Sequence quality is maintained after multiple displacement amplification of non-invasively obtained macaque semen DNA

Whole genome amplification protocols are revolutionizing the fields of molecular and conservation biology as they open the possibility of obtaining a large number of copies of a complete genome from minute amounts of sample. Multiple displacement amplification (MDA) is a whole genome amplification technique based on the properties of the phi29 DNA polymerase, which leads to a uniform representation of the genome with very low error rates. In this study we performed MDA on 28 macaque DNA samples extracted from blood or non-invasively collected semen from which we obtained mitochondrial control region sequences both before and after MDA. The length of the readable sequences was longer for the original samples than for the MDA products, but the number of unresolved positions was comparable both before and after MDA. We conclude that the MDA technique is useful for increasing the amount of DNA for sequencing mitochondrial regions in the case of non-invasively collected semen samples.     

Rapid mitochondrial genome sequencing based on Oxford Nanopore Sequencing and a proxy for vertebrate species identification

Molecular information is crucial for species identification when facing challenging morphology‐based specimen identifications. The use of DNA barcodes partially solves this problem, but in some cases when PCR is not an option (i.e., primers are not available, problems in reaction standardization), amplification‐free approaches could be an optimal alternative. Recent advances in DNA sequencing, like the MinION device from Oxford Nanopore Technologies (ONT), allow to obtain genomic data with low laboratory and technical requirements, and at a relatively low cost. In this study, we explore ONT sequencing for molecular species identification from a total DNA sample obtained from a neotropical rodent and we also test the technology for complete mitochondrial genome reconstruction via genome skimming. We were able to obtain “de novo” the complete mitogenome of a specimen from the genus Melanomys (Cricetidae: Sigmodontinae) with average depth coverage of 78X using ONT‐only data and by combining multiple assembly routines. Our pipeline for an automated species identification was able to identify the sample using unassembled sequence data (raw) in a reasonable computing time, which was substantially reduced when a priori information related to the organism identity was known. Our findings suggest ONT sequencing as a suitable candidate to solve species identification problems in metazoan nonmodel organisms and generate complete mtDNA datasets.     

Assessment of Whole Genome Amplification for Sequence Capture and Massively Parallel Sequencing

Exome sequence capture and massively parallel sequencing can be combined to achieve inexpensive and rapid global analyses of the functional sections of the genome. The difficulties of working with relatively small quantities of genetic material, as may be necessary when sharing tumor biopsies between collaborators for instance, can be overcome using whole genome amplification. However, the potential drawbacks of using a whole genome amplification technology based on random primers in combination with sequence capture followed by massively parallel sequencing have not yet been examined in detail, especially in the context of mutation discovery in tumor material. In this work, we compare mutations detected in sequence data for unamplified DNA, whole genome amplified DNA, and RNA originating from the same tumor tissue samples from 16 patients diagnosed with non-small cell lung cancer. The results obtained provide a comprehensive overview of the merits of these techniques for mutation analysis. We evaluated the identified genetic variants, and found that most (74%) of them were observed in both the amplified and the unamplified sequence data. Eighty-nine percent of the variations found by WGA were shared with unamplified DNA. We demonstrate a strategy for avoiding allelic bias by including RNA-sequencing information.     

Primers for a PCR-based approach to mitochondrial genome sequencing in birds and other vertebrates.

A PCR-based approach to sequencing complete mitochondrial genomes is described along with a set of 86 primers designed primarily for avian mitochondrial DNA (mtDNA). This PCR-based approach allows an accurate determination of complete mtDNA sequences that is faster than sequencing cloned mtDNA. The primers are spaced at about 500-base intervals along both DNA strands. Many of the primers incorporate degenerate positions to accommodate variation in mtDNA sequence among avian taxa and to reduce the potential for preferential amplification of nuclear pseudogenes. Comparison with published vertebrate mtDNA sequences suggests that many of the primers will have broad taxonomic utility. In addition, these primers should make available a wider variety of mitochondrial genes for studies based on smaller data sets.     

Conserved primers for DNA barcoding historical and modern samples from New Zealand and Antarctic birds

Our ability to DNA barcode the birds of the world is based on the effective amplification and sequencing of a 648 base pair (bp) region of the mitochondrial cytochrome c oxidase (COI or cox1) gene. For many geographic regions the large numbers of vouchered specimens necessary for the construction of a DNA barcoding database have already been collected and are available in museums and other institutions. However, many of these specimens are old (>20 years) and are stored as either fixed study skins or dried skeletons. DNA extracted from such historical samples is typically degraded and, generally, only short DNA fragments can be recovered from such specimens making the recovery of the barcoding region as a single fragment difficult. We report two sets of conserved primers that allow the amplification of the entire DNA barcoding region in either three or five overlapping fragments. These primer sets allow the recovery of DNA barcodes from valuable historical specimens that in many cases are unique in that they are unable or unlikely to be collected again. We also report three new primers that in combination allow the effective amplification from modern samples of the entire DNA barcoding region as a single DNA fragment for 17 orders of Southern Hemisphere birds.     

