Characterizing short read sequencing for gene discovery and RNA-Seq analysis in Crassostrea gigas

Population structure and adaptive differentiation in the sea cucumber Apostichopus californicus and implications for spatial resource management

A growing body of evidence suggests that spatial population structure can develop in marine species despite large population sizes and high gene flow. Characterizing population structure is important for the effective management of exploited species, as it can be used to identify appropriate scales of management in fishery and aquaculture contexts. The California sea cucumber, Apostichopus californicus, is one such exploited species whose management could benefit from further characterization of population structure. Using restriction site-associated DNA (RAD) sequencing, we developed 2075 single nucleotide polymorphisms (SNPs) to quantify genetic structure over a broad section of the species' range along the North American west coast and within the Salish Sea, a region supporting the Washington State A. californicus fishery and developing aquaculture production of the species. We found evidence for population structure (global fixation index (FST) = 0.0068) with limited dispersal driving two patterns of differentiation: isolation-by-distance and a latitudinal gradient of differentiation. Notably, we found detectable population differences among collection sites within the Salish Sea (pairwise FST = 0.001-0.006). Using FST outlier detection and gene-environment association, we identified 10.2% of total SNPs as putatively adaptive. Environmental variables (e.g., temperature, salinity) from the sea surface were more correlated with genetic variation than those same variables measured near the benthos, suggesting that selection on pelagic larvae may drive adaptive differentiation to a greater degree than selection on adults. Our results were consistent with previous estimates of and patterns in population structure for this species in other extents of the range. Additionally, we found that patterns of neutral and adaptive differentiation co-varied, suggesting that adaptive barriers may limit dispersal. Our study provides guidance to decision-makers regarding the designation of management units for A. californicus and adds to the growing body of literature identifying genetic population differentiation in marine species despite large, nominally connected populations.

Transcriptome analysis of hepatopancreas of Eriocheir sinensis with hepatopancreatic necrosis disease (HPND)

Hepatopancreatic necrosis disease (HPND) is a newly emerging disease in the Chinese mitten crab, Eriocheir sinensis, which has resulted in large economic losses. However, the underlying cause of this disease remains unclear. To better understand the pathogenesis and pathogenic mechanism of HPND, we compared the transcriptome differences of the hepatopancreas of E. sinensis with and without HPND. The analysis yielded > 30 million reads for each sample of three test (with HPND) and three control groups (without HPND). We observed 978 downregulated genes and 644 upregulated genes. Among the gene ontology categories "biological process," "cellular component," and "molecular function", the subcategories cellular process, single-organism process, biological regulation, metabolic process, cell part, organelle, organelle part, binding, and catalytic were enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that "metabolism of xenobiotics by cytochrome P450," "drug metabolism-cytochrome P450," "chemical carcinogenesis," and "material metabolism" were the "five" most significantly enriched pathways in the hepatopancreas of E. sinensis with HPND. The results revealed that material metabolic abnormalities and drug effects from the external environment might be associated with HPND in the Chinese mitten crab. Considering the wide use of pyrethroids for pond cleaning in Xinghua city, we speculated that pyrethroids might cause HPND in the Chinese mitten crab. Our study provided useful information about the cause and pathogenetic mechanisms of HPND and could help to prevent this disease in production practice.

Transcriptome analysis of the Chinese giant salamander (Andrias davidianus) using RNA-sequencing

The Chinese giant salamander (Andrias davidianus) is an economically important animal on academic value. However, the genomic information of this species has been less studied. In our study, the transcripts of A. davidianus were obtained by RNA-seq to conduct a transcriptomic analysis. In total 132,912 unigenes were generated with an average length of 690 bp and N50 of 1263 bp by de novo assembly using Trinity software. Using a sequence similarity search against the nine public databases (CDD, KOG, NR, NT, PFAM, Swiss-prot, TrEMBL, GO and KEGG databases), a total of 24,049, 18,406, 36,711, 15,858, 20,500, 27,515, 36,705, 28,879 and 10,958 unigenes were annotated in databases, respectively. Of these, 6323 unigenes were annotated in all database and 39,672 unigenes were annotated in at least one database. Blasted with KEGG pathway, 10,958 unigenes were annotated, and it was divided into 343 categories according to different pathways. In addition, we also identified 29,790 SSRs. This study provided a valuable resource for understanding transcriptomic information of A. davidianus and laid a foundation for further research on functional gene cloning, genomics, genetic diversity analysis and molecular marker exploitation in A. davidianus.

