hybridizable regions in this mtDNA are found in three clusters that are separated by several thousand base pairs of sequence deficient in restriction endonuclease sites. This observation together with the low guanine and cytosine content of the mtDNA suggests that the regions separating the sequence clusters are mostly adenine and thymine residues.     

Mitochondrial genome architecture in non‐alcoholic fatty liver disease

Non‐alcoholic fatty liver disease (NAFLD) is associated with mitochondrial dysfunction, a decreased liver mitochondrial DNA (mtDNA) content, and impaired energy metabolism. To understand the clinical implications of mtDNA diversity in the biology of NAFLD, we applied deep‐coverage whole sequencing of the liver mitochondrial genomes. We used a multistage study design, including a discovery phase, a phenotype‐oriented study to assess the mutational burden in patients with steatohepatitis at different stages of liver fibrosis, and a replication study to validate findings in loci of interest. We also assessed the potential protein‐level impact of the observed mutations. To determine whether the observed changes are tissue‐specific, we compared the liver and the corresponding peripheral blood entire mitochondrial genomes. The nuclear genes POLG and POLG2 (mitochondrial DNA polymerase‐γ) were also sequenced. We observed that the liver mtDNA of patients with NAFLD harbours complex genomes with a significantly higher mutational (1.28‐fold) rate and degree of heteroplasmy than in controls. The analysis of liver mitochondrial genomes of patients with different degrees of fibrosis revealed that the disease severity is associated with an overall 1.4‐fold increase in mutation rate, including mutations in genes of the oxidative phosphorylation (OXPHOS) chain. Significant differences in gene and protein expression patterns were observed in association with the cumulative number of OXPHOS polymorphic sites. We observed a high degree of homology (～98%) between the blood and liver mitochondrial genomes. A missense POLG p.Gln1236His variant was associated with liver mtDNA copy number. In conclusion, we have demonstrated that OXPHOS genes contain the highest number of hotspot positions associated with a more severe phenotype. The variability of the mitochondrial genomes probably originates from a common germline source; hence, it may explain a fraction of the ‘missing heritability’ of NAFLD. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Mitochondrial ND5 T12338C, tRNA(Cys) T5802C, and tRNA(Thr) G15927A variants may have a modifying role in the phenotypic manifestation of deafness-associated 12S rRNA A1555G mutation in three Han Chinese pedigrees

We report here on the clinical, genetic, and molecular characterization of three Han Chinese pedigrees with aminoglycoside-induced and nonsyndromic hearing loss. Clinical evaluation revealed the variable phenotype of hearing impairment including severity, age-at-onset, audiometric configuration in these subjects. The penetrance of hearing loss in WZD8, WZD9, and WZD10 pedigrees were 46%, 46%, and 50%, respectively, when aminoglycoside-induced deafness was included. When the effect of aminoglycosides was excluded, the penetrance of hearing loss in these pedigrees were 23%, 31%, and 37.5%, respectively. Mutational analysis of the complete mitochondrial genomes showed the homoplasmic A1555G mutation and distinct sets of mitochondrial DNA variants belonging to haplogroups D4b2b, B5b1, and F2, respectively. Of these, the tRNA(Cys) T5802C, tRNA(Thr) A15924C, and ND5 T12338C variants are of special interest as these variants occur at positions which are highly evolutionarily conserved nucleotides of tRNAs or amino acid of polypeptide. These homoplasmic mtDNA variants were absent among 156 unrelated Chinese controls. The T5802C and G15927A variants disrupted a highly conserved A-U or C-G base-pairing at the anticodon-stem of tRNA(Cys) or tRNA(Thr), while the ND5 T12338C mutation resulted in the replacement of the translation-initiating methionine with a threonine, and also located in two nucleotides adjacent to the 3' end of the tRNA(Leu(CUN)). Thus, mitochondrial dysfunctions, caused by the A1555G mutation, would be worsened by these mtDNA variants. Therefore, these mtDNA mutations may have a potential modifier role in increasing the penetrance and expressivity of the deafness-associated 12S rRNA A1555G mutation in those Chinese pedigrees.     