Validation of whole genome amplification for analysis of the p53 tumor suppressor gene in limited amounts of tumor samples

Personalized cancer treatment requires molecular characterization of individual tumor biopsies. These samples are frequently only available in limited quantities hampering genomic analysis. Several whole genome amplification (WGA) protocols have been developed with reported varying representation of genomic regions post amplification. In this study we investigate region dropout using a φ29 polymerase based WGA approach. DNA from 123 lung cancers specimens and corresponding normal tissue were used and evaluated by Sanger sequencing of the p53 exons 5-8. To enable comparative analysis of this scarce material, WGA samples were compared with unamplified material using a pooling strategy of the 123 samples. In addition, a more detailed analysis of exon 7 amplicons were performed followed by extensive cloning and Sanger sequencing. Interestingly, by comparing data from the pooled samples to the individually sequenced exon 7, we demonstrate that mutations are more easily recovered from WGA pools and this was also supported by simulations of different sequencing coverage. Overall this data indicate a limited random loss of genomic regions supporting the use of whole genome amplification for genomic analysis.     

北京鸭线粒体基因组全序列测定和分析

线粒体DNA作为遗传标记,已在家鸡(Gallus gallus)和家鹅(Anser anser)的研究中取得了重大进展,而对家鸭(Anas platyrhychos domesticus)的研究却很少.本研究参照近源物种线粒体基因组序列设计15对引物,通过PCR扩增、测序、拼接,获得北京鸭(A.platyrhychos)线粒体基因组全序列,初步分析其特点和各基因的定位.结果显示,北京鸭线粒体基因组全长16 604 bp,碱基组成为29.19%A、22.20%T、15.80%G、32.81%C,包含13个蛋白质编码基因、2个rRNA基因、22个tRNA基因和1个非编码控制区(D-loop),基因组成及排列顺序与其他鸟类相似.基于线粒体D-loop区全序列,用N-J法构建了7种雁形目鸟类系统进化树,结果表明,北京鸭与绿头鸭(A.platyrhychos)系统进化关系较近.     

Conservation and versatility of a new set of primers for long‐PCR amplification of complete insect mitochondrial genomes based on Haematobia irritans mtDNA sequences

The amplification of complete mitochondrial genomes by long PCR (polymerase chain reaction) has been a major contribution to the large‐scale sequencing of arthropodan mitochondrial genomes. In this work, we designed six conserved long‐PCR primers to successfully recover the entire mitochondrial genome of the horn fly Haematobia irritans (Diptera: Muscidae) in two overlapping fragments. The conservation and versatility of these primers were tested for 17 other species from four major insect orders: Diptera (14), Coleoptera (1), Lepidoptera (1) and Hymenoptera (1). The amplification of complete mitochondrial genomes in orders other than Diptera suggested an even broader application of these primers, especially within the Hexapoda.     

甜果螨全线粒体基因组测序与分析

【目的】测定和分析甜果螨Carpoglyphus lactis线粒体基因组全序列,并在线粒体基因组水平探讨其在真螨总目(Acariformes)中的系统发育地位,为真螨总目分类及果螨科线粒体基因组研究提供科学依据。【方法】挑取实验室饲养的甜果螨成螨,用传统的酚氯仿抽提法和试剂盒提取法提取甜果螨基因组DNA。然后采用节肢动物或螨类线粒体基因的通用引物PCR扩增出甜果螨线粒体基因cox1,cob,rrnS和nad4-nad5的部分序列;再设计种特异性引物进行Long-PCR扩增和步移法测序,测出甜果螨线粒体基因组全序列。应用SeqMan, SEQUIN 9.0和tRNAscan等生物信息学软件,对甜果螨线粒体基因组的基因结构等进行生物信息学分析。最后基于17种真螨总目螨类的蛋白质编码基因,采用最大似然法构建系统发育树。【结果】甜果螨线粒体全基因组总长为14 060 bp(GenBank登录号:MN073839),为典型的闭合双链DNA分子,共由37个基因组成,包括13个蛋白质编码基因(PCGs)、22个tRNA基因和2个rRNA基因;甜果螨线粒体基因组还包括1个大的非编码区(large non-coding region, LNR)。系统发育分析结果显示,甜果螨Carpoglyphus lactis属于无气门亚目粉螨总科(Acaroidae),与椭圆食粉螨Aleuroglyphus ovatus构成一支。粉螨总科(Acaroidae)和薄口螨总科(Histiostomatoidae)聚成一簇,与痒螨股(Psoroptidia)构成姐妹群。【结论】本研究首次获得并分析了甜果螨线粒体基因组全序列。甜果螨与椭圆食粉螨的亲缘关系较近。     

