Knockdown of the myostatin gene by RNA interference in caprine fibroblast cells

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 (MSTN) Gene Indel Variation and Its Associations with Body Traits in Shaanbei White Cashmere Goat

Myostatin (MSTN) gene, also known as growth differentiation factor 8 (GDF8), is a member of the transforming growth factor-beta super-family and plays a negative role in muscle development. It acts as key points during pre- and post-natal life of amniotes that ultimately determine the overall muscle mass of animals. There are several studies that concentrate on the effect of a 5 bp insertion/deletion (indel) within the 5' untranslated region (5' UTR) of goat MSTN gene in goats. However, almost all sample sizes were below 150 individuals. Only in Boer goats, the sample sizes reached 482. Hence, whether the 5 bp indel was still associated with the growth traits of goats in large sample sizes which were more reliable is not clear. To find an effective and dependable DNA marker for goat rearing, we first enlarged the sample sizes (n = 1074, Shaanbei White Cashmere goat) which would enhance the robustness of the analysis and did the association analyses between the 5 bp indel and growth traits. Results uncovered that the 5 bp indel was significantly related to body height, height at hip cross, and chest width index (p < 0.05). In addition, individuals with DD genotype had a superior growing performance than those with the ID genotype. These findings suggested that the 5 bp indel in MSTN gene are significantly associated with growth traits and the specific genotype might be promising for maker-assisted selection (MAS) of goats.

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.

Dietary sodium propionate affects mucosal immune parameters, growth and appetite related genes expression: Insights from zebrafish model

Propionate is a short-chain fatty acid (SCFA) that improves physiological and pathophysiological properties. However, there is limited information available about the effects of SCFAs on mucosal immune parameters as well as growth and appetite related genes expression. The aim of the present study was to evaluate the effect of sodium propionate (SP) intake on the mucosal immune parameters, growth and appetite related genes expression using zebrafish (Danio rerio) as model organism. Zebrafish fed control or diet supplemented with different levels (0.5, 1 and 2%) of SP for 8weeks. At the end of feeding trial, the expression of the key genes related to growth and appetite (GH, IGF1, MYSTN and Ghrl) was evaluated. Also, mucosal immune parameters (Total Ig, lysozyme and protease activity) were studied in skin mucus of zebrafish. The results showed that dietary administration of SP significantly (P<0.05) up-regulated the expression of GH, IGF1 and down-regulated MYSTN gene. Also, feeding zebrafish with SP supplemented diet significantly increased appetite related gene expression (P<0.05) with a more pronounced effect in higher inclusion levels. Compared with control group, the expression of appetite related gene (Ghrl) was remarkably (P<0.05) higher in SP fed zebrafish. Also, elevated mucosal immune parameters was observed in zebrafish fed SP supplemented diet. The present results revealed beneficial effects of dietary SP on mucosal immune response and growth and appetite related genes expression. These results also highlighted the potential use of SP as additive in human diets.

Effect of Co-transfection of Anti-myostatin shRNA Constructs in Caprine Fetal Fibroblast Cells

Knockdown of myostatin gene (MSTN), transforming growth factor-β superfamily, and a negative regulator of the skeletal muscle growth, by RNA interference (RNAi), has been reported to increase muscle mass in mammals. The current study was aimed to cotransfect two anti-MSTN short hairpin RNA (shRNA) constructs in caprine fetal fibroblast cells for transient silencing of MSTN gene. In the present investigation, approximately 89% MSTN silencing was achieved in transiently transfected caprine fetal fibroblast cells by cotransfection of two best out of four anti-MSTN shRNA constructs. Simultaneously, we also monitored the induction of IFN responsive genes (IFN), pro-apoptotic gene (caspase3) and anti-apoptotic gene (MCL-1) due to cotransfection of different anti-MSTN shRNA constructs. We observed induction of 0.66-19.12, 1.04-4.14, 0.50-3.43, and 0.42-1.98 for folds IFN-β, OAS1, caspase3, and MCL-1 genes, respectively (p < 0.05). This RNAi based cotransfection method could provide an alternative strategy of gene knockout and develop stable caprine fetal fibroblast cells. Furthermore, these stable cells can be used as a cell donor for the development of transgenic cloned embryos by somatic cell nuclear transfer (SCNT) technique.

