Functional Non-coding RNA During Embryonic Myogenesis and Postnatal Muscle Development and Disease

Acetate Alleviates Gut Microbiota Depletion-Induced Retardation of Skeletal Muscle Growth and Development in Young Mice

The normal growth and development of skeletal muscle is essential for the health of the body. The regulation of skeletal muscle by intestinal microorganisms and their metabolites has been continuously demonstrated. Acetate is the predominant short-chain fatty acids synthesized by gut microbiota through the fermentation of dietary fiber; however, the underlying molecular mechanisms governing the interaction between acetate and skeletal muscle during the rapid growth stage remains to be further elucidated. Herein, specific pathogen-free (SPF) mice, germ-free (GF) mice, and germ-free mice supplemented with sodium acetate (GS) were used to evaluate the effects of acetate on the skeletal muscle growth and development of young mice with gut microbiota deficiency. We found that the concentration of serum acetate, body mass gain, succinate dehydrogenase activity, and expression of the myogenesis maker gene of skeletal muscle in the GS group were higher than those in the GF group, following sodium acetate supplementation. Furthermore, the transcriptome analysis revealed that acetate activated the biological processes that regulate skeletal muscle growth and development in the GF group, which are otherwise inhibited due to a gut microbiota deficiency. The in vitro experiment showed that acetate up-regulated Gm16062 to promote skeletal muscle cell differentiation. Overall, our findings proved that acetate promotes skeletal muscle growth and development in young mice via increasing Gm16062 expression.

circUBE3C modulates myoblast development by binding to miR-191 and upregulating the expression of p27

Noncoding RNAs, including miRNAs (microRNAs) and circRNAs (circular RNA), are crucial regulators of myoblast proliferation and differentiation during muscle development. However, the specific roles and molecular mechanisms of circRNAs in muscle development remain poorly understood. Based on the existing circRNA-miRNA-mRNA network, our study focuses on circUBE3C, exploring its differential expression in fetal and adult muscle tissue of the cattle and investigating its impact on myoblast proliferation, apoptosis, and differentiation. The functional analysis of overexpression plasmids and siRNAs (small interfering RNAs) targeting circUBE3C was comprehensively evaluated by employing an array of advanced assays, encompassing CCK-8 (cell counting kit-8), EdU (5-ethynyl-20-deoxyuridine), flow cytometry, western blot analysis, and RT-qPCR. In vivo investigations indicated that overexpression of circUBE3C impedes the process of skeletal muscle regeneration. Mechanistically, we demonstrated that circUBE3C interacts with miR-191 and alleviates the suppression of p27 through cytoplasmic separation, bioinformatics prediction, dual-luciferase reporter assay, and RIP (RNA immunoprecipitation). Our findings indicate that the novel circRNA circUBE3C competitively binds to miR-191, thereby inhibiting proliferation and promoting apoptosis in bovine primary myoblasts and unveiling a regulatory pathway in bovine skeletal muscle development. These findings expand our understanding of circRNA functions in mammals and provide a basis for further exploration of their role in myogenesis and muscle diseases.

Functional SNPs in SYISL promoter significantly affect muscle fiber density and muscle traits in pigs

Our previous studies showed that SYISL is a negative regulator of muscle growth and regeneration in mice, pigs and humans. SYISL knockout resulted in an increase in the density of muscle fibers and muscle growth. However, it is unclear whether there are natural mutations in pig SYNPO2 intron sense-overlapping lncRNA (pSYISL) that affect the expression of pSYISL and muscle growth traits. In this study, three SNPs in exons and six SNPs within the promoter of pSYISL were identified. Association analysis showed that the two SNPs in exons are significantly associated with loin muscle area (p < 0.05); the six SNPs in the promoter that show complete linkage are significantly associated with live backfat thickness and live loin muscle area in American Large White pigs. Bioinformatics and luciferase reporter assays as well as in vitro binding experiments indicated that the mutation of SNP rs702045770 (g.539G>A) leads to the loss of YY1 binding to the promoter, thus affecting the expression level of pSYISL, and we found that Jiangshan Black pigs with genotype GG have a higher expression level of pSYISL than genotype AA individuals, but the muscle fiber density was significantly lower than in genotype AA individuals. Furthermore, the association analysis showed that the carcass backfat thickness of genotype GG of SNP rs702045770 was significantly higher than that of other genotypes in (Pietrain × Duroc) × (Landrace × Yorkshire) crossbred pigs (p < 0.05). The glycolytic potential of genotype GG was significantly higher than that of other genotypes (p < 0.05). These results provide novel insight into the identification of functional SNPs in non-coding genomic regions.