Physical map of the COB region in mitochondrial DNA of Saccharomyces cerevisiae

Summary A physical map of the COB region in mtDNA of yeast has been established. This region harbours a split gene coding for apocytochrome b. It includes restriction sites of seven endonucleases (EcoRI, HindII, HindIII, HaeIII, HpaII, AluI and BamHI). Various mtDNA sequences of this region, retained in a series of genetically characterized rho^– clones have been allocated to this map. The combination of this physical map with a genetic map of the rho^– clones revealed that 1) cob^– mutational sites spread over 8,400 bp, 2) mutations in sequences coding for apocytochrome b map in five distinct segments which are separated by intervening sequences with minimum lengths from 350 to 1,900 bp.Abbreviations mtDNA mitochondrial DNA - b bases - bp basepairs     

Direct linkage of mitochondrial genome variation to risk factors for type 2 diabetes in conplastic strains

Recently, the relationship of mitochondrial DNA (mtDNA) variants to metabolic risk factors for diabetes and other common diseases has begun to attract increasing attention. However, progress in this area has been limited because (1) the phenotypic effects of variation in the mitochondrial genome are difficult to isolate owing to confounding variation in the nuclear genome, imprinting phenomena, and environmental factors; and (2) few animal models have been available for directly investigating the effects of mtDNA variants on complex metabolic phenotypes in vivo. Substitution of different mitochondrial genomes on the same nuclear genetic background in conplastic strains provides a way to unambiguously isolate effects of the mitochondrial genome on complex traits. Here we show that conplastic strains of rats with identical nuclear genomes but divergent mitochondrial genomes that encode amino acid differences in proteins of oxidative phosphorylation exhibit differences in major metabolic risk factors for type 2 diabetes. These results (1) provide the first direct evidence linking naturally occurring variation in the mitochondrial genome, independent of variation in the nuclear genome and other confounding factors, to inherited variation in known risk factors for type 2 diabetes; and (2) establish that spontaneous variation in the mitochondrial genome per se can promote systemic metabolic disturbances relevant to the pathogenesis of common diseases.     

Echoes from Sepharad: signatures on the maternal gene pool of crypto-Jewish descendants

The majority of genetic studies on Jewish populations have been focused on Ashkenazim, and genetic data from the Sephardic original source, the Iberian Peninsula, are particularly scarce. Regarding the mitochondrial genome, the available information is limited to a single Portuguese village, Belmonte, where just two different lineages (a single one corresponding to 93.3%) were found in 30 individuals. Aiming at disclosing the ancestral maternal background of the Portuguese Jewry, we enlarged the sampling to other crypto-Jewish descendants in the Bragança district (NE Portugal). Fifty-seven complete mtDNA genomes were newly sequenced and — in contrast with Belmonte — a high level of diversity was found, with five haplogroups (HV0b, N1, T2b11, T2e and U2e) being putatively identified as Sephardic founding lineages. Therefore — in sharp contrast with Belmonte — these communities have managed to escape the expected inbreeding effects caused by centuries of religious repression and have kept a significant proportion of the Sephardic founder gene pool. This deeper analysis of the surviving Sephardic maternal lineages allowed a much more comprehensive and detailed perspective on the origins and survival of the Sephardic genetic heritage. In line with previously published results on Sephardic paternal lineages, our findings also show a surprising resistance to the erosion of genetic diversity in the maternal lineages.     

