Inhibition of Myostatin Gene Expression in Skeletal Muscle of Fish by In Vivo Electrically Mediated dsRNA and shRNAi Delivery

A scalable and tunable platform for functional interrogation of peptide hormones in fish

Pituitary hormones play a central role in shaping vertebrate life history events, including growth, reproduction, metabolism, and aging. The regulation of these traits often requires precise control of hormone levels across diverse timescales. However, fine tuning circulating hormones in-vivo has traditionally been experimentally challenging. Here, using the naturally short-lived turquoise killifish (N. furzeri), we describe a high-throughput platform that combines loss- and gain-of-function of peptide hormones. Mutation of three primary pituitary hormones, growth hormone (gh1), follicle stimulating hormone (fshb), and thyroid stimulating hormone (tshb), alters somatic growth and reproduction. Thus, suggesting that while the killifish undergoes extremely rapid growth and maturity, it still relies on vertebrate-conserved genetic networks. As the next stage, we developed a gain-of-function vector system in which a hormone is tagged using a self-cleavable fluorescent reporter, and ectopically expressed in-vivo through intramuscular electroporation. Following a single electroporation, phenotypes, such as reproduction, are stably rescued for several months. Notably, we demonstrate the versatility of this approach by using multiplexing, dose-dependent, and doxycycline-inducible systems to achieve tunable and reversible expression. In summary, this method is relatively high-throughput, and facilitates large-scale interrogation of life-history strategies in fish. Ultimately, this approach could be adapted for modifying aquaculture species and exploring pro-longevity interventions.

Characterisation of Single Nucleotide Polymorphisms and Haplotypes of MSTN Associated with Growth Traits in European Sea Bass (Dicentrarchus labrax)

The myostatin (MSTN) gene, known as growth differentiation factor-8 (GDF-8), is a member of the transforming growth factor-β (TGF-β) superfamily and plays a specific inhibitory role during the critical phases of skeletal muscle mass development in vertebrates. This study was conducted to investigate MSTN polymorphisms in harvest size European sea bass reared in Turkey. Nine single nucleotide polymorphisms (SNPs) and two indels were identified in exons 1-3 of MSTN in the European sea bass population The associations between the g.16612A indel located in intron 1 and standard length were significant. The MSTN g.15252 T > A locus in intron 2 was significantly related to the total weight, fillet weight and standard length (P < 0.05). The relationship between the g.14873C > T locus in exon 3 of MSTN and standard height, head length, body length, pre-anal length, abdominal length, post-anal length and head width was significant (P < 0.05). According to the results of the haplotype analysis, two haplogroup and eight haplotype combinations were detected in the population. The haplogroup 2 had significant associations with all measured growth traits (P < 0.05). Thus, SNPs and haplotypes identified in this study could be useful for European sea bass breeding and marker-assisted selection.

Differentiation and Maturation of Muscle and Fat Cells in Cultivated Seafood: Lessons from Developmental Biology

Cultivated meat, also known as cultured or cell-based meat, is meat produced directly from cultured animal cells rather than from a whole animal. Cultivated meat and seafood have been proposed as a means of mitigating the substantial harms associated with current production methods, including damage to the environment, antibiotic resistance, food security challenges, poor animal welfare, and-in the case of seafood-overfishing and ecological damage associated with fishing and aquaculture. Because biomedical tissue engineering research, from which cultivated meat draws a great deal of inspiration, has thus far been conducted almost exclusively in mammals, cultivated seafood suffers from a lack of established protocols for producing complex tissues in vitro. At the same time, fish such as the zebrafish Danio rerio have been widely used as model organisms in developmental biology. Therefore, many of the mechanisms and signaling pathways involved in the formation of muscle, fat, and other relevant tissue are relatively well understood for this species. The same processes are understood to a lesser degree in aquatic invertebrates. This review discusses the differentiation and maturation of meat-relevant cell types in aquatic species and makes recommendations for future research aimed at recapitulating these processes to produce cultivated fish and shellfish.

