Myofiber Differentiation Research Articles

Effect of precursor amino acids for carnosine synthesis on breast fiber microstructures and myofiber differentiation-related gene expression in slow-growing chicken.

: The effects of carnosine synthesis on the structural and microstructural determinants of meat quality have not been studied to date. Therefore, this study aimed to investigate the effect of supplementation with carnosine synthesis precursors on the characteristics and microstructure of breast muscle fibers in slow-growing Korat chickens (KR). : Slow-growing KR were fed a non-supplemented commercial diet (control group) or a commercial diet supplemented with 1.0% β-alanine, 0.5% L-histidine, or a combination of both 1.0% β-alanine and 0.5% L-histidine. At 10 weeks, KR were slaughtered, and the breast muscle was collected. Samples were fixed and extracted to study the microstructure, fat level, and porosity of the meat using X-ray and scanning electron microscopy, and real-time polymerase chain reaction was performed to analyze the expression of genes related to myofiber differentiation. : L-histidine supplementation significantly altered myofiber diameter and muscle fiber density and compactness by regulating muscle fiber-type differentiation via carnosine synthase (CARNS1) and myocyte enhancer factor 2C (MEF2C) expression, as well as myogenic differentiation antigen (MyoD) and myogenic regulatory factor 5 (Myf5) expression. While excess L-histidine potentially stimulated CARNS1 to modify muscle fiber arrangement and tenderness in breast meat, dietary β-alanine supplementation alone or in combination with L-histidine supplementation induced a relatively less remarkable but not significant (p<0.05) effect on the breast meat characteristics studied. : Interestingly, the combination of β-alanine and L-histidine supplementation had no effect on meat microstructure, meat porosity, and fat content in comparison with the control group. Thus, this combination had the best selectivity for improving meat quality. However, further studies are required to clarify the effects of carnosine levels on meat processing.

Integrative metabolomics and transcriptomics analysis revealed specific genes and metabolites affecting meat quality of chickens under different rearing systems

Different rearing systems have varying effect on animal welfare and meat quality of poultry. Currently, there are no established standards for the rearing systems of Chinese indigenous chickens. Our study aimed to investigate the effects of different rearing systems on the meat quality, gene profiles, and metabolites of Chinese indigenous chickens (Nanchuan chicken). 10-wk-old Nanchuan chickens (n=360) were randomly divided into 3 groups (cage, net, and free-range groups), with 6 replicates per group (20 chickens per replicate). The experiment lasted for 12 wk. At 154-days-old, 36 healthy chickens (6 males and 6 females per group) were randomly selected, euthanized, and their breast muscles were collected to assess the meat quality parameters and histomorphological characteristics. Additionally, breast muscles from 18 random hens (3 males and 3 females per group) were used for metabolomics and RNA-seq analysis. The results showed that rearing systems significantly affected the meat quality and myofiber characteristics. The meat quality of breast muscles from free-range chickens was superior to that of caged chickens, characterized by more tender meat and smaller myofiber cross-sectional areas. Integrative metabolomics and transcriptomics analysis revealed that the differentially expressed genes of chicken breast muscles were primarily involved in the myofiber differentiation. Mechanically, the improved meat quality of breast muscle in free-range chickens were mainly associated with enhanced skeletal muscle differentiation facilitated by fibromodulin, increased levels of up-regulated Acetyl-L-carnitine and Propionylcarnitine level, and decreased levels of Nonanoic acid and Elaidic acid abundance (Graphical abstract). This provides a comprehensive understanding of the most effective and sustainable breeding, production, and rearing systems for Chinese indigenous chickens. It also contributes to the current knowledge of the molecular mechanisms underlying the effects of rearing systems on growth performance and meat quality of chickens.