Mitochondrial DNA inheritance in sexual crosses of Pleurotus ostreatus

The inheritance of mitochondrial DNA (mtDNA) in sexual crosses was investigated to expand our understanding of the large genetic divergence in mtDNAs among natural populations of the higher basidiomycete Pleurotus ostreatus. Reciprocal crosses were made between compatible monokaryons with distinguishable mtDNA restriction fragment length polymorphisms (PFLPs). Almost all of the dikaryons produced by these crosses had mtDNA genotypes from one of the parental monokaryons. However, for dikaryons isolated from the junction-zone of crossed monokaryons, recombinant mitochondrial genomes commonly appeared. These results showed that P. ostreatus mtDNA can be inherited biparentally, via mtDNA recombination, as well as uniparentally. Further, it was suggested that mtDNA recombination may be an important source of variation in mitochondrial genomes among natural populations of P. ostreatus. Received: 4 June / 14 August 1996     

Origin,cellular expression,and cybrid transmission of mitochondrial CAP-R,PYR-IND,and OLI-R mutant phenotypes

Chloramphenicol-resistant (CAP-R) mouse and Chinese hamster lines were isolated in a single selection step in drug medium containing pyruvate. Cellular expression of the CAP-R phenotype required pyruvate— or an appropriate substitute—as a nutritional supplement. Subclone lines which were pyruvate independent (PYR-IND) arose in second-step selections at a high frequency. CAP-R PYR-IND Chinese hamster mutants could be directly isolated in single-step selections but at a very low frequency. Subclone lines (OLI-R) which were cross-resistant to oligomycin were isolated in a third selection cycle. The PYR-IND and OLI-R phenotypes were cotransmitted with the CAP-R mtDNA mutation but were expressed at the cellular level only if the number of mutant mitochondrial genomes exceeded a minimum threshold value. Analysis of a mtDNA restriction fragment alteration in one series of mutants supported this model. Threshold limits for cellular expression of mitochondrial mutant phenotypes are likely to be a general phenomenon and will constrain models of the origin and segregation of mtDNA mutations.     

Complete mitogenomes document substantial genetic contribution from the Eurasian Steppe into northern Pakistani Indo-Iranian speakers

To elucidate whether Bronze Age population dispersals from the Eurasian Steppe to South Asia contributed to the gene pool of Indo-Iranian-speaking groups, we analyzed 19,568 mitochondrial DNA (mtDNA) sequences from northern Pakistani and surrounding populations, including 213 newly generated mitochondrial genomes (mitogenomes) from Iranian and Dardic groups, both speakers from the ancient Indo-Iranian branch in northern Pakistan. Our results showed that 23% of mtDNA lineages with west Eurasian origin arose in situ in northern Pakistan since ~5000 years ago (kya), a time depth very close to the documented Indo-European dispersals into South Asia during the Bronze Age. Together with ancient mitogenomes from western Eurasia since the Neolithic, we identified five haplogroups (~8.4% of maternal gene pool) with roots in the Steppe region and subbranches arising (age ~5–2 kya old) in northern Pakistan as genetic legacies of Indo-Iranian speakers. Some of these haplogroups, such as W3a1b that have been found in the ancient samples from the late Bronze Age to the Iron Age period individuals of Swat Valley northern Pakistan, even have sub-lineages (age ~4 kya old) in the southern subcontinent, consistent with the southward spread of Indo-Iranian languages. By showing that substantial genetic components of Indo-Iranian speakers in northern Pakistan can be traced to Bronze Age in the Steppe region, our study suggests a demographic link with the spread of Indo-Iranian languages, and further highlights the corridor role of northern Pakistan in the southward dispersal of Indo-Iranian-speaking groups.Subject terms: Evolutionary biology, Molecular biology     

