Short-hairpin Mediated Myostatin Knockdown Resulted in Altered Expression of Myogenic Regulatory Factors with Enhanced Myoblast Proliferation in Fetal Myoblast Cells of Goats

When Less Is More: Targeting the Myostatin Gene in Livestock for Augmenting Meat Production

How to increase meat production is one of the main questions in animal breeding. Selection for improved body weight has been made and, due to recent genomic advances, naturally occurring variants that are responsible for controlling economically relevant phenotypes have been revealed. The myostatin (MSTN) gene, a superstar gene in animal breeding, was discovered as a negative controller of muscle mass. In some livestock species, natural mutations in the MSTN gene could generate the agriculturally desirable double-muscling phenotype. However, some other livestock species or breeds lack these desirable variants. Genetic modification, particularly gene editing, offers an unprecedented opportunity to induce or mimic naturally occurring mutations in livestock genomes. To date, various MSTN-edited livestock species have been generated using different gene modification tools. These MSTN gene-edited models have higher growth rates and increased muscle mass, suggesting the high potential of utilizing MSTN gene editing in animal breeding. Additionally, post-editing investigations in most livestock species support the favorable influence of targeting the MSTN gene on meat quantity and quality. In this Review, we provide a collective discussion on targeting the MSTN gene in livestock to further encourage its utilization opportunities. It is expected that, shortly, MSTN gene-edited livestock will be commercialized, and MSTN-edited meat will be on the tables of ordinary customers.

Myostatin suppresses adipogenic differentiation and lipid accumulation by activating crosstalk between ERK1/2 and PKA signaling pathways in porcine subcutaneous preadipocytes

The current study was undertaken to determine the effect of myostatin (MSTN) on lipid accumulation in porcine subcutaneous preadipocytes (PSPAs) and to further explore the potential molecular mechanisms. PSPAs isolated from Meishan weaned piglets were added with various concentrations of MSTN recombinant protein during the entire period of adipogenic differentiation process. Results showed that MSTN treatment significantly reduced the lipid accumulation, intracellular triglyceride (TG) content, glucose consumption and glycerol phosphate dehydrogenase activity, while increased glycerol and free fatty acid release. Consistent with above results, the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway was obviously activated and thus key adipogenic transcription factors peroxisome proliferator-activated receptor-gamma (PPAR-γ), CCAAT/enhancer-binding protein-alpha (C/EBP-α) and their downstream engymes fatty acid synthase and acetyl-CoA carboxylase were all inhibited. However, chemical inhibition of ERK1/2 signaling pathway by PD98059 markedly reversed the decreased TG content by increasing PPAR-γ expression. In addition, MSTN activated the cyclic AMP/protein kinase A (cAMP/PKA) pathway and stimulated lipolysis by reducing the expression of antilipolytic gene perilipin, thus elevated key lipolytic enzymes adipose triglyceride lipase and hormone-sensitive lipase expression and enzyme activity. On the contrary, pretreatment with PKA inhibitor H89 significantly reversed TG accumulation by increasing PPAR-γ expression and thus inhibiting ERK1/2, perilipin and HSL phosphorylation, supporting the crosstalk between PKA and ERK1/2 pathways in both the anti-adipogenic and pro-lipolytic effects. In summary, our results suggested that MSTN suppressed adipogenesis and stimulated lipolysis, which was mainly mediated by activating crosstalk of ERK1/2 and PKA signaling pathways, and consequently decreased lipid accumulation in PSPAs, our findings may provide novel insights for further exploring MSTN as a potent inhibitor of porcine subcutaneous lipid accumulation.

Overexpression of the Tuberous sclerosis complex 2 (TSC2) gene inhibits goat myoblasts proliferation and differentiation in understanding the underlying mechanism of muscle development

The growth of animal skeletal muscle is mainly determined by the synthesis processes of total proteins in skeletal muscle cells, which has a significant impact on the postnatal growth of young animals. An increasing number of studies are focusing on the functions of Tuberous sclerosis complex 2 (TSC2) during the process of cell protein synthesis and growth. However, it is still unclear the effect of whether and how TSC2 on goat myoblasts proliferation and differentiation. Here, we found that TSC2 gene has opposite expression patterns in proliferation and differentiation of myoblasts. An expression vector containing goat TSC2 cDNA sequences linked with pcDNA3.1 plasmid was constructed. Myoblasts proliferation activity was significantly inhibited and cell cycle transition slowed down after the transfection of pcDNA3.1-TSC2 plasmid into goat primary myoblasts by EdU staining, CCK-8 and flow cytometry. Mechanically, we further confirmed that the overexpression TSC2 was able to down-regulate the mRNA and protein expression of mechanistic target of rapamycin (mTOR), p70 ribosomal S6 kinase 1 (p70S6K) and some cell cycle related genes. In addition, the expression of myogenic genes and myotube formation were attenuated. Collectively, all our results of the experiment demonstrate that TSC2 could regulate myoblasts cells proliferation and differentiation via the activation of the mTOR/p70S6K signaling pathway.

