Mitochondrial Sequence Variation Research Articles

Mitochondrial sequence variants: testing imputation accuracy and their association with dairy cattle milk traits

BackgroundMitochondrial genomes differ from the nuclear genome and in humans it is known that mitochondrial variants contribute to genetic disorders. Prior to genomics, some livestock studies assessed the role of the mitochondrial genome but these were limited and inconclusive. Modern genome sequencing provides an opportunity to re-evaluate the potential impact of mitochondrial variation on livestock traits. This study first evaluated the empirical accuracy of mitochondrial sequence imputation and then used real and imputed mitochondrial sequence genotypes to study the role of mitochondrial variants on milk production traits of dairy cattle.ResultsThe empirical accuracy of imputation from Single Nucleotide Polymorphism (SNP) panels to mitochondrial sequence genotypes was assessed in 516 test animals of Holstein, Jersey and Red breeds using Beagle software and a sequence reference of 1883 animals. The overall accuracy estimated as the Pearson’s correlation squared (R2) between all imputed and real genotypes across all animals was 0.454. The low accuracy was attributed partly to the majority of variants having low minor allele frequency (MAF < 0.005) but also due to variants in the hypervariable D-loop region showing poor imputation accuracy. Beagle software provides an internal estimate of imputation accuracy (DR2), and 10 percent of the total 1927 imputed positions showed DR2 greater than 0.9 (N = 201). There were 151 sites with empirical R2 > 0.9 (of 954 variants segregating in the test animals) and 138 of these overlapped the sites with DR2 > 0.9. This suggests that the DR2 statistic is a reasonable proxy to select sites that are imputed with higher accuracy for downstream analyses. Accordingly, in the second part of the study mitochondrial sequence variants were imputed from real mitochondrial SNP panel genotypes of 9515 Australian Holstein, Jersey and Red dairy cattle. Then, using only sites with DR2 > 0.900 and real genotypes, we undertook a genome-wide association study (GWAS) for milk, fat and protein yields. The GWAS mitochondrial SNP effects were not significant.ConclusionThe accuracy of imputation of mitochondrial genotypes from the SNP panel to sequence was generally low. The Beagle DR2 statistic enabled selection of sites imputed with higher empirical accuracy. We recommend building larger reference populations with mitochondrial sequence to improve the accuracy of imputing less common variants and ensuring that SNP panels include common variants in the D-loop region.

Haplotype variability in mitochondrial rRNA predisposes to metabolic syndrome

Metabolic syndrome is a growing concern in developed societies and due to its polygenic nature, the genetic component is only slowly being elucidated. Common mitochondrial DNA sequence variants have been associated with symptoms of metabolic syndrome and may, therefore, be relevant players in the genetics of metabolic syndrome. We investigate the effect of mitochondrial sequence variation on the metabolic phenotype in conplastic rat strains with identical nuclear but unique mitochondrial genomes, challenged by high-fat diet. We find that the variation in mitochondrial rRNA sequence represents risk factor in the insulin resistance development, which is associated with diacylglycerols accumulation, induced by tissue-specific reduction of the oxidative capacity. These metabolic perturbations stem from the 12S rRNA sequence variation affecting mitochondrial ribosome assembly and translation. Our work demonstrates that physiological variation in mitochondrial rRNA might represent a relevant underlying factor in the progression of metabolic syndrome.

Genetic incompatibilities in reciprocal hybrids between populations of Tigriopus californicus with low to moderate mitochondrial sequence divergence.

All mitochondrial-encoded proteins and RNAs function through interactions with nuclear-encoded proteins, which are critical for mitochondrial performance and eukaryotic fitness. Coevolution maintains inter-genomic (i.e., mitonuclear) compatibility within a taxon, but hybridization can disrupt coevolved interactions, resulting in hybrid breakdown. Thus, mitonuclear incompatibilities may be important mechanisms underlying reproductive isolation and, potentially, speciation. Here we utilize Pool-seq to assess the effects of mitochondrial genotype on nuclear allele frequencies in fast- and slow-developing reciprocal inter-population F2 hybrids between relatively low-divergence populations of the intertidal copepod Tigriopus californicus. We show that mitonuclear interactions lead to elevated frequencies of coevolved (i.e., maternal) nuclear alleles on two chromosomes in crosses between populations with 1.5% or 9.6% fixed differences in mitochondrial DNA nucleotide sequence. However, we also find evidence of excess mismatched (i.e., noncoevolved) alleles on three or four chromosomes per cross, respectively, and of allele frequency differences consistent with effects involving only nuclear loci (i.e., unaffected by mitochondrial genotype). Thus, our results for low-divergence crosses suggest an underlying role for mitonuclear interactions in variation in hybrid developmental rate, but despite substantial effects of mitonuclear coevolution on individual chromosomes, no clear bias favoring coevolved interactions overall.

