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Asset Tag: animal genome

July 19, 2019

The Florida manatee (Trichechus manatus latirostris) T cell receptor loci exhibit V subgroup synteny and chain-specific evolution.

The Florida manatee (Trichechus manatus latirostris) has limited diversity in the immunoglobulin heavy chain. We therefore investigated the antigen receptor loci of the other arm of the adaptive immune system: the T cell receptor. Manatees are the first species from Afrotheria, a basal eutherian superorder, to have an in-depth characterization of all T cell receptor loci. By annotating the genome and expressed transcripts, we found that each chain has distinct features that correlates to their individual functions. The genomic organization also plays a role in modulating sequence conservation between species. There were extensive V subgroup synteny blocks in the TRA and TRB loci between T. m. latirostris and human. Increased genomic locus complexity correlated to increased locus synteny. We also identified evidence for a VHD pseudogene for the first time in a eutherian mammal. These findings emphasize the value of including species within this basal eutherian radiation in comparative studies. Copyright © 2018. Published by Elsevier Ltd.

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July 19, 2019

Adaptation and conservation insights from the koala genome.

The koala, the only extant species of the marsupial family Phascolarctidae, is classified as ‘vulnerable’ due to habitat loss and widespread disease. We sequenced the koala genome, producing a complete and contiguous marsupial reference genome, including centromeres. We reveal that the koala’s ability to detoxify eucalypt foliage may be due to expansions within a cytochrome P450 gene family, and its ability to smell, taste and moderate ingestion of plant secondary metabolites may be due to expansions in the vomeronasal and taste receptors. We characterized novel lactation proteins that protect young in the pouch and annotated immune genes important for response to chlamydial disease. Historical demography showed a substantial population crash coincident with the decline of Australian megafauna, while contemporary populations had biogeographic boundaries and increased inbreeding in populations affected by historic translocations. We identified genetically diverse populations that require habitat corridors and instituting of translocation programs to aid the koala’s survival in the wild.

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July 19, 2019

A high-quality, long-read de novo genome assembly to aid conservation of Hawaii’s last remaining crow species

Genome-level data can provide researchers with unprecedented precision to examine the causes and genetic consequences of population declines, which can inform conservation management. Here, we present a high-quality, long-read, de novo genome assembly for one of the world’s most endangered bird species, the ?Alala (Corvus hawaiiensis; Hawaiian crow). As the only remaining native crow species in Hawai?i, the ?Alala survived solely in a captive-breeding program from 2002 until 2016, at which point a long-term reintroduction program was initiated. The high-quality genome assembly was generated to lay the foundation for both comparative genomics studies and the development of population-level genomic tools that will aid conservation and recovery efforts. We illustrate how the quality of this assembly places it amongst the very best avian genomes assembled to date, comparable to intensively studied model systems. We describe the genome architecture in terms of repetitive elements and runs of homozygosity, and we show that compared with more outbred species, the ?Alala genome is substantially more homozygous. We also provide annotations for a subset of immunity genes that are likely to be important in conservation management, and we discuss how this genome is currently being used as a roadmap for downstream conservation applications.

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July 19, 2019

High-quality genome assemblies reveal long non-coding RNAs expressed in ant brains.

Ants are an emerging model system for neuroepigenetics, as embryos with virtually identical genomes develop into different adult castes that display diverse physiology, morphology, and behavior. Although a number of ant genomes have been sequenced to date, their draft quality is an obstacle to sophisticated analyses of epigenetic gene regulation. We reassembled de novo high-quality genomes for two ant species, Camponotus floridanus and Harpegnathos saltator. Using long reads enabled us to span large repetitive regions and improve genome contiguity, leading to comprehensive and accurate protein-coding annotations that facilitated the identification of a Gp-9-like gene as differentially expressed in Harpegnathos castes. The new assemblies also enabled us to annotate long non-coding RNAs in ants, revealing caste-, brain-, and developmental-stage-specific long non-coding RNAs (lncRNAs) in Harpegnathos. These upgraded genomes, along with the new gene annotations, will aid future efforts to identify epigenetic mechanisms of phenotypic and behavioral plasticity in ants. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

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July 19, 2019

Degradation and remobilization of endogenous retroviruses by recombination during the earliest stages of a germ-line invasion.

