Primary analysis of repeat elements of the Asian seabass (Lates calcarifer) transcriptome and genome

As part of our Asian seabass genome project, we are generating an inventory of repeat elements in the genome and transcriptome. The karyotype showed a diploid number of 2n = 24 chromosomes with a variable number of B-chromosomes. The transcriptome and genome of Asian seabass were searched for repetitive elements with experimental and bioinformatics tools. Six different types of repeats constituting 8–14% of the genome were characterized. Repetitive elements were clustered in the pericentromeric heterochromatin of all chromosomes, but some of them were preferentially accumulated in pretelomeric and pericentromeric regions of several chromosomes pairs and have chromosomes specific arrangement. From the dispersed class of fish-specific non-LTR retrotransposon elements Rex1 and MAUI-like repeats were analyzed. They were wide-spread both in the genome and transcriptome, accumulated on the pericentromeric and peritelomeric areas of all chromosomes. Every analyzed repeat was represented in the Asian seabass transcriptome, some showed differential expression between the gonads. The other group of repeats analyzed belongs to the rRNA multigene family. FISH signal for 5S rDNA was located on a single pair of chromosomes, whereas that for 18S rDNA was found on two pairs. A BAC-derived contig containing rDNA was sequenced and assembled into a scaffold containing incomplete fragments of 18S rDNA. Their assembly and chromosomal position revealed that this part of Asian seabass genome is extremely rich in repeats containing evolutionarily conserved and novel sequences. In summary, transcriptome assemblies and cDNA data are suitable for the identification of repetitive DNA from unknown genomes and for comparative investigation of conserved elements between teleosts and other vertebrates

Nutrigenomic and nutritional analyses reveal the effects of pelleted feeds on Asian Seabass (Lates calcarifer)

As nutrition-related expenses constitute the majority of the costs for aquaculture farms, it is essential for them to use feeds that provide an ideal combination of nutrients for the species of choice. In this study, the relative effect of consuming three different pelleted feeds (B, C and D) in comparison to frozen baitfish (A; control) were compared on juvenile Asian seabass (77.3 ± 22.4g) that were selected for increased growth rate over two generations. Our objectives were: 1) to evaluate the effects of different pelleted feeds based on overall physiological changes and nutritional quality of fillets; 2) improve our understanding of the underlying mechanisms with transcriptomic analysis; 3) if possible, identify the feed type that supports the growth of these fishes without substantially reducing the nutritional quality of fillet. The growth performance, fatty acid composition of fillet, hepatic histology and transcriptome of the fishes (Groups A-D) were analyzed. The majority of fatty acids of the fillets, except γ-linolenic acid (GLA, C18:3n6), correlated significantly with the respective diets. Asian seabass fed Feed C showed highest specific growth rate (SGR) and feed conversion efficiency (FCE) with closest histology and transcriptomic profile to control, but their fillet contained the highest n6/n3 ratio. When the liver-based transcriptomes were analyzed, a complex set of differentially expressed genes were detected between groups fed pelleted feeds and controls as well as among the pellet-fed groups themselves. Significant enrichment of genes with growth-related function tallied with the morphological data measured. When compared with control (Group A), ‘Biosynthesis of unsaturated fatty acids’ and ‘Steroid biosynthesis’ pathways were significantly enriched in pellet-fed groups. Reduced goblet cell numbers were observed in the gut of pellet-fed fish compared to controls and fads6 was found to be a suitable candidate gene to separate wild-caught Asian seabass, from pellet-fed ones. These results provide insights for researchers on the various effects of feeds on the biochemistry and global gene expression of the fish and potentially for seabass farms to make more informed feed choices

Insights into the microbiome of farmed Asian sea bass (Lates calcarifer) with symptoms of tenacibaculosis and description of Tenacibaculum singaporense sp. nov.

Outbreaks of diseases in farmed fish remain a recurring problem despite the development of vaccines and improved hygiene standards on aquaculture farms. One commonly observed bacterial disease in tropical aquaculture of the South-East Asian region is tenacibaculosis, which is attributed to members of the genus Tenacibaculum (family Flavobacteriaceae, phylum Bacteroidetes), most notably Tenacibaculum maritimum. The impact of tenacibaculosis on the fish microbiota remains poorly understood. In this study, we analysed the microbiota of different tissues of commercially reared Asian seabass (Lates calcarifer) that showed symptoms of tenacibaculosis and compared the microbial communities to those of healthy and experimentally infected fish that were exposed to diseased farmed fish. The relative abundance of Tenacibaculum species in experimentally infected fish was significantly lower than in commercially reared diseased fish and revealed a higher prevalence of different Tenacibaculum species. One isolated strain, TLL-A2T, shares 98.7% 16S rRNA gene identity with Tenacibaculum mesophilum DSM 13764T. The genome of strain TLL-A2T was sequenced and compared to that of T. mesophilum DSM 13764T. Analysis of average nucleotide identity and comparative genome analysis revealed only 92% identity between T. mesophilum DSM 13764T and strain TLL-A2T and differences between the two strains in predicted carbohydrate activating enzymes respectively. Phenotypic comparison between strain TLL-A2T and T. mesophilum DSM 13764T indicated additional differences, such as growth response at different salt concentrations. Based on molecular and phenotypic differences, strain TLL-A2T (=DSM 106434T, KCTC 62393T) is proposed as the type strain of Tenacibaculum singaporense sp. nov

