A chromosome-level genome assembly of the jade perch (Scortum barcoo).

Endemic to Australia, jade perch (Scortum barcoo) is a highly profitable freshwater bass species. It has extraordinarily high levels of omega-3 polyunsaturated fatty acids (PUFAs), which detailed genes involved in are largely unclear. Meanwhile, there were four chromosome-level bass species have been previous sequenced, while the bass ancestor genome karyotypes have not been estimated. Therefore, we sequenced, assembled and annotated a genome of jade perch to characterize the detailed genes for biosynthesis of omega-3 PUFAs and to deduce the bass ancestor genome karyotypes. We constructed a chromosome-level genome assembly with 24 pairs of chromosomes, 657.7 Mb in total length, and the contig and the scaffold N50 of 4.8 Mb and 28.6 Mb respectively. We also identified repetitive elements (accounting for 19.7% of the genome assembly) and predicted 26,905 protein-coding genes. Meanwhile, we performed genome-wide localization and characterization of several important genes encoding some key enzymes in the biosynthesis pathway of PUFAs. These genes may contribute to the high concentration of omega-3 in jade perch. Moreover, we conducted a series of comparative genomic analyses among four representative bass species at a chromosome level, resulting in a series of sequences of a deductive bass ancestor genome.

Research on the Morphology Reconstruction of Deep Cryogenic Treatment on PtRu/nitrogen-Doped Graphene Composite Carbon Nanofibers.

To improve the performance of PtRu/nitrogen-doped graphene composite carbon nanofibers, the composite carbon nanofibers were thermally compensated by deep cryogenic treatment (DCT), which realized the morphology reconstruction of composite carbon nanofibers. The effects of different DCT times were compared: 12 h, 18 h, and 24 h. The morphology reconstruction mechanism was explored by combining the change of inner chain structure and material group. The results showed that the fibers treated for 12 h had better physical and chemical properties, where the diameter is evenly distributed between 500 and 800 nm. Combined with Fourier infrared analysis, the longer the cryogenic time, the more easily the water vapor and nitrogen enter polymerization reaction, causing changes of chain structure and degradation performance. With great performance of carbonization and group transformation, the PtRu/nitrogen-doped graphene composite carbon nanofibers can be used as an efficient direct alcohol fuel cell catalyst and promote its commercialization.

Gill physiological and transcriptomic response of the threatened freshwater mussel Solenaia oleivora to salinity shift.

Solenaia oleivora, a freshwater shellfish endemic to China, is becoming one of the most threatened freshwater mussels owing to water pollution, habitat fragmentation, and overfishing. Hence, exploring its response to different environmental factors is important for its conservation. In this work, we investigated the physiological and transcriptomic response of S. oleivora to increased salinity. We found that increased salinity caused the death of S. oleivora. High salinity caused shrinking and deformation of gill filaments, reduced gill cilia, and induced cell apoptosis in gills. The activities of superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP), alkaline phosphatase (AKP), as well as glutathione (GSH) content were increased at the beginning of salinity stress (3-12 h), while SOD and ACP activities decreased at 48 h. Transcriptome data revealed that high salinity stress (48 h) induced 766 differentially expressed genes (DEGs). Among these DEGs, the majority of the stress response and ion transport-related genes were up-regulated, while most of the immune-related genes were down-regulated. In conclusion, these findings suggest that the antioxidant and immune functions of S. oleivora can be inhibited by high salinity, which may be one of the main reasons for its low survival rate under conditions of increasing salinity.

The first Conus genome assembly reveals a primary genetic central dogma of conopeptides in C. betulinus.