Skeletal muscle regeneration after extensive cryoinjury of caudal myomeres in adult zebrafish

Skeletal muscles can regenerate after minor injuries, but severe structural damage often leads to fibrosis in mammals. Whether adult zebrafish possess the capacity to reproduce profoundly destroyed musculature remains unknown. Here, a new cryoinjury model revealed that several myomeres efficiently regenerated within one month after wounding the zebrafish caudal peduncle. Wound clearance involved accumulation of the selective autophagy receptor p62, an immune response and Collagen XII deposition. New muscle formation was associated with proliferation of Pax7 expressing muscle stem cells, which gave rise to MyoD1 positive myogenic precursors, followed by myofiber differentiation. Monitoring of slow and fast muscles revealed their coordinated replacement in the superficial and profound compartments of the myomere. However, the final boundary between the muscular components was imperfectly recapitulated, allowing myofibers of different identities to intermingle. The replacement of connective with sarcomeric tissues required TOR signaling, as rapamycin treatment impaired new muscle formation, leading to persistent fibrosis. The model of zebrafish myomere restoration may provide new medical perspectives for treatment of traumatic injuries.

Multi-Omics Analysis Reveals the Potential Effects of Maternal Dietary Restriction on Fetal Muscle Growth and Development.

In terms of fetal muscle growth, development, and health, maternal nutrition is a crucial influence, although the exact biochemical mechanism by which this occurs is still not fully understood. To examine the potential impacts of maternal dietary restriction on fetal muscle development, the sheep maternal dietary restriction model was developed for this study. In our study, 12 pregnant ewes were evenly split into two experimental groups and fed either 75% or 100% of a maternal nutrient. In addition, a multi-omics analysis was used to study the embryonic longissimus dorsis on gestational days (GD) 85 and 135. The fetal weight at GD 135 was significantly below normal due to the maternal restricted diet (p < 0.01). When fetuses were exposed to the dietary deficit, 416 mRNAs and 40 proteins were significantly changed. At GD 85, the multi-omics analysis revealed that maternal dietary restriction led to a significant up-regulation of the cell cycle regulator CDK2 gene in the cellular senescence signaling pathway, and the results of the qRT-PCR were similar to the multi-omics analysis, which showed that SIX1, PAX7, the cell cycle factors CDK4 and CDK6, and the BCL-2 apoptosis factor were up-regulated and several skeletal muscle marker genes, such as MYF5 and MyoD were down-regulated. At GD 135, maternal dietary restriction blocks the muscle fiber differentiation and maturation. The multi-omics analysis revealed that the TEAD1 gene was in the Hippo signaling pathway, the muscle marker genes MYF5 and MyoG were significantly down-regulated, and the TEAD1 binding of the down-regulated VGLL3 gene might be potential mechanisms affecting myofiber differentiation and maturation. Knocking down the CDK2 gene could inhibit the proliferation of primary embryonic myoblasts, and the expression levels of cell cycle regulatory factors CDK4 and CDK6 were significantly changed. Under low nutrient culture conditions, the number of myoblasts decreased and the expression of CDK2, CDK6, MYF5, PAX7 and BCL-2 changed, which was in perfect agreement with the multi-omics analysis. All of the findings from our study helped to clarify the potential effects of maternal dietary restriction on fetal muscle growth and development. They also provided a molecular foundation for understanding the molecular regulatory mechanisms of maternal nutrition on fetal muscle growth and development, as well as for the development of new medications and the management of related metabolic diseases.