BAC-pool sequencing and analysis confirms growth-associated QTLs in the Asian seabass genome

The Asian seabass is an important marine food fish that has been cultured for several decades in Asia Pacific. However, the lack of a high quality reference genome has hampered efforts to improve its selective breeding. A 3D BAC pool set generated in this study was screened using 22 SSR markers located on linkage group 2 which contains a growth-related QTL region. Seventy-two clones corresponding to 22 FPC contigs were sequenced by Illumina MiSeq technology. We co-assembled the MiSeq-derived scaffolds from each FPC contig with error-corrected PacBio reads, resulting in 187 sequences covering 9.7 Mb. Eleven genes annotated within this region were found to be potentially associated with growth and their tissue-specific expression was investigated. Correlation analysis demonstrated that SNPs in ctsb, skp1 and ppp2ca can be potentially used as markers for selecting fast-growing fingerlings. Conserved syntenies between seabass LG2 and five other teleosts were identified. This study i) provided a 10 Mb targeted genome assembly; ii) demonstrated NGS of BAC pools as a potential approach for mining candidates underlying QTLs of this species; iii) detected eleven genes potentially responsible for growth in the QTL region; and iv) identified useful SNP markers for selective breeding programs of Asian seabass

Differential transcriptomic response in the spleen and head kidney following vaccination and infection of Asian seabass with Streptococcus iniae

Vaccination is an important strategy in the protection of aquaculture species from major diseases. However, we still do not have a good understanding of the mechanisms underlying vaccine-induced disease resistance. This is further complicated by the presence of several lymphoid organs that play different roles when mounting an immune response. In this study, we attempt to elucidate some of these mechanisms using a microarray-based approach. Asian seabass (Lates calcarifer) were vaccinated against Streptococcus iniae and the transcriptomic changes within the spleen and head kidney at one and seven days post-vaccination were profiled. We subsequently challenged the seabass at three weeks post-vaccination with live S. iniae and similarly profiled the transcriptomes of the two organs after the challenge. We found that vaccination induced an early, but transient transcriptomic change in the spleens and a delayed response in the head kidneys, which became more similar to one another compared to un-vaccinated ones. When challenged with the pathogen, the spleen, but not the head kidneys, responded transcriptomically at 25-29 hours post-challenge. A unique set of genes, in particular those involved in the activation of NF-κB signaling, was up-regulated in the vaccinated spleens upon pathogen challenge but not in the unvaccinated spleens. A semi-quantitative PCR detection of S. iniae using metagenomic DNA extracted from the water containing the seabass also revealed that vaccination resulted in reduction of pathogen shedding. This result indicated that vaccination not only led to a successful immune defense against the infection, but also reduced the chances for horizontal transmission of the pathogen. In conclusion, we have provided a transcriptomic analysis of how the teleost spleen and head kidneys responded to vaccination and subsequent infection. The different responses from the two organs are suggestive of their unique roles in establishing a vaccine-induced disease resistance

Structure-function coupling within the reward network in preschool children predicts executive functioning in later childhood

10.1016/j.dcn.2022.101107Developmental Cognitive Neuroscience5510110

The first transcriptome and genetic linkage map for Asian arowana

Asian arowana or dragonfish (Scleropages formosus) is an important fish species due to its unusual breeding biology and high economic value in the ornamental fish markets. In the present study, we aimed to (i) create the first transcriptome by Roche 454 pyrosequencing of Asian arowana brain and gonad samples; (ii) identify differentially expressed genes between the two sexes and develop microsatellite (SSR) markers; and (iii) construct a first-generation SSR-based genetic linkage map. A total of over 1.3 million reads were obtained from the brain and gonad of adult Asian arowana individuals through pyrosequencing. These reads were assembled into 16 242 contigs that were further grouped into 13 639 isogroups. BLASTX annotation identified a total of 8316 unique proteins from this data set. Many genes with sexually dimorphic expression levels and some putatively involved in sex development were identified. A total of 316 EST-SSRs and 356 new genomic-SSRs were developed by screening through the current transcriptome data set and SSR-enriched genomic libraries. The first genetic linkage map of the species was constructed based on these markers. Linkage analysis allowed for mapping of 308 markers to 28 linkage groups (LGs), ranging in size from 14.9 to 160.6 cM. The potentially sex-associated gene sox9 was mapped to LG4 on the consensus linkage map. Pairwise putative conserved syntenies between the Asian arowana, zebrafish, and three-spined stickleback were also established. These resources will help the conservation of the species through better understanding of its phylogenetics, genomics and biology, and comparative genome analysis within the Osteoglossidae family