Considerations for enhanced mesenchymal stromal/stem cell myogenic commitment in vitro

The generation of tissue from stem cells is an alluring concept as it holds a number of potential applications in clinical therapeutics and regenerative medicine. Mesenchymal stromal/stem cells (MSCs) can be isolated from a number of different somatic sources, and have the capacity to differentiate into adipogenic, osteogenic, chondrogenic, and myogenic lineages. Although the first three have been extensively investigated, there remains a paucity of literature on the latter. This review looks at the various strategies available in vitro to enhance harvested MSC commitment and differentiation into the myogenic pathway. These include chemical inducers, myogenic-enhancing cell culture substrates, and mechanical and dynamic culturing conditions. Drawing on information from embryonic and postnatal myogenesis from somites, satellite, and myogenic progenitor cells, the mechanisms behind the chemical and mechanical induction strategies can be studied, and the sequential gene and signaling cascades can be used to monitor the progression of myogenic differentiation in the laboratory. Increased understanding of the stimuli and signaling mechanisms in the initial stages of MSC myogenic commitment will provide tools with which we can enhance their differentiation efficacy and advance the process to clinical translation.

Interaction between Rumen Epithelial miRNAs-Microbiota-Metabolites in Response to Cold-Season Nutritional Stress in Tibetan Sheep

Tibetan sheep are already well adapted to cold season nutrient stress on the Tibetan Plateau. Rumen, an important nutrient for metabolism and as an absorption organ in ruminants, plays a vital role in the cold stress adaptations of Tibetan sheep. Ruminal microbiota also plays an indispensable role in rumen function. In this study, combined multiomics data were utilized to comprehensively analyze the interaction mechanism between rumen epithelial miRNAs and microbiota and their metabolites in Tibetan sheep under nutrient stress in the cold season. A total of 949 miRNAs were identified in the rumen epithelium of both cold and warm seasons. A total of 62 differentially expressed (DE) miRNAs were screened using FC > 1.5 and p value < 0.01, and a total of 20,206 targeted genes were predicted by DE miRNAs. KEGG enrichment analysis revealed that DE miRNA-targeted genes were mainly enriched in axon guidance(ko04360), tight junction(ko04530), inflammatory mediator regulation of TRP channels(ko04750) and metabolism-related pathways. Correlation analysis revealed that rumen microbiota, rumen VFAs and DE miRNAs were all correlated. Further study revealed that the targeted genes of cold and warm season rumen epithelial DE miRNAs were coenriched with differential metabolites of microbiota in glycerophospholipid metabolism (ko00564), apoptosis (ko04210), inflammatory mediator regulation of TRP channels (ko04750), small cell lung cancer (ko05222), and choline metabolism in cancer (ko05231) pathways. There are several interactions between Tibetan sheep rumen epithelial miRNAs, rumen microbiota, and microbial metabolites, mainly through maintaining rumen epithelial barrier function and host homeostasis of choline and cholesterol, improving host immunity, and promoting energy metabolism pathways, thus enabling Tibetan sheep to effectively respond to cold season nutrient stress. The results also suggest that rumen microbiota have coevolved with their hosts to improve the adaptive capacity of Tibetan sheep to cold season nutrient stress, providing a new perspective for the study of cold season nutritional stress adaptation in Tibetan sheep.

MicroRNA-668-3p inhibits myoblast proliferation and differentiation by targeting Appl1

BACKGROUND

Skeletal muscle is the largest tissue in the body, and it affects motion, metabolism and homeostasis. Skeletal muscle development comprises myoblast proliferation, fusion and differentiation to form myotubes, which subsequently form mature muscle fibres. This process is strictly regulated by a series of molecular networks. Increasing evidence has shown that noncoding RNAs, especially microRNAs (miRNAs), play vital roles in regulating skeletal muscle growth. Here, we showed that miR-668-3p is highly expressed in skeletal muscle.