The pathophysiology of mitochondrial disease as modeled in the mouse

It is now clear that mitochondrial defects are associated with a plethora of clinical phenotypes in man and mouse. This is the result of the mitochondria''s central role in energy production, reactive oxygen species (ROS) biology, and apoptosis, and because the mitochondrial genome consists of roughly 1500 genes distributed across the maternal mitochondrial DNA (mtDNA) and the Mendelian nuclear DNA (nDNA). While numerous pathogenic mutations in both mtDNA and nDNA mitochondrial genes have been identified in the past 21 years, the causal role of mitochondrial dysfunction in the common metabolic and degenerative diseases, cancer, and aging is still debated. However, the development of mice harboring mitochondrial gene mutations is permitting demonstration of the direct cause-and-effect relationship between mitochondrial dysfunction and disease. Mutations in nDNA-encoded mitochondrial genes involved in energy metabolism, antioxidant defenses, apoptosis via the mitochondrial permeability transition pore (mtPTP), mitochondrial fusion, and mtDNA biogenesis have already demonstrated the phenotypic importance of mitochondrial defects. These studies are being expanded by the recent development of procedures for introducing mtDNA mutations into the mouse. These studies are providing direct proof that mtDNA mutations are sufficient by themselves to generate major clinical phenotypes. As more different mtDNA types and mtDNA gene mutations are introduced into various mouse nDNA backgrounds, the potential functional role of mtDNA variation in permitting humans and mammals to adapt to different environments and in determining their predisposition to a wide array of diseases should be definitively demonstrated.     

Inheritance of mitochondrial DNA in sexual crosses and protoplast cell fusions in Lentinula edodes

By using mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) as genetic markers, the modes of mitochondrial inheritance in sexual crosses and protoplast cell fusions of the higher basidiomycete Lentinula edodes were examined. All newly established dikaryons from reciprocal crosses between compatible monokaryons carrying different mtDNA RFLP phenotypes retained mtDNA genotypes from one of the monokaryons, suggesting that mitochondrial inheritance is principally uniparental. In contrast, it was shown that recombinant mtDNA genomes arose in some dikaryons obtained after protoplast cell fusion. Based on these results, a possible mechanism for mitochondrial inheritance in L. edodes is discussed.     

Mitochondrial DNA and Y chromosome diversity and the peopling of the Americas: evolutionary and demographic evidence.

A number of important insights into the peopling of the New World have been gained through molecular genetic studies of Siberian and Native American populations. While there is no complete agreement on the interpretation of the mitochondrial DNA (mtDNA) and Y chromosome (NRY) data from these groups, several generalizations can be made. To begin with, the primary migration of ancestral Asians expanded from south-central Siberia into the New World and gave rise to ancestral Amerindians. The initial migration seems to have occurred between 20,000-15,000 calendar years before present (cal BP), i.e., before the emergence of Clovis lithic sites (13,350-12,895 cal BP) in North America. Because an interior route through northern North America was unavailable for human passage until 12,550 cal BP, after the last glacial maximum (LGM), these ancestral groups must have used a coastal route to reach South America by 14,675 cal BP, the date of the Monte Verde site in southern Chile. The initial migration appears to have brought mtDNA haplogroups A-D and NRY haplogroups P-M45a and Q-242/Q-M3 to the New World, with these genetic lineages becoming widespread in the Americas. A second expansion that perhaps coincided with the opening of the ice-free corridor probably brought mtDNA haplogroup X and NRY haplogroups P-M45b, C-M130, and R1a1-M17 to North and Central America. Finally, populations that formerly inhabited Beringia expanded into northern North America after the LGM, and gave rise to Eskimo-Aleuts and Na-Dené Indians.     

Linear mitochondrial genome organization in vivo in the genus Pythium

Pulsed-field gel electrophoresis (PFGE) of isolates of Pythium oligandrum with linear mitochondrial genomes revealed a distinct band in ethidium bromide-stained gels similar in size to values estimated by restriction mapping of mitochondrial DNA (mtDNA). Southern analysis confirmed that these bands were mtDNA and indicated that linear genomes were present in unit-length size as well as multimers. Isolates of this species with circular mtDNA restriction maps also had low levels of linear mono- and multimers. visualized by Southern analysis of PFGE gels. Examination of 17 additional species revealed similar results; three species had distinct linear mtDNA bands in ethidium bromide-stained gels while the remainder had linear mono- and multi-mers in lower amounts detected only by Southern analysis. Sequence analysis of an isolate of P. oligandrum with a primarily circular mitochondrial genomic map and a low amount of linear molecules revealed that the small unique region of the circular map (which corresponded to the terminal region of linear genomes) was flanked by palindromic intrastrand complementary sequences separated by a unique 194-bp sequence. Sequences with similarity to ATPase9 coding regions from other organisms were located adjacent to this region. Sequences with similarity to mitochondrial origins of replication and autonomously replicating sequences were also located in this region: their potential involvement in the generation of linear molecules is discussed.     