Integrated multiple-omics reveals the regulatory mechanism underlying the effects of artificial feed and grass feeding on growth and muscle quality of grass carp (Ctenopharyngodon idellus)

The muscle quality of farmed fish has attracted widespread public attention. To understand a comprehensive molecular mechanism underlying the effects of artificial formula feed- (AF) and grass-feeding (GF) on muscle quality and growth of grass carp (Ctenopharyngodon idellus), muscular transcriptomics and proteomics of GF and AF C. idellus were characterized. A total of 834 DEGs (484 up-, 350 down-regulated genes) and 487 DEPs (271 up- and 216 down-regulations) were identified between groups. Then, the functional enrichment analysis of DEGs & DEPs (DEs) and the integration of multiple-Omics (SDFs), further reflected that the stronger myofiber differentiation and protein synthesis capacities are likely the main strategy of more muscle mass gain in AF C. idellus, while the muscle growth in GF C. idellus is consequent to the stronger muscle cell proliferation and hypertrophy. Secondly, there was a significant difference in muscle fiber types between GF and AF groups, this has a noticeable effect on muscle tenderness and quality. In combination with previously metabolic results, we established DEG-DEP-SDM interaction network, which validated that the slow-MyHC-I fiber, dense in AF C. idellus muscles, accumulated more glycogen and exhibited more powerful glycolytic activity. Meanwhile, the suppressed activity of eIF2α in AF C. idellus muscles promoted protein synthesis, the “Ubiquitin mediated proteolysis” was simultaneously restrained. However, the activities of TCA cycle and fatty acid oxidation were significantly enhanced in GF muscles (rich in fast-MyHC-IIb). Accordingly, the up-regulated ACSL1, ACADS, ppara, etc. were quantified in GF C. idellus samples with stronger fatty acids β-oxidation activity, then led to the reduction of cellular triglycerides and lipid droplet formation. Additionally, our results also provide key information for further understanding of the molecular mechanisms (e.g. MAPK and PI3K signaling pathways, Necroptosis and so on) of C. idellus under dietary treatments. In summary, the grass-feeding could effectively alleviate the negative effects of AF on fish, namely, reducing fat deposition, improving nutrients, flavor and texture of muscle, relieving insulin resistance and stress tolerance, finally lead to better nourishing and healthy C. idellus.

BMAL1 drives muscle repair through control of hypoxic NAD+ regeneration in satellite cells.

The process of tissue regeneration occurs in a developmentally timed manner, yet the role of circadian timing is not understood. Here, we identify a role for the adult muscle stem cell (MuSC)-autonomous clock in the control of muscle regeneration following acute ischemic injury. We observed greater muscle repair capacity following injury during the active/wake period as compared with the inactive/rest period in mice, and loss of Bmal1 within MuSCs leads to impaired muscle regeneration. We demonstrate that Bmal1 loss in MuSCs leads to reduced activated MuSC number at day 3 postinjury, indicating a failure to properly expand the myogenic precursor pool. In cultured primary myoblasts, we observed that loss of Bmal1 impairs cell proliferation in hypoxia (a condition that occurs in the first 1-3 d following tissue injury in vivo), as well as subsequent myofiber differentiation. Loss of Bmal1 in both cultured myoblasts and in vivo activated MuSCs leads to reduced glycolysis and premature activation of prodifferentiation gene transcription and epigenetic remodeling. Finally, hypoxic cell proliferation and myofiber formation in Bmal1-deficient myoblasts are restored by increasing cytosolic NAD+ Together, we identify the MuSC clock as a pivotal regulator of oxygen-dependent myoblast cell fate and muscle repair through the control of the NAD+-driven response to injury.

Dyrk1b promotes autophagy during skeletal muscle differentiation by upregulating 4e-bp1

