MEF2: a transcriptional target for signaling pathways controlling skeletal muscle growth and differentiation

FoxP1 Represses MEF2A in Striated Muscle

Myocyte enhancer factor 2 (MEF2) proteins are involved in multiple developmental, physiological, and pathological processes in vertebrates. Protein-protein interactions underlie the plethora of biological processes impacted by MEF2A, necessitating a detailed characterization of the MEF2A interactome. A nanobody based affinity-purification/mass spectrometry strategy was employed to achieve this goal. Specifically, the MEF2A protein complexes were captured from myogenic lysates using a GFP-tagged MEF2A protein immobilized with a GBP-nanobody followed by LC-MS/MS proteomic analysis to identify MEF2A interactors. After bioinformatic analysis, we further characterized the interaction of MEF2A with a transcriptional repressor, FOXP1. FOXP1 coprecipitated with MEF2A in proliferating myogenic cells which diminished upon differentiation (myotube formation). Ectopic expression of FOXP1 inhibited MEF2A driven myogenic reporter genes (derived from the creatine kinase muscle and myogenin genes) and delayed induction of endogenous myogenin during differentiation. Conversely, FOXP1 depletion enhanced MEF2A transactivation properties and myogenin expression. The FoxP1:MEF2A interaction is also preserved in cardiomyocytes and FoxP1 depletion enhanced cardiomyocyte hypertrophy. FOXP1 prevented MEF2A phosphorylation and activation by the p38MAPK pathway. Overall, these data implicate FOXP1 in restricting MEF2A function in order to avoid premature differentiation in myogenic progenitors and also to possibly prevent re-activation of embryonic gene expression in cardiomyocyte hypertrophy.

Identifying key antioxidative stress factors regulating Nrf2 in the genioglossus with human umbilical cord mesenchymal stem-cell therapy

Intermittent hypoxia in patients with obstructive sleep apnea (OSA) hypopnea syndrome (OSAHS) is associated with pharyngeal cavity collapse during sleep. The effect of human umbilical cord mesenchymal stem cells (HUCMSCs) on OSA-induced oxidative damage in the genioglossus and whether nuclear factor erythroid 2-related factor 2 (Nrf2) or its upstream genes play a key role in this process remains unclear. This study aimed to identify the key factors responsible for oxidative damage during OSAHS through Nrf2 analysis and hypothesize the mechanism of HUCMSC therapy. We simulated OSA using an intermittent hypoxia model, observed the oxidative damage in the genioglossus and changes in Nrf2 expression during intermittent hypoxia, and administered HUCMSCs therapy. Nrf2 initially increased, then decreased, aggravating the oxidative damage in the genioglossus; Nrf2 protein content decreased during hypoxia. Using transcriptomics, we identified seven possible factors in HUCMSCs involved in ameliorating oxidative stress by Nrf2, of which DJ-1 and MEF2A, showing trends similar to Nrf2, were selected by polymerase chain reaction. HUCMSCs may reduce oxidative stress induced by intermittent hypoxia through Nrf2, and the possible upstream target genes in this process are MEF2A and DJ-1. Further studies are needed to verify these findings.

A newly identified lncRNA lnc000100 regulates proliferation and differentiation of cattle skeletal muscle cells

Cattle skeletal muscle development is a complex and highly coordinated biological process mediated by a series of myogenic regulators, which plays a critical role in beef yield and quality. Long non-coding RNAs (lncRNAs) have been shown to regulate skeletal muscle development. However, the molecular mechanism by which lncRNAs regulate skeletal muscle development is largely unknown. We performed transcriptome analysis of muscle tissues of adult and embryo Angus cattle to investigate the mechanism by which lncRNA regulates skeletal muscle development between adult and embryo cattle. A total of 37,115 candidate lncRNAs were detected, and a total of 1,998 lncRNAs were differentially expressed between the muscle tissue libraries of adult and embryo cattle, including 1,229 up-regulated lncRNAs and 769 down-regulated lncRNAs (adult cattle were the control group). We verified the expression of 7 differentially expressed lncRNAs by quantitative real-time PCR (RT-qPCR), and analysed the tissue expression profile of lnc000100, which is down-regulated in the longest dorsal muscle during foetal life and which is highly specifically expressed in muscle tissue. We found that the interference of lnc000100 significantly inhibited cell proliferation and promoted cell differentiation. Lnc000100 was located in the nucleus by RNA-FISH. Our research provides certain resources for the analysis of lncRNA regulating cattle skeletal muscle development, and may also provide new insights for improving beef production and breed selection.

In ovo probiotic supplementation promotes muscle growth and development in broiler embryos

In chickens, muscle development during embryonic growth is predominantly by myofiber hyperplasia. Following hatch, muscle growth primarily occurs via hypertrophy of the existing myofibers. Since myofiber number is set at hatch, production of more muscle fibers during embryonic growth would provide a greater myofiber number at hatch and potential for posthatch muscle growth by hypertrophy. Therefore, to improve performance in broilers, this study investigated the effect of in ovo spray application of probiotics on overall morphometry and muscle development in broiler embryos. For the study, fertile Ross 308 eggs were sprayed with different probiotics; Lactobacillus paracasei DUP 13076 (LP) and L. rhamnosus NRRL B 442 (LR) prior to and during incubation. The embryos were sacrificed on d 7, 10, 14, and 18 for embryo morphometry and pectoralis major muscle (PMM) sampling. Muscle sections were stained and imaged to quantify muscle fiber density (MFD), myofiber cross-sectional area (CSA), and nuclei density. Additionally, gene expression assays were performed to elucidate the effect of probiotics on myogenic genes. In ovo probiotic supplementation was found to significantly improve embryo weight, breast weight, and leg weight (P < 0.05). Further, histological analysis of PMM revealed a significant increase in MFD and nuclei number in the probiotic-treated embryos when compared to the control (P < 0.05). In 18-day-old broiler embryos, myofibers in the treatment group had a significantly smaller CSA (LP: 95.27 ± 3.28 μm², LR: 178.84 ± 15.1 μm²) when compared to the control (211.41 ± 15.67 μm²). This decrease in CSA was found to be associated with a concomitant increase in MFD (fibers/mm²) in the LP (13,647 ± 482.15) and LR (13,957 ± 463.13) group when compared to the control (7,680 ± 406.78). Additionally, this increase in myofibrillar hyperplasia in the treatment groups was associated with upregulation in the expression of key genes regulating muscle growth including MYF5, MYOD, MYOG, and IGF-1. In summary, in ovo spray application of probiotics promoted overall embryo growth and muscle development in broilers.

Linoleic acid-induced ANGPTL4 inhibits C2C12 skeletal muscle differentiation by suppressing Wnt/β-catenin

Skeletal muscle differentiation is an essential process in embryonic development as well as regeneration and repair throughout the lifespan. It is well-known that dietary fat intake impacts biological and physiological function in skeletal muscle, however, understanding of the contribution of nutritional factors in skeletal muscle differentiation is limited. Therefore, the objective of the current study was to evaluate the effects of free fatty acids (FFAs) on skeletal muscle differentiation in vitro. We used C2C12 murine myoblasts and treated them with various FFAs, which revealed a unique response of angiopoietin-like protein-4 (ANGPTL4) with linoleic acid (LA) treatment that was associated with reduced differentiation. LA significantly inhibited myotube formation and lowered the protein expression of myogenic regulatory factors, including MyoD and MyoG and increased Pax7 during cell differentiation. Next, recombinant ANGPTL4 protein or siRNA knockdown of ANGPTL4 was employed to examine its role in skeletal muscle differentiation, and we confirmed that ANGPTL4 knockdown at day 2 and -6 of differentiation restored myotube formation in the presence of LA. RNA-sequencing analysis revealed that ANGPTL4-mediated inhibition of skeletal muscle differentiation at day 2 as well as LA at day 2 or -6 led to a reduction in Wnt/β-catenin signaling pathways. We confirmed that LA reduced Wnt11 and Axin2 while increasing expression of the Wnt inhibitor, Dkk2. ANGPTL4 knockdown increased β-catenin protein in the nucleus in response to LA and increased Axin2 and Wnt11 expression. Taken together, these results demonstrate that LA induced ANGPTL4 inhibits C2C12 differentiation by suppressing Wnt/β-catenin signaling.