Transcriptional responses in the hepatopancreas of Eriocheir sinensis exposed to deltamethrin

Deltamethrin is an important pesticide widely used against ectoparasites. Deltamethrin contamination has resulted in a threat to the healthy breeding of the Chinese mitten crab, Eriocheir sinensis. In this study, we investigated transcriptional responses in the hepatopancreas of E. sinensis exposed to deltamethrin. We obtained 99,087,448, 89,086,478, and 100,117,958 raw sequence reads from control 1, control 2, and control 3 groups, and 92,094,972, 92,883,894, and 92,500,828 raw sequence reads from test 1, test 2, and test 3 groups, respectively. After filtering and quality checking of the raw sequence reads, our analysis yielded 79,228,354, 72,336,470, 81,859,826, 77,649,400, 77,194,276, and 75,697,016 clean reads with a mean length of 150 bp from the control and test groups. After deltamethrin treatment, a total of 160 and 167 genes were significantly upregulated and downregulated, respectively. Gene ontology terms "biological process," "cellular component," and "molecular function" were enriched with respect to cell killing, cellular process, other organism part, cell part, binding, and catalytic. Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes showed that the metabolic pathways were significantly enriched. We found that the CYP450 enzyme system, carboxylesterase, glutathione-S-transferase, and material (including carbohydrate, lipid, protein, and other substances) metabolism played important roles in the metabolism of deltamethrin in the hepatopancreas of E. sinensis. This study revealed differentially expressed genes related to insecticide metabolism and detoxification in E. sinensis for the first time and will help in understanding the toxicity and molecular metabolic mechanisms of deltamethrin in E. sinensis.

Characterization of mussel H2A.Z.2: a new H2A.Z variant preferentially expressed in germinal tissues from Mytilus

Histones are the fundamental constituents of the eukaryotic chromatin, facilitating the physical organization of DNA in chromosomes and participating in the regulation of its metabolism. The H2A family displays the largest number of variants among core histones, including the renowned H2A.X, macroH2A, H2A.B (Bbd), and H2A.Z. This latter variant is especially interesting because of its regulatory role and its differentiation into 2 functionally divergent variants (H2A.Z.1 and H2A.Z.2), further specializing the structure and function of vertebrate chromatin. In the present work we describe, for the first time, the presence of a second H2A.Z variant (H2A.Z.2) in the genome of a non-vertebrate animal, the mussel Mytilus. The molecular and evolutionary characterization of mussel H2A.Z.1 and H2A.Z.2 histones is consistent with their functional specialization, supported on sequence divergence at promoter and coding regions as well as on varying gene expression patterns. More precisely, the expression of H2A.Z.2 transcripts in gonadal tissue and its potential upregulation in response to genotoxic stress might be mirroring the specialization of this variant in DNA repair. Overall, the findings presented in this work complement recent reports describing the widespread presence of other histone variants across eukaryotes, supporting an ancestral origin and conserved role for histone variants in chromatin.

Generation and analysis of expressed sequence tags (ESTs) of Camelina sativa to mine drought stress-responsive genes

Camelina sativa is an oil-producing crop belonging to the family of Brassicaceae. Due to exceptionally high content of omega fatty acid, it is commercially grown around the world as edible oil, biofuel, and animal feed. A commonly referred 'false flax' or gold-of-pleasure Camelina sativa has been interested as one of biofuel feedstocks. The species can grow on marginal land due to its superior drought tolerance with low requirement of agricultural inputs. This crop has been unexploited due to very limited transcriptomic and genomic data. Use of gene-specific molecular markers is an important strategy for new cultivar development in breeding program. In this study, Illumina paired-end sequencing technology and bioinformatics tools were used to obtain expression profiling of genes responding to drought stress in Camelina sativa BN14. A total of more than 60,000 loci were assembled, corresponding to approximately 275 K transcripts. When the species was exposed to 10 kPa drought stress, 100 kPa drought stress, and rehydrated conditions, a total of 107, 2,989, and 982 genes, respectively, were up-regulated, while 146, 3,659, and 1189 genes, respectively, were down-regulated compared to control condition. Some unknown genes were found to be highly expressed under drought conditions, together with some already reported gene families such as senescence-associated genes, CAP160, and LEA under 100 kPa soil water condition, cysteine protease, 2OG, Fe(II)-dependent oxygenase, and RAD-like 1 under rehydrated condition. These genes will be further validated and mapped to determine their function and loci. This EST library will be favorably applied to develop gene-specific molecular markers and discover genes responsible for drought tolerance in Camelina species.