Rare gain of function mutations in the gene encoding Dyrk1b, a key regulator of skeletal muscle differentiation, have been associated with sarcopenic obesity (SO) and metabolic syndrome (MetS) in humans. So far, the global gene networks regulated by Dyrk1b during myofiber differentiation have remained elusive. Here, we have performed untargeted proteomics to determine Dyrk1b-dependent gene-network in differentiated C2C12 myofibers. This analysis led to identification of translational inhibitor, 4e-bp1 as a post-transcriptional target of Dyrk1b in C2C12 cells. Accordingly, CRISPR/Cas9 mediated knockout of Dyrk1b in zebrafish identified 4e-bp1 as a downstream target of Dyrk1b in-vivo. The Dyrk1b knockout zebrafish embryos exhibited markedly reduced myosin heavy chain 1 expression in poorly developed myotomes and were embryonic lethal. Using knockdown and overexpression approaches in C2C12 cells, we found that 4e-bp1 enhances autophagy and mediates the effects of Dyrk1b on skeletal muscle differentiation. Dyrk1bR102C, the human sarcopenic obesity-associated mutation impaired muscle differentiation via excessive activation of 4e-bp1/autophagy axis in C2C12 cells. Strikingly, the defective muscle differentiation in Dyrk1bR102C cells was rescued by reduction of autophagic flux. The identification of Dyrk1b-4e-bp1-autophagy axis provides significant insight into pathways that are relevant to human skeletal muscle development and disorders.

Eccentric Overload during Resistance Exercise: A Stimulus for Enhanced Satellite Cell Activation.

This study aimed to assess if one bout of concentric/eccentric exercise with damaging eccentric overload (CON/ECC+) provides a sufficient stimulus to induce SC activation, proliferation, and differentiation. Biopsies from the vastus lateralis muscle of recreationally active men were obtained in the rested condition and again from the contralateral leg 7 d after exhaustive concentric/eccentric (CON/ECC) (n = 15) or CON/ECC+ (n = 15) leg extension exercise and in a nonexercising control group (CG) (n = 10). Total SC number (Pax7+), activated (Pax7+/MyoD+), and differentiating (myogenin+) SCs, fiber type distribution, and myofibers expressing neonatal myosin heavy chain (MHCneo) were determined immunohistochemically. Creatine kinase and myoglobin were measured in venous blood. Isokinetic strength tests were repeatedly conducted. Significant increases in creatine kinase and myoglobin (P = 0.001) indicated myofiber damage, whereas maximal strength was not impaired. Only after CON/ECC+, SC content (P = 0.019) and SC related to type II fibers (P = 0.011) were significantly increased. A significant increase in the proportion of activated SCs occurred after CON/ECC+ only (P = 0.003), the increase being significantly (P < 0.05) different from the changes after CON/ECC and in CG. The number of differentiating SC and MHCneo remained unchanged. Eccentric overload during leg extension exercise induced significant SC activation, increases in SC content and in SC number related to type II myofibers. However, there were no signs of increased SC differentiation or formation of new myofibers.

Ras/MAPK dysregulation in development causes a skeletal myopathy in an activating BrafL597V mouse model for cardio-facio-cutaneous syndrome.

Cardio-facio-cutaneous (CFC) syndrome is a human multiple congenital anomaly syndrome that is caused by activating heterozygous mutations in either BRAF, MEK1, or MEK2, three protein kinases of the Ras/mitogen-activated protein kinase (MAPK) pathway. CFC belongs to a group of syndromes known as RASopathies. Skeletal muscle hypotonia is a ubiquitous phenotype of RASopathies, especially in CFC syndrome. To better understand the underlying mechanisms for the skeletal myopathy in CFC, a mouse model with an activating BrafL597V allele was utilized. The activating BrafL597V allele resulted in phenotypic alterations in skeletal muscle characterized by a reduction in fiber size which leads to a reduction in muscle size which are functionally weaker. MAPK pathway activation caused inhibition of myofiber differentiation during embryonic myogenesis and global transcriptional dysregulation of developmental pathways. Inhibition in differentiation can be rescued by MEK inhibition. A skeletal myopathy was identified in the CFC BrafL597V mouse validating the use of models to study the effect of Ras/MAPK dysregulation on skeletal myogenesis. RASopathies present a novel opportunity to identify new paradigms of myogenesis and further our understanding of Ras in development. Rescue of the phenotype by inhibitors may help advance the development of therapeutic options for RASopathy patients.

Systemic and Local Phenotypes of Barium Chloride Induced Skeletal Muscle Injury in Mice.