Goat MyoD1: mRNA expression, InDel and CNV detection and their associations with growth traits

The Myogenic differentiation 1 (MyoD1) gene is a crucial regulator of muscle formation and differentiation. However, there are few studies on the mRNA expression pattern of the goat MyoD1 gene and its effect on goat growth and development. To address this, we investigated the mRNA expression of the MyoD1 gene in several tissues of fetal and adult goats, containing heart, liver, spleen, lung, kidney and skeletal muscle. The results focused on the expression of the MyoD1 gene in skeletal muscle of fetal goats was much higher than adult goats, suggesting its important role in skeletal muscle formation and development. Following, a total of 619 Shaanbei White Cashmere goats (SBWCs) were used to monitor the InDel (Insertion/Deletion) and CNV (Copy Number Variation) variations of the MyoD1 gene. Three InDel loci were identified, and there was no significant correlation with goat growth traits. Furthermore, a CNV locus containing the MyoD1 gene exon with three types (Loss type, Normal type, Gain type) were identified. The association analysis results showed that the CNV locus was significantly associated with body weight, height at hip cross, heart girth and hip width in SBWCs (P < 0.05). Meanwhile, the Gain type of CNV exhibited the best growth traits and good consistency among three types in goats, suggesting its potential as a DNA marker for marker-assisted breeding of goats. Overall, our study provided a scientific basis for breeding goats with better growth and development traits.

Functional, structural, and molecular characterizations of the leukemogenic driver MEF2D-HNRNPUL1 fusion

Recurrent MEF2D fusions with poor prognosis have been identified in B-cell precursor ALL (BCP-ALL). The molecular mechanisms underlying the pathogenic function of MEF2D fusions are poorly understood. Here, we show that MEF2D-HNRNPUL1 (MH) knock-in mice developed a progressive disease from impaired B-cell development at the pre-pro-B stage to pre-leukemia over 10 to 12 months. When cooperating with NRASG12D, MH drove an outbreak of BCP-ALL, with a more aggressive phenotype than the NRASG12D-induced leukemia. RNA-sequencing identified key networks involved in disease mechanisms. In chromatin immunoprecipitation-sequencing experiments, MH acquired increased chromatin-binding ability, mostly through MEF2D-responsive element (MRE) motifs in target genes, compared with wild-type MEF2D. Using X-ray crystallography, the MEF2D-MRE complex was characterized in atomic resolution, whereas disrupting the MH-DNA interaction alleviated the aberrant target gene expression and the B-cell differentiation arrest. The C-terminal moiety (HNRNPUL1 part) of MH was proven to contribute to the fusion protein's trans-regulatory activity, cofactor recruitment, and homodimerization. Furthermore, targeting MH-driven transactivation of the HDAC family by using the histone deacetylase inhibitor panobinostat in combination with chemotherapy improved the overall survival of MH/NRASG12D BCP-ALL mice. Altogether, these results not only highlight MH as an important driver in leukemogenesis but also provoke targeted intervention against BCP-ALL with MEF2D fusions.

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.

Identification and functional analysis of circRNAs in the skeletal muscle of juvenile and adult largemouth bass (Micropterus salmoides)

Circular RNA (circRNA) is a novel emerging type of endogenous regulatory non-coding RNA molecules with a covalent closed-loop configuration, which exerts important functions in multiple biological processes. CircRNAs are known to regulate gene expression as functional regulators interacting with miRNAs by sponge, which have been reported to regulate skeletal muscle development. Nevertheless, the information of circRNAs involved in regulating muscle growth and development in fish is largely unknown. Here, we first identified 312 and 511 circRNAs in skeletal muscle of juvenile and adult largemouth bass (LMB) using RNA sequencing, respectively. The differentially expressed circRNAs (DE-circRNAs) analysis showed that there are 44 DE-circRNAs at two different skeletal muscle growth stages. Six circRNAs were chosen randomly and their relative expression levels in juvenile and adult LMB were confirmed by real-time PCR, indicating that these circRNAs were existed authenticity. In addition, Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis showed that these hose genes (their linear mRNAs) of DE-circRNAs were mainly enriched in the regulation of actin cytoskeleton signaling pathways. The circRNA-miRNA interaction regulatory networks indicated that one circRNA can regulate one or more miRNA. For instance, more than 30 miRNAs were regulated by two circRNAs (circRNA389 and circRNA399). Of them, the muscle-related miRNAs including the let-7 family, miR-133 and miR-26 and so on were found acting as miRNAs sponge regulated by circRNAs, indicating the roles of circRNAs in regulating muscle growth-related genes expression. Overall, these findings will not only broaden our understanding of circRNAs regulation mechanisms underlying muscle growth and development in LMB but also provides a novel clue for further functional research in carnivorous fish genetic breeding.

MEF2C Expression Is Regulated by the Post-transcriptional Activation of the METTL3-m6A-YTHDF1 Axis in Myoblast Differentiation

N⁶-methyladenosine (m⁶A) plays an essential role in regulating gene expression. However, the effect of m⁶A on skeletal myoblast differentiation and the underlying mechanisms are still unclear. Here, we ascertained mRNA m⁶A methylation exhibited declined changes during bovine skeletal myoblast differentiation, and both MEF2C mRNA expression and m⁶A levels were significantly increased during myoblast differentiation. We found that MEF2C with mutated m⁶A sites significantly inhibited myoblast differentiation compared with wild-type MEF2C. METTL3 promoted MEF2C protein expression through posttranscriptional modification in an m⁶A-YTHDF1-dependent manner. Moreover, MEF2C promoted the expression of METTL3 by binding to its promoter. These results revealed that there is a positive feedback loop between these molecules in myoblast differentiation. Our study provided new insights into skeletal muscle differentiation and fusion, which may provide an RNA methylation-based approach for molecular genetics and breeding in livestock as well as for the treatment of muscle-related diseases.

Profiling and Functional Analysis of mRNAs during Skeletal Muscle Differentiation in Goats

Skeletal myogenesis is a complicated biological event that involves a succession of tightly controlled gene expressions. In order to identify novel regulators of this process, we performed mRNA-Seq studies of goat skeletal muscle satellite cells (MuSCs) cultured under proliferation (GM) and differentiation (DM1/DM5) conditions. A total of 19,871 goat genes were expressed during these stages, 198 of which represented novel transcripts. Notably, in pairwise comparisons at the different stages, 2551 differentially expressed genes (DEGs) were identified (p < 0.05), including 1560 in GM vs. DM1, 1597 in GM vs. DM5, and 959 in DM1 vs. DM5 DEGs. The time-series expression profile analysis clustered the DEGs into eight gene groups, three of which had significantly upregulated and downregulated patterns (p < 0.05). Functional enrichment analysis showed that DEGs were enriched for essential biological processes such as muscle structure development, muscle contraction, muscle cell development, striated muscle cell differentiation, and myofibril assembly, and were involved in pathways such as the MAPK, Wnt and PPAR signaling pathways. Moreover, the expression of eight DEGs (MYL2, DES, MYOG, FAP, PLK2, ADAM, WWC1, and PRDX1) was validated. These findings offer novel insights into the transcriptional regulation of skeletal myogenesis in goats.