Although there are various Conus species with publicly available transcriptome and proteome data, no genome assembly has been reported yet. Here, using Chinese tubular cone snail (C. betulinus) as a representative, we sequenced and assembled the first Conus genome with original identification of 133 genome-widely distributed conopeptide genes. After integration of our genomics, transcriptomics, and peptidomics data in the same species, we established a primary genetic central dogma of diverse conopeptides, assuming a rough number ratio of ~1:1:1:10s for the total genes: transcripts: proteins: post-translationally modified peptides. This ratio may be special for this worm-hunting Conus species, due to the high diversity of various Conus genomes and the big number ranges of conopeptide genes, transcripts, and peptides in previous reports of diverse Conus species. Only a fraction (45.9%) of the identified conotopeptide genes from our achieved genome assembly are transcribed with transcriptomic evidence, and few genes individually correspond to multiple transcripts possibly due to intraspecies or mutation-based variances. Variable peptide processing at the proteomic level, generating a big diversity of venom conopeptides with alternative cleavage sites, post-translational modifications, and N-/C-terminal truncations, may explain how the 133 genes and ~123 transcripts can generate thousands of conopeptides in the venom of individual C. betulinus. We also predicted many conopeptides with high stereostructural similarities to the putative analgesic ω-MVIIA, addiction therapy AuIB and insecticide ImI, suggesting that our current genome assembly for C. betulinus is a valuable genetic resource for high-throughput prediction and development of potential pharmaceuticals.

Genome and population sequencing of a chromosome-level genome assembly of the Chinese tapertail anchovy (Coilia nasus) provides novel insights into migratory adaptation.

BACKGROUND: Seasonal migration is one of the most spectacular events in nature; however, the molecular mechanisms related to this phenomenon have not been investigated in detail. The Chinese tapertail, or Japanese grenadier anchovy, Coilia nasus, is a valuable migratory fish of high economic importance and special migratory dimorphism (with certain individuals as non-migratory residents). RESULTS: In this study, an 870.0-Mb high-quality genome was assembled by the combination of Illumina and Pacific Biosciences sequencing. Approximately 812.1 Mb of scaffolds were linked to 24 chromosomes using a high-density genetic map from a family of 104 full siblings and their parents. In addition, population sequencing of 96 representative individuals from diverse areas along the putative migration path identified 150 candidate genes, which are mainly enriched in 3 Ca2+-related pathways. Based on integrative genomic and transcriptomic analyses, we determined that the 3 Ca2+-related pathways are critical for promotion of migratory adaption. A large number of molecular markers were also identified, which distinguished migratory individuals and non-migratory freshwater residents. CONCLUSIONS: We assembled a chromosome-level genome for the Chinese tapertail anchovy. The genome provided a valuable genetic resource for understanding of migratory adaption and population genetics and will benefit the aquaculture and management of this economically important fish.

Genome Sequencing of the Japanese Eel (Anguilla japonica) for Comparative Genomic Studies on tbx4 and a tbx4 Gene Cluster in Teleost Fishes.

Limbs originated from paired fish fins are an important innovation in Gnathostomata. Many studies have focused on limb development-related genes, of which the T-box transcription factor 4 gene (tbx4) has been considered as one of the most essential factors in the regulation of the hindlimb development. We previously confirmed pelvic fin loss in tbx4-knockout zebrafish. Here, we report a high-quality genome assembly of the Japanese eel (Anguilla japonica), which is an economically important fish without pelvic fins. The assembled genome is 1.13 Gb in size, with a scaffold N50 of 1.03 Mb. In addition, we collected 24 tbx4 sequences from 22 teleost fishes to explore the correlation between tbx4 and pelvic fin evolution. However, we observed complete exon structures of tbx4 in several pelvic-fin-loss species such as Ocean sunfish (Mola mola) and ricefield eel (Monopterus albus). More interestingly, an inversion of a special tbx4 gene cluster (brip1-tbx4-tbx2b- bcas3) occurred twice independently, which coincides with the presence of fin spines. A nonsynonymous mutation (M82L) was identified in the nuclear localization sequence (NLS) of the Japanese eel tbx4. We also examined variation and loss of hindlimb enhancer B (HLEB), which may account for pelvic fin loss in Tetraodontidae and Diodontidae. In summary, we generated a genome assembly of the Japanese eel, which provides a valuable genomic resource to study the evolution of fish tbx4 and helps elucidate the mechanism of pelvic fin loss in teleost fishes. Our comparative genomic studies, revealed for the first time a potential correlation between the tbx4 gene cluster and the evolutionary development of toxic fin spines. Because fin spines in teleosts are usually venoms, this tbx4 gene cluster may facilitate the genetic engineering of toxin-related marine drugs.