Next‐generation DNA barcoding: using next‐generation sequencing to enhance and accelerate DNA barcode capture from single specimens

DNA barcoding is an efficient method to identify specimens and to detect undescribed/cryptic species. Sanger sequencing of individual specimens is the standard approach in generating large‐scale DNA barcode libraries and identifying unknowns. However, the Sanger sequencing technology is, in some respects, inferior to next‐generation sequencers, which are capable of producing millions of sequence reads simultaneously. Additionally, direct Sanger sequencing of DNA barcode amplicons, as practiced in most DNA barcoding procedures, is hampered by the need for relatively high‐target amplicon yield, coamplification of nuclear mitochondrial pseudogenes, confusion with sequences from intracellular endosymbiotic bacteria (e.g. Wolbachia) and instances of intraindividual variability (i.e. heteroplasmy). Any of these situations can lead to failed Sanger sequencing attempts or ambiguity of the generated DNA barcodes. Here, we demonstrate the potential application of next‐generation sequencing platforms for parallel acquisition of DNA barcode sequences from hundreds of specimens simultaneously. To facilitate retrieval of sequences obtained from individual specimens, we tag individual specimens during PCR amplification using unique 10‐mer oligonucleotides attached to DNA barcoding PCR primers. We employ 454 pyrosequencing to recover full‐length DNA barcodes of 190 specimens using 12.5% capacity of a 454 sequencing run (i.e. two lanes of a 16 lane run). We obtained an average of 143 sequence reads for each individual specimen. The sequences produced are full‐length DNA barcodes for all but one of the included specimens. In a subset of samples, we also detected Wolbachia, nontarget species, and heteroplasmic sequences. Next‐generation sequencing is of great value because of its protocol simplicity, greatly reduced cost per barcode read, faster throughout and added information content.     

Extracting DNA from museum bird eggs, and whole genome amplification of archive DNA

We present a comprehensive protocol for extracting DNA from egg membranes and other internal debris recovered from the interior of blown museum bird eggs. A variety of commercially available DNA extraction methods were found to be applicable. DNA sequencing of polymerase chain reaction (PCR) products for a 176‐bp fragment of mitochondrial DNA was successful for most egg samples (> 78%) even though the amount of DNA extracted (mean = 14.71 ± 4.55 ng/µL) was significantly less than that obtained for bird skin samples (mean = 67.88 ± 4.77 ng/µL). For PCR and sequencing of snipe (Gallinago) DNA, we provide eight new primers for the ‘DNA barcode’ region of COI mtDNA. In various combinations, the primers target a range of PCR products sized from 72 bp to the full ‘barcode’ of 751 bp. Not all possible combinations were tested with archive snipe DNA, but we found a significantly better success rate of PCR amplification for a shorter 176‐bp target compared with a larger 288‐bp fragment (67% vs. 39%). Finally, we explored the feasibility of whole genome amplification (WGA) for extending the use of archive DNA in PCR and sequencing applications. Of two WGA approaches, a PCR‐based method was found to be able to amplify whole genomic DNA from archive skins and eggs from museum bird collections. After WGA, significantly more archive egg samples produced visible PCR products on agarose (56.9% before WGA vs. 79.0% after WGA). However, overall sequencing success did not improve significantly (78.8% compared with 83.0%).     

Affinity generation of single-stranded DNA for dideoxy sequencing following the polymerase chain reaction

A method to rapidly generate single stranded DNA for dideoxy sequencing following the polymerase chain reaction is described. By incorporating biotin in one of the amplification primers, we are able to physically separate the two DNA strands produced in the polymerase chain reaction. After amplification, the mixture is passed through a column containing streptavidin agarose. The strand produced by the biotinylated primer is bound in this matrix. The unbiotinylated strand is eluted with 0.2 N NaOH and sequenced by the dideoxy method. This method was utilized to sequence mitochondrial DNA from crude genomic DNA and to determine the sequences of four clones containing human mitochondrial DNA as a test of its accuracy. The use of biotin-facilitated separation permitted us to amplify and sequence DNA samples in a single day.     