METHODS

Proliferating and differentiated C2C12 cells were transfected with miR-668-3p mimics and/or inhibitor, and the mRNA and protein levels of its target gene were evaluated by RT‒qPCR and Western blotting analysis. The targeting of Appl1 by miR-668-3p was confirmed by dual luciferase assay. The interdependence of miR-668-3p and Appl1 was verified by cotransfection of C2C12 cells.

RESULTS

Our data reveal that miR-668-3p can inhibit myoblast proliferation and myogenic differentiation. Phosphotyrosine interacting with PH domain and leucine zipper 1 (Appl1) is a target gene of miR-668-3p, and it can promote myoblast proliferation and differentiation by activating the p38 MAPK pathway. Furthermore, the inhibitory effect of miR-668-3p on myoblast cell proliferation and myogenic differentiation could be rescued by Appl1.

CONCLUSION

Our results indicate a new mechanism by which the miR-668-3p/Appl1/p38 MAPK pathway regulates skeletal muscle development.

Transcriptome sequencing reveals the effects of circRNA on testicular development and spermatogenesis in Qianbei Ma goats

Circular RNAs (circRNAs) play an important role in regulating the mammalian reproductive system, especially testicular development and spermatogenesis. However, their functions in testicular development and spermatogenesis in the Qianbei Ma goat, the Guizhou endemic breed are still unclear. In this study, tissue sectioning and circRNAs transcriptome analysis were conducted to compare the changes of morphology and circular RNAs gene expression profile at four different developmental stages (0Y, 0-month-old; 6Y, 6-month-old; 12Y, 12-month-old; 18Y, 18-month-old). The results showed that the circumferences and area of the seminiferous tubule gradually increased with age, and the lumen of the seminiferous tubule in the testis differentiated significantly. 12,784 circRNAs were detected from testicular tissues at four different developmental stages by RNA sequencing, and 8,140 DEcircRNAs (differentially expressed circRNAs) were found in 0Y vs. 6Y, 6Y vs. 12Y, 12Y vs. 18Y and 0Y vs. 18Y, 0Y vs. 12Y, 6Y vs. 18Y Functional enrichment analysis of the source genes showed that they were mainly enriched in testicular development and spermatogenesis. In addition, the miRNAs and mRNAs associated with DECircRNAs in 6 control groups were predicted by bioinformatics, and 81 highly expressed DECircRNAs and their associated miRNAs and mRNAs were selected to construct the ceRNA network. Through functional enrichment analysis of the target genes of circRNAs in the network, some candidate circRNAs related to testicular development and spermatogenesis were obtained. Such as circRNA_07172, circRNA_04859, circRNA_07832, circRNA_00032 and circRNA_07510. These results will help to reveal the mechanism of circRNAs in testicular development and spermatogenesis, and also provide some guidance for goat reproduction.

DNA Methylation Analysis Reveals Distinct Patterns in Satellite Cell-Derived Myogenic Progenitor Cells of Subjects with Spastic Cerebral Palsy

Spastic type cerebral palsy (CP) is a complex neuromuscular disorder that involves altered skeletal muscle microanatomy and growth, but little is known about the mechanisms contributing to muscle pathophysiology and dysfunction. Traditional genomic approaches have provided limited insight regarding disease onset and severity, but recent epigenomic studies indicate that DNA methylation patterns can be altered in CP. Here, we examined whether a diagnosis of spastic CP is associated with intrinsic DNA methylation differences in myoblasts and myotubes derived from muscle resident stem cell populations (satellite cells; SCs). Twelve subjects were enrolled (6 CP; 6 control) with informed consent/assent. Skeletal muscle biopsies were obtained during orthopedic surgeries, and SCs were isolated and cultured to establish patient-specific myoblast cell lines capable of proliferation and differentiation in culture. DNA methylation analyses indicated significant differences at 525 individual CpG sites in proliferating SC-derived myoblasts (MB) and 1774 CpG sites in differentiating SC-derived myotubes (MT). Of these, 79 CpG sites were common in both culture types. The distribution of differentially methylated 1 Mbp chromosomal segments indicated distinct regional hypo- and hyper-methylation patterns, and significant enrichment of differentially methylated sites on chromosomes 12, 13, 14, 15, 18, and 20. Average methylation load across 2000 bp regions flanking transcriptional start sites was significantly different in 3 genes in MBs, and 10 genes in MTs. SC derived MBs isolated from study participants with spastic CP exhibited fundamental differences in DNA methylation compared to controls at multiple levels of organization that may reveal new targets for studies of mechanisms contributing to muscle dysregulation in spastic CP.