A comparative transcriptomic study on developmental gonads provides novel insights into sex change in the protandrous black porgy (Acanthopagrus schlegelii).

Protandrous black porgy (Acanthopagrus schlegelii) is a popular and valuable commercial marine fish in China and East Asian countries. Controlling and managing its breeding has been an imperative step towards obtaining a sustainable supply of this fish in aquaculture production systems. Therefore, study on the molecular mechanisms of sex change in black porgy has both scientific and commercial importance. Previously, we identified some candidate genes related to sex determination and differentiation from a high-quality genome assembly of the black porgy. In the present study, transcriptome sequencing of developmental gonads (including testis, ovotestis and ovary) of black porgy was performed to further investigate the sex-change mechanisms. Our results showed that the highly expressed male-related genes (dmrt1, piwi1, piwi2, sox9, sox30 and amh) at the male phase were significantly down-regulated to a substantial degree at the intersexual stage, and the female-related genes (jnk1, vasa, wnt4, figla and foxl2) were distinctly up-regulated when the fish grows into a female adult, suggesting the potential roles of these genes in sex change of the black porgy. These data also support a previous hypothesis that the femaleness will be switched on when the testis is entering the degenerated stage through the diminished dmrt1 expression. Our transcriptome data provide a very useful genomic resource for future studies on sex change and practical aquaculture in the black porgy.

Whole-Genome Sequencing of Chinese Yellow Catfish Provides a Valuable Genetic Resource for High-Throughput Identification of Toxin Genes.

Naturally derived toxins from animals are good raw materials for drug development. As a representative venomous teleost, Chinese yellow catfish (Pelteobagrus fulvidraco) can provide valuable resources for studies on toxin genes. Its venom glands are located in the pectoral and dorsal fins. Although with such interesting biologic traits and great value in economy, Chinese yellow catfish is still lacking a sequenced genome. Here, we report a high-quality genome assembly of Chinese yellow catfish using a combination of next-generation Illumina and third-generation PacBio sequencing platforms. The final assembly reached 714 Mb, with a contig N50 of 970 kb and a scaffold N50 of 3.65 Mb, respectively. We also annotated 21,562 protein-coding genes, in which 97.59% were assigned at least one functional annotation. Based on the genome sequence, we analyzed toxin genes in Chinese yellow catfish. Finally, we identified 207 toxin genes and classified them into three major groups. Interestingly, we also expanded a previously reported sex-related region (to ≈6 Mb) in the achieved genome assembly, and localized two important toxin genes within this region. In summary, we assembled a high-quality genome of Chinese yellow catfish and performed high-throughput identification of toxin genes from a genomic view. Therefore, the limited number of toxin sequences in public databases will be remarkably improved once we integrate multi-omics data from more and more sequenced species.

Draft genome of the protandrous Chinese black porgy, Acanthopagrus schlegelii.

Background: As one of the most popular and valuable commercial marine fishes in China and East Asian countries, the Chinese black porgy (Acanthopagrus schlegelii), also known as the blackhead seabream, has some attractive characteristics such as fast growth rate, good meat quality, resistance to diseases, and excellent adaptability to various environments. Furthermore, the black porgy is a good model for investigating sex changes in fish due to its protandrous hermaphroditism. Here, we obtained a high-quality genome assembly of this interesting teleost species and performed a genomic survey on potential genes associated with the sex-change phenomenon. Findings: We generated 175.4 gigabases (Gb) of clean sequence reads using a whole-genome shotgun sequencing strategy. The final genome assembly is approximately 688.1 megabases (Mb), accounting for 93% of the estimated genome size (739.6 Mb). The achieved scaffold N50 is 7.6 Mb, reaching a relatively high level among sequenced fish species. We identified 19 465 protein-coding genes, which had an average transcript length of 17.3 kb. By performing a comparative genomic analysis, we found 3 types of genes potentially associated with sex change, which are useful for studying the genetic basis of the protandrous hermaphroditism. Conclusions: We provide a draft genome assembly of the Chinese black porgy and discuss the potential genetic mechanisms of sex change. These data are also an important resource for studying the biology and for facilitating breeding of this economically important fish.