A luminal breast cancer genome atlas: progress and barriers

The challenge of developing an atlas that catalogs all the functionally important genomic changes associated with the development of luminal-type breast cancer is discussed in this article. The development of genome-wide techniques such as expression profiling, array-based comparative genomic hybridization and unbiased sequencing have put a cancer genome atlas within reach. However these techniques have revealed that the somatic DNA alterations associated with the development of a common solid tumor such as breast cancer are extremely complex. For example, large scale tumor DNA resequencing projects, focused on a small number of cell lines and the analysis of many genes, suggest that as many as 100 somatic mutations may have accumulated by the time a diagnosis is made. Similarly, array comparative hybridization experiments have uncovered multiple gene amplification and deletion events. Dealing with this complexity requires access to tumor and matched normal DNA from a large number of cases, with sufficient material to complete a spectrum of analytical techniques. Second, an acceptable approach to patient consent or sample de-identification must be in place if DNA sequencing traces are to be entered into public databases. Third, samples must be linked to detailed information on disease outcomes in order to identify lesions associated with aggressive clinical behavior. We conclude that samples from neoadjuvant endocrine therapy clinical protocols offer the best sample sets to initiate a luminal breast cancer genome atlas because these studies are amongst the few in which investigators have obtained high quality frozen tumor samples associated with both short term information on the estrogen dependence of individual ER+ tumors, as well as conventional data on long-term cancer survival.     

Genome-Tagged Amplification (GTA): a PCR-based method to prepare sample-tagged amplicons from hundreds of individuals for next generation sequencing

Sampling the sequence of a relatively small fraction of the genome in large numbers of individuals is an important objective for population genetics and association genetics approaches. However, currently available ‘sequence capture’ methods either require expensive instrumentation or have problems dealing with high sample numbers and relatively small target sizes. We have developed Genome-Tagged Amplification (GTA) as a flexible PCR-based method for preparing pools of hundreds of amplicons from hundreds of samples for next generation sequencing. The method involves tagging of genomic DNA with barcode adapters at restriction sites, followed by PCR amplification from flanking DNA. It is freely scalable for both sample number and amplicon number and has no specialized equipment requirement. An optimized protocol is presented which provides a matrix of 96 × 192 combinations of samples x amplicons, corresponding to a complete 454 Titanium run. Initially, we used 454 sequencing; however, GTA could easily be adapted to Illumina sequencing platforms as read lengths have significantly increased in this system.     

Noncoding mitochondrial loci for corals

We developed five degenerate primer pairs for the amplification and sequencing of two noncoding regions found in the mitochondrial genome of corals. These primers amplify products ranging from 380 to 950 bp, and work in a wide variety of scleractinian taxa from both the Pacific and Caribbean. Based on our initial analysis of ～300 sequences from 13 scleractinian taxa, both these noncoding regions appear to have equivalent levels of variability to the most variable of previously published coral mitochondrial loci, but work in a wider variety of taxa. We believe these primers will be of use to coral biologists studying questions above the level of species; as with other mithochondrial DNA markers in corals, these loci will likely provide little resolution for within‐species studies.     

An isothermal method for whole genome amplification of fresh and degraded DNA for comparative genomic hybridization, genotyping and mutation detection.

Molecular genotyping has important biomedical and forensic applications. However, limiting amounts of human biological material often yield genomic DNA (gDNA) in insufficient quantity and of poor quality for a reliable analysis. This motivated the development of an efficient whole genome amplification method with quantitatively unbiased representation usable on fresh and degraded gDNA. Amplification of fresh frozen, formalin-fixed paraffin-embedded (FFPE) and DNase-degraded DNA using degenerate oligonucleotide-primed PCR or primer extension amplification using a short primer sequence bioinformatically optimized for coverage of the human genome was compared with amplification using current primers by chromosome-based and BAC-array comparative genomic hybridization (CGH), genotyping at short tandem repeats (STRs) and single base mutation detection. Compared with current primers, genome amplification using the bioinformatically optimized primer was significantly less biased on CGH in self-self hybridizations, and replicated tumour genome copy number aberrations, even from FFPE tissue. STR genotyping could be performed on degraded gDNA amplified using our technique but failed with multiple displacement amplification. Of the 18 different single base mutations 16 (89.5%) were correctly identified by sequencing gDNA amplified from clinical samples using our technique. This simple and efficient isothermal method should be helpful for genetic research and clinical and forensic applications.     

