Construction of a high-density genetic map and mapping of growth related QTLs in the grass carp (Ctenopharyngodon idellus)

Whole-genome resequencing and RNA-seq analysis implicates GPR75 as a potential genetic basis related to retarded growth in South China carp (Cyprinus carpio rubrofuscus)

The south China carp (Cyprinus carpio rubrofuscus) is an indigenous and important fish species, widely cultured in south China. However, part of individuals experienced retarded growth, the genetic basis of which has yet to be elucidated. In this study, whole-genome resequencing of 35 fast-growing and 35 retarded-growing south China carp were conducted to identify promising genes associated with retarded growth. Twelve candidate SNPs were detected and annotated to the Gpr75 gene, which has been reported to be related with body weight through regulating insulin homeostasis. RNA-seq analysis of muscle suggested that differentially expressed genes were significantly enriched in the insulin signaling pathway. Additionally, the fasting serum insulin level was significantly lower while the blood glucose level was significantly higher in the retarded-growing group. Our preliminary study provides insights into the genetic basis underlying the retarded growth and may facilitate further genetic improvement of south China carp.

Construction of a high-density genetic linkage map and QTL mapping of growth and cold tolerance traits in Takifugu fasciatus

Takifugu fasciatus is an aquaculture species with high economic value. In recent years, problems such as environmental pollution and inbreeding have caused a serious decline in T. fasciatus germplasm resources. In this study, a high-density genetic linkage map was constructed by whole-genome resequencing. The map consists of 4891 bin markers distributed across 22 linkage groups (LGs), with a total genetic coverage of 2381.353 cM and a mean density of 0.535 cM. Quantitative trait locus (QTL) localization analysis showed that a total of 19 QTLs associated with growth traits of T. fasciatus in the genome-wide significance threshold range, distributed on 11 LGs. In addition, 11 QTLs associated with cold tolerance traits were identified, each scattered on a different LG. Furthermore, we used QTL localization analysis to screen out three candidate genes (IGF1, IGF2, ADGRB) related to growth in T. fasciatus. Meanwhile, we screened three candidate genes (HSP90, HSP70, and HMGB1) related to T. fasciatus cold tolerance. Our study can provide a theoretical basis for the selection and breeding of cold-tolerant or fast-growing T. fasciatus.

Transcriptome analysis revealed the existence of family-specific regulation of growth traits in grass carp

The grass carp (Ctenopharyngodon idella) is the world's most prolific freshwater fish. Little is known, however, about the functional genes and genetic regulatory networks that govern its growth traits. We created three grass carp families in this study by using two grass carp parents with fast-growing offspring and two grass carp parents with slow-growing offspring, namely the fast-growing × fast-growing family (FF), the slow-growing × slow-growing family (SS), and the fast-growing × slow-growing family (FS). Under the satiation and starvation feeding modes, the average body weight of these families' offspring exhibited a consistent ordering (FF > FS > SS). The transcriptomes of grass carp whole brain and hepatopancreas were then acquired for each family, and it was discovered that the number of differentially expressed genes (DEGs) in the different organs demonstrated family specificity. DEGs were mostly identified in the hepatopancreas of FF and the whole brain of SS, but they were more evenly distributed in FS. There were 14 DEGs that were found in all three families, including three that were negatively correlated in hepatopancreas (ahsg2, lect2) or in brain (drd5), and 11 that were positively connected in hepatopancreas (sycn, pabpc4, zgc:112294, cel, endou, ela2, prss3, zbtb41, ela3) or in brain (fabp7, endod1). The deletion of ahsg2 boosted the growth rate only in certain zebrafish, suggesting that the growth-promoting effects of ahsg2 varies among individuals. Furthermore, we examined the SNP in each family and conducted preliminary research on the probable genetic pathways of family-specific control of growth traits. The family specificity of the growth regulation mechanism of grass carp at the transcriptional level was revealed for the first time in this study, and it was discovered that growth differences among individuals in the FF family were primarily due to differences in nutrient metabolism, whereas growth differences among individuals in the SS family may be primarily due to differences in foraging ability caused by differences in brain development. This research adds to our understanding of the genetic regulatory mechanism of grass carp growth.

Animal board invited review: Widespread adoption of genetic technologies is key to sustainable expansion of global aquaculture

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The extent of application of genetic technologies to aquaculture production varies widely by species and geography.

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Achieving a more universal application of seed derived from scientifically based breeding programmes is an important goal in order to meet increasing global demands for seafood production.

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This article reviews the status of genetic technologies across the world’s top 10 highly produced species.

