Genome-wide identification and expression analysis of mitogen-activated protein kinase (MAPK) genes in response to salinity stress in channel catfish (Ictalurus punctatus).

The mitogen-activated protein kinase (MAPK) gene family has been systematically described in several fish species, but less so in channel catfish (Ictalurus punctatus), which is an important global aquaculture species. In this study, 16 MAPK genes were identified in the channel catfish genome and classified into three subfamilies based on phylogenetic analysis, including six extracellular signal regulated kinase (ERK) genes, six p38-MAPK genes and four C-Jun N-terminal kinase (JNK) genes. All MAPK genes were distributed unevenly across 10 chromosomes, of which three (IpMAPK8, IpMAPK12 and IpMAPK14) underwent teleost-specific whole genome duplication during evolution. Gene expression profiles in channel catfish during salinity stress were analysed using transcriptome sequencing and qRT-PCR (quantitative reverse transcription PCR). Results from reads per kilobase million (RPKM) analysis showed IpMAPK13, IpMAPK14a and IpMAPK14b genes were differentially expressed when compared with other genes between treatment and control groups. Furthermore, three of these genes were validated by qRT-PCR, of which IpMAPK14a expression levels were significantly upregulated in treatment groups (high and low salinity) when compared with the control group, with the highest expression levels in the low salinity group (P < 0.05). Therefore, IpMAPK14a may have important response roles to salinity stress in channel catfish.

Genome-Wide Identification, Phylogeny, and Expression Profile of the Dmrt (Doublesex and Mab-3 Related Transcription Factor) Gene Family in Channel Catfish (Ictalurus punctatus).

The Dmrt (Doublesex and Mab-3 related transcription factor) gene family is a class of crucial transcription factors characterized by a conserved DM domain related to sex determination and differentiation, which has been systematically described in various teleost fish, but less in channel catfish (Ictalurus punctatus), an important global aquaculture species in the US and China. In this study, seven Dmrt genes from channel catfish genome were identified and analyzed using bioinformatics methods. Seven IpDmrt genes were distributed unevenly across five chromosomes. Synteny analysis revealed that Dmrt1, Dmrt2a, Dmrt2b, Dmrt3, Dmrt4, and Dmrt5 were relatively conserved in teleost fish. Tissue distribution analysis showed that IpDmrt1, IpDmrt2b, IpDmrt5, and IpDmrt6 exhibited sexually dimorphic expression patterns and, among them, IpDmrt1 and IpDmrt6 had high expression levels in the testes, while IpDmrt2b and IpDmrt5 had more significant expression levels in the ovaries than in other tissues. After 17ß-estradiol treatment, IpDmrt2b and IpDmrt5 were significantly up regulated, while the expression of IpDmrt1 and IpDmrt6 was significantly repressed in XY channel catfish ovaries compared with XX channel catfish ovaries. The present study provides a comprehensive insight into the Dmrt gene family of channel catfish. The results suggest that IpDmrt1 and IpDmrt6 may play an important role in testis differentiation/development, while IpDmrt2b and IpDmrt5 are critical in ovary development in this species.

Liver transcriptome analysis and cortisol immune-response modulation in lipopolysaccharide-stimulated in channel catfish (Ictalurus punctatus).

Channel catfish (Ictalurus punctatus) is an important aquaculture species in China. In channel catfish, diseases such as haemorrhagic, sepsis and tail-rot disease are all caused by bacteria as general in China. Most of the pathogenic bacteria are Gram-negative bacteria. Liver transcriptome analysis of the co-injection of cortisol and lipopolysaccharide (LPS) was performed in this study. Preliminary evidence from the results suggest that after the emergence of immune stress, cortisol will up-regulate the complement cascade pathway, down-regulate the coagulation cascade pathway, down-regulate the platelet activation pathway, down-regulate antigen presentation pathway, and show complex regulation relationship to inflammatory factors. At 12 h, the number of differential genes regulated by cortisol was about half less than the number of differential genes regulated by LPS. At 24 h, there was no significant difference between the number of differential genes regulated by cortisol and LPS, but the types of differential genes vary widely. KEGG enrichment analysis found that cortisol regulated LPS-stimulated immune responses mainly focus on cytokines, complement and coagulation cascades pathways, antigen presentation pathways, haematopoiesis, and inflammation. It is suggested that there may be some strategic choice in the regulation of immune response by cortisol. These results will help understand the pathogenesis and host defence system in bacterial disease caused by Gram-negative bacteria.

Functional identification and characterization of IpMSTNa, a novel orthologous myostatin (MSTN) gene in channel catfish Ictalurus punctatus.