Quantitative Evaluation of Myostatin Gene in Stably Transfected Caprine Fibroblast Cells by Anti-Myostatin shRNA

Skeletal muscle is the major component of lean tissue that is used for consumption, and myostatin is a negative regulator of skeletal muscle growth. Downregulation of this gene therefore offers a strategy for developing superior animals with enhanced muscle growth. Knockdown of myostatin was achieved by RNA interference technology. The anti-myostatin shRNA were designed and stably transfected in caprine fibroblast cells. The reduced expression of target gene was achieved and measured in clonal fibroblast cells by real-time PCR. Two single-cell clones induced significant decrease of myostatin gene expression by 73.96 and 72.66 %, respectively (P < 0.05). To ensure the appropriate growth of transfected cell, seven media were tested. The best suited media was used for transfected fibroblast cell proliferation. The findings suggest that shRNA provides a novel potential tool for gene knockdown and these stably transfected cells can be used as the donor cells for animal cloning.

Stable suppression of myostatin gene expression in goat fetal fibroblast cells by lentiviral vector-mediated RNAi

Myostatin (MSTN) is a secreted growth factor that negatively regulates skeletal muscle mass, and therefore, strategies to block myostatin-signaling pathway have been extensively pursued to increase the muscle mass in livestock. Here, we report a lentiviral vector-based delivery of shRNA to disrupt myostatin expression into goat fetal fibroblasts (GFFs) that were commonly used as karyoplast donors in somatic-cell nuclear transfer (SCNT) studies. Sh-RNA positive cells were screened by puromycin selection. Using real-time polymerase chain reaction (PCR), we demonstrated efficient knockdown of endogenous myostatin mRNA with 64% down-regulation in sh2 shRNA-treated GFF cells compared to GFF cells treated by control lentivirus without shRNA. Moreover, we have also demonstrated both the induction of interferon response and the expression of genes regulating myogenesis in GFF cells. The results indicate that myostatin-targeting siRNA produced endogenously could efficiently down-regulate myostatin expression. Therefore, targeted knockdown of the MSTN gene using lentivirus-mediated shRNA transgenics would facilitate customized cell engineering, allowing potential use in the establishment of stable cell lines to produce genetically engineered animals.

MicroRNA-mediated myostatin silencing in caprine fetal fibroblasts

Myostatin functions as a negative regulator of skeletal muscle growth by suppressing proliferation and differentiation of myoblasts. Dysfunction of the myostatin gene, either due to natural mutation or genetic manipulations such as knockout or knockdown, has been reported to increase muscle mass in mammalian species. RNA interference (RNAi) mediated by microRNAs (miRNAs) is a promising method for gene knockdown studies. In the present study, transient and stable silencing of the myostatin gene in caprine fetal fibroblasts (CFF) was evaluated using the two most effective constructs selected from four different miRNA expression constructs screened in 293FT cells. Using these two miRNA constructs, we achieved up to 84% silencing of myostatin mRNA in transiently transfected CFF cells and up to 31% silencing in stably transfected CFF cells. Moreover, off-target effects due to induction of interferon (IFN) response genes, such as interferon beta (IFN-β) and 2′-5′-oligoadenylate synthetase 2 (OAS2), were markedly fewer in stably transfected CFF cells than in transiently transfected cells. Stable expression of anti-myostatin miRNA with minimal induction of interferon shows great promise for increasing muscle mass in transgenic goats.

Myostatin knockdown and its effect on myogenic gene expression program in stably transfected goat myoblasts

Myostatin, a negative regulator of skeletal muscle mass, is a proven candidate to modulate skeletal muscle mass through targeted gene knockdown approach. Here, we report myostatin (MSTN) knockdown in goat myoblasts stably expressing small hairpin RNA (shRNAs) against MSTN gene through lentivirus vector-mediated integration. We observed 72% (p = 0.003) and 54% (p = 0.022) downregulation of MSTN expression with sh2 shRNA compared to empty vector control and untransduced myoblasts, respectively. The knockdown of MSTN expression was accompanied with concomitant downregulation of myogenic regulatory factor MYOD (77%, p = 0.001), MYOG (94%, p = 0.000), and MYF5 (36%, p = 0.000), cell cycle regulator p21 (62%, p = 0.000), MSTN receptor ACVR2B (23%, p = 0.061), MSTN antagonist follistatin (81%, p = 0.000), and downstream signaling mediators SMAD2 (20%, p = 0.060) and SMAD3 (49%, p = 0.006). However, the expression of MYF6 was upregulated by 14% compared to control lentivirus-transduced myoblasts (p = 0.354) and 79% compared to untransduced myoblasts (p = 0.018) in sh2 shRNA-transduced goat myoblasts cells. Although, MSTN knockdown led to sustained cell proliferation of myoblasts, the myoblasts fusion was suppressed in both MSTN knocked down and control lentivirus-transduced myoblasts. The expression of interferon response gene OAS1 was significantly upregulated in control lentivirus (10.86-fold; p = 0.000)- and sh2 (1.71-fold; p = 0.002)-integrated myoblasts compared to untransduced myoblasts. Our study demonstrates stable knockdown of MSTN in goat myoblasts cells and its potential for use in generation of transgenic goat by somatic cell nuclear transfer.

