Research Note: Association of temporal expression of myostatin with hypertrophic muscle growth in different Japanese quail lines

A review of myostatin gene mutations: Enhancing meat production and potential in livestock genetic selection

Myostatin (MSTN) is an essential gene that regulates muscle growth and development in livestock animals, influencing meat production and carcass quality. This review looks at MSTN genetic diversity in a variety of animals, including cattle, sheep, goats, and poultry, focusing on correlations between particular mutations and phenotypic parameters such as muscle mass and growth rate. Mutations in the MSTN gene have been linked to desirable features such as greater body weight and higher meat quality, making it an ideal candidate for genetic selection in breeding programs. Animals carrying this mutation frequently transform feed into muscle more efficiently, resulting in faster growth with less feed input. This is advantageous for growers seeking to cut feed costs while raising yields. MSTN-mutated animals convert feed into muscle more efficiently, lowering production costs over time and making them more appealing for commercial breeding operations. Advances in molecular genetics, especially CRISPR-Cas9 technology, have made it possible to precisely manipulate the MSTN gene, allowing for the development of calves with enhanced muscle mass. This article also examines the effects of MSTN variation on meat production efficiency, as well as current issues in animal genetics. This research synthesis emphasizes the significance of MSTN in cattle breeding, specifically its potential as a genetic marker to improve production and meat quality in commercial farming.

Myostatin gene role in regulating traits of poultry species for potential industrial applications

The myostatin (MSTN) gene is considered a potential genetic marker to improve economically important traits in livestock, since the discovery of its function using the MSTN knockout mice. The anti-myogenic function of the MSTN gene was further demonstrated in farm animal species with natural or induced mutations. In poultry species, myogenesis in cell culture was regulated by modulation of the MSTN gene. Also, different expression levels of the MSTN gene in poultry models with different muscle mass have been reported, indicating the conserved myogenic function of the MSTN gene between mammalian and avian species. Recent advances of CRISPR/Cas9-mediated genome editing techniques have led to development of genome-edited poultry species targeting the MSTN gene to clearly demonstrate its anti-myogenic function and further investigate other potential functions in poultry species. This review summarizes research conducted to understand the function of the MSTN gene in various poultry models from cells to whole organisms. Furthermore, the genome-edited poultry models targeting the MSTN gene are reviewed to integrate diverse effects of the MSTN gene on different traits of poultry species.

Research Note: Growth promoting potential in Mstn mutant quail dependent and independent of increased egg size

In avian species, positive relationships between egg weight (EW) and body weight (BW) have been reported. However, the correlation between the body growth rate and different weights of eggs from genetically mutated avian species was not studied yet. Myostatin (Mstn), an anti-myogenic factor, mutant quail were recently developed, and it was reported that EW produced from Mstn homozygous mutant quail (HO) was heavier compared to those from wild-type quail (WT). In the current study, distributions of pre-incubated EW and associations between EW and BW were compared between the Mstn mutant and WT quail lines. Average egg weight for the HO group was significantly heavier than the WT (P < 0.001) and the number of eggs having heavier EW (over 11 g) was higher in the HO compared to the WT (P < 0.01). BWs at wk (W) 0, 4, and 6 after hatch were also significantly greater in the HO (P < 0.001 in all groups). In addition, linear regression analyses revealed positive relationships between EW and BW from W0 to W6, regardless of sexes and genotypes. Furthermore, Mstn mutant quail were a heavier BW compared to the WT quail originated from eggs with similar weights. These data indicate that increased BW by Mstn mutation is contributed by increased EW and/or growth promoting activity of Mstn mutation independent of increasing egg sizes. These findings provide Mstn as a desirable genetic factor for selection of poultry breeds with superior growth. In addition, the knowledge gained from this study could inspire similar proof-of-concept studies involving standard and commercial lines of poultry.