Analysis of Heteroplasmic Variants in the Cardiac Mitochondrial Genome of Individuals with Down Syndrome

Individuals with Down syndrome (DS, trisomy 21) exhibit a pro‐oxidative cellular environment as well as mitochondrial dysfunction. Increased oxidative stress may damage the mitochondrial DNA (mtDNA). The coexistence of mtDNA variants in a cell or tissue (i.e., heteroplasmy) may contribute to mitochondrial dysfunction. Given the evidence on mitochondrial dysfunction and the relatively high incidence of multiorganic disorders associated with DS, we hypothesized that cardiac tissue from subjects with DS may exhibit higher frequencies of mtDNA variants in comparison to cardiac tissue from donors without DS. This study documents the analysis of mtDNA variants in heart tissue samples from donors with (n = 12) and without DS (n = 33) using massively parallel sequencing. Contrary to the original hypothesis, the study's findings suggest that the cardiac mitochondrial genomes from individuals with and without DS exhibit many similarities in terms of (1) total number of mtDNA variants per sample, (2) the frequency of mtDNA variants, (3) the type of mtDNA variants, and (4) the patterns of distribution of mtDNA variants. In both groups of samples, the mtDNA control region showed significantly more heteroplasmic variants in comparison to the number of variants in protein‐ and RNA‐coding genes (P < 1.00×10^?4, ANOVA).     

Diseases caused by nuclear genes affecting mtDNA stability

Diseases caused by nuclear genes that affect mitochondrial DNA (mtDNA) stability are an interesting group of mitochondrial disorders, involving both cellular genomes. In these disorders, a primary nuclear gene defect causes secondary mtDNA loss or deletion formation, which leads to tissue dysfunction. Therefore, the diseases clinically resemble those caused by mtDNA mutations, but follow a Mendelian inheritance pattern. Several clinical entities associated with multiple mtDNA deletions have been characterized, the most frequently described being autosomal dominant progressive external ophthalmoplegia (adPEO). MtDNA depletion syndrome (MDS) is a severe disease of childhood, in which tissue-specific loss of mtDNA is seen. Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) patients may have multiple mtDNA deletions and/or mtDNA depletion. Recent reports of thymidine phosphorylase mutations in MNGIE and adenine nucleotide translocator mutations in adPEO have given new insights into the mechanisms of mtDNA maintenance in mammals. The common mechanism underlying both of these gene defects could be disturbed mitochondrial nucleoside pools, the building blocks of mtDNA. Future studies on MNGIE and adPEO pathogenesis, and identification of additional gene defects in adPEO and MDS will provide further understanding about the mammalian mtDNA maintenance and the crosstalk between the nuclear and mitochondrial genomes.     

Reaching for the ring: the study of mitochondrial genome structure

The linear molecules that comprise most of the mitochondrial DNA (mtDNA) isolated from most organisms result from the artifactual degradation of circular genomes that exist within mitochondria. This view has been adopted by most investigators and is based on DNA fragment mapping data as well as analogy to the genomesized circular mtDNA molecules obtained in high yield from animals. The alternative view that linear molecules actually represent the major form of DNA within mitochondria is supported by two observations: (1) over a 1000-fold range of genome size among fungi and plants we find the same size distribution of linear mtDNA molecules, and (2) linear mtDNA molecules much larger than genome size can be found for some fungi and plants. The circles that represent only a small fraction of the mtDNA obtained from most eukaryotes could be optional sequence forms unimportant for mitochondrial function; they may also participate in mtDNA replication. The circles might result from incidental recombination events between directly repeated sequences within or between tandemly arrayed genome units on linear mtDNA molecules.