Transcription Regulation of Tceal7 by the Triple Complex of Mef2c, Creb1 and Myod

Simple Summary

We have previously reported a striated muscle-specific gene during embryogenesis, Tceal7. Our studies have characterized the 0.7 kb promoter of the Tceal7 gene, which harbors important E-box motifs driving the LacZ reporter in the myogenic lineage. However, the underlying mechanism regulating the dynamic expression of Tceal7 during skeletal muscle regeneration is still elusive. In the present work, we have defined a cluster of Mef2#3–CRE#3–E#4 motifs through bioinformatic analysis and transcription assays. Our studies suggested that the triple complex of Mef2c, Creb1 and Myod binds to the Mef2#3–CRE#3–E#4 cluster region, therefore driving the dynamic expression of Tceal7 during skeletal muscle regeneration. The novel mechanism may throw new light on understanding transcription regulation in skeletal muscle myogenesis.

Abstract

Tceal7 has been identified as a direct, downstream target gene of MRF in the skeletal muscle. The overexpression of Tceal7 represses myogenic proliferation and promotes cell differentiation. Previous studies have defined the 0.7 kb upstream fragment of the Tceal7 gene. In the present study, we have further determined two clusters of transcription factor-binding motifs in the 0.7 kb promoter: CRE#2–E#1–CRE#1 in the proximal region and Mef2#3–CRE#3–E#4 in the distal region. Utilizing transcription assays, we have also shown that the reporter containing the Mef2#3–CRE#3–E#4 motifs is synergistically transactivated by Mef2c and Creb1. Further studies have mapped out the protein–protein interaction between Mef2c and Creb1. In summary, our present studies support the notion that the triple complex of Mef2c, Creb1 and Myod interacts with the Mef2#3–CRE#3–E#4 motifs in the distal region of the Tceal7 promoter, thereby driving Tceal7 expression during skeletal muscle development and regeneration.

Beneficial impact of dietary methyl methionine sulfonium chloride and/or L-carnitine supplementation on growth performance, feed efficiency, and serum biochemical parameters in broiler chicken: role of IGF-1 and MSTN genes

The purpose of this study was to examine the effect of dietary supplementation with methyl methionine sulfonium chloride (MMSC), and L-carnitine (L-CAR) alone or in combination on the growth performance of broilers through their impact on the expression of IGF-1 and MSTN genes associated with growth in broilers. One-day-old female Ross 308 broiler chicks were allocated into four groups, each of which received a broiler starter diet and water daily ad libitum. The control group (group 1) was given drinking water without any additives. Group 2 received 0.25 g L-carnitine per liter of drinking water, group 3 received 0.25 g MMSC per liter of drinking water, and group 4 received 0.25 g of both L-carnitine and MMSC per liter of drinking water. Birds were given a starter diet to 21 days after which they received a broiler grower diet to 35 days when the experiment ended. There were five replicate groups of 12 birds per treatment. Body weights and feed intake were recorded weekly. Compared to the control group of birds, supplementation with MMSC either alone or in combination with L-carnitine resulted in an increase in growth rate or feed utilization efficiency; L-carnitine by itself had no effect. MMSC supplementation, again either alone or in combination with L-carnitine, increased jejunal and ileal villi height, increased serum total proteins and globulins, downregulated myostatin (MSTN) mRNA, and upregulated insulin growth factor-1 (IGF-1) mRNA expression. Supplementation with L-carnitine alone showed none of these effects. We conclude that MMSC supplementation improved growth performance through the upregulation of IGF-1 mRNA expression and downregulation of MSTN mRNA expression.

Gene coexpression networks reveal molecular interactions underlying cichlid jaw modularity

Background

The oral and pharyngeal jaw of cichlid fishes are a classic example of evolutionary modularity as their functional decoupling boosted trophic diversification and contributed to the success of cichlid adaptive radiations. Most studies until now have focused on the functional, morphological, or genetic aspects of cichlid jaw modularity. Here we extend this concept to include transcriptional modularity by sequencing whole transcriptomes of the two jaws and comparing their gene coexpression networks.

Results

We show that transcriptional decoupling of gene expression underlies the functional decoupling of cichlid oral and pharyngeal jaw apparatus and the two units are evolving independently in recently diverged cichlid species from Lake Tanganyika. Oral and pharyngeal jaw coexpression networks reflect the common origin of the jaw regulatory program as there is high preservation of gene coexpression modules between the two sets of jaws. However, there is substantial rewiring of genetic architecture within those modules. We define a global jaw coexpression network and highlight jaw-specific and species-specific modules within it. Furthermore, we annotate a comprehensive in silico gene regulatory network linking the Wnt and AHR signalling pathways to jaw morphogenesis and response to environmental cues, respectively. Components of these pathways are significantly differentially expressed between the oral and pharyngeal jaw apparatus.

Conclusion

This study describes the concerted expression of many genes in cichlid oral and pharyngeal jaw apparatus at the onset of the independent life of cichlid fishes. Our findings suggest that – on the basis of an ancestral gill arch network—transcriptional rewiring may have driven the modular evolution of the oral and pharyngeal jaws, highlighting the evolutionary significance of gene network reuse. The gene coexpression and in silico regulatory networks presented here are intended as resource for future studies on the genetics of vertebrate jaw morphogenesis and trophic adaptation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01787-9.

Transcriptomic investigation of embryonic pectoral muscle reveals increased myogenic processes in Shitou geese compared to Wuzong geese

1.Embryonic stages before birth are crucial for poultry muscle development, as this determines muscle mass in adulthood. This study characterised the distinction in embryonic pectoral muscle development between Wuzong (WZE, small) and Shitou (STE, large) geese (two indigenous goose breeds in Guangdong Province, China) at embryonic days 15 (E15), 23 (E23) and the day of hatching (P1) to gain insights into the regulatory mechanisms of muscle development.2.The results showed that STE had significantly higher myofibre density during E15-P1 and had significantly larger myofibre diameter at E15 than WZE. By RNA-sequencing analysis, 19 507 genes were detected, and 7121 differentially expressed genes (DEGs) were identified.3.Gene expression distinctions between breeds began increasing from E23, and WZE had different gene expression profiles compared to STE. A GO analysis of DEGs indicated that myo-genes involved at E15 may influence distinct pectoral muscle development characteristics between WZE and STE. The RT-qPCR results were consistent with the RNA-sequencing analysis. Four muscle structure protein coding genes (MYL2, MYL3, TNNI2 and TNNC2 and three other functional genes (CAV3, CACNA1S and NOS1) were identified in a predicted interaction network. These functional genes may interact with muscle structural protein coding genes to regulate embryonic pectoral muscle development in WZE and STE geese.4.The study revealed that STE and WZE had divergent embryonic pectoral muscle development patterns and these differences may begin before E15.