Draft genome of the lined seahorse, Hippocampus erectus.

Background: The lined seahorse, Hippocampus erectus , is an Atlantic species and mainly inhabits shallow sea beds or coral reefs. It has become very popular in China for its wide use in traditional Chinese medicine. In order to improve the aquaculture yield of this valuable fish species, we are trying to develop genomic resources for assistant selection in genetic breeding. Here, we provide whole genome sequencing, assembly, and gene annotation of the lined seahorse, which can enrich genome resource and further application for its molecular breeding. A total of 174.6 Gb (Gigabase) raw DNA sequences were generated by the Illumina Hiseq2500 platform. The final assembly of the lined seahorse genome is around 458 Mb, representing 94% of the estimated genome size (489 Mb by k-mer analysis). The contig N50 and scaffold N50 reached 14.57 kb and 1.97 Mb, respectively. Quality of the assembled genome was assessed by BUSCO with prediction of 85% of the known vertebrate genes and evaluated using the de novo assembled RNA-seq transcripts to prove a high mapping ratio (more than 99% transcripts could be mapped to the assembly). Using homology-based, de novo and transcriptome-based prediction methods, we predicted 20 788 protein-coding genes in the generated assembly, which is less than our previously reported gene number (23 458) of the tiger tail seahorse ( H. comes ). We report a draft genome of the lined seahorse. These generated genomic data are going to enrich genome resource of this economically important fish, and also provide insights into the genetic mechanisms of its iconic morphology and male pregnancy behavior.

Monogonont Rotifer, Brachionus calyciflorus, Possesses Exceptionally Large, Fragmented Mitogenome.

In contrast to the highly conserved mitogenomic structure and organisation in most animals (including rotifers), the two previously sequenced monogonont rotifer mitogenomes were fragmented into two chromosomes similar in size, each of which possessed one major non-coding region (mNCR) of about 4-5 Kbp. To further explore this phenomenon, we have sequenced and analysed the mitogenome of one of the most studied monogonont rotifers, Brachionus calyciflorus. It is also composed of two circular chromosomes, but the chromosome-I is extremely large (27 535 bp; 3 mNCRs), whereas the chromosome-II is relatively small (9 833 bp; 1 mNCR). With the total size of 37 368 bp, it is one of the largest metazoan mitogenomes ever reported. In comparison to other monogononts, gene distribution between the two chromosomes and gene order are different and the number of mNCRs is doubled. Atp8 was not found (common in rotifers), and Cytb was present in two copies (the first report in rotifers). A high number (99) of SNPs indicates fast evolution of the Cytb-1 copy. The four mNCRs (5.3-5.5 Kb) were relatively similar. Publication of this sequence shall contribute to the understanding of the evolutionary history of the unique mitogenomic organisation in this group of rotifers.

A chromosome-level genome assembly of the Asian arowana, Scleropages formosus.

Asian arowana (Scleropages formosus), an ancient teleost belonging to the Order Osteoglossomorpha, has been a valuable ornamental fish with some varieties. However, its biological studies and breeding germplasm have been remarkably limited by the lack of a reference genome. To solve these problems, here we report high-quality genome sequences of three common varieties of Asian arowana (the golden, red and green arowana). We firstly generated a chromosome-level genome assembly of the golden arowana, on basis of the genetic linkage map constructed with the restriction site-associated DNA sequencing (RAD-seq). In addition, we obtained draft genome assemblies of the red and green varieties. Finally, we annotated 22,016, 21,256 and 21,524 protein-coding genes in the genome assemblies of golden, red and green varieties respectively. Our data were deposited in publicly accessible repositories to promote biological research and molecular breeding of Asian arowana.