Skeletal muscle regeneration in mice has traditionally been studied using local freeze burn or snake venom injection models. More recently, a barium chloride (BaCl2)-induced muscle injury model has been established and is gaining popularity due to the relatively simple procedure and accessibility to required reagents. Here we sought to characterize the local and systemic effects of BaCl2-induced muscle injury. For this study, a 1.2% BaCl2 solution was locally administered to the tibialis anterior (TA) muscle and local and systemic phenotypes were analyzed at different timepoints. When 50 μL of the solution was injected unilaterally in the TA muscle, no mortality was observed. However, when 100 μL of the solution was injected, 50% of the mice died within 24 h. Serum analysis of the mice injected with 50 μL of BaCl2 solution at days 1 and 7 revealed changes resembling rhabdomyolysis. At day 1 post-injection of 50 μL of the BaCl2 solution, acute suppurative inflammation was observed in gross examination of the TA muscle, while extensive hemorrhagic necrosis was revealed on histological examination. At day 7, regenerated myofibers with centralized nuclei appeared with the resolution of acute inflammatory infiltration and the muscle tissue displayed molecular signatures consistent with myofiber differentiation. The overall muscle injury and regeneration phenotypes in the BaCl2-induced muscle injury model were similar to those of the well-established freeze burn or snake venom injection models. Taken together, the BaCl2-induced muscle injury model is comparable to conventional muscle injury and regeneration models, with considerations for possible systemic effects.

Differential Transcriptome Analysis of Early Postnatal Developing Longissimus Dorsi Muscle from Two Pig Breeds Characterized in Divergent Myofiber Traits and Fatness

ABSTRACTMeat quality traits (MQTs) are very important in the porcine industry, which are mainly determined by skeletal muscle fiber composition, extra-muscular and/or intramuscular fat content. To identify the differentially expressed candidate genes affecting the meat quality traits, first we compared the MQTs and skeletal muscle fiber characteristics in the longissimus dorsi muscle (LDM) of the Northeast Min pig (NM) and the Changbaishan wild boar (CW) with their body weight approaching 90 kg. The significant divergences in the skeletal muscle fiber phenotypes and fatness traits between the two porcine breeds established an ideal model system for further identifying potential key functional genes that dominated MQTs. Further, a transcriptome profile analysis was performed using the Illumina sequencing method in early postnatal developing LDM from the two breeds at the ages of 42 days. Comparative analysis between these two cDNA libraries showed that there were 17,653 and 22,049 unambiguous tag-mapped sense transcripts detected from NM and CW, respectively. 4522 differentially expressed genes (DEGs) were revealed between the two tissue samples, of them, 4176 genes were found as having been upregulated and 346 genes were identified as having been downregulated in the NM library. By pathway enrichment analysis, a set of significantly enriched pathways were identified for the DEGs, which are potentially involved in myofiber development, differentiation and growth, lipogenesis and lipolysis in porcine skeletal muscle. The expression levels of 30 out of the DEGs were validated by real-time quantitative reverse transcriptase PCR (qRT-PCR) and the observed result was consistent noticeably with the Illumina transcriptome profiles. The findings from this study can contribute to future investigations of skeletal muscle growth and development mechanism and to establishing molecular approaches to improve meat quality traits in pig breeding.

ATP Citrate Lyase Regulates Myofiber Differentiation and Increases Regeneration by Altering Histone Acetylation

ATP citrate lyase (ACL) plays a key role in regulating mitochondrial function, as well as glucose and lipid metabolism in skeletal muscle. We report here that ACL silencing impairs myoblast and satellite cell (SC) differentiation, and it is accompanied by a decrease in fast myosin heavy chain isoforms and MYOD. Conversely, overexpression of ACL enhances MYOD levels and promotes myogenesis. Myogenesis is dependent on transcriptional but also other mechanisms. We show that ACL regulates the net amount of acetyl groups available, leading to alterations in acetylation of H3(K9/14) and H3(K27) at the MYOD locus, thus increasing MYOD expression. ACL overexpression in murine skeletal muscle leads to improved regeneration after cardiotoxin-mediated damage. Thus, our findings suggest a mechanism forregulating SC differentiation and enhancing regeneration, which might be exploited for devising therapeutic approaches for treating skeletal muscle disease.