Circular RNA circMYBPC1 promotes skeletal muscle differentiation by targeting MyHC

Skeletal muscle development is a complex and highly orchestrated biological process mediated by a series of myogenesis regulatory factors. Numerous studies have demonstrated that circular RNAs (circRNAs) are involved in muscle differentiation, but the exact molecular mechanisms involved remain unclear. Here, we analyzed the expression of circRNAs at the adult and embryo development stages of cattle musculus longissimus. A stringent set of 1,318 circRNAs candidates were identified, and we found that 495 circRNAs were differentially expressed between embryonic and adult tissue libraries. We subsequently focused on one of the most downregulated circRNAs (using the adult stage expression as control), and this was named muscle differentiation-associated circular RNA (circMYBPC1). With RNA binding protein immunoprecipitation (RIP) and RNA pull-down assays, circMYBPC1 was identified to promote myoblast differentiation by directly binding miR-23a to relieve its inhibition on myosin heavy chain (MyHC). In addition, RIP assays demonstrated that circMYBPC1 could directly bind MyHC protein. In vivo observations also suggested that circMYBPC1 may stimulate skeletal muscle regeneration after muscle damage. These results revealed that the novel non-coding circRNA circMYBPC1 promotes differentiation of myoblasts and may promote skeletal muscle regeneration. Our results provided a basis for in-depth analysis of the role of circRNA in myogenesis and muscle diseases.

Circular RNA Profiling Reveals an Abundant circEch1 That Promotes Myogenesis and Differentiation of Bovine Skeletal Muscle

Beef is considered to be a good quality meat product because it contains linoleic acid and specific proteins, which can bring significant benefits to health. Circular RNAs (circRNAs) have been reported to regulate skeletal myogenesis. RNA-seq was used to investigate the circRNA molecular regulatory mechanisms with respect to differences in muscle quality between buffalo and cattle. A total of 10,449 circRNA candidates were detected, and 1128 of these were found to be differentially expressed between cattle and buffalo muscle tissue libraries. Differentially expressed 23 circRNAs were verified by qPCR. CircEch1, one of the most up-regulated circRNAs during muscle development, was subsequently characterized. CCK-8 (65.05 ± 2.33%, P < 0.0001), EdU (72.99 ± 0.04%, P < 0.001), and Western blotting assays showed that overexpression of circEch1 inhibited the proliferation of bovine myoblasts but promoted differentiation. In vivo studies suggested that circEch1 stimulates skeletal muscle regeneration. These results demonstrate that the novel regulator circEch1 induces myoblast differentiation and skeletal muscle regeneration. They also provide new insights into the mechanisms of circRNA regulation of beef quality.

lncRNA IGF2 AS Regulates Bovine Myogenesis through Different Pathways

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.

Disabled-2: a positive regulator of the early differentiation of myoblasts

Dab2 is an adaptor protein and a tumor suppressor. Our previous study has found that Dab2 was expressed in early differentiating skeletal muscles in mouse embryos. In this study, we determined the role of Dab2 in the skeletal muscle differentiation using C2C12 myoblasts in vitro and Xenopus laevis embryos in vivo. The expression of Dab2 was increased in C2C12 myoblasts during the formation of myotubes in vitro. Knockdown of Dab2 expression in C2C12 myoblasts resulted in a reduction of myotube formation, whereas the myotube formation was enhanced upon overexpression of Dab2. Re-expression of Dab2 in C2C12 myoblasts with downregulated expression of Dab2 restored their capacity to form myotubes. Microarray profiling and subsequent network analyses on the 155 differentially expressed genes after Dab2 knockdown showed that Mef2c was an important myogenic transcription factor regulated by Dab2 through the p38 MAPK pathway. It was also involved in other pathways that are associated with muscular development and functions. In Xenopus embryos developed in vivo, XDab2 was expressed in the myotome of somites where various myogenic markers were also expressed. Knockdown of XDab2 expression with antisense morpholinos downregulated the expression of myogenic markers in somites. In conclusion, this study is the first to provide solid evidence to show that Dab2 is a positive regulator of the early myoblast differentiation.

Changes in Nup62 content affect contact-induced differentiation of cultured myoblasts

Differentiation of cultured skeletal myoblasts is induced by extrinsic signals that include reduction in ambient mitogen concentration and increased cell density. Using an established murine myoblast cell line (C2C12), we have found that experimental reduction of the nucleoporin p62 (Nup62) content of myoblasts enhances differentiation in high-mitogen medium, while forced expression of Nup62 inhibits density-induced differentiation. In contrast, differentiation of myoblasts induced by low-mitogen medium was unaffected by ectopic Nup62 expression. Further analyses suggested that Nup62 content affects density-induced myoblast differentiation through a mechanism involving activation of p38 MAP kinase. Nuclear pore complex (NPC) composition, in particular changes in NUP62 content, may be altered during viral infection, differentiation, and in neoplastic growth. The results support a functional role for changes in Nup62 composition in NPCs and density-induced myogenic differentiation, and suggest a link between loss of Nup62 content and induction of an intracellular stress signaling pathways.

Timing Is Everything-The High Sensitivity of Avian Satellite Cells to Thermal Conditions During Embryonic and Posthatch Periods

Myofiber formation is essentially complete at hatch, but myofiber hypertrophy increases posthatch through the assimilation of satellite cell nuclei into myofibers. Satellite cell proliferation and differentiation occur during the early growth phase, which in meat-type poultry terminates at around 8 days posthatch. Thus, any factor that affects the accumulation of satellite cells during late-term embryogenesis or early posthatch will dictate long-term muscle growth. This review will focus on the intimate relationship between thermal conditions during chick embryogenesis and the early posthatch period, and satellite cell myogenesis and pectoralis growth and development. Satellite cells are highly sensitive to temperature changes, particularly when those changes occur during crucial periods of their myogenic activity. Therefore, timing, temperature, and duration of thermal treatments have a great impact on satellite cell activity and fate, affecting muscle development and growth in the long run. Short and mild thermal manipulations during embryogenesis or thermal conditioning in the early posthatch period promote myogenic cell proliferation and differentiation, and have long-term promotive effects on muscle growth. However, chronic heat stress during the first 2 weeks of life has adverse effects on these parameters and may lead to muscle myopathies.

FGF6 enhances muscle regeneration after nerve injury by relying on ERK1/2 mechanism

BACKGROUND

Severe peripheral nerve injury leads to skeletal muscle atrophy and impaired limb function that is not sufficiently improved by existing treatments. Fibroblast growth factor 6 (FGF6) is involved in tissue regeneration and is dysregulated in denervated rat muscles. However, the way that FGF6 affects skeletal muscle repair after peripheral nerve injury has not been fully elucidated.

METHODS

In this study, we investigated the role of FGF6 in the regeneration of denervated muscles using myoblast cells and an in vivo model of peripheral nerve injury.

RESULTS

FGF6 promoted the viability and migration of C2C12 and primary myoblasts in a dose-dependent manner through FGFR1-mediated upregulation of cyclin D1. Low concentrations of FGF6 promoted myoblast differentiation through FGFR4-mediated activation of ERK1/2, which upregulated expression of MyHC, MyoD, and myogenin. FGFR-1, FGFR4, MyoD, and myogenin were not upregulated when FGF6 expression was inhibited in myoblasts by shRNA-mediated knockdown. Injection of FGF6 into denervated rat muscles enhanced the MyHC-IIb muscle fiber phenotype and prevented muscular atrophy.

CONCLUSION

These findings indicate that FGF6 reduces skeletal muscle atrophy by relying on the ERK1/2 mechanism and enhances the conversion of slow muscle to fast muscle fibers, thereby promoting functional recovery of regenerated skeletal muscle after innervation.

CDR1as/miRNAs-related regulatory mechanisms in muscle development and diseases

Muscles are critical tissues for mammals due to their close association with movement and physiology. Myogenesis involves proliferation, differentiation, and fusion of myoblast, in which many well-known protein-coding genes, as well as linear non-coding RNAs such as microRNAs (miRNAs), are involved. Recently, circular RNAs (circRNAs) have attracted much attention since several circRNAs are known to play significant roles in muscle development and diseases through limited mechanisms, particularly through sponging miRNAs. Through advanced researches, increasing evidence suggests that Cerebellar Degeneration-Related protein 1 antisense (CDR1as) is an important circRNA that regulates the levels of mRNAs expression via competitively sponged miRNAs. Here, we reviewed the robust expression and base pairing relationships of CDR1as and several myogenic miRNAs, as well as these miRNAs and their targeted genes in muscles or some muscle-related diseases. These potential CDR1as/miRNAs/mRNA pathways will provide the basis for further research on the function of CDR1as in muscle development, and eventually extend the versatile roles of CDR1as in mammals.