Impact of fetal exposure to mycotoxins on longissimus muscle fiber hypertrophy and miRNA profile

BACKGROUND

Longissimus muscle samples were collected from lambs exposed in utero to mycotoxins [E-, endophyte-free tall fescue seed without ergot alkaloids (negative control) or E + , endophyte-infected tall fescue seed containing ergot alkaloids] during mid-gestation (MID; E + /E-) or late-gestation (LATE; E-/E +) harvested at two developmental stages (FETAL, gestational d133) or (MAT, near maturity, 250 d of age; n = 3/treatment/developmental stage). Muscle samples were examined to determine the impact of in utero mycotoxin exposure on skeletal muscle fiber hypertrophy and the miRNA profile at FETAL and MAT.

RESULTS

Longissimus weight was greater (P < 0.05) in E + /E- lambs compared to E-/E + lambs at MAT; however, FETAL longissimus weight did not differ (P > 0.10) between fescue treatments. Type I fiber cross sectional area was larger (P < 0.10) for E + /E- than E-/E + at MAT but did not differ (P > 0.10) between fescue treatments at FETAL. Type II fiber area was larger (P < 0.05) at MAT in E + /E- compared to E-/E + but did not differ (P < 0.05) between fescue treatments at FETAL. Cross-sectional Type I and Type II longissimus muscle fiber area increased (P < 0.05) from FETAL to MAT by 6.86-fold and 10.83-fold, respectively. The ratio of Type II:Type I muscle fibers was lower (P = 0.04) at MAT compared to FETAL. There were 120 miRNA differentially expressed (q < 0.05) between FETAL and MAT. Maternal fescue treatment did not alter (q > 0.05) expression of miRNAs in the longissimus muscle. miR-133, -29a, -22-3p, and -410-3p were identified as highly significant with a log₂ fold change > 4. In vitro satellite cell cultures showed that selected miRNAs (miR-22-3p, 29a, 27a, and 133a) are differentially regulated during proliferation and differentiation indicating a role of miRNA in muscle hypertrophy.

CONCLUSIONS

Exposure to mycotoxins did not alter fiber type but had long-term impacts on postnatal muscle hypertrophy and cross-sectional area. The miRNA profile of the longissimus was not altered by Maternal mycotoxin exposure at FETAL or MAT. Developmental age altered the miRNA transcriptome and mRNA expression of known genes related to muscle growth. These results indicate that Maternal exposure to E + fescue seed during LATE gestation can alter postnatal muscle hypertrophy in sheep; however, these changes are not regulated by the miRNA transcriptome of the longissimus muscle.

Long non-coding RNA Gm10561 promotes myogenesis by sponging miR-432

Skeletal myogenesis is a highly ordered process finely regulated by various factors. Long non-coding RNAs play an important regulatory role in myogenesis via multiple mechanisms. In this study, we identified the lncRNA Gm10561, which was upregulated during myogenic differentiation and is highly expressed in skeletal muscle. Knockdown of Gm10561 inhibited the proliferation and differentiation of C2C12 myoblasts in vitro and muscle growth in vivo. Overexpression of Gm10561 promoted the proliferation and differentiation of both C2C12 myoblasts and porcine muscle satellite cells. Notably, lncRNA Gm10561 is localized in the cytoplasm and competitively bound to miR-432, which directly targets MEF2C and E2F3. It was confirmed that lncRNA Gm10561 regulates the proliferation and differentiation of myoblasts by acting as a sponge of miR-432 to modulate MEF2C and E2F3 expression. Thus, the lncRNA-Gm10561-miR-432-MEF2C/E2F3 axis plays an important role in myogenesis.