Muscle Hyperplasia in Japanese Quail by Single Amino Acid Deletion in MSTN Propeptide

Mutation in myostatin (MSTN), a negative regulator of muscle growth in skeletal muscle, resulted in increased muscle mass in mammals and fishes. However, MSTN mutation in avian species has not been reported. The objective of this study was to generate MSTN mutation in quail and investigate the effect of MSTN mutation in avian muscle growth. Recently, a new targeted gene knockout approach for the avian species has been developed using an adenoviral CRISPR/Cas9 system. By injecting the recombinant adenovirus containing CRISPR/Cas9 into the quail blastoderm, potential germline chimeras were generated and offspring with three base-pair deletion in the targeted region of the MSTN gene was identified. This non-frameshift mutation in MSTN resulted in deletion of cysteine 42 in the MSTN propeptide region and homozygous mutant quail showed significantly increased body weight and muscle mass with muscle hyperplasia compared to heterozygous mutant and wild-type quail. In addition, decreased fat pad weight and increased heart weight were observed in MSTN mutant quail in an age- and sex-dependent manner, respectively. Taken together, these data indicate anti-myogenic function of MSTN in the avian species and the importance of cysteine 42 in regulating MSTN function.

Sheep and Goat Genome Engineering: From Random Transgenesis to the CRISPR Era

Sheep and goats are valuable livestock species that have been raised for their production of meat, milk, fiber, and other by-products. Due to their suitable size, short gestation period, and abundant secretion of milk, sheep and goats have become important model animals in agricultural, pharmaceutical, and biomedical research. Genome engineering has been widely applied to sheep and goat research. Pronuclear injection and somatic cell nuclear transfer represent the two primary procedures for the generation of genetically modified sheep and goats. Further assisted tools have emerged to enhance the efficiency of genetic modification and to simplify the generation of genetically modified founders. These tools include sperm-mediated gene transfer, viral vectors, RNA interference, recombinases, transposons, and endonucleases. Of these tools, the four classes of site-specific endonucleases (meganucleases, ZFNs, TALENs, and CRISPRs) have attracted wide attention due to their DNA double-strand break-inducing role, which enable desired DNA modifications based on the stimulation of native cellular DNA repair mechanisms. Currently, CRISPR systems dominate the field of genome editing. Gene-edited sheep and goats, generated using these tools, provide valuable models for investigations on gene functions, improving animal breeding, producing pharmaceuticals in milk, improving animal disease resistance, recapitulating human diseases, and providing hosts for the growth of human organs. In addition, more promising derivative tools of CRISPR systems have emerged such as base editors which enable the induction of single-base alterations without any requirements for homology-directed repair or DNA donor. These precise editors are helpful for revealing desirable phenotypes and correcting genetic diseases controlled by single bases. This review highlights the advances of genome engineering in sheep and goats over the past four decades with particular emphasis on the application of CRISPR/Cas9 systems.

Oxidative and glycolytic skeletal muscles show marked differences in gene expression profile in Chinese Qingyuan partridge chickens

Oxidative and glycolytic myofibers have different structures and metabolic characteristics and their ratios are important in determining poultry meat quality. However, the molecular mechanisms underlying their differences are unclear. In this study, global gene expression profiling was conducted in oxidative skeletal muscle (obtained from the soleus, or SOL) and glycolytic skeletal muscle (obtained from the extensor digitorum longus, or EDL) of Chinese Qingyuan partridge chickens, using the Agilent Chicken Gene Expression Chip. A total of 1224 genes with at least 2-fold differences were identified (P < 0.05), of which 654 were upregulated and 570 were downregulated in SOL. GO, KEGG pathway, and co-expressed gene network analyses suggested that PRKAG3, ATP2A2, and PPARGC1A might play important roles in myofiber composition. The function of PPARGC1A gene was further validated. PPARGC1A mRNA expression levels were higher in SOL than in EDL muscles throughout the early postnatal development stages. In myoblast cells, shRNA knockdown of PPARGC1A significantly inhibited some muscle development and transition-related genes, including PPP3CA, MEF2C, and SM (P < 0.01 or P < 0.05), and significantly upregulated the expression of FWM (P < 0.05). Our study demonstrates strong transcriptome differences between oxidative and glycolytic myofibers, and the results suggest that PPARGC1A is a key gene involved in chicken myofiber composition and transition.