A Novel Long Noncoding RNA, lncR-125b, Promotes the Differentiation of Goat Skeletal Muscle Satellite Cells by Sponging miR-125b

Long noncoding RNAs (lncRNAs) have emerged as essential regulators of skeletal myogenesis, but few myogenesis-associated lncRNAs have been identified and our understanding of their regulatory mechanisms remains limited, particularly in goat. Here, we identified a novel lncRNA, TCONS_00006810 (named lncR-125b), from our previous lncRNA sequencing data on fetal (45, 60, and 105 days of gestation, three biological replicates for each point) and postnatal (3 days after birth, n = 3) goat skeletal muscle, and found that it is highly expressed in skeletal muscle and gradually upregulated during skeletal muscle satellite cell (SMSC) differentiation in goat. Notably, overexpression of lncR-125b accelerated the expression of myogenic differentiation 1 (MyoD 1) and myogenin (MyoG), and the formation of myotubes, and knockdown of lncR-125b showed opposite effects in SMSCs. Results of dual-luciferase assay and quantitative real-time polymerase chain reaction revealed that lncR-125b acts as a molecular sponge for miR-125b and that insulin-like growth factor 2 (IGF2), a critical regulator of skeletal myogenesis, is a direct target gene of miR-125b. Further analyses showed that lncR-125b negatively regulates miR-125b expression and positively regulates IGF2 expression in SMSCs. Mechanistically, lncR-125b promotes SMSC differentiation by functioning as a competing endogenous RNA (ceRNA) for miR-125b to control IGF2 expression. These findings identify lncR-125b as a novel noncoding regulator of muscle cell differentiation and skeletal muscle development in goat.

The Expression Pattern of p32 in Sheep Muscle and Its Role in Differentiation, Cell Proliferation, and Apoptosis of Myoblasts

The complement 1q binding protein C (C1QBP), also known as p32, is highly expressed in rapidly growing tissues and plays a crucial role in cell proliferation and apoptosis. However, there are no data interpreting its mechanisms in muscle development. To investigate the role of p32 in sheep muscle development, an 856 bp cDNA fragment of p32 containing an 837 bp coding sequence that encodes 278 amino acids was analyzed. We then revealed that the expression of p32 in the longissimus and quadricep muscles of fetal sheep was more significantly up-regulated than expression at other developmental stages. Furthermore, we found that the expression of p32 was increased during myoblasts differentiation in vitro. Additionally, the knockdown of p32 in sheep myoblasts effectively inhibited myoblast differentiation, proliferation, and promoted cell apoptosis in vitro. The interference of p32 also changed the energy metabolism from Oxidative Phosphorylation (OXPHOS) to glycolysis and activated AMP-activated protein kinase (AMPK) phosphorylation in sheep myoblasts in vitro. Taken together, our data suggest that p32 plays a vital role in the development of sheep muscle and provides a potential direction for future research on muscle development and some muscle diseases.

Integrated miRNA-mRNA transcriptomic analysis reveals epigenetic-mediated embryonic muscle growth differences between Wuzhishan and Landrace pigs1

Pig is one of the major dietary protein sources for human consumption, from which muscle is the largest protein origin. However, molecular mechanisms concerning early porcine embryonic muscle development distinctions between pig breeds are still unclear. In this study, an integrated analysis of transcriptome and miRNAome was conducted using longissimus dorsi muscle of 4 early embryonic stages around the primary myofiber formation time (18-, 21-, 28-, and 35-d post coitus) from 2 pig breeds (Landrace [LR] and Wuzhishan [WZS]) differing in meat mass. The global miRNA/mRNA expression profile showed that WZS prepared for myogenic developmental processes earlier than LR. After identifying and analyzing the interaction network of top 100 up-/down-regulated miRNA and their target genes, we were able to find 3 gene clusters: chromatin modification-related (Chd2, H3f3a, Chd6, and Mll1), myogenesis-related (Pax3, Pbx1, Mef2a, and Znf423), and myosin component-related (Mylk, Myo5a, Mylk4, Myh9, and Mylk2) gene clusters. These genes may involve in miRNA-gene myogenic regulatory network that plays vital role in regulating distinct early porcine embryonic myogenic processes between LR and WZS. In summary, our study reveals an epigenetic-mediated myogenic regulatory axial that will help us to decipher molecular mechanisms concerning early porcine embryonic muscle development distinctions between pig breeds.

Developmental atlas of the RNA editome in Sus scrofa skeletal muscle

Adenosine-to-inosine (A-to-I) RNA editing meditated by adenosine deaminases acting on RNA (ADARs) enzymes is a widespread post-transcriptional event in mammals. However, A-to-I editing in skeletal muscle remains poorly understood. By integrating strand-specific RNA-seq, whole genome bisulphite sequencing, and genome sequencing data, we comprehensively profiled the A-to-I editome in developing skeletal muscles across 27 prenatal and postnatal stages in pig, an important farm animal and biomedical model. We detected 198,892 A-to-I editing sites and found that they occurred more frequently at prenatal stages and showed low conservation among pig, human, and mouse. Both the editing level and frequency decreased during development and were positively correlated with ADAR enzymes expression. The hyper-edited genes were functionally related to the cell cycle and cell division. A co-editing module associated with myogenesis was identified. The developmentally differential editing sites were functionally enriched in genes associated with muscle development, their editing levels were highly correlated with expression of their host mRNAs, and they potentially influenced the gain/loss of miRNA binding sites. Finally, we developed a database to visualize the Sus scrofa RNA editome. Our study presents the first profile of the dynamic A-to-I editome in developing animal skeletal muscle and provides evidences that RNA editing is a vital regulator of myogenesis.

Common Carp mef2 Genes: Evolution and Expression

The MEF2 (myocyte enhancer factor 2) family belongs to the MADS-box superfamily of eukaryotic transcription factors. The vertebrate genes compose four distinct subfamilies designated MEF2A, -B, -C, and -D. There are multiple mef2 genes in the common carp (Cyprinus carpio). So far, the embryonic expression patterns of these genes and the evolution of fish mef2 genes have been barely investigated. In this study, we completed the coding information of C. carpio mef2ca2 and mef2d1 genes via gene cloning and presented two mosaic mef2 sequences as evidence for recombination. We also analyzed the phylogenetic relationship and conserved synteny of mef2 genes and proposed a new evolutionary scenario. In our version, MEF2B and the other three vertebrate subfamilies were generated in parallel from the single last ancestor via two rounds of whole genome duplication events that occurred at the dawn of vertebrates. Moreover, we examined the expression patterns of C. carpio mef2 genes during embryogenesis, by using whole-mount in situ hybridization, and found the notochord to be a new expression site for these genes except for mef2ca1&2. Our results thus provide new insights into the evolution and expression of mef2 genes.