Endogenous retroviruses (ERVs) are proviral sequences that result from colonization of the host germ line by exogenous retroviruses. The majority of ERVs represent defective retroviral copies. However, for most ERVs, endogenization occurred millions of years ago, obscuring the stages by which ERVs become defective and the changes in both virus and host important to the process. The koala retrovirus, KoRV, only recently began invading the germ line of the koala (Phascolarctos cinereus), permitting analysis of retroviral endogenization on a prospective basis. Here, we report that recombination with host genomic elements disrupts retroviruses during the earliest stages of germ-line invasion. One type of recombinant, designated recKoRV1, was formed by recombination of KoRV with an older degraded retroelement. Many genomic copies of recKoRV1 were detected across koalas. The prevalence of recKoRV1 was higher in northern than in southern Australian koalas, as is the case for KoRV, with differences in recKoRV1 prevalence, but not KoRV prevalence, between inland and coastal New South Wales. At least 15 additional different recombination events between KoRV and the older endogenous retroelement generated distinct recKoRVs with different geographic distributions. All of the identified recombinant viruses appear to have arisen independently and have highly disrupted ORFs, which suggests that recombination with existing degraded endogenous retroelements may be a means by which replication-competent ERVs that enter the germ line are degraded. Copyright © 2018 the Author(s). Published by PNAS.

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July 19, 2019

De novo assembly of haplotype-resolved genomes with trio binning.

Complex allelic variation hampers the assembly of haplotype-resolved sequences from diploid genomes. We developed trio binning, an approach that simplifies haplotype assembly by resolving allelic variation before assembly. In contrast with prior approaches, the effectiveness of our method improved with increasing heterozygosity. Trio binning uses short reads from two parental genomes to first partition long reads from an offspring into haplotype-specific sets. Each haplotype is then assembled independently, resulting in a complete diploid reconstruction. We used trio binning to recover both haplotypes of a diploid human genome and identified complex structural variants missed by alternative approaches. We sequenced an F1 cross between the cattle subspecies Bos taurus taurus and Bos taurus indicus and completely assembled both parental haplotypes with NG50 haplotig sizes of >20 Mb and 99.998% accuracy, surpassing the quality of current cattle reference genomes. We suggest that trio binning improves diploid genome assembly and will facilitate new studies of haplotype variation and inheritance.

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July 19, 2019

Improved reference genome of Aedes aegypti informs arbovirus vector control.

Female Aedes aegypti mosquitoes infect more than 400 million people each year with dangerous viral pathogens including dengue, yellow fever, Zika and chikungunya. Progress in understanding the biology of mosquitoes and developing the tools to fight them has been slowed by the lack of a high-quality genome assembly. Here we combine diverse technologies to produce the markedly improved, fully re-annotated AaegL5 genome assembly, and demonstrate how it accelerates mosquito science. We anchored physical and cytogenetic maps, doubled the number of known chemosensory ionotropic receptors that guide mosquitoes to human hosts and egg-laying sites, provided further insight into the size and composition of the sex-determining M locus, and revealed copy-number variation among glutathione S-transferase genes that are important for insecticide resistance. Using high-resolution quantitative trait locus and population genomic analyses, we mapped new candidates for dengue vector competence and insecticide resistance. AaegL5 will catalyse new biological insights and intervention strategies to fight this deadly disease vector.

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July 7, 2019

Do echinoderm genomes measure up?

Echinoderm genome sequences are a corpus of useful information about a clade of animals that serve as research models in fields ranging from marine ecology to cell and developmental biology. Genomic information from echinoids has contributed to insights into the gene interactions that drive the developmental process at the molecular level. Such insights often rely heavily on genomic information and the kinds of questions that can be asked thus depend on the quality of the sequence information. Here we describe the history of echinoderm genomic sequence assembly and present details about the quality of the data obtained. All of the sequence information discussed here is posted on the echinoderm information web system, Echinobase.org. Copyright © 2015 Elsevier B.V. All rights reserved.

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July 7, 2019

Best practices in insect genome sequencing: What works and what doesn’t.

The last decade of decreasing DNA sequencing costs and proliferating sequencing services in core labs and companies has brought the de-novo genome sequencing and assembly of insect species within reach for many entomologists. However, sequence production alone is not enough to generate a high quality reference genome, and in many cases, poor planning can lead to extremely fragmented genome assemblies preventing high quality gene annotation and other desired analyses. Insect genomes can be problematic to assemble, due to combinations of high polymorphism, inability to breed for genome homozygocity, and small physical sizes limiting the quantity of DNA able to be isolated from a single individual. Recent advances in sequencing technology and assembly strategies are enabling a revolution for insect genome reference sequencing and assembly. Here we review historical and new genome sequencing and assembly strategies, with a particular focus on their application to arthropod genomes. We highlight both the need to design sequencing strategies for the requirements of the assembly software, and new long-read technologies that are enabling a return to traditional assembly approaches. Finally, we compare and contrast very cost effective short read draft genome strategies with the long read approaches that although entailing additional cost, bring a higher likelihood of success and the possibility of archival assembly qualities approaching that of finished genomes.