Two new spotted species of the Cyrtodactylus (Geckoella) collegalensis (Beddome, 1870) complex from the south-eastern coast of India (Reptilia: Squamata)

We describe two new spotted species of ground-dwelling gecko of the genus Cyrtodactylus (Geckoella) from southeastern India in an integrative taxonomic framework. The new species are recovered as sister taxa within the C. collegalensis species complex, with 13.0–16.7% uncorrected mitochondrial sequence divergence from the other eight members of the C. collegalensis complex and 10.4% from one another. The new species are morphologically diagnosed by a spotted dorsal pattern of four pairs of spots (occasionally fused into figure 8-shaped markings) from the banded species C. aravindi, C. speciosus, C. rishivalleyensis and C. yakhuna; and from the spotted species with three or fewer pairs of spots in C. collegalensis and C. srilekhae; and from C. chengodumalaensis by the absence of any enlarged dorsal scales and from C. varadgirii by the absence of a patch of enlarged roughly hexagonal scales on the canthus rostralis and beneath the angle of the lower jaw. The two new species can only be differentiated from each other based on slight differences in body size, relative body width and other statistically significant, size-corrected morphometric characters. These are among the first endemic lizards from Tropical Dry Evergreen habitats along the southeast coast of India.

Clinical Validation of Tagmentation-Based Genome Sequencing for Germline Disorders

Genome sequencing (GS) is a powerful clinical tool used for the comprehensive diagnosis of germline disorders. GS library preparation typically involves mechanical DNA fragmentation, end repair, and bead-based library size selection followed by adapter ligation, which can require a large amount of input genomic DNA. Tagmentation using bead-linked transposomes can simplify the library preparation process and reduce the DNA input requirement. Here we describe the clinical validation of tagmentation-based PCR-free GS as a clinical test for rare germline disorders. Compared with the Genome-in-a-Bottle Consortium benchmark variant sets, GS had a recall >99.7% and a precision of 99.8% for single nucleotide variants and small insertion-deletions. GS also exhibited 100% sensitivity for clinically reported sequence variants and the copy number variants examined. Furthermore, GS detected mitochondrial sequence variants above 5% heteroplasmy and showed reliable detection of disease-relevant repeat expansions and SMN1 homozygous loss. Our results indicate that while lowering DNA input requirements and reducing library preparation time, GS enables uniform coverage across the genome as well as robust detection of various types of genetic alterations. With the advantage of comprehensive profiling of multiple types of genetic alterations, GS is positioned as an ideal first-tier diagnostic test for germline disorders.

A New Spotted Species of the Cyrtodactylus (Geckoella) collegalensis (Beddome, 1870) (Reptilia: Squamata) Complex from Coastal Kerala, Southwestern India

We describe a new spotted species of ground-dwelling gecko of the genus Cyrtodactylus (Geckoella) from coastal Kerala, southwestern India, by using an integrative taxonomic approach. The new species is a member of the C. collegalensis species complex, with 10.0–13.5% uncorrected mitochondrial sequence divergence from the other six members of the C. collegalensis complex. The new species is also recognized in tree-based delimitation methods and can be morphologically diagnosed by a spotted dorsal pattern of four to six pairs of spots (occasionally fused into figure 8–shaped markings) from the banded species C. speciosus, C. rishivalleyensis, and C. yakhuna and from the spotted C. collegalensis, C. srilekhae, and C. varadgirii by the presence of a few scattered enlarged dorsal scales. This is the only Indian member of the C. collegalensis complex with a relatively broad distribution at low elevations, other than C. varadgirii from western India (distributed in Maharashtra, southern Gujarat, and western Madhya Pradesh). The sister species to the new species is the Sri Lankan C. yakhuna, which is a banded form from low elevations. The new species is the second gecko to have been described from Chengodumala and endemic to northern and central Kerala, highlighting the importance of this area, which is under increasing anthropogenic pressure. We also provide notes on the dorsal pholidosis of C. rishivalleyensis, which was overlooked in its original description.

