Exosomes are membrane‐bound extracellular vesicles that are produced in the endosomal compartment of most mammalian cell types and then released. Exosomes are effective carriers for the intercellular material transfer of material that can influence a series of physiological and pathological processes in recipient cells. Among loaded cargoes, non‐coding RNAs (ncRNAs) vary for the exosome‐producing cell and its homeostatic state, and characterization of the biogenesis and secretion of exosomal ncRNAs and the functions of these ncRNAs in skeletal muscle myogenesis remain preliminary. In this review, we will describe what is currently known of exosome biogenesis, release and uptake of exosomal ncRNAs, as well as the varied functions of exosomal miRNAs in skeletal muscle myogenesis.

There is growing evidence that non-coding RNAs are emerging as critical regulators of skeletal muscle development. In order to reveal their functional roles and regulatory mechanisms, we constructed a lncRNA–miRNA–mRNA network according to the ceRNA (competitive endogenous RNA) theory, using our high-throughput sequencing data. Subsequently, the network analysis, GO (Gene Ontology) analysis, and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis were performed for functional annotation and exploration of lncRNA ceRNAs. The results uncovered a scale-free characteristics network which exhibited high functional specificity for bovine skeletal muscle development: co-expression lncRNAs were significantly enriched in muscle development related biological processes and the Wnt signaling pathway. Furthermore, GSEA (Gene Set Enrichment Analysis) indicated that the risk score has a tendency to associate with myogenesis, and differentially expressed RNAs were validated by qPCR, further confirming the credibility of our network. In summary, this study provides insights into lncRNA-mediated ceRNA function and mechanisms in bovine skeletal muscle development and will expand our understanding of lncRNA biology in mammals.

Myogenesis is controlled by a well-established transcriptional hierarchy that coordinates the activities of a set of muscle genes. Recently, roles in myogenesis have been described for non-coding RNAs, including a role of circular RNA (circRNA) to regulate muscle gene expression. However, the functions of circRNA and the underlying mechanism by which circRNAs affect myogenesis remain poorly understood. In this study, we analyzed circRNA high-throughput sequencing results of bovine skeletal muscle samples and constructed a circRNA-miRNA-mRNA network according to the competitive endogenous RNA (ceRNA) theory. The putative circHUWE1-miR-29b-AKT3 network was analyzed and its involvement in myogenesis was confirmed through a series of assays. To assess the potential function of this regulation, bovine myoblasts were infected with overexpression plasmids and small interfering RNAs (siRNAs) that target circHUWE1. Next, cell proliferation, apoptosis, and differentiation were analyzed using Cell Counting Kit-8 (CCK-8), 5-ethynyl-2 0 -deoxyuridine (EdU), flow cytometry, western blotting, and qRT-PCR assays. The results suggest that circHUWE1 facilitates bovine myoblast proliferation and inhibits cell apoptosis and differentiation. Next, bioinformatics, dual-luciferase reporter assay, and AGO2 RNA immunoprecipitation (RIP) approaches were used to verify the interaction between circHUWE1, miR-29b, and AKT3. Subsequently, we identified that circHUWE1 could directly interfere with the ability of miR-29b to relieve AKT3 suppression, which ultimately activates the AKT signaling pathway. These findings suggested a new regulatory pathway for bovine skeletal muscle development, and they also expand our understanding of circRNA functions in mammals.

Exosomes are a subset of nano-sized extracellular vesicles originating from endosomes. Exosomes mediate cell-to-cell communication with their cargos, which includes mRNAs, miRNAs, lncRNAs, and circRNAs. Exosomal RNAs have cell specificity and reflect the conditions of their donor cells. Notably, their detection in biofluids can be used as a diagnostic marker for various diseases. Exosomal RNAs are ideal biomarkers because their surrounding membranes confer stability and they are detectable in almost all biofluids, which helps to reduce trauma and avoid invasive examinations. However, knowledge of exosomal biomarkers remains scarce. The present review summarizes the biogenesis, secretion, and uptake of exosomes, the current researches exploring exosomal mRNAs, miRNAs, lncRNAs, and circRNAs as potential biomarkers for the diagnosis of human diseases, as well as recent techniques of exosome isolation.

RNA m 6 A methylation is a post-transcriptional modification that occurs at the nitrogen-6 position of adenine. This dynamically reversible modification is installed, removed and recognized by methyltransferases, demethylases and readers, respectively. This modification has been found in most eukaryotic mRNA, tRNA, rRNA and other non-coding RNA. Recent studies have revealed important regulatory functions of the m 6 A including effects on gene expression regulation, organism development and cancer development. In this review, we summarize the discovery and features of m 6 A, and briefly introduce the mammalian m 6 A writers, erasers and readers. Finally, we discuss progress in identifying additional functions of m 6 A and the outstanding questions about the regulatory effect of this widespread modification.

The role of long non-coding RNA (lncRNA) in the regulation of bovine skeletal muscle development remains poorly understood. The present study investigated the function and regulatory mechanism of a novel lncRNA, insulin-like growth factor 2 antisense transcript (IGF2 AS), in bovine myoblast proliferation and differentiation. Gain or loss of IGF2 AS was performed using an expression plasmid or small interfering RNA (siRNA), respectively. Bovine myoblasts were used to investigate the biological function and mechanisms of IGF2 AS in vitro. Results were conjointly analyzed by celluar and molecular biology experiments as well as bioinformatics. Functionally, IGF2 AS could promote proliferation and differentiation of bovine myoblasts. The preliminary mechanism suggests, on the one hand, that IGF2 AS could complement the IGF2 gene intron region and affect the stability and expression of IGF2 mRNA. On the other hand, RNA pull-down and immunoprecipitation assays demonstrated that IGF2 AS could directly bind to the interleukin enhancer binding factor 3 (ILF3) protein and maybe partly though it to regulate myogenesis. In conclusion, the novel identified lncRNA IGF2 AS promoted proliferation and differentiation of bovine myoblasts through various pathways.

MicroRNAs (miRNAs or miRs) are small noncoding RNAs that play critical roles in muscle cell proliferation and differentiation via post-transcriptional regulation of gene expression. Here, based on our previous high-throughput sequencing results, we evaluated miRNA-499 (miR-499) functions during myoblast proliferation and differentiation. In addition, we analyzed miR-499 expression profiles and characterized the associated functional roles. MiR-499 is known to be a skeletal muscle fiber-type-associated miRNA. However, its roles in skeletal myoblast proliferation and differentiation are poorly understood. MiR-499 overexpression promoted C2C12 cell proliferation and significantly attenuated C2C12 cell myogenic differentiation. Furthermore, miR-499 inhibition enhanced C2C12 cell proliferation and suppressed C2C12 cell differentiation. Using dual-luciferase reporter assays and western blot analysis, we confirmed that miR-499 targeted transforming growth factor β receptor 1 (TGFβR1), a known regulator of skeletal myoblast development. Additionally, our RNA interference analysis, in which TGFβR1 was downregulated, showed that TGFβR1 significantly promoted the differentiation of C2C12 cells and inhibited their proliferation.

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