Heterosis of growth trait regulated by DNA methylation and miRNA in allotriploid fish

DNA methylation regulates growth traits by influencing metabolic pathways in Pacific white shrimp (Litopenaeus vannamei)

BACKGROUND

DNA methylation is a critical epigenetic modification that dynamically regulates gene expression associated with economic traits. Pacific white shrimp (Litopenaeus vannamei) is one of the most important aquatic species for culturing, and growth trait is one of the most important economic traits for its production. However, research on DNA methylation regulation of growth traits is still at an early stage. This study explored DNA methylome dynamics and their associations with the regulatory mechanism behind growth traits using full-subfamily individuals with discrepant growth performance.

RESULTS

The DNA methylation-related genes in L. vannamei were identified, and the expression of DNA methylation genes showed significantly higher levels in the slow growth (SG) group compared to the fast-growing (FG) individuals. The Whole Genome Bisulfite Sequencing (WGBS) analysis revealed that the methylation levels in the muscles of shrimp were notably decreased in SG individuals compared to FG individuals. A total of 532 differentially methylated promoters and 2,067 differentially methylated regions were identified. Through integrative analysis of DNA methylation and transcriptomic data from SG and FG group shrimp, a total of 47 genes were screened out with differential methylation levels (DMGs) and expression levels (DEGs). Functional enrichment analysis revealed that the overlapping DEGs/DMGs were enriched mainly in metabolic pathways, starch and sucrose metabolism, linoleic acid metabolism, ascorbate and aldarate metabolism, pentose and glucuronate interconversions.

CONCLUSIONS

DNA methylation plays a role in the regulation of growth traits in L. vannamei. The level of DNA methylation was found to be negatively correlated with growth traits. Through comprehensive analysis, it was discovered that DNA methylation predominantly affects growth performance by up-regulating the expression of genes involved in metabolic pathways, such as glucose metabolism and amino acid metabolism in L. vannamei. This suggests a higher metabolism activity in SG individuals derived DNA methylation to cope with some unknown internal stress or environmental stress rather than being allocated for growth.

Variation and Interaction of Distinct Subgenomes Contribute to Growth Diversity in Intergeneric Hybrid Fish

Intergeneric hybridization greatly reshapes regulatory interactions among allelic and non-allelic genes. However, their effects on growth diversity remain poorly understood in animals. In this study, we conducted whole-genome sequencing and RNA sequencing analyses in diverse hybrid varieties resulting from the intergeneric hybridization of goldfish (Carassius auratus red var.) and common carp (Cyprinus carpio). These hybrid individuals were characterized by distinct mitochondrial genomes and copy number variations. Through a weighted gene correlation network analysis, we identified 3693 genes as candidate growth-regulating genes. Among them, the expression of 3672 genes in subgenome R (originating from goldfish) displayed negative correlations with body weight, whereas 20 genes in subgenome C (originating from common carp) exhibited positive correlations. Notably, we observed intriguing expression patterns of solute carrier family 2 member 12 (slc2a12) in subgenome C, showing opposite correlations with body weight that changed with water temperatures, suggesting differential interactions between feeding activity and weight gain in response to seasonal changes for hybrid animals. In 40.30% of alleles, we observed dominant trans-regulatory effects in the regulatory interactions between distinct alleles from subgenomes R and C. Integrating analyses of allele-specific expression and DNA methylation data revealed that DNA methylation on both subgenomes shaped the relative contribution of allelic expression to the growth rate. These findings provide novel insights into the interactions of distinct subgenomes that underlie heterosis in growth traits and contribute to a better understanding of multiple allelic traits in animals.

Growth Superiority and Genetic Characterization of the Hybrid from Female Ussuri Catfish (Pseudobagrus ussuriensis) and Male Longsnout Catfish (Leiocassis longirostris)

Crossbreeding is a traditional breeding technique and has been performed successfully in many fish species. However, distant hybridization between different genera is hard to be successful because of reproductive isolation. In this study, diploid hybrids (PL) were successfully derived from the hybridization of Ussuri catfish (Pseudobagrus ussuriensis, PU, ♀, 2n = 52) and longsnout catfish (Leiocassis longirostris, LL, ♂, 2n = 52). And the morphological data, external frame parameters, chromosomal karyotypes, DNA content measurement, mitochondrial DNA control region, and species-specific marker identification were applied to investigate the traits and genetic characterization of the PL hybrid offspring and their parents. Both quantifiable traits and shape frame parameters of the PL hybrid offspring were revealed to be intermediate between those of their parents; however, cluster analysis showed that their external morphology was more in favor of the maternal PU. The growth comparisons showed that the hybrids had significant growth advantages over maternal PU. Based on karyotype patterns, DNA contents and mitochondrial DNA, the hybrid origin and maternal inheritance of hybrid offspring were further confirmed. According to the sequence variations identified from the genome sequences of the two catfish species, one species-specific marker was developed to distinguish the PL hybrid offspring and their parents. Therefore, this study provides a successful case for intergeneric hybridization and hybrid superiority, and the PL hybrid shows promise for commercial application, pending further studies into its husbandry, health, and welfare with larger populations of fish.