Differential Expression of KCNJ12 Gene and Association Analysis of Its Missense Mutation with Growth Traits in Chinese Cattle

Simple Summary

A central goal of livestock genomic study is to find causal genes underlying economic traits and identify effective variations which can be used as molecular markers for livestock breeding. The cattle KCNJ12 gene is an important candidate gene. To date, however, there have been no reports about the use of its missense mutation as a marker in cattle stature. In this study, missense mutation in KCNJ12 was firstly verified, which led to a change in its protein sequence. Further, a significant association was detected between the mutation of KCNJ12 and cattle stature, and we determined that the mutation in KCNJ12 could be used as a molecular marker in beef breeding programs. In addition, expression analysis of the KCNJ12 gene revealed high abundance in muscle and potential roles in bovine myocyte differentiation, which may be the subject of our future research.

Abstract

The potassium inwardly rectifying channel, subfamily J, member 12 (KCNJ12) gene is a promising candidate for economic traits because of its crucial roles in myoblast development. Here, a missense mutation (Cys > Arg) was first detected to be located in exon 3 of KCNJ12 from three Chinese cattle breeds by DNA-pool sequencing. Then, we performed an association analysis of this single-nucleotide polymorphism (SNP) with stature in three Chinese cattle populations (n = 820). A significantly positive correlation was revealed by a reduced animal general linear model and the CC genotype was the most favorable in three breeds. Further, we measured the expression profile of the KCNJ12 gene in various cattle tissues and primary bovine skeletal muscle cells. Ubiquitous expression with high abundance in muscle was observed. Further, in primary bovine skeletal muscle cells, the KCNJ12 mRNA expression was gradually up-regulated in differentiation medium (DM) compared with that in growth medium (GM), suggesting that the KCNJ12 gene is involved in bovine myocyte differentiation. Conclusively, the KCNJ12 gene is a functional candidate gene which can be used as a molecular marker for cattle breeding.

Nontranslational function of leucyl-tRNA synthetase regulates myogenic differentiation and skeletal muscle regeneration

Aside from its catalytic function in protein synthesis, leucyl-tRNA synthetase (LRS) has a nontranslational function in regulating cell growth via the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) pathway by sensing amino acid availability. mTOR also regulates skeletal myogenesis, but the signaling mechanism is distinct from that in cell growth regulation. A role of LRS in myogenesis has not been reported. Here we report that LRS negatively regulated myoblast differentiation in vitro. This function of LRS was independent of its regulation of protein synthesis, and it required leucine-binding but not tRNA charging activity of LRS. Local knock down of LRS accelerated muscle regeneration in a mouse injury model, and so did the knock down of Rag or Raptor. Further in vitro studies established a Rag-mTORC1 pathway, which inhibits the IRS1-PI3K-Akt pathway, to be the mediator of the nontranslational function of LRS in myogenesis. BC-LI-0186, an inhibitor reported to disrupt LRS-Rag interaction, promoted robust muscle regeneration with enhanced functional recovery, and this effect was abolished by cotreatment with an Akt inhibitor. Taken together, our findings revealed what we believe is a novel function for LRS in controlling the homeostasis of myogenesis, and suggested a potential therapeutic strategy to target a noncanonical function of a housekeeping protein.

Long non-coding RNA Irm enhances myogenic differentiation by interacting with MEF2D

Recent studies suggest important roles for long non-coding RNAs as essential regulators of myogenic differentiation. Here, we report that lncRNA Irm is upregulated during myogenesis. Functional analyses show that the overexpression of Irm enhances myogenic differentiation, whereas the inhibition of Irm has completely opposite effects in vitro. Notably, the inhibition of Irm blocks damage-induced muscle regeneration in vivo. Mechanistically, Irm regulates the expression of myogenic genes by directly binding to MEF2D, which in turn promotes the assembly of MyoD/MEF2D on the regulatory elements of target genes. Collectively, we have identified a novel lncRNA that interacts with MEF2D to regulate myogenesis.

TGF-β Family Signaling in Mesenchymal Differentiation

Mesenchymal stem cells (MSCs) can differentiate into several lineages during development and also contribute to tissue homeostasis and regeneration, although the requirements for both may be distinct. MSC lineage commitment and progression in differentiation are regulated by members of the transforming growth factor-β (TGF-β) family. This review focuses on the roles of TGF-β family signaling in mesenchymal lineage commitment and differentiation into osteoblasts, chondrocytes, myoblasts, adipocytes, and tenocytes. We summarize the reported findings of cell culture studies, animal models, and interactions with other signaling pathways and highlight how aberrations in TGF-β family signaling can drive human disease by affecting mesenchymal differentiation.

The Transcriptome of the Zebrafish Embryo After Chemical Exposure: A Meta-Analysis

Numerous studies have been published in the past years investigating the transcriptome of the zebrafish embryo (ZFE) upon being subjected to chemical stress. Aiming at a more mechanistic understanding of the results of such studies, knowledge about commonalities of transcript regulation in response to chemical stress is needed. Thus, our goal in this study was to identify and interpret genes and gene sets constituting a general response to chemical exposure. Therefore, we aggregated and reanalyzed published toxicogenomics data obtained with the ZFE. We found that overlap of differentially transcribed genes in response to chemical stress across independent studies is generally low and the most commonly differentially transcribed genes appear in less than 50% of all treatments across studies. However, effect size analysis revealed several genes showing a common trend of differential expression, among which genes related to calcium homeostasis emerged as key, especially in exposure settings up to 24 h post-fertilization. Additionally, we found that these and other downregulated genes are often linked to anatomical regions developing during the respective exposure period. Genes showing a trend of increased expression were, among others, linked to signaling pathways (e.g., Wnt, Fgf) as well as lysosomal structures and apoptosis. The findings of this study help to increase the understanding of chemical stress responses in the developing zebrafish embryo and provide a starting point to improve experimental designs for this model system. In future, improved time- and concentration-resolved experiments should offer better understanding of stress response patterns and access to mechanistic information.

HDAC4 regulates satellite cell proliferation and differentiation by targeting P21 and Sharp1 genes

Skeletal muscle exhibits a high regenerative capacity, mainly due to the ability of satellite cells to replicate and differentiate in response to appropriate stimuli. Epigenetic control is effective at different stages of this process. It has been shown that the chromatin-remodeling factor HDAC4 is able to regulate satellite cell proliferation and commitment. However, its molecular targets are still uncovered. To explain the signaling pathways regulated by HDAC4 in satellite cells, we generated tamoxifen-inducible mice with conditional inactivation of HDAC4 in Pax7⁺ cells (HDAC4 KO mice). We found that the proliferation and differentiation of HDAC4 KO satellite cells were compromised, although similar amounts of satellite cells were found in mice. Moreover, we found that the inhibition of HDAC4 in satellite cells was sufficient to block the differentiation process. By RNA-sequencing analysis we identified P21 and Sharp1 as HDAC4 target genes. Reducing the expression of these target genes in HDAC4 KO satellite cells, we also defined the molecular pathways regulated by HDAC4 in the epigenetic control of satellite cell expansion and fusion.