Multilocus phylogeography, population genetics and niche evolution of Australian brown and black-tailed treecreepers (Aves:Climacteris)

AbstractThe Carpentarian barrier across north-eastern Australia is a major biogeographic barrier and a generator of biodiversity within the Australian Monsoonal Tropics. Here we present a continent-wide analysis of mitochondrial (control region) and autosomal (14 anonymous loci) sequence and indel variation and niche modelling of brown and black-tailed treecreepers (Climacteris picumnus and Climacteris melanurus), a clade with a classic distribution on either side of the Carpentarian barrier. mtDNA control region sequences exhibited reciprocal monophyly and strong differentiation (Fst = 0.91), and revealed a signature of a recent selective sweep in C. picumnus. A variety of tests support an isolation-with-migration model of divergence, albeit with low levels of gene flow across the Carpentarian barrier and a divergence time between species of ~1.7–2.8 Mya. Palaeoecological niche models show that both range size as measured by available habitat and estimated historical population sizes of both species declined in the past ~600 kyr and that the area of interspecific range overlap was never historically large, perhaps decreasing opportunities for extensive gene flow. The relatively long divergence time and low opportunity for gene flow may have facilitated speciation more so than in other co-distributed bird taxa across the Australian Monsoonal Tropics.

A Pilot Mitochondrial Genome-Wide Association on Migraine Among Saudi Arabians.

BackgroundMitochondrial DNA (mtDNA) mutations have been reported in multiple neurological diseases and helped to explain the pathophysiology of these diseases. Similarly, variations in mtDNA might exist in migraine and can explain the effect of low ATP production in the neurons on the initiation of migraine attack. Therefore, in the current study we aim to explore the association of mtDNA mutations on migraine in the Saudi population.Subjects and MethodsOver 1950 young Saudi female students were screened for migraine, among that a total of 103 satisfied the ICHD-3 criteria. However, 20 migraine cases confirmed in the neurology clinic and gave consent to participate in the study. Another 20 age-matched healthy controls were also recruited. Mitochondrial sequence variations were filtered from exome sequencing using NCBI GenBank Reference Sequence: NC_012920.1 and analysed using MITOMAP. Genes with significant single nucleotide polymorphisms (SNPs) were investigated by the gene functional classification tool DAVID and functional enrichment analysis of protein–protein interaction networks through STRING 11.5 for the most significant associated genes.ResultsGenome wide analysis of the mitochondrial sequence variations between the patients with migraine and control revealed the association of 30 SNPs (p < 0.05) in the mitochondrial genome. The highest significance (p = 0.001033) was observed in a coding SNP (rs1603225278) in the CYTB gene and rs386829281 in the region of origin of replication. Twenty-four significant SNPs were in the coding region of nine (ND5, ND4, COX2, COX1, ND3, CYTB, COX3, ND2 and ND1) genes.ConclusionThis is the first study to demonstrate the association of mtDNA variations with migraine in the Saudi population. The current findings will help to highlight the significance of mtDNA mutations to migraine pathophysiology and will serve as a reference data for larger national and international studies.

Conservation genomics of urban populations of Streamside Salamander (Ambystoma barbouri).

In Tennessee, populations of the state endangered Streamside Salamander (Ambystoma barbouri) are in decline as their distribution lies mostly within rapidly developing areas in the Nashville Basin. Information regarding the partitioning of genetic variation among populations of A. barbouri and the taxonomic status of these populations relative to northern populations and their congener, the Small-mouthed Salamander (A. texanum), have important implications for management and conservation of this species. Here we combined mitochondrial sequencing and genome-wide single nucleotide polymorphism (SNP) data generated using Genotyping-by-Sequencing (GBS) to investigate patterns of genetic variation within Tennessee populations of A. barbouri, to assess their relationship to populations in Kentucky, and to examine their phylogenetic relationship to the closely related A. texanum. Results from phylogenetic reconstructions reveal a complex history of Tennessee A. barbouri populations with regards to northern populations, unisexual A. barbouri, and A. texanum. Patterns of mitochondrial sequence variation suggest that A. barbouri may have originated within Tennessee and expanded north multiple times into Kentucky, Ohio, Indiana, and West Virginia. Phylogenetic reconstructions based on genome-wide SNP data contradict results based on mitochondrial DNA and correspond to geographic and taxonomic boundaries. Variation in allele frequencies at SNP genotypes, as identified by multivariate analyses and Bayesian assignment tests, identified three evolutionary significant units (ESUs) for A. barbouri within Tennessee. Collectively, these results emphasize the need for prioritizing conservation needs for Tennessee populations of A. barbouri to ensure the long-term persistence of this species.