Genetic improvement and genomic resources of important cyprinid species: status and future perspectives for sustainable production

Cyprinid species are the most cultured aquatic species around the world in terms of quantity and total value. They account for 25% of global aquaculture production and significantly contribute to fulfilling the demand for fish food. The aquaculture of these species is facing severe concerns in terms of seed quality, rising feed costs, disease outbreaks, introgression of exotic species, environmental impacts, and anthropogenic activities. Numerous researchers have explored biological issues and potential methods to enhance cyprinid aquaculture. Selective breeding is extensively employed in cyprinid species to enhance specific traits like growth and disease resistance. In this context, we have discussed the efforts made to improve important cyprinid aquaculture practices through genetic and genomic approaches. The recent advances in DNA sequencing technologies and genomic tools have revolutionized the understanding of biological research. The generation of a complete genome and other genomic resources in cyprinid species has significantly strengthened molecular-level investigations into disease resistance, growth, reproduction, and adaptation to changing environments. We conducted a comprehensive review of genomic research in important cyprinid species, encompassing genome, transcriptome, proteome, metagenome, epigenome, etc. This review reveals that considerable data has been generated for cyprinid species. However, the seamless integration of this valuable data into genetic selection programs has yet to be achieved. In the upcoming years, genomic techniques, gene transfer, genome editing tools are expected to bring a paradigm shift in sustainable cyprinid aquaculture production. The comprehensive information presented here will offer insights for the cyprinid aquaculture research community.

DNA Methylation and Subgenome Dominance Reveal the Role of Lipid Metabolism in Jinhu Grouper Heterosis

Heterosis of growth traits in economic fish has benefited the production of aquaculture for many years, yet its genetic and molecular basis has remained obscure. Nowadays, a new germplasm of hybrid Jinhu grouper (Epinephelus fuscoguttatus ♀ × E. tukula ♂), abbreviated as EFT, exhibiting paternal-biased growth heterosis, has provided an excellent model for investigating the potential regulatory mechanisms of heterosis. We integrated transcriptome and methylome to unravel the changes of gene expression, epigenetic modification, and subgenome dominance in EFT compared with maternal E. fuscoguttatus. Integration analyses showed that the heterotic hybrids showed lower genomic DNA methylation levels than the purebred parent, and the up-regulated genes were mostly DNA hypomethylation. Furthermore, allele-specific expression (ASE) detected paternal subgenome dominance-regulated paternal-biased heterosis, and paternal bias differentially expressed genes (DEGs) were wholly up-regulated in the muscle. Multi-omics results highlighted the role of lipid metabolism, particularly "Fatty acid synthesis", "EPA biosynthesis", and "Signaling lipids", in EFT heterosis formation. Coherently, our studies have proved that the eicosapentaenoic acid (EPA) of EFT was greater than that of maternal E. fuscoguttatus (8.46% vs. 7.46%). Finally, we constructed a potential regulatory network for control of the heterosis formation in EFT. Among them, fasn, pparg, dgat1, igf1, pomca, fgf8a, and fgfr4 were identified as key genes. Our results provide new and valuable clues for understanding paternal-biased growth heterosis in EFT, taking a significant step towards the molecular basis of heterosis.

DNA Methylation Profiling in Genetically Selected Clarias magur (Hamilton, 1822) Provides Insights into the Epigenetic Regulation of Growth and Development

DNA methylation is an epigenetic alteration that impacts gene expression without changing the DNA sequence affecting an organism's phenotype. This study utilized a reduced representation bisulfite sequencing (RRBS) approach to investigate the patterns of DNA methylation in genetically selected Clarias magur stocks. RRBS generated 249.22 million reads, with an average of 490,120 methylation sites detected in various parts of genes, including exons, introns, and intergenic regions. A total of 896 differentially methylated regions (DMRs) were identified; 356 and 540 were detected as hyper-methylated and hypo-methylated regions, respectively. The DMRs and their association with overlapping genes were explored using whole genome data of magur, which revealed 205 genes in exonic, 210 in intronic, and 480 in intergenic regions. The analysis identified the maximum number of genes enriched in biological processes such as RNA biosynthetic process, response to growth factors, nervous system development, neurogenesis, and anatomical structure morphogenesis. Differentially methylated genes (DMGs) such as myrip, mylk3, mafb, egr3, ndnf, meis2a, foxn3, bmp1a, plxna3, fgf6, sipa1l1, mcu, cnot8, trim55b, and myof were associated with growth and development. The selected DMGs were analyzed using real-time PCR, which showed altered mRNA expression levels. This work offers insights into the epigenetic mechanisms governing growth performance regulation in magur stocks. This work provides a valuable resource of epigenetic data that could be integrated into breeding programs to select high-performing individuals.