Small interfering RNA (siRNA)-mediated knockdown of myostatin influences the expression of myogenic regulatory factors in caprine foetal myoblasts

Myostatin (MSTN) acts as a negative regulator of skeletal muscle development. Naturally occurring inactivating mutations in the coding region and knockout as well as knockdown of MSTN result in an increase in the muscle mass. However, the effect of MSTN knockdown on the expression of myogenic regulatory factors (MRFs) has not been studied in farm animals including goats. In the present study, using different synthetic siRNAs (n = 3), we demonstrated as high as 69 (p < 0.01) and 89% downregulation of MSTN mRNA and protein in the primary caprine foetal myoblast cells. Further, we also examined the effect of MSTN knockdown on the transcripts of MRFs including MyoD, Myf5 and MYOG. The expression of Myf5 remained unaffected (p = 0.60); however, MSTN downregulation caused a significant (p < 0.05) decrease and increase of MYOG and MyoD expression, respectively. Assessment of OAS1 expression confirmed the absence of any siRNA-elicited interferon response. Our results demonstrate that the downregulation of MSTN expression was accompanied by differential expressions of MRFs without any adverse interferon response. This study also suggests the importance of siRNA-mediated knockdown of MSTN as a potential alternative to increase muscle mass and meat production.

Significant role of μ-calpain (CANP1) in proliferation/survival of bovine skeletal muscle satellite cells

Calpains are a family of Ca²⁺-dependent intracellular cysteine proteases, including the ubiquitously expressed μ-calpain (CANP1) and m-calpain (CANP2). The CANP1 has been found to play a central role in postmortem proteolysis and meat tenderization. However, the physiological roles of CANP1 in cattle skeletal satellite cells remain unclear. In this study, three small interference RNA sequences (siRNAs) targeting CANP1 gene were designed and ligated into pSilencer plasmid vector to construct shRNA expression constructs. Suppression of CANP1 in satellite cells was evaluated using these shRNA expressing constructs. Our results revealed that all three siRNAs could downregulate the expression of CANP1. Suppression of CANP1 significantly reduced cell viability in cell proliferation when compared with control cells. We found a crosstalk between CANP1 and caspase systems, particularly suppression of CANP1 resulted in an increase in the expressions of apoptotic caspases such as caspase-3, caspase-6, caspase-7, caspase-8, and caspase-9, as well as heat-shock protein (HSP) systems. Additionally, suppression of CANP1 led to the upregulation of other apoptosis and DNA damage-regulating genes whilst at the same time downregulating proliferation, migration, and differentiation-regulating genes. The results of our findings report for the first time that suppression of CANP1 resulted in the activation of caspase and HSP systems which might in turn regulate apoptosis through the caspase-dependent cell death pathway. This clearly demonstrates the key roles of CANP1 in regulation of cell proliferation and survival.

In vitro silencing of myostatin gene by shRNAs in chicken embryonic myoblast cells

RNA interference represents one of the potential mechanisms of regulation of gene expression. Selective downregulation of myostatin (MSTN), a member of transforming growth factor-β (TGF-β) superfamily and a negative regulator of myogenesis, has been demonstrated to enhance skeletal muscle growth. In this study, we studied short hairpin RNA (shRNA)-induced myostatin gene silencing in chicken embryonic myoblast cells using seven different shRNA-expressing constructs by reverse transcription-quantitative real time PCR (RT-qPCR). Myostatin-silencing efficiency of all shRNA constructs were first evaluated in human embryonic kidney cell line 293T (HEK293T) cells, where we observed 30-75.6% reduction in myostatin expression, followed by chicken embryo myoblast cells that revealed up to 55% reduction in myostatin expression along with upregulation of MyoD by 4.65-folds. Consistent with the earlier observations, the transfection of cells with plasmids led to significant increase in interferon responsive genes OAS1 and IFN β (2-112-folds), independent of myostatin silencing in both HEK293T and chicken embryonic myoblast cells. Our study suggests that apart from shRNA sequences, cell type-specific factors may play a significant role in determining the knockdown efficiency of shRNAs.