Transcriptome Response of Differentiating Muscle Satellite Cells to Thermal Challenge in Commercial Turkey

Early muscle development involves the proliferation and differentiation of stem cells (satellite cells, SCs) in the mesoderm to form multinucleated myotubes that mature into muscle fibers and fiber bundles. Proliferation of SCs increases the number of cells available for muscle formation while simultaneously maintaining a population of cells for future response. Differentiation dramatically changes properties of the SCs and environmental stressors can have long lasting effects on muscle growth and physiology. This study was designed to characterize transcriptional changes induced in turkey SCs undergoing differentiation under thermal challenge. Satellite cells from the pectoralis major (p. major) muscle of 1-wk old commercial fast-growing birds (Nicholas turkey, NCT) and from a slower-growing research line (Randombred Control Line 2, RBC2) were proliferated for 72 h at 38 °C and then differentiated for 48 h at 33 °C (cold), 43 °C (hot) or 38 °C (control). Gene expression among thermal treatments and between turkey lines was examined by RNAseq to detect significant differentially expressed genes (DEGs). Cold treatment resulted in significant gene expression changes in the SCs from both turkey lines, with the primary effect being down regulation of the DEGs with overrepresentation of genes involved in regulation of skeletal muscle tissue regeneration and sarcomere organization. Heat stress increased expression of genes reported to regulate myoblast differentiation and survival and to promote cell adhesion particularly in the NCT line. Results suggest that growth selection in turkeys has altered the developmental potential of SCs in commercial birds to increase hypertrophic potential of the p. major muscle and sarcomere assembly. The biology of SCs may account for the distinctly different outcomes in response to thermal challenge on breast muscle growth, development, and structure of the turkey.

Skeletal muscle and metabolic flexibility in response to changing energy demands in wild birds

Phenotypically plastic responses of animals to adjust to environmental variation are pervasive. Reversible plasticity (i.e., phenotypic flexibility), where adult phenotypes can be reversibly altered according to prevailing environmental conditions, allow for better matching of phenotypes to the environment and can generate fitness benefits but may also be associated with costs that trade-off with capacity for flexibility. Here, we review the literature on avian metabolic and muscle plasticity in response to season, temperature, migration and experimental manipulation of flight costs, and employ an integrative approach to explore the phenotypic flexibility of metabolic rates and skeletal muscle in wild birds. Basal (minimum maintenance metabolic rate) and summit (maximum cold-induced metabolic rate) metabolic rates are flexible traits in birds, typically increasing with increasing energy demands. Because skeletal muscles are important for energy use at the organismal level, especially to maximum rates of energy use during exercise or shivering thermogenesis, we consider flexibility of skeletal muscle at the tissue and ultrastructural levels in response to variations in the thermal environment and in workloads due to flight exercise. We also examine two major muscle remodeling regulatory pathways: myostatin and insulin-like growth factor -1 (IGF-1). Changes in myostatin and IGF-1 pathways are sometimes, but not always, regulated in a manner consistent with metabolic rate and muscle mass flexibility in response to changing energy demands in wild birds, but few studies have examined such variation so additional study is needed to fully understand roles for these pathways in regulating metabolic flexibility in birds. Muscle ultrastrutural variation in terms of muscle fiber diameter and associated myonuclear domain (MND) in birds is plastic and highly responsive to thermal variation and increases in workload, however, only a few studies have examined ultrastructural flexibility in avian muscle. Additionally, the relationship between myostatin, IGF-1, and satellite cell (SC) proliferation as it relates to avian muscle flexibility has not been addressed in birds and represents a promising avenue for future study.