LncRNA OIP5-AS1-directed miR-7 degradation promotes MYMX production during human myogenesis

Long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) modulate gene expression programs in physiology and disease. Here, we report a noncoding RNA regulatory network that modulates myoblast fusion into multinucleated myotubes, a process that occurs during muscle development and muscle regeneration after injury. In early stages of human myogenesis, the levels of lncRNA OIP5-AS1 increased, while the levels of miR-7 decreased. Moreover, OIP5-AS1 bound and induced miR-7 decay via target RNA-directed miRNA decay; accordingly, loss of OIP5-AS1 attenuated, while antagonizing miR-7 accelerated, myotube formation. We found that the OIP5-AS1-mediated miR-7 degradation promoted myoblast fusion, as it derepressed the miR-7 target MYMX mRNA, which encodes the fusogenic protein myomixer (MYMX). Remarkably, an oligonucleotide site blocker interfered with the OIP5-AS1-directed miR-7 degradation, allowing miR-7 to accumulate, lowering MYMX production and suppressing myotube formation. These results highlight a mechanism whereby lncRNA OIP5-AS1-mediated miR-7 decay promotes myotube formation by stimulating a myogenic fusion program.

The Targeting of Noncoding RNAs by Quercetin in Cancer Prevention and Therapy

The dietary flavonoid quercetin is ubiquitously distributed in fruits, vegetables, and medicinal herbs. Quercetin has been a focal point in recent years due to its versatile health-promoting benefits and high pharmacological values. It has well documented that quercetin exerts anticancer actions by inhibiting cell proliferation, inducing apoptosis, and retarding the invasion and metastasis of cancer cells. However, the exact mechanism of quercetin-mediated cancer chemoprevention is still not fully understood. With the advances in high-throughput sequencing technologies, the intricate oncogenic signaling networks have been gradually characterized. Increasing evidence on the close association between noncoding RNA (ncRNAs) and cancer etiopathogenesis emphasizes the potential of ncRNAs as promising molecular targets for cancer treatment. Available experimental studies indicate that quercetin can dominate multiple cancer-associated ncRNAs, hence repressing carcinogenesis and cancer development. Thus, modulation of ncRNAs serves as a key mechanism responsible for the anticancer effects of quercetin. In this review, we focus on the chemopreventive effects of quercetin on cancer pathogenesis by targeting cancer-relevant ncRNAs, supporting the viewpoint that quercetin holds promise as a drug candidate for cancer chemoprevention and chemotherapy. An in-depth comprehension of the interplay between quercetin and ncRNAs in the inhibition of cancer development and progression will raise the possibility of developing this bioactive compound as an anticancer agent that could be highly efficacious and safe in clinical practice.

Long noncoding RNA ZFP36L2-AS functions as a metabolic modulator to regulate muscle development

Skeletal muscle is the largest metabolic organ in the body, and its metabolic flexibility is essential for maintaining systemic energy homeostasis. Metabolic inflexibility in muscles is a dominant cause of various metabolic disorders, impeding muscle development. In our previous study, we found lncRNA ZFP36L2-AS (for “ZFP36L2-antisense transcript”) is specifically enriched in skeletal muscle. Here, we report that ZFP36L2-AS is upregulated during myogenic differentiation, and highly expressed in breast and leg muscle. In vitro, ZFP36L2-AS inhibits myoblast proliferation but promotes myoblast differentiation. In vivo, ZFP36L2-AS facilitates intramuscular fat deposition, as well as activates fast-twitch muscle phenotype and induces muscle atrophy. Mechanistically, ZFP36L2-AS interacts with acetyl-CoA carboxylase alpha (ACACA) and pyruvate carboxylase (PC) to induce ACACA dephosphorylation and damaged PC protein stability, thus modulating muscle metabolism. Meanwhile, ZFP36L2-AS can activate ACACA to reduce acetyl-CoA content, which enhances the inhibition of PC activity. Our findings present a novel model about the regulation of lncRNA on muscle metabolism.

LncEDCH1 improves mitochondrial function to reduce muscle atrophy by interacting with SERCA2

Skeletal muscle is a regulator of the body's energy expenditure and metabolism. Abnormal regulation of skeletal muscle-specific genes leads to various muscle diseases. Long non-coding RNAs (lncRNAs) have been demonstrated to play important roles in muscle growth and muscle atrophy. To explore the potential function of muscle-associated lncRNA, we analyzed our previous RNA-sequencing data and selected the lncRNA (LncEDCH1) as the research object. In this study, we report that LncEDCH1 is specifically enriched in skeletal muscle, and its transcriptional activity is positively regulated by transcription factor SP1. LncEDCH1 regulates myoblast proliferation and differentiation in vitro. In vivo, LncEDCH1 reduces intramuscular fat deposition, activates slow-twitch muscle phenotype, and inhibits muscle atrophy. Mechanistically, LncEDCH1 binds to sarcoplasmic/ER calcium ATPase 2 (SERCA2) protein to enhance SERCA2 protein stability and increase SERCA2 activity. Meanwhile, LncEDCH1 improves mitochondrial efficiency possibly through a SERCA2-mediated activation of the AMPK pathway. Our findings provide a strategy for using LncEDCH1 as an effective regulator for the treatment of muscle atrophy and energy metabolism.