The key role of myostatin b in somatic growth in fishes derived from distant hybridization

The basic mechanism of heterosis has not been systematically and completely characterized. In previous studies, we obtained three economically important fishes that exhibit rapid growth, WR (WCC ♀ × RCC ♂), WR-II (WR ♀ × WCC ♂), and WR-III (WR-II ♀ × 4nAU ♂), through distant hybridization. However, the mechanism underlying this rapid growth remains unclear. In this study, we found that WR, WR-II, and WR-III showed muscle hypertrophy and higher muscle protein and fat contents compared with their parent species (RCC and WCC). Candidate genes responsible for this rapid growth were then obtained through an analysis of 12 muscle transcriptomes. Notably, the mRNA level of mstnb (myostatin b), which is a negative regulator of myogenesis, was significantly reduced in WR, WR-II, and WR-III compared with the parent species. To verify the function of mstnb, a mstnb-deficient mutant RCC line was generated using the CRISPR-Cas9 technique. The average body weight of mstnb-deficient RCC at 12 months of age was significantly increased by 29.57% compared with that in wild-type siblings. Moreover, the area and number of muscle fibers were significantly increased in mstnb-deficient RCC, indicating hypertrophy and hyperplasia. Furthermore, the muscle protein and fat contents were significantly increased in mstnb-deficient RCC. The molecular regulatory mechanism of mstnb was then revealed by transcription profiling, which showed that genes related to myogenesis (myod, myog, and myf5), protein synthesis (PI3K-AKT-mTOR), and lipogenesis (pparγ and fabp3) were highly activated in hybrid fishes and mstnb-deficient RCC. This study revealed that low expression or deficiency of mstnb regulates somatic growth by promoting myogenesis, protein synthesis, and lipogenesis in hybrid fishes and mstnb-deficient RCC, which provides evidence for the molecular mechanism of heterosis via distant hybridization.

Microplastics induced inflammation and apoptosis via ferroptosis and the NF-κB pathway in carp

Microplastics (MPs), a new class of pollutant that threatens aquatic biodiversity, are becoming increasingly prevalent around the world. Fish growth may be severely inhibited by microplastics, resulting in severe mortality. Exposure to microplastics increases the likelihood of intestinal injuries, but the underlying mechanisms remain equivocal. The objective of this study was to investigate the potential toxic mechanisms underlying microplastic-induced intestinal injury in fish and to assist researchers in identifying novel therapeutic targets. In this study, a model of carp exposed to microplastics was established successfully. Histological observation showed that exposure to polyethylene microplastics caused damage to the intestinal mucosal surface and a significant increase in goblet cells, which aggregated on the surface of the mucosa. The mucosal layer was observed to fall off. Lymphocytes in the intestinal wall proliferated and aggregated. TUNEL staining showed that apoptosis occurred in the group exposed to microplastics. The qPCR results showed that the expression of Ferroptosis apoptotic factors COX-2 and ACSL4 was upregulated, while the expression of TFRC, FIH1, SLC7A11, and GPX4 was downregulated. The NF-κB pathway (p-p65, IκBα), inflammatory cytokines (TNF-α, IL-8, IL-6) and apoptosis genes (Bax, Caspase3) were upregulated. Semi-quantitative detection of related proteins by Western blotting was consistent with the gene expression results. In addition, the ELISA assay showed that lipid peroxidation and inflammatory cytokines (TNF-α, IL-1β, IL-6) were increased in the microplastic exposed group. To conclude, lipid peroxidation induced by microplastics activates the NF-κB pathway and causes ferroptosis, ultimately resulting in intestinal damage and cellular apoptosis.

Genetic and epigenetic regulation of growth, reproduction, disease resistance and stress responses in aquaculture

Major progress has been made with genomic and genetic studies in aquaculture in the last decade. However, research on epigenetic regulation of aquaculture traits is still at an early stage. It is apparent that most, if not all, aquaculture traits are regulated at both genetic and epigenetic levels. This paper reviews recent progress in understanding of genetic and epigenetic regulation of important aquaculture traits such as growth, reproduction, disease resistance, and stress responses. Although it is challenging to make generalized statements, DNA methylation is mostly correlated with down-regulation of gene expression, especially when at promoters and enhancers. As such, methylation of growth factors and their receptors is negatively correlated with growth; hypomethylation of genes important for stress tolerance is correlated with increased stress tolerance; hypomethylation of genes important for male or female sex differentiation leads to sex differentiation into males or females, respectively. It is apparent that environmental regulation of aquaculture traits is mediated at the level of epigenetic regulation, and such environment-induced epigenetic changes appeared to be intergenerationally inherited, but evidences for transgenerational inheritance are still limited.