Lineage diversity within a widespread endemic Australian skink to better inform conservation in response to regional-scale disturbance.

Much attention is paid in conservation planning to the concept of a species, to ensure comparability across studies and regions when classifying taxa against criteria of endangerment and setting priorities for action. However, various jurisdictions now allow taxonomic ranks below the level of species and nontaxonomic intraspecific divisions to be factored into conservation planning—subspecies, key populations, evolutionarily significant units, or designatable units. Understanding patterns of genetic diversity and its distribution across the landscape is a key component in the identification of species boundaries and determination of substantial geographic structure within species. A total of 12,532 reliable polymorphic SNP loci were generated from 63 populations (286 individuals) covering the distribution of the Australian eastern three‐lined skink, Bassiana duperreyi, to assess genetic population structure in the form of diagnosable lineages and their distribution across the landscape, with particular reference to the recent catastrophic bushfires of eastern Australia. Five well‐supported diagnosable operational taxonomic units (OTUs) existed within B. duperreyi. Low levels of divergence of B. duperreyi between mainland Australia and Tasmania (no fixed allelic differences) support the notion of episodic exchange of alleles across Bass Strait (ca 60 m, 25 Kya) during periods of low sea level during the Upper Pleistocene rather than the much longer period of isolation (1.7 My) indicated by earlier studies using mitochondrial sequence variation. Our study provides foundational work for the detailed taxonomic re‐evaluation of this species complex and the need for biodiversity assessment to include an examination of cryptic species and/or cryptic diversity below the level of species. Such information on lineage diversity within species and its distribution in the context of disturbance at a regional scale can be factored into conservation planning regardless of whether a decision is made to formally diagnose new species taxonomically and nomenclaturally.

A new toad species of the genus Brachytarsophrys Tian & Hu, 1983 (Anura, Megophryidae) from Guizhou Province, China.

BackgroundThe toads of the genus Brachytarsophrys Tian & Hu, 1983 are distributed in southern China, Myanmar, Vietnam, Laos and northern Thailand. Seven species of the genus have been recognised, of which five of them are known from China so far.New informationBrachytarsophrysqiannanensis sp. nov., a new species of the short-legged toad genus is here described from southern Guizhou Province, China. Diagnostic characters of the new species are illustrated and comparisons with its congeners are provided. Its validity is also affirmed by its distinct mitochondrial gene sequence divergence with all congeners and its monophyly recovered in the mitochondrial gene-based phylogenetic analyses.

Mitochondrial sequence diversity reveals the hybrid origin of invasive gibel carp (Carassius gibelio) populations in Hungary.