Maternal undernutrition alters the skeletal muscle development and methylation of myogenic factors in goat offspring

Objective

The effects of maternal undernutrition during midgestation on muscle fiber histology, myosin heavy chain (MyHC) expression, methylation modification of myogenic factors, and the mammalian target of rapamycin (mTOR) signaling pathway in the skeletal muscles of prenatal and postnatal goats were examined.

Methods

Twenty-four pregnant goats were assigned to a control (100% of the nutrients requirement, n = 12) or a restricted group (60% of the nutrients requirement, n = 12) between 45 and 100 days of gestation. Descendants were harvested at day 100 of gestation and at day 90 after birth to collect the femoris muscle tissue.

Results

Maternal undernutrition increased (p<0.05) the fiber area of the vastus muscle in the fetuses and enhanced (p<0.01) the proportions of MyHCI and MyHCIIA fibers in offspring, while the proportion of MyHCIIX fibers was decreased (p<0.01). DNA methylation at the +530 cytosine-guanine dinucleotide (CpG) site of the myogenic factor 5 (MYF5) promoter in restricted fetuses was increased (p<0.05), but the methylation of the MYF5 gene at the +274,280 CpG site and of the myogenic differentiation (MYOD) gene at the +252 CpG site in restricted kids was reduced (p<0.05). mTOR protein signals were downregulated (p<0.05) in the restricted offspring.

Conclusion

Maternal undernutrition altered the muscle fiber type in offspring, but its relationship with methylation in the promoter regions of myogenic genes needs to be elucidated.

Characterization of Long Non-coding RNAs Modified by m6A RNA Methylation in Skeletal Myogenesis

Proper development of mammalian skeletal muscle relies on precise gene expression regulation. Our previous studies revealed that muscle development is regulated by both mRNA and long non-coding RNAs (lncRNAs). Accumulating evidence has demonstrated that N⁶-methyladenosine (m⁶A) plays important roles in various biological processes, making it essential to profile m⁶A modification on a transcriptome-wide scale in developing muscle. Patterns of m⁶A methylation in lncRNAs in developing muscle have not been uncovered. Here, we reveal differentially expressed lncRNAs and report temporal m⁶A methylation patterns in lncRNAs expressed in mouse myoblasts and myotubes by RNA-seq and methylated RNA immunoprecipitation (MeRIP) sequencing. Many lncRNAs exhibit temporal differential expression, and m⁶A-lncRNAs harbor the consensus m⁶A motif “DRACH” along lncRNA transcripts. Interestingly, we found that m⁶A methylation levels of lncRNAs are positively correlated with the transcript abundance of lncRNAs. Overexpression or knockdown of m⁶A methyltransferase METTL3 alters the expression levels of these lncRNAs. Furthermore, we highlight that the function of m⁶A genic lncRNAs might correlate to their nearby mRNAs. Our work reveals a fundamental expression reference of m⁶A-mediated epitranscriptomic modifications in lncRNAs that are temporally expressed in developing muscle.

Non-Coding RNAs as Regulators of Myogenesis and Postexercise Muscle Regeneration

miRNAs and lncRNAs do not encode proteins, but they play an important role in the regulation of gene expression. They differ in length, biogenesis, and mode of action. In this work, we focus on the selected miRNAs and lncRNAs involved in the regulation of myogenesis and muscle regeneration. We present selected miRNAs and lncRNAs that have been shown to control myogenic differentiation and show that manipulation of their levels could be used to improve myogenic differentiation of various types of stem and progenitor cells. Finally, we discuss how physical activity affects miRNA and lncRNA expression and how it affects muscle well-being.