Exercise-Induced Hypertrophic and Oxidative Signaling Pathways and Myokine Expression in Fast Muscle of Adult Zebrafish

Skeletal muscle is a plastic tissue that undergoes cellular and metabolic adaptations under conditions of increased contractile activity such as exercise. Using adult zebrafish as an exercise model, we previously demonstrated that swimming training stimulates hypertrophy and vascularization of fast muscle fibers, consistent with the known muscle growth-promoting effects of exercise and with the resulting increased aerobic capacity of this tissue. Here we investigated the potential involvement of factors and signaling mechanisms that could be responsible for exercise-induced fast muscle remodeling in adult zebrafish. By subjecting zebrafish to swimming-induced exercise, we observed an increase in the activity of mammalian target of rapamycin (mTOR) and Mef2 protein levels in fast muscle. We also observed an increase in the protein levels of the mitotic marker phosphorylated histone H3 that correlated with an increase in the protein expression levels of Pax7, a satellite-like cell marker. Furthermore, the activity of AMP-activated protein kinase (AMPK) was also increased by exercise, in parallel with an increase in the mRNA expression levels of pgc1α and also of pparda, a β-oxidation marker. Changes in the mRNA expression levels of slow and fast myosin markers further supported the notion of an exercise-induced aerobic phenotype in zebrafish fast muscle. The mRNA expression levels of il6, il6r, apln, aplnra and aplnrb, sparc, decorin and igf1, myokines known in mammals to be produced in response to exercise and to signal through mTOR/AMPK pathways, among others, were increased in fast muscle of exercised zebrafish. These results support the notion that exercise increases skeletal muscle growth and myogenesis in adult zebrafish through the coordinated activation of the mTOR-MEF2 and AMPK-PGC1α signaling pathways. These results, coupled with altered expression of markers for oxidative metabolism and fast-to-slow fiber-type switch, also suggest improved aerobic capacity as a result of swimming-induced exercise. Finally, the induction of myokine expression by swimming-induced exercise support the hypothesis that these myokines may have been produced and secreted by the exercised zebrafish muscle and acted on fast muscle cells to promote metabolic remodeling. These results support the use of zebrafish as a suitable model for studies on muscle remodeling in vertebrates, including humans.

MEF2 Transcription Factor Regulates Osteogenic Differentiation of Dental Pulp Stem Cells

The myocyte enhancer factor-2 (MEF2) is a member of the MADS-box family. It controls the expression of genes that are critical for biological processes such as proliferation, cell death, and differentiation. Some studies have shown that MEF2 expression is enhanced in osteogenic progenitor cells established from bone marrow stromal cells with other types of mesenchymal progenitor cells. However, the effect of MEF2 on dental pulp stem cells (DPSCs) is unclear. In this study, we investigate the effect of MEF2 on regulating osteogenic differentiation and proliferation of DPSCs. We find that MEF2 is stably expressed in DPSCs, and the expression is increased time-dependently along with cell osteogenic differentiation. MEF2 expression also increases the alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2) activity, and enhances mineralization in DPSCs. SB202190, inhibitor of p38, blocks the p38/MEF2 pathway and osteogenic differentiation. In addition, MEF2 overexpression inhibits DPSC proliferation. In summary, our data indicate that MEF2 not only regulates DPSCs as an inhibitor of cell proliferation but is also a promoter of osteogenic differentiation through the p38/MEF2 signaling pathway.

Dynamic transcriptomic analysis in hircine longissimus dorsi muscle from fetal to neonatal development stages

Muscle growth and development from fetal to neonatal stages consist of a series of delicately regulated and orchestrated changes in expression of genes. In this study, we performed whole transcriptome profiling based on RNA-Seq of caprine longissimus dorsi muscle tissue obtained from prenatal stages (days 45, 60, and 105 of gestation) and neonatal stage (the 3-day-old newborn) to identify genes that are differentially expressed and investigate their temporal expression profiles. A total of 3276 differentially expressed genes (DEGs) were identified (Q value < 0.01). Time-series expression profile clustering analysis indicated that DEGs were significantly clustered into eight clusters which can be divided into two classes (Q value < 0.05), class I profiles with downregulated patterns and class II profiles with upregulated patterns. Based on cluster analysis, GO enrichment analysis found that 75, 25, and 8 terms to be significantly enriched in biological process (BP), cellular component (CC), and molecular function (MF) categories in class I profiles, while 35, 21, and 8 terms to be significantly enriched in BP, CC, and MF in class II profiles. KEGG pathway analysis revealed that DEGs from class I profiles were significantly enriched in 22 pathways and the most enriched pathway was Rap1 signaling pathway. DEGs from class II profiles were significantly enriched in 17 pathways and the mainly enriched pathway was AMPK signaling pathway. Finally, six selected DEGs from our sequencing results were confirmed by qPCR. Our study provides a comprehensive understanding of the molecular mechanisms during goat skeletal muscle development from fetal to neonatal stages and valuable information for future studies of muscle development in goats.

Cellular, biochemical and molecular changes in muscles from patients with X-linked myotubular myopathy due to MTM1 mutations

Centronuclear myopathies are early-onset muscle diseases caused by mutations in several genes including MTM1, DNM2, BIN1, RYR1 and TTN. The most severe and often fatal X-linked form of myotubular myopathy (XLMTM) is caused by mutations in the gene encoding the ubiquitous lipid phosphatase myotubularin, an enzyme specifically dephosphorylating phosphatidylinositol-3-phosphate and phosphatidylinositol-3,5-bisphosphate. Because XLMTM patients have a predominantly muscle-specific phenotype a number of pathogenic mechanisms have been proposed, including a direct effect of the accumulated lipid on the skeletal muscle calcium channel ryanodine receptor 1, a negative effect on the structure of intracellular organelles and defective autophagy. Animal models knocked out for MTM1 show severe reduction of ryanodine receptor 1 mediated calcium release but, since knocking out genes in animal models does not necessarily replicate the human phenotype, we considered it important to study directly the effect of MTM1 mutations on patient muscle cells. The results of the present study show that at the level of myotubes MTM1 mutations do not dramatically affect calcium homeostasis and calcium release mediated through the ryanodine receptor 1, though they do affect myotube size and nuclear content. On the other hand, mature muscles such as those obtained from patient muscle biopsies exhibit a significant decrease in expression of the ryanodine receptor 1, a decrease in muscle-specific microRNAs and a considerable up-regulation of histone deacetylase-4. We hypothesize that the latter events consequent to the primary genetic mutation, are the cause of the severe decrease in muscle strength that characterizes these patients.

Risk of Myopathy in Patients in Therapy with Statins: Identification of Biological Markers in a Pilot Study

Statin therapy may induce skeletal muscle damage ranging from myalgia to severe rhabdomyolysis. Our previous preclinical studies showed that statin treatment in rats involves the reduction of skeletal muscle ClC-1 chloride channel expression and related chloride conductance (gCl). An increase of the activity of protein kinase C theta (PKC theta) isoform, able to inactivate ClC-1, may contribute to destabilize sarcolemma excitability. These effects can be detrimental for muscle function leading to drug-induced myopathy. Our goal is to study the causes of statin-induced muscle side effects in patients at the aim to identify biological markers useful to prevent and counteract statin-induced muscle damage. We examined 10 patients, who experienced myalgia and hyper-CK-emia after starting statin therapy compared to 9 non-myopathic subjects not using lipid-lowering drugs. Western Blot (WB) analysis showed a 40% reduction of ClC-1 protein and increased expression of phosphorylated PKC in muscle biopsies of statin-treated patients with respect to untreated subjects, independently from their age and statin type. Real-time PCR analysis showed that despite reduction of the protein, the ClC-1 mRNA was not significantly changed, suggesting post-transcriptional modification. The mRNA expression of a series of genes was also evaluated. MuRF-1 was increased in accord with muscle atrophy, MEF-2, calcineurin (CN) and GLUT-4 transporter were reduced, suggesting altered transcription, alteration of glucose homeostasis and energy deficit. Accordingly, the phosphorylated form of AMPK, measured by WB, was increased, suggesting cytoprotective process activation. In parallel, mRNA expression of Notch-1, involved in muscle cell proliferation, was highly expressed in statin-treated patients, indicating active regeneration. Also, PGC-1-alpha and isocitrate-dehydrogenase increased expression together with increased activity of mitochondrial citrate-synthase, measured by spectrophotometric assay, suggests mitochondrial biogenesis. Thus, the reduction of ClC-1 protein and consequent sarcolemma hyperexcitability together with energy deficiency appear to be among the most important alterations to be associated with statin-related risk of myopathy in humans. Thus, it may be important to avoid statin treatment in pathologies characterized by energy deficit and chloride channel malfunction. This study validates the measure of ClC-1 expression as a reliable clinical test for assessing statin-dependent risk of myopathy.