RNA-Seq in Mytilus galloprovincialis: comparative transcriptomics and expression profiles among different tissues

Background

The Mediterranean mussel (Mytilus galloprovincialis) is a cosmopolitan, cultured bivalve with worldwide commercial and ecological importance. However, there is a qualitative and quantitative lack of knowledge of the molecular mechanisms involved in the physiology and immune response of this mollusc. In order to start filling this gap, we have studied the transcriptome of mantle, muscle and gills from naïve Mediterranean mussels and hemocytes exposed to distinct stimuli.

Results

A total of 393,316 million raw RNA-Seq reads were obtained and assembled into 151,320 non-redundant transcripts with an average length of 570 bp. Only 55 % of the transcripts were shared across all tissues. Hemocyte and gill transcriptomes shared 60 % of the transcripts while mantle and muscle transcriptomes were most similar, with 77 % shared transcripts. Stimulated hemocytes showed abundant defense and immune-related proteins, in particular, an extremely high amount of antimicrobial peptides. Gills expressed many transcripts assigned to both structure and recognition of non-self patterns, while in mantle many transcripts were related to reproduction and shell formation. Moreover, this tissue presented additional and interesting hematopoietic, antifungal and sensorial functions. Finally, muscle expressed many myofibril and calcium-related proteins and was found to be unexpectedly associated with defense functions. In addition, many metabolic routes related to cancer were represented.

Conclusions

Our analyses indicate that whereas the transcriptomes of these four tissues have characteristic expression profiles in agreement with their biological structures and expected functions, tissue-specific transcriptomes reveal a complex and specialized functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1817-5) contains supplementary material, which is available to authorized users.

RNA-Seq analysis and gene discovery of Andrias davidianus using Illumina short read sequencing

The Chinese giant salamander, Andrias davidianus, is an important species in the course of evolution; however, there is insufficient genomic data in public databases for understanding its immunologic mechanisms. High-throughput transcriptome sequencing is necessary to generate an enormous number of transcript sequences from A. davidianus for gene discovery. In this study, we generated more than 40 million reads from samples of spleen and skin tissue using the Illumina paired-end sequencing technology. De novo assembly yielded 87,297 transcripts with a mean length of 734 base pairs (bp). Based on the sequence similarities, searching with known proteins, 38,916 genes were identified. Gene enrichment analysis determined that 981 transcripts were assigned to the immune system. Tissue-specific expression analysis indicated that 443 of transcripts were specifically expressed in the spleen and skin. Among these transcripts, 147 transcripts were found to be involved in immune responses and inflammatory reactions, such as fucolectin, β-defensins and lymphotoxin beta. Eight tissue-specific genes were selected for validation using real time reverse transcription quantitative PCR (qRT-PCR). The results showed that these genes were significantly more expressed in spleen and skin than in other tissues, suggesting that these genes have vital roles in the immune response. This work provides a comprehensive genomic sequence resource for A. davidianus and lays the foundation for future research on the immunologic and disease resistance mechanisms of A. davidianus and other amphibians.

RNA-seq as a powerful tool for penaeid shrimp genetic progress

The sequences of all different RNA transcripts present in a cell or tissue that are related to the gene expression and its functional control represent what it is called a transcriptome. The transcripts vary between cells, tissues, ontogenetic and environmental conditions, and the knowledge that can be gained through them is of a solid relevance for genetic applications in aquaculture. Some of the techniques used in transcriptome studies, such as microarrays, are being replaced for next-generation sequencing approaches. RNA-seq emerges as a new possibility for the transcriptome complexity analysis as well as for the candidate genes and polymorphisms identification of penaeid species. Thus, it may also help to understand the determination of complex traits mechanisms and genetic improvement of stocks. In this review, it is first introduced an overview of transcriptome analysis by RNA-seq, followed by a discussion of how this approach may be applied in genetic progress within penaeid stocks.

Early environment influences later performance in fishes

Conditions fish encounter during embryogenesis and early life history can leave lasting effects not only on morphology, but also on growth rate, life-history and behavioural traits. The ecology of offspring can be affected by conditions experienced by their parents and mother in particular. This review summarizes such early impacts and their ecological influences for a variety of teleost species, but with special reference to salmonids. Growth and adult body size, sex ratio, egg size, lifespan and tendency to migrate can all be affected by early influences. Mechanisms behind such phenotypically plastic impacts are not well known, but epigenetic change appears to be one central mechanism. The thermal regime during development and incubation is particularly important, but also early food consumption and intraspecific density can all be responsible for later life-history variation. For behavioural traits, early experiences with effects on brain, sensory development and cognition appear essential. This may also influence boldness and other social behaviours such as mate choice. At the end of the review, several issues and questions for future studies are given.