Short hairpin RNA-induced myostatin gene silencing in caprine myoblast cells in vitro

Myostatin (MSTN) belongs to the transforming growth factor (TGF)-β superfamily and is a potent negative regulator of skeletal muscle development and growth. Dysfunction of MSTN gene either by natural mutation or induced through genetic manipulation (knockout or knockdown) has been reported to increase the remarkable muscle mass in mammalian species. RNA interference (RNAi) is the most promising method for inhibition of gene expression that can be utilized for MSTN gene knockdown by developing short hairpin RNA (shRNA) construct against it. We utilized three antisense RNA expressing vectors with six constructs to knockdown MSTN gene in in vitro caprine myoblast cell culture system. We observed that all six shRNA constructs were successful in MSTN silencing with efficiency ranging from 7 to 46 % by quantitative real-time PCR and up to 19 % by western blotting. The significant upregulation of interferon response gene OAS1 (5- to 11-fold) in cells transfected with shRNA constructs were indicative of induction of interferon response. This RNAi-based method of increasing muscle mass could provide an alternative strategy to gene knockout methods for improving the production traits and economic properties of livestock.

Evaluation of interferon response induced by anti-myostatin shRNA constructs in goat (Capra hircus) fetal fibroblasts by quantitative real time-polymerase chain reaction

RNAi is an evolutionary conserved, highly efficient, and cost effective technique of gene silencing. It holds considerable promise and success has been achieved both in vitro and in vivo experiments. However, it is not devoid of undesirable side effects as dsRNA can trigger the immune response and can also cause non-specific off-target gene silencing. In the present study, silencing of myostatin gene, a negative regulator of myogenesis, was evaluated in caprine fetal fibroblasts using three different shRNA constructs. Out of these three constructs, two constructs sh1 and sh2 showed, 72% and 50% reduction (p<0.05) of myostatin mRNA, respectively. Efficient suppression (42-86%) of MSTN gene (p<0.05) was achieved even by reducing the concentration of shRNA constructs. The induction of classical interferon stimulated gene (Oligoandenylate Synthetase-1, OAS-1) was studied to analyze the immune response against shRNAs. Notably, a reduction in the potency of shRNAs to induce interferon response was observed at lower concentration for OAS1 gene. The results obtained in the study would be helpful in the abrogation of the bystander effects of RNAi for long term stable expression of anti-MSTN expression constructs in the muscle.

Selection of an effective small interference RNA to silence myostatin gene expression in sheep fibroblast cells

Myostatin (MSTN), a member of the TGF-β superfamily, has been identified as a negative regulator of skeletal muscle mass. Inactivating mutations in the MSTN gene are responsible for the development of a hypermuscular phenotype. The aim of this study was to identify an effective small interfering RNA (siRNA) to knockdown the myostatin gene in sheep fibroblast cells. Four siRNAs targeting sheep myostatin were synthesized and tested. Quantitative RT-PCR showed that siRNA1, siRNA2, siRNA3, and siRNA5 significantly reduced myostatin transcript levels by 72, 68, 56, and 76 % (P < 0.05), respectively. Western blot analysis showed that myostatin protein expression was significantly reduced by 76 % using siRNA1 and by 65 % using siRNA5 (P < 0.05). Therefore, siRNA1 and siRNA5 may have the potential to knockdown myostatin gene expression and increase sheep meat production, which should be a focus of future studies.