BackgroundInvasive gibel carp, Carassius gibelio (Bloch, 1782) has become well-established in the Hungarian waters and now are spreading in the European waters. On major concern now is the potential hybridization between gibel carp and the other invasive species in the Carassius auratus complex (CAC), which may further accelerate the spread of the whole invasive species complex. The identification of gibel carp and their hybrids is difficult because of its morphological similarity to the other species in CAC. Here we carry out a genomic assessment to understand the history of gibel carp invasion and its phylogenetic relationship with the other species in CAC. Three loci of the mitochondrial genome (D-loop, CoI, Cytb) were used to determine the phylogenetic origin of individuals and relarionship among six gibel carp populations and the other species in the CAC.MethodolgyA total of 132 gibel carp samples from six locations in Southern Transdanubia (Hungary) were collected after phenotypic identification to measure the genetic diversity within and among gibel carp populations of Southern Transdanubia (Hungary). The genetic background was examined by the sequences of the mitochondrial genome: D-loop, Cytochrome c oxidase I (CoI) and Cytochrome b (Cytb). Mitochondrial genetic markers are excellent tools for phylogenetic studies because they are maternally inherited. Successfully identified haplotypes were aligned and with reference sequences in nucleotide databases (i.e., NCBI-BLAST: National Centre for Biotechnology Information and BOLD: Barcode of Life Data System). The phylogenetic relationships among gibel carp populations were then analyzed together with the reference sequences to understand the relationship and the level of hybridization with the species in CAC.ResultsAmong the 132 aligned D-loop sequences 22 haplotypes were identified. Further examination of representative individuals of the 22 haplotypes, six Cytb and four CoI sequences were detected. The largest number of haplotypes of all three loci were found in Lake Balaton, the largest shallow lake in Central Europe. Based on the NCBI-BLAST alignment of the D-loop, haplotypes of Carassius auratus auratus and Carassius a. buergeri in CAC were identified in the C. gibelio samples. Further analysis of haplotypes with the other two mitochondrial markers confirmed the occurrence of intragenus hybridization of C. gibelio in the Hungarian waters.ConclusionBy using three mitochondrial markers (D-loop, Cytb, CoI), we genomically characterized a gibel carp-complex in Hungarian waters and assessed the C. gibelio phylogenetic status between them. Hybrid origin of locally invasive Carassius taxon was detected in Hungary. It points out that invasive species are not only present in Hungary but reproduce with each other in the waters, further accelerating their spread.

Sequence and structure comparison of ATP synthase F0 subunits 6 and 8 in notothenioid fish.

Mitochondrial changes such as tight coupling of the mitochondria have facilitated sustained oxygen and respiratory activity in haemoglobin-less icefish of the Channichthyidae family. We aimed to characterise features in the sequence and structure of the proteins directly involved in proton transport, which have potential physiological implications. ATP synthase subunit a (ATP6) and subunit 8 (ATP8) are proteins that function as part of the F0 component (proton pump) of the F0F1complex. Both proteins are encoded by the mitochondrial genome and involved in oxidative phosphorylation. To explore mitochondrial sequence variation for ATP6 and ATP8 we analysed sequences from C. gunnari and C. rastrospinosus and compared them with their closely related red-blooded species and eight other vertebrate species. Our comparison of the amino acid sequence of these proteins reveals important differences that could underlie aspects of the unique physiology of the icefish. In this study we find that changes in the sequence of subunit a of the icefish C. gunnari at position 35 where there is a hydrophobic alanine which is not seen in the other notothenioids we analysed. An amino acid change of this type is significant since it may have a structural impact. The biology of the haemoglobin-less icefish is necessarily unique and any insights about these animals will help to generate a better overall understanding of important physiological pathways.

Genetic Diversity and Relatedness among Captive African Painted Dogs in North America.

African painted dogs (Lycaon pictus, APD) are highly endangered, with fewer than 7000 remaining in nature. Captive breeding programs can preserve a genetically diverse population and provide a source of individuals for reintroductions. However, most programs are initiated from few founders and suffer from low genetic diversity and inbreeding. The aims of this study were to use molecular markers to assess genetic variation, inbreeding, and relatedness among APDs in the North American captive population, to use these data to realign studbook records, and to compare these data to wild populations and to the European captive population to facilitate the development of a global management plan. We sequenced mitochondrial and major histocompatibility (MHC) class II loci and genotyped 14 microsatellite loci from 109 APDs from 34 institutions in North America. We identified three likely studbook errors and resolved ten cases of uncertain paternity. Overall, microsatellite heterozygosity was higher than reported in Europe, but effective population size estimates were lower. Mitochondrial sequence variation was extremely limited, and there were fewer MHC haplotypes than in Europe or the wild. Although the population did not show evidence of significant inbreeding overall, several individuals shared high relatedness values, which should be incorporated into future breeding programs.

A new species of the genus Hemiphyllodactylus Bleeker, 1860 (Squamata: Gekkonidae) from Goa, India.