Exposure to microgravity for 30 days onboard Bion M1 caused muscle atrophy and impaired regeneration in murine femoral Quadriceps

Mechanical unloading in microgravity during spaceflight is known to cause muscular atrophy, changes in muscle fiber composition, gene expression, and reduction in regenerative muscle growth. Although some limited data exists for long-term effects of microgravity in human muscle, these processes have mostly been studied in rodents for short periods of time. Here we report on how long-term (30-day long) mechanical unloading in microgravity affects murine muscles of the femoral Quadriceps group. To conduct these studies we used muscle tissue from 6 microgravity mice, in comparison to habitat (7), and vivarium (14) ground control mice from the NASA Biospecimen Sharing Program conducted in collaboration with the Institute for Biomedical Problems of the Russian Academy of Sciences, during the Russian Bion M1 biosatellite mission in 2013. Muscle histomorphology from microgravity specimens showed signs of extensive atrophy and regenerative hypoplasia relative to ground controls. Specifically, we observed a two-fold decrease in the number of myonuclei, compared to vivarium and ground controls, and central location of myonuclei, low density of myofibers in the tissue, and of myofibrils within a fiber, as well as fragmentation and swelling of myofibers. Despite obvious atrophy, muscle regeneration nevertheless appeared to have continued after 30 days in microgravity as evidenced by thin and short newly formed myofibers. Many of them, however, showed evidence of apoptotic cells and myofibril degradation, suggesting that long-term unloading in microgravity may affect late stages of myofiber differentiation. Ground asynchronous and vivarium control animals demonstrated normal, well-developed tissue structure with sufficient blood and nerve supply and evidence of regenerative formation of new myofibers free of apoptotic nuclei. Regenerative activity of satellite cells in muscles was observed both in microgravity and ground control groups, using Pax7 and Myogenin immunolocalization, as well as Myogenin expression analysis. In addition, we have detected positive nuclear immunolocalization of c-Jun and c-Myc proteins indicating their sensitivity to changes in gravitational loading in a given model. In summary, long-term spaceflight in microgravity caused significant atrophy and degeneration of the femoral Quadriceps muscle group, and it may interfere with muscle regenerative processes by inducing apoptosis in newly-formed myofibrils during their differentiation phase.

Divergent Roles of IRS (Insulin Receptor Substrate) 1 and 2 in Liver and Skeletal Muscle

IRS1 and IRS2 are the most important representatives of the IRS protein family and critical nodes in insulin/IGF1-signaling. Although they are quite similar in their structural and functional features they show tissue-specific differences. In this review, we outline the functions of IRS1 and IRS2 in skeletal muscle and liver with regard to their importance for metabolism, growth and differentiation. Mechanisms contributing to IRS1 and IRS2 dysregulation in disease states as well as consequences thereof are discussed. IRS1 plays the dominant role in skeletal muscle. It is crucial for normal growth and differentiation of myofibers, insulin-dependent glucose uptake and glycogen synthesis. The presence of IRS2 in skeletal muscle is negligible for insulin-induced glucose uptake and the general role of IRS2 in muscle is still not fully understood. In liver IRS1 and IRS2 are important to mediate insulindependent regulation of glucose and lipid metabolism and complement each other in the diurnal regulation thereof. IRS1 in the liver is more important for signaling in the late refeeding period, whereas IRS2 signaling is mostly dominating in the period directly after food intake and during fasting. Importantly, the expression level of IRS1 and IRS2 is different within the liver lobule, which could be an explanation for the phenomenon of selective insulin resistance. Dysregulated muscular or hepatic abundance and/or phosphorylation status of IRS1 and IRS2 are important factors in the pathogenesis of insulin resistance, type 2 diabetes and muscle wasting.