A Potential Negative Regulatory Function of Myostatin in the Growth of the Pacific Abalone, Haliotis discus hannai

Myostatin, also known as GDF8, is a member of the transforming growth factor-β (TGF-β) superfamily. In vertebrates, myostatin negatively regulates the growth of skeletal muscle. In invertebrates, it has been reported to be closely related to animal growth. However, knowledge concerning the molecular mechanisms involved in the myostatin regulation of molluscan growth is limited. In this study, we found that the hdh-myostatin open reading frame (ORF) comprised 1470 base pairs that encoded 489 amino acids and contained structural characteristics typical of the TGF-β superfamily, including a C-terminal signal peptide, a propeptide domain, and TGF-β region. Gene expression analysis revealed that hdh-myostatin mRNA was widely expressed at different levels in all of the examined tissues of Haliotis discus hannai. Nine single nucleotide polymorphisms (SNPs) were associated with the growth traits. RNA interference (RNAi) against hdh-myostatin mRNA significantly downregulated hdh-myostatin at days 1, 15, and 30 post injection, and the pattern was correlated with downregulation of the genes TGF-β receptor type-I (hdh-TβR I), activin receptor type-IIB (hdh-ActR IIB), and mothers against decapentaplegic 3 (hdh-Smad3). After one month of the RNAi experiment, the shell lengths and total weights increased in the abalone, Haliotis discus hannai. The results of qRT-PCR showed that the hdh-myostatin mRNA level was higher in the slow-growing group than in the fast-growing group. These results suggest that hdh-myostatin is involved in the regulation of growth, and that these SNPs would be informative for further studies on selective breeding in abalone.

Both TGF-β1 and Smad4 regulate type I collagen expression in the muscle of grass carp, Ctenopharyngodon idella

Type I collagen is proven to make an important contribution to fish muscle quality. Our previous study has shown the Smad4-dependent regulation of type I collagen expression in the muscle of crisp grass carp fed with faba bean. However, the regulatory roles of TGF-β1 or TGF-β1/Smad4 on type I collagen remain unclear in ordinary grass carp fed with normal diets or in other fish species. To clarify this point, the effect of TGF-β1 and Smad4 over-expression and RNAi knockdown on type I collagen (COL1-α1 and COL1-α2) expression were tested in vitro (zebrafish ZF4 cells) and in vivo (grass carp) along with the TGF-β1/Smad4 co-expression and co-knockdown. The mRNA levels of TGF-β1, Smad4, and type I collagen were upregulated in the groups with over-expressed TGF-β1 and Smad4 and downregulated in the groups of TGF-β1 and Smad4 RNAi in comparison to controls in vitro (P < 0.05). Similarly, in the in vivo experiment, the mRNA abundance of TGF-β1, Smad4, and type I collagen of over-expression group was higher than the controls at 36 h (P < 0.05). Co-injection of TGF-β1/Smad4 over-expression and RNAi vectors generally showed the higher efficacy. This study revealed that TGF-β1 and Smad4 genes regulated type I collagen expression in grass carp muscle and zebrafish. These findings will provide references for the collagen regulation of other freshwater fishes.

Genome-Wide Association Study of Body Shape-Related Traits in Large Yellow Croaker (Larimichthys crocea)

Large yellow croaker (Larimichthys crocea) is one of the most important cultured marine fish on the southeast coast of China. Its body shape is important for the aquaculture industry since it affects the behavior such as swimming, ingesting, and evading, as well as customer preference. Due to the greater consumer demand of small head, slender body large yellow croaker, selecting and breeding of slender individuals with the assistance of genetic markers will benefit the industry quickly. In this study, several traits were employed to represent body shape, including body depth/body length (BD/BL), body thickness/body length (BT/BL), caudal peduncle depth/caudal peduncle length (CPDLR), tail length/body length (TL/BL), and body area/head area (BA/HA). Genome-wide association study was conducted with a panmictic population of 280 individuals to identify SNP and genes potentially associated with body shape. A set of 20 SNPs on 12 chromosomes were identified to be significantly associated with body shape-related traits. Besides, 5 SNPs were identified to be suggestive associated with CPDLR and BT/BL. Surrounding these SNPs, we found some body shape-related candidate genes, including fabp1, acrv1, bcor, mstn, bambi, and neo1, which involved in lipid metabolism, TGF-β signaling, and BMP pathway and other important regulatory pathways. These results will be useful for the understanding of the genetic basis of body shape formation and helpful for body shape controlling of large yellow croaker by using marker-assisted selection.