We describe a distinct new species of the genus Hemiphyllodactylus based on three specimens collected from semi-urban areas in Goa state of India. The new species can be easily distinguished from all peninsular Indian congeners by its small body size (SVL up to 32.4 mm), having 1618 dorsal scales and 13 or 14 ventral scales at mid-body contained within one longitudinal eye diameter, nine or ten precloacal pores separated by 15 poreless scales from a series of 1012 femoral pores on each thigh in males, lamellar formula of manus 2222 and of pes 2323 2333, as well as subtle colour pattern differences. Mitochondrial sequence divergence confirms the distinctiveness of the new species, which is not closely allied to either the South Indian or Eastern Ghats clades of Indian Hemiphyllodactylus and appears to be a member of a third Indian Hemiphyllodactylus clade. Hemiphyllodactylus goaensis sp. nov. is the first member of the genus to be described from the northern Western Ghats region as well as Goa state, and also only the second Indian Hemiphyllodactylus known from 100 m asl. Hemiphyllodactylus goaensis sp. nov. extends the known distribution of the genus in western India ~ 560 km north in aerial distance and highlights that the genus is more widely distributed than previously thought and most likely contains numerous undescribed species. We also provide final museum numbers for type specimens of H. arakuensis and the holotype of H. kolliensis.

Distribution of Culicoides biting midges (Diptera: Ceratopogonidae) in southern Australia and insight into the Culicoides victoriae morpho‐variants

AbstractCertain Culicoides species (biting midges) are important vectors globally of a range of viruses, protozoa and filarial parasites, imposing a significant economic and health burden. In a changing climate, understanding which Culicoides species occur in a region is important for biosecurity risk management. We examined the occurrence of predominant Culicoides species in south‐east Australia and provide insight into five Culicoides victoriae morpho‐variants. Culicoides were surveyed using Centre for Disease Control light traps and Yellow Sticky traps, with identification performed morphologically and molecularly. Two polymerase chain reaction – restriction fragment length polymorphism (PCR‐RFLP) assays based on mitochondrial cytochrome c oxidase subunit I were developed to differentiate morphologically similar C. victoriae, with a subset sequenced for nuclear carbomoylphosphate synthase. The structure of the five C. victoriae morpho‐variants was investigated through phylogenetic trees, haplotype networks and the Barcode Index Number system (BINs) in the Barcode of Life Data (BOLD) database. Twenty‐five different Culicoides species were identified in the sampled region with Culicoides austropalpalis, C. victoriae, C. marksi and C. molestus Gp sp No 2 being the most common. Two PCR‐RFLP assays were developed using either one or three enzymes, with a 90% or 99% success rate, respectively, of being able to differentiate the five C. victoriae morpho‐variants. Mitochondrial and nuclear sequence divergence supported by wing patterning allowed the recognition of multiple potentially new species of C. victoriae and identified species in uncharacterised regions.

Response diversity in corals: hidden differences in bleaching mortality among cryptic Pocillopora species.

Variation among functionally similar species in their response to environmental stress buffers ecosystems from changing states. Functionally similar species may often be cryptic species representing evolutionarily distinct genetic lineages that are morphologically indistinguishable. However, the extent to which cryptic species differ in their response to stress, and could therefore provide a source of response diversity, remains unclear because they are often not identified or are assumed to be ecologically equivalent. Here, we uncover differences in the bleaching response between sympatric cryptic species of the common Indo‐Pacific coral, Pocillopora. In April 2019, prolonged ocean heating occurred at Moorea, French Polynesia. 72% of pocilloporid colonies bleached after 22 d of severe heating (>8oC‐days) at 10 m depth on the north shore fore reef. Colony mortality ranged from 11% to 42% around the island four months after heating subsided. The majority (86%) of pocilloporids that died from bleaching belonged to a single haplotype, despite twelve haplotypes, representing at least five species, being sampled. Mitochondrial (open reading frame) sequence variation was greater between the haplotypes that experienced mortality versus haplotypes that all survived than it was between nominal species that all survived. Colonies > 30 cm in diameter were identified as the haplotype experiencing the most mortality, and in 1125 colonies that were not genetically identified, bleaching and mortality increased with colony size. Mortality did not increase with colony size within the haplotype suffering the highest mortality, suggesting that size‐dependent bleaching and mortality at the genus level was caused instead by differences among cryptic species. The relative abundance of haplotypes shifted between February and August, driven by declines in the same common haplotype for which mortality was estimated directly, at sites where heat accumulation was greatest, and where larger colony sizes occurred. The identification of morphologically indistinguishable species that differ in their response to thermal stress, but share a similar ecological function in terms of maintaining a coral‐dominated state, has important consequences for uncovering response diversity that drives resilience, especially in systems with low or declining functional diversity.