Identification of the essential protein domains for Mib2 function during the development of the Drosophila larval musculature and adult flight muscles.

The proper differentiation and maintenance of myofibers is fundamental to a functional musculature. Disruption of numerous mostly structural factors leads to perturbations of these processes. Among the limited number of known regulatory factors for these processes is Mind bomb2 (Mib2), a muscle-associated E3 ubiquitin ligase, which was previously established to be required for maintaining the integrity of larval muscles. In this study, we have examined the mechanistic aspects of Mib2 function by performing a detailed functional dissection of the Mib2 protein. We show that the ankyrin repeats, in its entirety, and the hitherto uncharacterized Mib-specific domains (MIB), are important for the major function of Mib2 in skeletal and visceral muscles in the Drosophila embryo. Furthermore, we characterize novel mib2 alleles that have arisen from a forward genetic screen aimed at identifying regulators of myogenesis. Two of these alleles are viable, but flightless hypomorphic mib2 mutants, and harbor missense mutations in the MIB domain and RING finger, respectively. Functional analysis of these new alleles, including in vivo imaging, demonstrates that Mib2 plays an additional important role in the development of adult thorax muscles, particularly in maintaining the larval templates for the dorsal longitudinal indirect flight muscles during metamorphosis.

Mouse myofibers lacking the SMYD1 methyltransferase are susceptible to atrophy, internalization of nuclei and myofibrillar disarray.

ABSTRACTThe Smyd1 gene encodes a lysine methyltransferase specifically expressed in striated muscle. Because Smyd1-null mouse embryos die from heart malformation prior to formation of skeletal muscle, we developed a Smyd1 conditional-knockout allele to determine the consequence of SMYD1 loss in mammalian skeletal muscle. Ablation of SMYD1 specifically in skeletal myocytes after myofiber differentiation using Myf6cre produced a non-degenerative myopathy. Mutant mice exhibited weakness, myofiber hypotrophy, prevalence of oxidative myofibers, reduction in triad numbers, regional myofibrillar disorganization/breakdown and a high percentage of myofibers with centralized nuclei. Notably, we found broad upregulation of muscle development genes in the absence of regenerating or degenerating myofibers. These data suggest that the afflicted fibers are in a continual state of repair in an attempt to restore damaged myofibrils. Disease severity was greater for males than females. Despite equivalent expression in all fiber types, loss of SMYD1 primarily affected fast-twitch muscle, illustrating fiber-type-specific functions for SMYD1. This work illustrates a crucial role for SMYD1 in skeletal muscle physiology and myofibril integrity.

Muscle composition is regulated by a Lox-TGFβ feedback loop

Muscle is an integrated tissue composed of distinct cell types and extracellular matrix. While much emphasis has been placed on the factors required for the specification of the cells that comprise muscle, little is known about the crosstalk between them that enables the development of a patterned and functional tissue. We find in mice that deletion of lysyl oxidase (Lox), an extracellular enzyme regulating collagen maturation and organization, uncouples the balance between the amount of myofibers and that of muscle connective tissue (MCT). We show that Lox secreted from the myofibers attenuates TGFβ signaling, an inhibitor of myofiber differentiation and promoter of MCT development. We further demonstrate that a TGFβ-Lox feedback loop between the MCT and myofibers maintains the dynamic developmental homeostasis between muscle components while also regulating MCT organization. Our results allow a better understanding of diseases such as Duchenne muscular dystrophy, in which LOX and TGFβ signaling have been implicated and the balance between muscle constituents is disturbed.

Muscle composition is regulated by a Lox-TGFβ feedback loop.