Smad4-dependent regulation of type I collagen expression in the muscle of grass carp fed with faba bean

Smad4 is the key regulator in the transforming growth factor β1 (TGF-β1)/Smads signal pathway, and is also the crux of the regulation of type I collagen expression in mammals. In fish, however, the relationship between Smad4 and type I collagen is still unknown. Given the widely accepted importance of type I collagen in fish muscle hardness, we seek to explore this issue by analyzing the expressions of the TGF-β1/Smads pathway molecules and type I collagen in the muscle of crisp grass carp fed with faba bean, which shows increased muscle hardness. The study found that (1) in the process of feeding the grass carp with faba bean, the mRNA and protein expressions of TGF-β1, Smad2 and Smad4 all increased along with the increase of type I collagen expression (Col1α1 and Col1α2); (2) one day after the injection of Smad4 over-expression vector, both mRNA and protein expressions of Col1α1 and Col1α2 significantly increased, reaching the maximum on the 2nd and 5th day, respectively; (3) one day after the injection of Smad4 RNAi interference vector, the mRNA and protein expressions of Col1α1 and Col1α2 decreased, reaching the minimum on the 5th day. These results revealed that Smad4 is the major regulator of type I collagen in the muscle of grass carp fed with faba bean. This study would provide an important mechanistic basis for nutritional regulation of type I collagen in the muscle of fish.

Using CRISPR/Cas9-mediated gene editing to further explore growth and trade-off effects in myostatin-mutated F4 medaka (Oryzias latipes)

Myostatin (MSTN) suppresses skeletal muscle development and growth in mammals, but its role in fish is less well understood. Here we used CRISPR/Cas9 to mutate the MSTN gene in medaka (Oryzias latipes) and evaluate subsequent growth performance. We produced mutant F0 fish that carried different frameshifts in the OlMSTN coding sequence and confirmed the heritability of the mutant genotypes to the F1 generation. Two F1 fish with the same heterozygous frame-shifted genomic mutations (a 22 bp insertion in one allele; a 32 bp insertion in the other) were then crossbred to produce subsequent generations (F2~F5). Body length and weight of the MSTN-/- F4 medaka were significantly higher than in the wild type fish, and muscle fiber density in the inner and outer compartments of the epaxial muscles was decreased, suggesting that MSTN null mutation induces muscle hypertrophy. From 3~4 weeks post hatching (wph), the expression of three major myogenic related factors (MRFs), MyoD, Myf5 and Myogenin, was also significantly upregulated. Some medaka had a spinal deformity, and we also observed a trade-off between growth and immunity in MSTN-/- F4 medaka. Reproduction was unimpaired in the fast-growth phenotypes.

Chitosan-Mediated shRNA Knockdown of Cytosolic Alanine Aminotransferase Improves Hepatic Carbohydrate Metabolism

Alanine aminotransferase (ALT) catalyses a transamination reaction that links carbohydrate and amino acid metabolism. In this study, we examined the effect of silencing cytosolic ALT (cALT) expression on the hepatic metabolism in Sparus aurata. A number of siRNA and shRNA designed to down-regulate cALT expression were validated in HEK-293 cells transfected with plasmids expressing S. aurata cALT or mitochondrial ALT (mALT) isoforms: ALT silencing significantly decreased the expression levels of S. aurata mRNA cALT1 to 62% (siRNA) and 48% (shRNA) of the values observed in control cells. The effect of cALT silencing was analysed in the liver of S. aurata 72 h after intraperitoneal injection of chitosan-tripolyphosphate (TPP) nanoparticles complexed with a plasmid encoding a shRNA to down-regulate cALT expression (pCpG-si1sh1). In fish fed diets with different ratio of protein to carbohydrate and treated with chitosan-TPP-pCpG-si1sh1, cALT1 and cALT2 mRNA levels significantly decreased irrespective of the diet. Consistently, ALT activity decreased in liver of treated animals. In the liver of S. aurata treated with chitosan-TPP-pCpG-si1sh1 nanoparticles, down-regulation of cALT expression increased the activity of key enzymes in glycolysis (6-phosphofructo-1-kinase and pyruvate kinase) and protein metabolism (glutamate dehydrogenase). Besides showing for the first time that administration of chitosan-TPP-pCpG-si1sh1 nanoparticles silences hepatic cALT expression in vivo, our data support that down-regulation of cALT could improve the use of dietary carbohydrates to obtain energy and spare protein catabolism.