Untargeted Metabolomics Reveals the Effect of Selective Breeding on the Quality of Chicken Meat

The selection for improved body weight is an effective approach in animal breeding. Guangxi Partridge chickens have differentiated into two lines under selective breeding, which include line S and line D that have shown statistically significant differences in body weight. However, the meat quality analysis in our study indicated that the quality of breast and thigh muscles in line S chickens changed, which included increased values of L*, b*, and drip loss and decreased a* value, pH, and shear force in skeletal muscles. To illuminate the effect of selection on skeletal muscles, LC-MS/MS metabolomics was performed to explore differentiated metabolites in divergent tissues from the two chicken lines. The results of principal component analysis and orthogonal projection to latent structures discriminant analysis suggested that metabolites of different groups were separated, which suggested that selective breeding certainly affected metabolism of skeletal muscles. KEGG analysis identified that valine, leucine, and isoleucine biosynthesis, glycerophospholipid metabolism, and glutathione metabolism noteworthily changed in breast muscle. Amino sugars and nucleotide sugar metabolism, ascorbate and aldarate metabolism, the pentose phosphate pathway, pentose and glucuronate interconversions, fructose and mannose metabolism, and glycerophospholipid metabolism were remarkedly identified in thigh muscle. These screened pathways suggested oxidative stress in breast and thigh muscles, which corresponded with our previous results. Therefore, this study determined that glycerophospholipid metabolism conservatively functioned in muscle flavor and development but exhibited different anti-oxidative patterns in different skeletal muscles. Overall, the present study identified several differentiated metabolites and pathways for exploring differences in meat quality between different broiler populations.

Differential Expression of MSTN Isoforms in Muscle between Broiler and Layer Chickens

Myostatin (Mstn)-A, the main isoform among Mstn splicing variants, functions as a negative regulator, whereas Mstn-B functions as a positive regulator in muscle development. Because broiler chickens are a fast-growing breed raised for meat production and layer chickens are a slow-growing breed raised for egg production, differences in the expression of Mstn isoforms between the two distinct breeds were analyzed in this study. There was no difference in the expression levels of total Mstn (Mstn-A and -B forms) during embryonic development and at D33 between the two breeds. Interestingly, the ratios of Mstn-B to -A were significantly higher in the broiler compared to the layer at most ages. In pectoralis major muscle (PM) tissue, the cross-sectional area (CSA) of muscle fiber was significantly greater in the broiler. The broiler also showed greater bundle CSA and a similar fiber number per bundle compared to the layer at D5 and D33. These data suggest that the greater bundle CSA with myofiber hypertrophy in the broilers is associated with greater muscle growth. The relationship between the expression of Mstn isoforms and growth rate can be used as a potential genetic marker for the selection of higher muscle growth in chickens.

Research Note: Increased myostatin expression and decreased expression of myogenic regulatory factors in embryonic ages in a quail line with muscle hypoplasia

Genetic selection of quail for a low body weight for more than 80 generations established a low-weight (LW) Japanese quail line that has been previously characterized to have a muscle hypoplasia phenotype. The aim of this study is to investigate the relationship of temporal expression levels of myostatin (Mstn) and myogenic regulatory factors (MRFs) with hypoplastic muscle growth in the LW line. During embryonic day (E) 13 to 15, gain of embryo weight was 2-fold lower (P < 0.001) in the LW line than that in the random bred control (CON). Gains in body weight and pectoralis muscle weight from hatch to posthatch day (P) 28 were also significantly lower (P < 0.01) in the LW line but increased by 4-fold (P < 0.05) during P42 to P75. PCR analysis showed that expression levels of Mstn were greater in the LW at embryonic stage (E12 to E14, P < 0.05), but there was no difference after hatch. In addition, expression levels of Pax7 and myogenin (MyoG) at E12 were 23-fold (P < 0.05) and 3.4-fold (P < 0.05) lesser in the LW line, respectively. At E14, expression of Pax3, Pax7, and MyoG gene was 3.5-fold (P < 0.05), 6.5-fold (P = 0.065), and 4.4-fold (P < 0.01) less than that in the CON. Taken together, high expression levels of Mstn and low expression of MRFs during embryonic stages can be associated with development of muscle hypoplasia and delayed muscle growth in the LW quail line. These data provide evidence that genetic selection for a low body weight resulting in an avian model with muscle hypoplasia has altered the expression profiles of myogenic factors.