Transcriptome profiling analysis on whole bodies of microbial challenged Eriocheir sinensis larvae for immune gene identification and SNP development

To study crab immunogenetics of individuals, newly hatched Eriocheir sinensis larvae were stimulated with a mixture of three pathogen strains (Gram-positive bacteria Micrococcus luteus, Gram-negative bacteria Vibrio alginolyticus and fungi Pichia pastoris; 10⁸ cfu·mL^-1). A total of 44,767,566 Illumina clean reads corresponding to 4.52 Gb nucleotides were generated and assembled into 100,252 unigenes (average length: 1,042 bp; range: 201-19,357 bp). 17,097 (26.09%) of 65,535 non-redundant unigenes were annotated in NCBI non-redundant protein (Nr) database. Moreover, 23,188 (35.38%) unigenes were assigned to three Gene Ontology (GO) categories, 15,071 (23.00%) to twenty-six Clusters of orthologous Groups (COG) and 8,574 (13.08%) to six Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, respectively. Numerous genes were further identified to be associated with multiple immune pathways, including Toll, immune deficiency (IMD), janus kinase (JAK)-signal transducers and activators of transcription (STAT) and mitogen-activated protein kinase (MAPK) pathways. Some of them, such as tumor necrosis factor receptor associated factor 6 (TRAF6), fibroblast growth factor (FGF), protein-tyrosine phosphatase (PTP), JNK-interacting protein 1 (JIP1), were first identified in E. sinensis. TRAF6 was even first discovered in crabs. Additionally, 49,555 single nucleotide polymorphisms (SNPs) were developed from over 13,309 unigenes. This is the first transcriptome report of whole bodies of E. sinensis larvae after immune challenge. Data generated here not only provide detail information to identify novel genes in genome reference-free E. sinensis, but also facilitate our understanding on host immunity and defense mechanism of the crab at whole transcriptome level.

Trascriptome analysis of the Pacific white shrimp Litopenaeus vannamei exposed to nitrite by RNA-seq

In the present study, transcriptome of nitrite-exposed Litopenaeus vannamei was performed using a newly developed high-throughput sequencing technology (Illumina RNA-seq). As many as 42,336 unigenes were generated with 561 bp of average length and 736 bp of unigene N50 after filtering and assembly. These unigenes from the de novo assembly were further annotated using BLAST and BLAST2GO softwares. A total of 23,532 unigenes were unambiguous alignments to the reference when BLAST against non-redundant protein sequence (Nr), non-redundant nucleotide (Nt), Swiss-Prot, Gene Ontology database (GO), Clusters of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases available at NCBI. Numerous candidate genes associated with immune response, detoxification, apoptosis pathway were identified. Ten candidate genes related to immune responses and apoptosis were selected for validating the results of assembly and annotation by real-time quantitative PCR. Results revealed that the expressions of all these ten genes were up-regulated after nitrite exposure. Combining to our previous study, we speculate that all these selected genes may be involved in the response to nitrite stress. The study shows a systematic overview of the transcriptome analysis in L. vannamei, and provides valuable gene information for studying molecular mechanisms under nitrite exposure.

Transcriptome analysis and discovery of genes involved in immune pathways from hepatopancreas of microbial challenged mitten crab Eriocheir sinensis

Background

The Chinese mitten crab Eriocheir sinensis is an important economic crustacean and has been seriously attacked by various diseases, which requires more and more information for immune relevant genes on genome background. Recently, high-throughput RNA sequencing (RNA-seq) technology provides a powerful and efficient method for transcript analysis and immune gene discovery.

Methods/Principal Findings

A cDNA library from hepatopancreas of E. sinensis challenged by a mixture of three pathogen strains (Gram-positive bacteria Micrococcus luteus, Gram-negative bacteria Vibrio alginolyticus and fungi Pichia pastoris; 10⁸ cfu·mL⁻¹) was constructed and randomly sequenced using Illumina technique. Totally 39.76 million clean reads were assembled to 70,300 unigenes. After ruling out short-length and low-quality sequences, 52,074 non-redundant unigenes were compared to public databases for homology searching and 17,617 of them showed high similarity to sequences in NCBI non-redundant protein (Nr) database. For function classification and pathway assignment, 18,734 (36.00%) unigenes were categorized to three Gene Ontology (GO) categories, 12,243 (23.51%) were classified to 25 Clusters of Orthologous Groups (COG), and 8,983 (17.25%) were assigned to six Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Potentially, 24, 14, 47 and 132 unigenes were characterized to be involved in Toll, IMD, JAK-STAT and MAPK pathways, respectively.

Conclusions/Significance

This is the first systematical transcriptome analysis of components relating to innate immune pathways in E. sinensis. Functional genes and putative pathways identified here will contribute to better understand immune system and prevent various diseases in crab.