Mitochondrial D-loop sequence variation and maternal lineage in the endangered Cleveland Bay horse.

Genetic diversity and maternal ancestry line relationships amongst a sample of 96 Cleveland Bay horses were investigated using a 479bp length of mitochondrial D-loop sequence. The analysis yielded at total of 11 haplotypes with 27 variable positions, all of which have been described in previous equine mitochondrial DNA d-loop studies. Four main haplotype clusters were present in the Cleveland Bay breed describing 89% of the total sample. This suggests that only four principal maternal ancestry lines exist in the present-day global Cleveland Bay population. Comparison of these sequences with other domestic horse haplotypes (Fig 2) shows a close association of the Cleveland Bay horse with Northern European (Clade C), Iberian (Clade A) and North African (Clade B) horse breeds. This indicates that the Cleveland Bay horse may not have evolved exclusively from the now extinct Chapman horse, as previous work as suggested. The Cleveland Bay horse remains one of only five domestic horse breeds classified as Critical on the Rare Breeds Survival Trust (UK) Watchlist and our results provide important information on the origins of this breed and represent a valuable tool for conservation purposes.

Precise annotation of tick mitochondrial genomes reveals multiple copy number variation of short tandem repeats and one transposon-like element

BackgroundIn the present study, we used long-PCR amplification coupled with Next-Generation Sequencing (NGS) to obtain complete mitochondrial (mt) genomes of individual ticks and unprecedently performed precise annotation of these mt genomes. We aimed to: (1) develop a simple, cost-effective and accurate method for the study of extremely high AT-content mt genomes within an individual animal (e.g. Dermacentor silvarum) containing miniscule DNA; (2) provide a high-quality reference genome for D. silvarum with precise annotation and also for future studies of other tick mt genomes; and (3) detect and analyze mt DNA variation within an individual tick.ResultsThese annotations were confirmed by the PacBio full-length transcriptome data to cover both entire strands of the mitochondrial genomes without any gaps or overlaps. Moreover, two new and important findings were reported for the first time, contributing fundamental knowledge to mt biology. The first was the discovery of a transposon-like element that may eventually reveal much about mechanisms of gene rearrangements in mt genomes. Another finding was that Copy Number Variation (CNV) of Short Tandem Repeats (STRs) account for mitochondrial sequence diversity (heterogeneity) within an individual tick, insect, mouse or human, whereas SNPs were not detected. The CNV of STRs in the protein-coding genes resulted in frameshift mutations in the proteins, which can cause deleterious effects. Mitochondria containing these deleterious STR mutations accumulate in cells and can produce deleterious proteins.ConclusionsWe proposed that the accumulation of CNV of STRs in mitochondria may cause aging or diseases. Future tests of the CNV of STRs hypothesis help to ultimately reveal the genetic basis of mitochondrial DNA variation and its consequences (e.g., aging and diseases) in animals. Our study will lead to the reconsideration of the importance of STRs and a unified study of CNV of STRs with longer and shorter repeat units (particularly polynucleotides) in both nuclear and mt genomes.

Continental island effect in Sichuan Basin based on the genetic structure of sparrow

Abstract Islands are ideal settings for the study of evolution, ecology and genetic diversity. The tree sparrow (Passer montanus), which is distributed both inside and outside the Sichuan Basin and is relatively easy to capture, was used as our study species to test whether any genetic differences exist between within and outside of the Sichuan Basin. We analyzed mitochondrial and nuclear gene sequence variations to illustrate the continental island effect within the Sichuan Basin. Overall, fragments from four mtDNA and one nuclear sequence (Cytb + COI + 12S rRNA + Dloop + Myo) were amplified, with the concatenated alignment comprising 3234 bp. The results of Bayesian and maximum parsimony trees indicated two major branches, one of which is composed mainly of populations within the Sichuan Basin, while the other comprised populations distributed in the surrounding mountains. The population in Sichuan Basin was more basal than that in the surrounding mountains. The genetic distance between inner and outer populations was 0.095 and genetic differentiation index (FST) between inner and outer populations was 0.342. This study shows that the overall distribution pattern of tree sparrow populations in the Sichuan Basin and its surrounding mountains is probably the result of a vicariance event due to spatial isolation.