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Opportunities and barriers to achieving broad-scale uptake of genetic technologies in global aquaculture are discussed.

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A future outlook for potential disruptive genetic technologies and how they might affect global aquaculture production is given.

Aquaculture production comprises a diverse range of species, geographies, and farming systems. The application of genetics and breeding technologies towards improved production is highly variable, ranging from the use of wild-sourced seed through to advanced family breeding programmes augmented by genomic techniques. This technical variation exists across some of the most highly produced species globally, with several of the top ten global species by volume generally lacking well-managed breeding programmes. Given the well-documented incremental and cumulative benefits of genetic improvement on production, this is a major missed opportunity. This short review focusses on (i) the status of application of selective breeding in the world’s most produced aquaculture species, (ii) the range of genetic technologies available and the opportunities they present, and (iii) a future outlook towards realising the potential contribution of genetic technologies to aquaculture sustainability and global food security.

Dynamic Transcriptional Landscape of Grass Carp (Ctenopharyngodon idella) Reveals Key Transcriptional Features Involved in Fish Development

A high-quality baseline transcriptome is a valuable resource for developmental research as well as a useful reference for other studies. We gathered 41 samples representing 11 tissues/organs from 22 important developmental time points within 197 days of fertilization of grass carp eggs in order to systematically examine the role of lncRNAs and alternative splicing in fish development. We created a high-quality grass carp baseline transcriptome with a completeness of up to 93.98 percent by combining strand-specific RNA sequencing and single-molecule real-time RNA sequencing technologies, and we obtained temporal expression profiles of 33,055 genes and 77,582 transcripts during development and tissue differentiation. A family of short interspersed elements was preferentially expressed at the early stage of zygotic activation in grass carp, and its possible regulatory components were discovered through analysis. Additionally, after thoroughly analyzing alternative splicing events, we discovered that retained intron (RI) alternative splicing events change significantly in both zygotic activation and tissue differentiation. During zygotic activation, we also revealed the precise regulatory characteristics of the underlying functional RI events.

De novo screening of disease-resistant genes from the chromosome-level genome of rare minnow using CRISPR-cas9 random mutation

BACKGROUND

Mutants are important for the discovery of functional genes and creation of germplasm resources. Mutant acquisition depends on the efficiency of mutation technology and screening methods. CRISPR-Cas9 technology is an efficient gene editing technology mainly used for editing a few genes or target sites, which has not been applied for the construction of random mutant libraries and for the de novo discovery of functional genes.

RESULTS

In this study, we first sequenced and assembled the chromosome-level genome of wild-type rare minnow (Gobiocypris rarus) as a susceptible model of hemorrhagic disease, obtained a 956.05 Mb genome sequence, assembled the sequence into 25 chromosomes, and annotated 26,861 protein-coding genes. Thereafter, CRISPR-Cas9 technology was applied to randomly mutate the whole genome of rare minnow with the conserved bases (TATAWAW and ATG) of the promoter and coding regions as the target sites. The survival rate of hemorrhagic disease in the rare minnow gradually increased from 0% (the entire wild-type population died after infection) to 38.24% (F3 generation). Finally, 7 susceptible genes were identified via genome comparative analysis and cell-level verification based on the rare minnow genome.

CONCLUSIONS

The results provided the genomic resources for wild-type rare minnow, and confirmed that the random mutation system designed using CRISPR-Cas9 technology in this study is simple and efficient and is suitable for the de novo discovery of functional genes and creation of a germplasm resource related to qualitative traits.

Comprehensive analysis of hub mRNA, lncRNA and miRNA, and associated ceRNA networks implicated in grass carp (Ctenopharyngodon idella) growth traits

Grass carp (Ctenopharyngodon idella) is the most productive freshwater aquaculture fish in worldwide. However, the molecular mechanism of its growth traits has not been fully elucidated. Whole transcriptome analysis of the brain and hepatopancreas of 29 six-month-old grass carp with different growth rates was performed. Weighted gene co-expression network analysis (WGCNA) was used to construct a weighted gene co-expression network of mRNA, miRNA and lncRNA separately. A total of 35 hub mRNAs, 47 hub lncRNAs and 33 hub miRNAs were identified from the brain, 37 hub mRNAs, 110 hub lncRNAs and 36 hub miRNAs were identified from the hepatopancreas. The ceRNA networks in the brain and hepatopancreas were involved in brain development and nutrient metabolism, respectively. Overall, this is the first investigation of the growth-related transcriptomic characteristics in the brain and hepatopancreas of grass carp, thus will help us to further explore the molecular mechanism of grass carp growth rate.