Muscle is an integrated tissue composed of distinct cell types and extracellular matrix. While much emphasis has been placed on the factors required for the specification of the cells that comprise muscle, little is known about the crosstalk between them that enables the development of a patterned and functional tissue. We find in mice that deletion of lysyl oxidase (Lox), an extracellular enzyme regulating collagen maturation and organization, uncouples the balance between the amount of myofibers and that of muscle connective tissue (MCT). We show that Lox secreted from the myofibers attenuates TGFβ signaling, an inhibitor of myofiber differentiation and promoter of MCT development. We further demonstrate that a TGFβ-Lox feedback loop between the MCT and myofibers maintains the dynamic developmental homeostasis between muscle components while also regulating MCT organization. Our results allow a better understanding of diseases such as Duchenne muscular dystrophy, in which LOX and TGFβ signaling have been implicated and the balance between muscle constituents is disturbed.

Periostin is temporally expressed as an extracellular matrix component in skeletal muscle regeneration and differentiation

The transcriptional events and pathways responsible for the acquisition of the myogenic phenotype during regeneration and myogenesis have been studied extensively. The modulators that shape the extracellular matrix in health and disease, however, are less understood. Understanding the components and pathways of this remodeling will aid the restoration of the architecture and prevent deterioration under pathological conditions such as fibrosis. Periostin, a matricellular protein associated with remodeling of the extracellular matrix and connective tissue architecture, is emerging in pathological conditions associated with fibrosis in adult life. Periostin also complicates fibrosis in degenerative skeletal muscle conditions such as dystrophies. This study primarily addresses the spatial and temporal involvement of periostin along skeletal muscle regeneration. In the acute skeletal muscle injury model that shows recovery without fibrosis, we show that periostin is rapidly disrupted along with the extensive necrosis and periostin mRNA is transiently upregulated during the myotube maturation. This expression is stringently initiated from the newly regenerating fibers. However, this observation is contrasting to a model that displays extensive fibrosis where upregulation of periostin expression is stable and confined to the fibrotic compartments of endomysial and perimysial space. In vitro myoblast differentiation further supports the claim that upregulation of periostin expression is a function of extracellular matrix remodeling during myofiber differentiation and maturation. We further seek to identify the expression kinetics of various periostin isoforms during the differentiation of rat and mouse myoblasts. Results depict that a singular periostin isoform dominated the rat muscle, contrasting to multiple isoforms in C2C12 myoblast cells. This study shows that periostin, a mediator with deleterious impact on conditions exhibiting fibrosis, is also produced and secreted by myoblasts and regenerating myofibers during architectural remodeling in the course of development and regeneration.

Expression, SNV identification, linkage disequilibrium, and combined genotype association analysis of the muscle-specific gene CSRP3 in Chinese cattle

The cysteine and glycine-rich protein 3 (CSRP3) plays an important role in the myofiber differentiation. Here, we identified five SNVs in all exon and intron regions of the CSRP3 gene using DNA sequencing, PCR-RFLP and forced-PCR-RFLP methods in 554 cattle. Four of the five SNVs were significantly associated with growth performance and carcass traits of the cattle. In addition, we evaluated haplotype frequency and linkage disequilibrium coefficient of five sequence variants. The result of haplotype analysis demonstrated 28 haplotypes present in Qinchuan and two haplotypes in Chinese Holstein. Only haplotypes 1 and 8 were being shared by two populations, haplotype 14 had the highest haplotype frequency in Qinchuan (17.4%) and haplotype 8 had the highest haplotype frequency in Chinese Holstein (94.4%). Statistical analyses of combined genotypes indicated that some combined genotypes were significantly or highly significantly associated with growth and carcass traits in the Qinchuan cattle population. qPCR analyses also showed that bovine CSRP3 gene was exclusively expressed in longissimus dorsi muscle and heart tissues. The data support the high potential of the CSRP3 as a marker gene for the improvement of growth performance and carcass traits in selection programs.