One-step PCR amplification of complete arthropod mitochondrial genomes

A new PCR primer set which enables one-step amplification of complete arthropod mitochondrial genomes was designed from two conserved 16S rDNA regions for the long PCR technique. For this purpose, partial 16S rDNAs amplified with universal primers 16SA and 16SB were newly sequenced from six representative arthropods: Armadillidium vulgare and Macrobrachium nipponense (Crustacea), Anopheles sinensis (Insecta), Lithobius forficatus and Megaphyllum sp. (Myriapoda), and Limulus polyphemus (Chelicerata). The genomic locations of two new primers, HPK16Saa and HPK16Sbb, correspond to positions 13314-13345 and 12951-12984, respectively, in the Drosophila yakuba mitochondrial genome. The usefulness of the primer set was experimentally examined and confirmed with five of the representative arthropods, except for A. vulgare, which has a linearized mitochondrial genome. With this set, therefore, we could easily and rapidly amplify complete mitochondrial genomes with small amounts of arthropod DNA. Although the primers suggested here were examined only with arthropod groups, a possibility of successful application to other invertebrates is very high, since the high degree of sequence conservation is shown on the primer sites in other invertebrates. Thus, this primer set can serve various research fields, such as molecular evolution, population genetics, and molecular phylogenetics based on DNA sequences, RFLP, and gene rearrangement of mitochondrial genomes in arthropods and other invertebrates.     

Genomic sequencing of uncultured microorganisms from single cells

Sequencing DNA from single cells has opened new windows onto the microbial world. It is becoming routine to sequence bacterial species directly from environmental samples or clinical specimens without the need to develop cultivation methods. Recent technical improvements often allow nearly complete genome assembly from these otherwise inaccessible species. New bioinformatics methods are also improving genome assembly from single cells. The use of single-cell sequencing in combination with metagenomic analysis is also emerging as a powerful new strategy to analyse bacterial communities. Here, the technical developments that have enabled single-cell sequencing, as well as some of the most exciting applications of this approach from the past few years, are reviewed.     

Combined hybridization capture and shotgun sequencing for ancient DNA analysis of extinct wild and domestic dromedary camel

The performance of hybridization capture combined with next‐generation sequencing (NGS) has seen limited investigation with samples from hot and arid regions until now. We applied hybridization capture and shotgun sequencing to recover DNA sequences from bone specimens of ancient‐domestic dromedary (Camelus dromedarius) and its extinct ancestor, the wild dromedary from Jordan, Syria, Turkey and the Arabian Peninsula, respectively. Our results show that hybridization capture increased the percentage of mitochondrial DNA (mtDNA) recovery by an average 187‐fold and in some cases yielded virtually complete mitochondrial (mt) genomes at multifold coverage in a single capture experiment. Furthermore, we tested the effect of hybridization temperature and time by using a touchdown approach on a limited number of samples. We observed no significant difference in the number of unique dromedary mtDNA reads retrieved with the standard capture compared to the touchdown method. In total, we obtained 14 partial mitochondrial genomes from ancient‐domestic dromedaries with 17–95% length coverage and 1.27–47.1‐fold read depths for the covered regions. Using whole‐genome shotgun sequencing, we successfully recovered endogenous dromedary nuclear DNA (nuDNA) from domestic and wild dromedary specimens with 1–1.06‐fold read depths for covered regions. Our results highlight that despite recent methodological advances, obtaining ancient DNA (aDNA) from specimens recovered from hot, arid environments is still problematic. Hybridization protocols require specific optimization, and samples at the limit of DNA preservation need multiple replications of DNA extraction and hybridization capture as has been shown previously for Middle Pleistocene specimens.     

Organization of the Mitochondrial Genome of Antarctic Krill <Emphasis Type="Italic">Euphausia superba</Emphasis> (Crustacea: Malacostraca)

We determined the nearly complete DNA sequence of the mitochondrial genome of Antarctic krill Euphausia superba (Crustacea: Malacostraca), one of the most ecologically and commercially important zooplankters in Antarctic waters. All of the genome sequences were purified by gene amplification using long polymerase chain reaction (PCR), and the products were subsequently used as templates for either direct sequencing using a primer-walking strategy or nested PCR with crustacea-versatile primers. Although we were unable to determine a portion of the genome owing to technical difficulties, the sequenced position, 14,606 bp long, contained all of the 13 protein-coding genes, 19 of the 22 transfer RNA genes, and the large subunit as well as a portion of the small subunit ribosomal RNA genes. Gene rearrangement was observed for 3 transfer RNA genes (tRNA^Cys, tRNA^Tyr, and tRNA^Trp) and the 2 leucine tRNA genes.