Transcript characteristic of myostatin in sheep fibroblasts

Myostatin, a secreted growth factor highly expressed in skeletal muscle, negatively regulates skeletal muscle growth and differentiation. Recently, myostatin is emerged as a potential target for anti-atrophy and anti-fibrotic therapies. Therefore, to investigate the regulation of myostatin in sheep adult fibroblasts, we used the RNA interference mediated by lentiviral vector to gene silence myostatin. Simultaneously, we also had constructed the sheep myostatin overexpression vector to further explore the function of myostatin in fibroblasts. The results here demonstrated that the lentiviral vector could significantly reduce myostatin gene both at mRNA and protein level by 71% and 67%, respectively (P < 0.01). Inhibition of myostatin also resulted in a remarkable increase of activin receptor 2B (ACV2B), p21, PPARγ, leptin, C/EBPβ, and MEF2A expression, and a decrease of Akt1, CDK2, MEF2C, and Myf5 expression. Ectopic myostatin mRNA and protein were also present in the fibroblasts transfection. Furthermore, we observed that overexpression of myostatin contributed to an increase of Akt1, CDK2, Myf5 and PPARγ, and a decrease of p21, C/EBPα and leptin at the transcript level. These results suggested that myostatin positively regulated Akt1, CDK2, Myf5, leptin, and C/EBPα, but negatively regulated p21 mRNA expression in adult fibroblasts, and it also expanded our understanding of the regulation mechanism of myostatin. Moreover, the lentiviral system inactivated myostatin gene in fibroblasts would be used to generate transgenic sheep and to ameliorate muscle fibrosis and atrophy by gene therapy in the future.

Myostatin gene silencing by RNA interference in chicken embryo fibroblast cells

Myostatin (MSTN), a member of transforming growth factor-β (TGF-β) superfamily, is a negative regulator of the skeletal muscle growth, and suppresses the proliferation and differentiation of myoblast cells. Dysfunction of MSTN gene either by natural mutation or genetic manipulation (knockout or knockdown) has been reported to interrupt its proper function and to increase the muscle mass in many mammalian species. RNA interference (RNAi) mediated by small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs) has become a powerful tool for gene knockdown studies. In the present study transient silencing of MSTN gene in chicken embryo fibroblast cells was evaluated using five different shRNA expression constructs. We report here up to 68% silencing of myostatin mRNA using these shRNA constructs in transiently transfected fibroblasts (p<0.05). This was, however, associated with induction of interferon responsive genes (OAS1, IFN-β) (3.7-64 folds; p<0.05). Further work on stable expression of antimyostatin shRNA with minimum interferon induction will be of immense value to increase the muscle mass in the transgenic animals.

Silencing myostatin gene by RNAi in sheep embryos

Myostatin (MSTN) gene is described as a negative regulator of the skeletal muscle growth. Controlling MSTN gene expression by genetic manipulation could accelerate the muscle growth and meat production of livestock animals. In the present study, several siRNAs targeting sheep MSTN gene were designed and their interfering efficiency was evaluated in vitro. The present study showed that one of the siRNAs, PSL1, could down-regulate the expression of MSTN significantly. PSL1 was ligated into lentivirus vector, GP-Supersilencing, to construct a siRNA expression lentivirus vector. Fibroblast cells were infected by lentivirus particles and positive cells were isolated by flow cytometry. Nucleus of the positive cell was transferred into enucleated oocytes of sheep. The present study showed that 99.4% of the sorted cells displayed green fluorescence. After enucleation of oocytes with microinjection, about 20% of reconstructed embryos can be developed into morulas, and strong green fluorescence could be observed using a fluorescence microscope. This method can be available to produce transgenic cell line for somatic cell nucleus transfer for transgenic animals.

Site-directed mutagenesis of the myostatin gene in ovine fetal myoblast cells in vitro

Myostatin is an important negative regulator of muscle growth and development. Natural mutations of the myostatin gene cause a double muscling phenotype in beef cattle, pigs and sheep. Therefore, it is feasible to produce a high growth domestic breed by generating a transgenic animal with a mutation, deletion or knockout of the myostatin gene. Our objective was to introduce a subtle mutation of G to A 281-bp upstream of the 3' untranslated region (3'UTR) end of the myostatin gene in Poll Dorset fetal myoblast cells in vitro. Fetal myoblast cells were isolated from fetuses at day 50 of gestation from Poll Dorset sheep and transfected with linear gene-targeting vector pMSTN-A using electroporation. We obtained seven gene-targeted cell colonies with homologous recombination, which were positive as confirmed by PCR, Southern blot. The Western blot analysis result demonstrated that the myostatin protein expression in positive colonies is lower than that of negative ones. These results strongly suggest that we successfully mutated the myostatin gene of Poll Dorset ovine fetal myoblast cells and the mutation can effectively downregulate the myostatin protein expression.