RNA-Binding Proteins in the Post-transcriptional Control of Skeletal Muscle Development, Regeneration and Disease

Embryonic myogenesis is a temporally and spatially regulated process that generates skeletal muscle of the trunk and limbs. During this process, mononucleated myoblasts derived from myogenic progenitor cells within the somites undergo proliferation, migration and differentiation to elongate and fuse into multinucleated functional myofibers. Skeletal muscle is the most abundant tissue of the body and has the remarkable ability to self-repair by re-activating the myogenic program in muscle stem cells, known as satellite cells. Post-transcriptional regulation of gene expression mediated by RNA-binding proteins is critically required for muscle development during embryogenesis and for muscle homeostasis in the adult. Differential subcellular localization and activity of RNA-binding proteins orchestrates target gene expression at multiple levels to regulate different steps of myogenesis. Dysfunctions of these post-transcriptional regulators impair muscle development and homeostasis, but also cause defects in motor neurons or the neuromuscular junction, resulting in muscle degeneration and neuromuscular disease. Many RNA-binding proteins, such as members of the muscle blind-like (MBNL) and CUG-BP and ETR-3-like factors (CELF) families, display both overlapping and distinct targets in muscle cells. Thus they function either cooperatively or antagonistically to coordinate myoblast proliferation and differentiation. Evidence is accumulating that the dynamic interplay of their regulatory activity may control the progression of myogenic program as well as stem cell quiescence and activation. Moreover, the role of RNA-binding proteins that regulate post-transcriptional modification in the myogenic program is far less understood as compared with transcription factors involved in myogenic specification and differentiation. Here we review past achievements and recent advances in understanding the functions of RNA-binding proteins during skeletal muscle development, regeneration and disease, with the aim to identify the fundamental questions that are still open for further investigations.

Morphological changes and functional circRNAs screening of rabbit skeletal muscle development

BACKGROUND

The temporal expression pattern of circular RNAs (circRNAs) across developmental stages is essential for skeletal muscle growth and functional analysis. However, there are few analyses on the potential functions of circRNAs in rabbit skeletal muscle development.

RESULTS

Initially, the paraffin sections showed extremely significant differences in the diameter, number, area and density of skeletal muscle fibers of the fetus, child, adult rabbit hind legs (P < 0.01). Then, RNA-seq libraries of these three stages were constructed. A total of 481 differentially expressed circRNAs (DE-circRNAs) and 5,658 differentially expressed genes (DEGs) were identified. Subsequently, DE-circRNAs, whose host genes were DEGs or non-DEGs, were analyzed by GO respectively. In the fetus vs. child group, up-regulated DE-circRNAs (whose host genes were DEGs) were related to muscle fiber structure, and down-regulated ones were related to mitosis. The up-regulated DE-circRNAs (whose host genes were non-DEGs) were involved in enzyme activity, methylation and glycosylation, and the down-regulated ones were involved in mitosis and catabolism. In the fetus vs. adult group, the up-regulated DE-circRNAs (whose host genes were DEGs) were related to skeletal muscle basic structure, and the down-regulated ones were also associated with cell proliferation. But the up-regulated DE-circRNAs (whose host genes were non-DEGs) were connected with regulation of histone ubiquitination, chromatin and organelles. The down-regulated DE-circRNAs were connected with the catabolism processes. In addition, novel_circ_0022663 and novel_circ_0005489, which might have coding potential, and novel_circ_0004210 and novel_circ_0001669, which might have miRNA sponge capability, were screened out.

CONCLUSIONS

In this study, hind leg muscles of fetus, child and adult rabbits were collected for paraffin section and RNA-seq to observe the structural changes of skeletal muscle and obtain circRNA expression profiles at different stages. These data provided a catalog of circRNAs related to muscle development in New Zealand rabbits, allowing us to better understand the functional transitions in mammalian muscle development.