Lentivirus-mediated RNA interference of myostatin gene affects MyoD and Myf5 gene expression in duck embryonic myoblasts

The aim of this study was to construct lentivirus-mediated short hairpin RNA (shRNA) vectors targeting the duck MSTN gene and investigate whether these vectors can affect the development of duck primary cultured embryonic myoblasts. MSTN mRNA levels in the myoblasts were detected using quantitative real-time polymerase chain reaction (PCR), cell proliferation was assessed by MTT assays and cell differentiation was assayed by photography. MSTN mRNA levels in PLL3.7-MSTN-shRNA1, PLL3.7-MSTN-shRNA2 and PLL3.7-MSTN-shRNA3 lentivirus-mediated shRNA groups were reduced by 61.6%, 76.9% and 79.1%, respectively, compared to control cells. Down-regulation of MSTN in duck embryonic myoblasts stimulated cell proliferation and inhibited differentiation, accompanied by a greater than twofold down-regulation of MyoD expression and up-regulation of Myf5 expression. These results revealed that silencing of MSTN changes the development of duck embryonic myoblasts by regulating the expression level of MyoD and Myf5 genes.

Revisiting the paradigm of myostatin in vertebrates: insights from fishes

In the last decade, myostatin (MSTN), a member of the TGFβ superfamily, has emerged as a strong inhibitor of muscle growth in mammals. In fish many studies reveal a strong conservation of mstn gene organization, sequence, and protein structures. Because of ancient genome duplication, teleostei may have retained two copies of mstn genes and even up to four copies in salmonids due to additional genome duplication event. In sharp contrast to mammals, the different fish mstn orthologs are widely expressed with a tissue-specific expression pattern. Quantification of mstn mRNA in fish under different physiological conditions, demonstrates that endogenous expression of mstn paralogs is rarely related to fish muscle growth rate. In addition, attempts to inhibit MSTN activity did not consistently enhance muscle growth as in mammals. In vitro, MSTN stimulates myotube atrophy and inhibits proliferation but not differentiation of myogenic cells as in mammals. In conclusion, given the strong mstn expression non-muscle tissues of fish, we propose a new hypothesis stating that fish MSTN functions as a general inhibitors of cell proliferation and cell growth to control tissue mass but is not specialized into a strong muscle regulator.

Electrotransfer of the epinecidin-1 gene into skeletal muscle enhances the antibacterial and immunomodulatory functions of a marine fish, grouper (Epinephelus coioides)

Electrotransfer of plasmid DNA into skeletal muscle is a common non-viral delivery system for the study of gene function and for gene therapy. However, the effects of epinecidin-1 (epi) on bacterial growth and immune system modulation following its electrotransfer into the muscle of grouper (Epinephelus coioides), a marine fish species, have not been addressed. In this study, pCMV-gfp-epi plasmid was electroporated into grouper muscle, and its effect on subsequent infection with Vibrio vulnificus was examined. Over-expression of epi efficiently reduced bacterial numbers at 24 and 48 h after infection, and augmented the expression of immune-related genes in muscle and liver, inducing a moderate innate immune response associated with pro-inflammatory infiltration. Furthermore, electroporation of pCMV-gfp-epi plasmid without V. vulnificus infection induced moderate expression of certain immune-related genes, particularly innate immune genes. These data suggest that electroporation-mediated gene transfer of epi into the muscle of grouper may hold potential as an antimicrobial therapy for pathogen infection in marine fish.