Channel catfish (Ictalurus punctatus) are one of the most important commercial freshwater fish in the world. China has been the major producer and consumer of channel catfish following the rapid development in the past three decades. In the present study, a novel orthologous myostatin gene, IpMSTNa, of channel catfish was identified based on homology cloning and genome locating. Multiple sequence alignments and gene structure analyses showed that the IpMSTNa gene and its deduced protein presented similar architectures to other known vertebrates. Phylogenetic and synteny analyses indicated that IpMSTNa belongs to MSTN1 orthologues. Pro-IpMSTNa protein is a typical disulphide-linked homodimer, with each chain containing an N-terminal pro-domain and a C-terminal unmatured GF domain, while pro-IpMSTNa present some significant differences in secondary structure and three-dimensional substances with pro-IpMSTNb. Relative expression level of the IpMSTNa gene upregulated rapidly and decreased dramatically during the embryonic and larval developmental stages, respectively. In addition, IpMSTNa displayed remarkably higher expression at most developmental stages compared to IpMSTNb. Tissue distribution analysis indicated that the IpMSTNa gene had a significantly higher level of expression than IpMSTNb in all selected tissues, with abundantly greater expression in the liver, muscle, gill and spleen, and moderately greater expression in the kidney, intestine, and head kidney. ISH analysis demonstrated that the expression signals of IpMSTNa and IpMSTNb at the selected developmental stages are consistent to qRT-PCR tests. Our study suggested that the IpMSTNa gene may have more biological functions, which have yet to be determined compared to the IpMSTNb gene.

Construction of a High-Density Linkage Map and QTL Fine Mapping for Growth- and Sex-Related Traits in Channel Catfish (Ictalurus punctatus).

A high-density genetic linkage map is of particular importance in the fine mapping for important economic traits and whole genome assembly in aquaculture species. The channel catfish (Ictalurus punctatus), a species native to North America, is one of the most important commercial freshwater fish in the world. Outside of the United States, China has become the major producer and consumer of channel catfish after experiencing rapid development in the past three decades. In this study, based on restriction site associated DNA sequencing (RAD-seq), a high-density genetic linkage map of channel catfish was constructed by using single nucleotide polymorphisms (SNPs) in a F1 family composed of 156 offspring and their two parental individuals. A total of 4,768 SNPs were assigned to 29 linkage groups (LGs), and the length of the linkage map reached 2,480.25 centiMorgans (cM) with an average distance of 0.55 cM between loci. Based on this genetic linkage map, 223 genomic scaffolds were anchored to the 29 LGs of channel catfish, and a total length of 704.66 Mb was assembled. Quantitative trait locus (QTL) mapping and genome-wide association analysis identified 10 QTLs of sex-related and six QTLs of growth-related traits at LG17 and LG28, respectively. Candidate genes associated with sex dimorphism, including spata2, spata5, sf3, zbtb38, and fox, were identified within QTL intervals on the LG17. A sex-linked marker with simple sequence repeats (SSR) in zbtb38 gene of the LG17 was validated for practical verification of sex in the channel catfish. Thus, the LG17 was considered as a sex-related LG. Potential growth-related genes were also identified, including important regulators such as megf9, npffr1, and gas1. In a word, we constructed the high-density genetic linkage map and developed the sex-linked marker in channel catfish, which are important genetic resources for future marker-assisted selection (MAS) of this economically important teleost.

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.

Complete mitochondrial genome of freshwater goby Rhinogobius cliffordpopei (Perciformes, Gobiidae): genome characterization and phylogenetic analysis.

Freshwater gobies Rhinogobius cliffordpopei and R. giurinus are invasive species with particular concern because they have become dominant and were fierce competitors in the invaded areas in Yunnan-Guizhou Plateau (southwest of China). Information about genetic characteristics of R. giurinus have been published, but there were still no relevant reports about R. cliffordpopei. In present study, the complete mitochondrial genome of R. cliffordpopei was determined, which was 16,511 bp in length with A + T content of 51.1%, consisting of 13 protein-coding genes, 22 tRNAs, 2 ribosomal RNAs, and a control region. The gene composition and the structural arrangement of the R. cliffordpopei complete mtDNA were identical to most of other teleosts. Phylogenetic analyses placed R. cliffordpopei in a well-supported monophyletic cluster with other Rhinogobius fish. But the phylogenetic relationship between genus Rhinogobius and Tridentiger remained to be resolved.

Dynamics of the bacterial community in a channel catfish nursery pond with a cage-pond integration system.