High-quality genome assembly of channel catfish, Ictalurus punctatus.

BACKGROUND: The channel catfish (Ictalurus punctatus), a species native to North America, is one of the most important commercial freshwater fish in the world, especially in the United States' aquaculture industry. Since its introduction into China in 1984, both cultivation area and yield of this species have been dramatically increased such that China is now the leading producer of channel catfish. To aid genomic research in this species, data sets such as genetic linkage groups, long-insert libraries, physical maps, bacterial artificial clones (BAC) end sequences (BES), transcriptome assemblies, and reference genome sequences have been generated. Here, using diverse assembly methods, we provide a comparable high-quality genome assembly for a channel catfish from a breeding stock inbred in China for more than three generations, which was originally imported to China from North America. FINDINGS: Approximately 201.6 gigabases (Gb) of genome reads were sequenced by the Illumina HiSeq 2000 platform. Subsequently, we generated high quality, cost-effective and easily assembled sequences of the channel catfish genome with a scaffold N50 of 7.2 Mb and 95.6 % completeness. We also predicted that the channel catfish genome contains 21,556 protein-coding genes and 275.3 Mb (megabase pairs) of repetitive sequences. CONCLUSIONS: We report a high-quality genome assembly of the channel catfish, which is comparable to a recent report of the "Coco" channel catfish. These generated genome data could be used as an initial platform for molecular breeding to obtain novel catfish varieties using genomic approaches.

Complete mitochondrial genome of Paracanthobrama guichenoti.

In this study, we sequenced the complete mitochondrial genome of Paracanthobrama guichenoti. This mitochondrial genome, consisting of 16,607 base pairs, encoded 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a non-coding control region as those found in other vertebrates, with the gene synteny identical to that of typical vertebrates. Control region (D-Loop), of 932 bp in length, is located between tRNA(Phe) and tRNA(Leu). The overall base composition of the heavy strand shows T 28.4%, C 24.6%, A 31.2% and G 15.7%, with an AT bias of 59.6%.

Complete mitochondrial genome of Caridina nilotica gracilipes.

In this study, we sequenced the complete mitochondrial genome of Caridina nilotica gracilipes. This mitochondrial genome, consisting of 15,550 base pairs, encoded 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a non-coding control region as those found in other Decapoda, with the gene synteny identical to that of typical invertebrates. Control region (D-Loop), of 673 bp in length, is located between 12S rRNA and tRNA(Ile). The overall base composition of the heavy strand shows T 30.4%, C 22.0%, A 33.0% and G 14.6%, with an AT bias of 63.4%.

In-depth transcriptome analysis of Coilia ectenes, an important fish resource in the Yangtze River: de novo assembly, gene annotation.

Coilia ectenes is an important teleost species in the Yangtze River and a model organism that can be used to study the protection of fish resources. In this report, we performed de novo transcriptome sequencing of ten cDNA libraries from the brain, gill, heart, intestine, kidney, liver, muscle, stomach, ovary, and testis tissues. A total of 352 million raw reads of 100 base pairs were generated, and 130,113 transcripts, corresponding to 65,350 non-redundant transcripts, with a mean length of 1520 bp, were assembled. BLASTx-based gene annotation (E-value<1 × 10(-5)) allowed the identification of 73,900 transcripts against at least one of four databases, including the NCBI non-redundant database, the GO database, the COG database, and the KEGG database. Our study provides a valuable resource for C. ectenes genomic and transcriptomic data that will facilitate future functional studies of C. ectenes.

Transcriptome analysis reveals the potential mechanism of the albino skin development in pufferfish Takifugu obscurus.