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July 7, 2019

It’s more than stamp collecting: how genome sequencing can unify biological research.

The availability of reference genome sequences, especially the human reference, has revolutionized the study of biology. However, while the genomes of some species have been fully sequenced, a wide range of biological problems still cannot be effectively studied for lack of genome sequence information. Here, I identify neglected areas of biology and describe how both targeted species sequencing and more broad taxonomic surveys of the tree of life can address important biological questions. I enumerate the significant benefits that would accrue from sequencing a broader range of taxa, as well as discuss the technical advances in sequencing and assembly methods that would allow for wide-ranging application of whole-genome analysis. Finally, I suggest that in addition to ‘big science’ survey initiatives to sequence the tree of life, a modified infrastructure-funding paradigm would better support reference genome sequence generation for research communities most in need. Copyright © 2015 Elsevier Ltd. All rights reserved.

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July 7, 2019

Comparative Analysis of the Shared Sex-Determination Region (SDR) among Salmonid Fishes.

Salmonids present an excellent model for studying evolution of young sex-chromosomes. Within the genus, Oncorhynchus, at least six independent sex-chromosome pairs have evolved, many unique to individual species. This variation results from the movement of the sex-determining gene, sdY, throughout the salmonid genome. While sdY is known to define sexual differentiation in salmonids, the mechanism of its movement throughout the genome has remained elusive due to high frequencies of repetitive elements, rDNA sequences, and transposons surrounding the sex-determining regions (SDR). Despite these difficulties, bacterial artificial chromosome (BAC) library clones from both rainbow trout and Atlantic salmon containing the sdY region have been reported. Here, we report the sequences for these BACs as well as the extended sequence for the known SDR in Chinook gained through genome walking methods. Comparative analysis allowed us to study the overlapping SDRs from three unique salmonid Y chromosomes to define the specific content, size, and variation present between the species. We found approximately 4.1 kb of orthologous sequence common to all three species, which contains the genetic content necessary for masculinization. The regions contain transposable elements that may be responsible for the translocations of the SDR throughout salmonid genomes and we examine potential mechanistic roles of each one. © The Author(s) 2015. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

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July 7, 2019

Tandem repeats in rodents genome and their mapping.

Tandemly-repeated sequences represent a unique class of eukaryotic DNA. Their content in the genome of higher eukaryotes mounts to tens of percents. However, the evolution of this class of sequences is poorly-studied. In our paper, 62 families of Mus musculus tandem repeats are analyzed by bioinformatic methods, and 7 of them are analyzed by fluorescence in situ hybridization. It is shown that the same tandem repeat sets co-occure only in closely related species of mice. But even in such species we observe differences in localization on the chromosomes and the number of individual tandem repeats. With increasing evolutionary distance only some of the tandem repeat families remain common for different species. It is shown, that the use of a combination of bioinformatics and molecular biology techniques is very perspective for further studies of the evolution of tandem repeats.

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July 7, 2019

GMcloser: closing gaps in assemblies accurately with a likelihood-based selection of contig or long-read alignments.

Genome assemblies generated with next-generation sequencing (NGS) reads usually contain a number of gaps. Several tools have recently been developed to close the gaps in these assemblies with NGS reads. Although these gap-closing tools efficiently close the gaps, they entail a high rate of misassembly at gap-closing sites.We have found that the assembly error rates caused by these tools are 20-500-fold higher than the rate of errors introduced into contigs by de novo assemblers. We here describe GMcloser, a tool that accurately closes these gaps with a preassembled contig set or a long read set (i.e. error-corrected PacBio reads). GMcloser uses likelihood-based classifiers calculated from the alignment statistics between scaffolds, contigs and paired-end reads to correctly assign contigs or long reads to gap regions of scaffolds, thereby achieving accurate and efficient gap closure. We demonstrate with sequencing data from various organisms that the gap-closing accuracy of GMcloser is 3-100-fold higher than those of other available tools, with similar efficiency.GMcloser and an accompanying tool (GMvalue) for evaluating the assembly and correcting misassemblies except SNPs and short indels in the assembly are available at https://sourceforge.net/projects/gmcloser/.shunichi.kosugi@riken.jpSupplementary data are available at Bioinformatics online. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

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