Regulatory Potential of Competing Endogenous RNAs in Myotonic Dystrophies

Non-coding RNAs (ncRNAs) have been reported to be implicated in cell fate determination and various human diseases. All ncRNA molecules are emerging as key regulators of diverse cellular processes; however, little is known about the regulatory interaction among these various classes of RNAs. It has been proposed that the large-scale regulatory network across the whole transcriptome is mediated by competing endogenous RNA (ceRNA) activity attributed to both protein-coding and ncRNAs. ceRNAs are considered to be natural sponges of miRNAs that can influence the expression and availability of multiple miRNAs and, consequently, the global mRNA and protein levels. In this review, we summarize the current understanding of the role of ncRNAs in two neuromuscular diseases, myotonic dystrophy type 1 and 2 (DM1 and DM2), and the involvement of expanded CUG and CCUG repeat-containing transcripts in miRNA-mediated RNA crosstalk. More specifically, we discuss the possibility that long repeat tracts present in mutant transcripts can be potent miRNA sponges and may affect ceRNA crosstalk in these diseases. Moreover, we highlight practical information related to innovative disease modelling and studying RNA regulatory networks in cells. Extending knowledge of gene regulation by ncRNAs, and of complex regulatory ceRNA networks in DM1 and DM2, will help to address many questions pertinent to pathogenesis and treatment of these disorders; it may also help to better understand general rules of gene expression and to discover new rules of gene control.

Mechanisms of exercise as a preventative measure to muscle wasting

Skeletal muscle is the most abundant tissue in healthy individuals and it has important roles in health beyond voluntary movement. The overall mass and energy requirements of skeletal muscle require it to be metabolically active and flexible to multiple energy substrates. The tissue has evolved to be largely load dependent and it readily adapts in a number of positive ways to repetitive overload, such as various forms of exercise training. However, unloading from extended bed rest and/or metabolic derangements in response to trauma, acute illness, or severe pathology, commonly results in rapid muscle wasting. Decline in muscle mass contributes to multimorbidity, reduces function, and exerts a substantial, negative impact on the quality of life. The principal mechanisms controlling muscle mass have been well described and these cellular processes are intricately regulated by exercise. Accordingly, exercise has shown great promise and efficacy in preventing or slowing muscle wasting through changes in molecular physiology, organelle function, cell signaling pathways, and epigenetic regulation. In this review, we focus on the role of exercise in altering the molecular landscape of skeletal muscle in a manner that improves or maintains its health and function in the presence of unloading or disease.epigenetics; exercise; muscle wasting; resistance training; skeletal muscle.

Prenatal Skeletal Muscle Transcriptome Analysis Reveals Novel MicroRNA-mRNA Networks Associated with Intrauterine Growth Restriction in Pigs

Intrauterine growth restriction (IUGR) occurs in 15–20% of pig neonates and poses huge economic losses to the pig industry. IUGR piglets have reduced skeletal muscle growth, which may persist after birth. Prenatal muscle growth is regulated by complex molecular pathways that are not well understood. MicroRNAs (miRNAs) have emerged as the main regulators of vital pathways and biological processes in the body. This study was designed to identify miRNA–mRNA networks regulating prenatal skeletal muscle development in pigs. We performed an integrative miRNA–mRNA transcriptomic analysis in longissimus dorsi muscle from IUGR fetuses and appropriate for gestational age (AGA) fetuses at 63 days post conception. Our data showed that 47 miRNAs and 3257 mRNAs were significantly upregulated, and six miRNAs and 477 mRNAs were significantly downregulated in IUGR compared to AGA fetuses. Moreover, 47 upregulated miRNAs were negatively correlated and can potentially target 326 downregulated genes, whereas six downregulated miRNAs were negatively correlated and can potentially target 1291 upregulated genes. These miRNA–mRNA networks showed enrichment in biological processes and pathways critical for fetal growth, development, and metabolism. The miRNA–mRNA networks identified in this study can potentially serve as indicators of prenatal fetal growth and development as well as postnatal carcass quality.

Non-Coding RNAs Regulate Placental Trophoblast Function and Participate in Recurrent Abortion

Recurrent spontaneous abortion (RSA) is a serious pregnancy complication with an increasing clinical incidence. The various causes of recurrent abortion are complicated. Developments in genetics, immunology, and cell biology have identified important roles of non-coding RNAs (ncRNAs) in the occurrence and progress of recurrent abortion. NcRNAs can affect the growth, migration, and invasion of placental trophoblasts by regulating cell processes such as the cell cycle, apoptosis, and epithelial-mesenchymal transformation. Therefore, their abnormal expression might lead to the occurrence and development of RSA. NcRNAs include small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), ribosomal RNA (rRNA), transfer, RNA (tRNA), circular RNA (cRNA), and Piwi-interacting RNA (piRNA). In this review, we discuss recent research that focused on the function and mechanism of microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNA (circRNA) in regulating placental trophoblasts. The use of ncRNAs as potential diagnostic and predictive biomarkers in RSA is also discussed to provide future research insights.