Our aim was to explore the potential mechanism underlying albino in Takifugu obscurus. The transcriptome sequencing of the skin samples from normal T. obscurus and albino ones was conducted in this paper. The differentially expressed genes (DEGs) in albino fish compared with controls were assayed. The gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis were performed to explore the differentially expressed gene (DEG)-related functions and pathways. A total of 32 genes were found to be differentially expressed, including eight upregulated ones and 24 downregulated ones. Five GO terms were significantly enriched such as hemoglobin complex and oxygen transporter activity. The significantly enriched pathways contained linoleic acid metabolism and arachidonic acid metabolism. Hemoglobin complex, linoleic, and arachidonic acid metabolism may dysregulated in albino fugu. Dietary control of the linoleic acid and arachidonic acid may be an effective management for mediating albino in T. obscurus.

Transcriptome analysis gene expression in the liver of Coilia nasus during the stress response.

BACKGROUND: The estuarine tapertail anchovy (Coilia nasus) is widely distributed in the Yangtze River, the coastal waters of China, Korea, and the Ariake Sound of Japan. It is a commercially important species owing to its nutritional value and delicate flavor. However, Coilia nasus is strongly responsive to stress, this often results in death, which causes huge losses. In this study, we used next-generation sequencing technologies to study changes in gene expression in response to loading stress and the mechanism of death caused by loading stress in Coilia nasus. RESULTS: Using next-generation RNA-seq technologies on an Illumina HiSeq 2000 platform, we assembled a de novo transcriptome and tested for differential expression in response to stress. A total of 65,129 unigenes were generated, the mean unigene size and N50 were 607 bp and 813 bp, respectively. Of the assembled unigenes, we identified 2,990 genes that were significantly up-regulated, while 3,416 genes were significantly down-regulated in response to loading stress. Pathway enrichment analysis based on loading stress-responsive unigenes identified significantly stress related pathways. "Metabolism" and "immunity" were the two most frequently represented categories. In the "metabolism" category, "glucose metabolism" and "lipid metabolism" were major subclasses. The transcriptional expression of rate-limiting enzymes in "glucose metabolism" and "lipid metabolism" was detected by RT-qPCR, all were significantly increased after stress. Apoptosis associated proteins tumor necrosis factor alpha (TNF-α), caspase 9, cytochrome c and caspase 3 in the stress group were significantly elevated, moreover, liver injury indicators (Alanine aminotransferase, ALT, and aspartate transaminase, AST) were also significantly elevated, which indicates that loading stress induced liver injury. CONCLUSION: This study provided abundant unigenes that could contribute greatly to the discovery of novel genes in fish. The alterations in predicted gene expression patterns reflected possible responses to stress. Loading stress may induce liver injury through the mitochondrial apoptosis pathway, which was activated by TNF-α. Taken together, our data not only provide information that will aid the identification of novel genes from fish, but also shed new light on the understanding of mechanisms by which physical stressors cause death in fish.

Molecular characterization and differential expression of the myostatin gene in Coilia nasus.

Estuarine tapertail anchovy (Coilia nasus, junior synonym C. ectenes) is a widely distributed and commercially important aquaculture species, although its growth in aquaculture settings is so slow as to pose a serious practical problem. In order to understand the molecular mechanisms of growth, we cloned the myostatin gene in C. nasus (CnMSTN) by homologous cloning methods. Its full-length cDNA is 2252 bp, with a 1125-bp open reading frame (ORF) that encodes a 374-amino acid protein. The CnMSTN protein is predicted to contain domains typical of MSTN, including a TGFb-propeptide domain and a TGFB domain. Gene expression patterns were detected by RT-qPCR. CnMSTN is expressed strongly in the muscle and brain, and comparatively lower in the gills, liver, spleen, intestine, trunk kidney and head kidney. The effects of stress on the muscle and brain MSTN levels were evaluated by RT-qPCR. CnMSTN in the muscle was positively regulated by loading and transport stress, but brain CnMSTN expression was not affected. We found NaCl could reduce the death rate caused by loading and transporting stress, and in this group, CnMSTN mRNA expression in the muscle revealed increased, but decreased in the brain. Further, in the fasting experiment, the CnMSTN mRNA revealed decrease in the muscle, on the contrary, it showed increase in the brain. Selection upon variants of the MSTN gene has shown great potential in breeding work for mammals, and our results provide the basic knowledge for breeding of C. nasus.