The changes in the bacterial community composition in a channel catfish nursery pond with a cage-pond integration system were investigated by sequencing of the 16S rRNA gene through Illumina MiSeq sequencing platforms. A total of 1 362 877 sequences and 1440 operational taxonomic units were obtained. Further analysis showed that the dominant phyla in the cage and pond groups were similar, including Actinobacteria, Cyanobacteria, Proteobacteria, and Bacteroidetes, although a significant difference was detected between them by ANOSIM (P < 0.05). Temporal changes and site variation were significantly related to the variation of the bacterial community. A comprehensive analysis of the diversity and evenness of the bacterial 16S rRNA gene, redundancy analysis (RDA), and partial Mantel test showed that the bacterial community composition in a cage-pond integration system was shaped more by temporal variation than by site variation. RDA also indicated that water temperature, total dissolved solids, and Secchi depth had the largest impact on bacterial populations.

Genome-wide identification, phylogeny and expressional profile of the Sox gene family in channel catfish (Ictalurus punctatus).

The Sox gene family has been systematically characterized in some fish species but not in catfish Ictalurus punctatus. In this study, 25 Sox genes were identified in the channel catfish genome and classified into seven families based on their conserved domains as follows: eight genes in SoxB group (six in SoxB1 subgroup and two in SoxB2 subgroup); five genes in SoxC group; three genes in SoxD and SoxF groups; four genes in SoxE group; and one gene in SoxH and SoxK groups. The mammalian Sox groups SoxA, G, I, and J were not present in catfish. The number of introns in channel catfish Sox genes varied from zero to 13. Sox genes were distributed unevenly across 17 chromosomes. Five members of the ancestral vertebrate Sox genes (Sox1, Sox4, Sox9, Sox11 and Sox19) experienced teleost-specific whole genome duplication during evolution, and now have two copies on different chromosomes. Expression profiles analyses indicated that the accumulation of Sox genes was associated with different tissues, and the expression pattern also differed among each Sox gene group and duplicated gene. This study constitutes a comprehensive overview of the Sox gene family in channel catfish and provides new insights into the evolution of this gene family.

Complete mitochondrial genome of Odontobutis haifengensis (Perciformes, Odontobutiae): A unique rearrangement of tRNAs and additional non-coding regions identified in the genus Odontobutis.

Herein, the complete mitochondrial genome of Odontobutis haifengensis was sequenced for the first time. The O. haifengensis mitogenome was 17,016bp in length and included 13 protein-coding genes, 22 transfer RNAs (tRNAs), 2 ribosomal RNAs (rRNAs), and a control region (CR). The genome organization, base composition, codon usage, and gene rearrangement was similar to other Odontobutis species. Furthermore, a tRNA gene rearrangement within the SLH cluster was found to be identical to other Odontobutis species. Moreover, the gene order and the positions of additional intergenic non-coding regions suggests that the observed unique gene rearrangement resulted from a tandem duplication and random loss of large-scale gene regions. Additionally, phylogenetic analysis showed that Odontobutis species form a monophyletic clade due to the conserved mitochondrial gene rearrangement. This study provides useful information that aids in a better understanding of mitogenomic diversity and evolutionary patterns of Odontobutidae species.

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 paradise fish Macropodus opercularis (Perciformes: Macropodusinae).

Macropodus opercularis is a popular ornamental fish and has been widely transported around the world. In this study, the complete mitochondrial genome of M. opercularis was reported. The circular genome is 16,496 bp in length and consists of 13 protein-coding genes, 22 tRNA genes, two ribosomal RNA genes, and one control region. The overall nucleotide composition was 30.9% A, 29.6% T, 24.7% C, and 14.8% G, with an A + T bias of 60.5%. The gene composition and the structural arrangement of the M. opercularis complete mtDNA were identical to most of the other vertebrates. The molecular data presented here could play a useful role in studying the evolutionary relationships and population genetics of Macropodusinae fish.

Complete mitochondrial genome of Chinese icefish Neosalanx tangkahkeiis (Salmoniformes, Salangidae): comparison reveals Neosalanx taihuensis not a valid name.

The complete mitochondrial genome of Neosalanx tangkahkeiis was determined to be 16,550 bp in length with (A+T) content of 49.7%, and it consists of 13 protein-coding genes, 22 tRNAs, 2 ribosomal RNAs, and a control region. The gene composition and the structural arrangement of the N. tangkahkeiis complete mtDNA were identical to most of other vertebrates. The sequence comparison showed that mitogenome of N. tangkahkeiis had a 99.9% of similarity with so-called N. taihuensis, indicating they are the same species and N. taihuensis is not a valid name.