Effects of dietary methionine on breast muscle growth, myogenic gene expression and IGF-I signaling in fast- and slow-growing broilers

This study investigated the responses of fast- (FG) and slow- (SG) growing broilers to dietary methionine (Met) status. The broilers were subjected to low (LM, 0.38 and 0.28 g/100 g), adequate (AM, 0.51 and 0.42 g/100 g) and high (HM, 0.65 and 0.52 g/100 g) Met during 1–21 and 22–42 d, respectively. Compared with the LM diets, the AM and HM diets increased body weight gain only in the FG broilers. The HM diets increased breast muscle yield only in the FG broilers, although insulin-like growth factor-I (IGF-I) concentration was increased in both strains of broilers. The HM diets increased mRNA levels of myogenic regulatory factors (MRF4, Myf5) and myocyte enhancer factor 2 (MEF2A and MEF2B) in the FG broilers, and increased MEF2A and decreased myostatin mRNA level in the SG broilers. Extracellular signal-regulated kinase (ERK) phosphorylation of breast muscle was increased by the HM diets in both strains of broilers, but mechanistic target of rapamycin (mTOR) phosphorylation was increased by the AM and HM diets only in the FG broilers. These results reflect a strain difference in broiler growth and underlying mechanism in response to dietary Met.

Study of bovine gene: the temporal-spatial expression patterns, polymorphism and association analysis with meat production traits

The gene () encodes a transcription factor belonging to the MEF2 family that plays an important role in myogenesis by transcriptional regulation of genes involved in skeletal muscle growth and development. Despite the established importance of the factors in the muscular growth and development, the temporal-spatial expression and biological function of have not been reported in cattle. The aim of this study was to analyze the level of expression in the developing longissimus dorsi muscle (LM) of 4 cattle breeds (Polish Holstein-Friesian [HF], Limousine [LIM], Hereford [HER], Polish Red [PR]), differing in terms of meat production and utility type, at 6, 9, and 12 mo of age. The genetic polymorphism and expression patterns in 6 tissues (heart, spleen, liver, semitendinosus muscle [ST], gluteus medius muscle [GM], and LM) were also investigated. The results showed that mRNA was expressed at a high level in adult skeletal and cardiac muscles. Moreover, expression was markedly greater in the GM than in the LM ( 0.05) and ST ( 0.01). An age-dependent and breed-specific comparison of mRNA level in skeletal muscle of HF, LIM, HER, and PR bulls showed that age was significant differentiating factor of transcript/protein abundance in the LM of HER and LIM ( 0.001) compared to HF and PR, for which the differences in mRNA level were not significant ( > 0.05). Regarding the breed effect on the expression, significantly greater mRNA/protein level was noticed in the LM of 9 and 12 mo-old HER than of LIM ( 0.01), HF ( 0.001), and PR ( 0.001). Four novel SNP, namely, (promoter), (exon 7), (exon 8), and (3'UTR), were identified. We found that 3'UTR variant, situated within the seed region of the miR-5187-3p and miR-6931-5p binding sites, was associated with the level of mRNA/protein in LM of 12-mo-old HF bulls. In addition, we observed a significant association between some carcass quality traits, including meat and carcass fatness quality traits, and various 3'UTR genotypes in the investigated population of HF cattle. Our finding provides new evidence of the significant role in the postnatal muscle growth and development in cattle, and indicates that can be a promising molecular marker for carcass quality-related traits in adult cattle.

From Nutrient to MicroRNA: a Novel Insight into Cell Signaling Involved in Skeletal Muscle Development and Disease

Skeletal muscle is a remarkably complicated organ comprising many different cell types, and it plays an important role in lifelong metabolic health. Nutrients, as an external regulator, potently regulate skeletal muscle development through various internal regulatory factors, such as mammalian target of rapamycin (mTOR) and microRNAs (miRNAs). As a nutrient sensor, mTOR, integrates nutrient availability to regulate myogenesis and directly or indirectly influences microRNA expression. MiRNAs, a class of small non-coding RNAs mediating gene silencing, are implicated in myogenesis and muscle-related diseases. Meanwhile, growing evidence has emerged supporting the notion that the expression of myogenic miRNAs could be regulated by nutrients in an epigenetic mechanism. Therefore, this review presents a novel insight into the cell signaling network underlying nutrient-mTOR-miRNA pathway regulation of skeletal myogenesis and summarizes the epigenetic modifications in myogenic differentiation, which will provide valuable information for potential therapeutic intervention.

The MADS-box XAANTAL1 increases proliferation at the Arabidopsis root stem-cell niche and participates in transition to differentiation by regulating cell-cycle components

Background Morphogenesis depends on the concerted modulation of cell proliferation and differentiation. Such modulation is dynamically adjusted in response to various external and internal signals via complex transcriptional regulatory networks that mediate between such signals and regulation of cell-cycle and cellular responses (proliferation, growth, differentiation). In plants, which are sessile, the proliferation/differentiation balance is plastically adjusted during their life cycle and transcriptional networks are important in this process. MADS-box genes are key developmental regulators in eukaryotes, but their role in cell proliferation and differentiation modulation in plants remains poorly studied. Methods We characterize the XAL1 loss-of-function xal1-2 allele and overexpression lines using quantitative cellular and cytometry analyses to explore its role in cell cycle, proliferation, stem-cell patterning and transition to differentiation. We used quantitative PCR and cellular markers to explore if XAL1 regulates cell-cycle components and PLETHORA1 (PLT1) gene expression, as well as confocal microscopy to analyse stem-cell niche organization. Key Results We previously showed that XAANTAL1 (XAL1/AGL12) is necessary for Arabidopsis root development as a promoter of cell proliferation in the root apical meristem. Here, we demonstrate that XAL1 positively regulates the expression of PLT1 and important components of the cell cycle: CYCD3;1, CYCA2;3, CYCB1;1, CDKB1;1 and CDT1a. In addition, we show that xal1-2 mutant plants have a premature transition to differentiation with root hairs appearing closer to the root tip, while endoreplication in these plants is partially compromised. Coincidently, the final size of cortex cells in the mutant is shorter than wild-type cells. Finally, XAL1 overexpression-lines corroborate that this transcription factor is able to promote cell proliferation at the stem-cell niche. Conclusion XAL1 seems to be an important component of the networks that modulate cell proliferation/differentiation transition and stem-cell proliferation during Arabidopsis root development; it also regulates several cell-cycle components.

Genome-wide identification and characterization of long non-coding RNAs in developmental skeletal muscle of fetal goat

Background

Long non-coding RNAs (lncRNAs) have been studied extensively over the past few years. Large numbers of lncRNAs have been identified in mouse, rat, and human, and some of them have been shown to play important roles in muscle development and myogenesis. However, there are few reports on the characterization of lncRNAs covering all the development stages of skeletal muscle in livestock.

Results

RNA libraries constructed from developing longissimus dorsi muscle of fetal (45, 60, and 105 days of gestation) and postnatal (3 days after birth) goat (Capra hircus) were sequenced. A total of 1,034,049,894 clean reads were generated. Among them, 3981 lncRNA transcripts corresponding to 2739 lncRNA genes were identified, including 3515 intergenic lncRNAs and 466 anti-sense lncRNAs. Notably, in pairwise comparisons between the libraries of skeletal muscle at the different development stages, a total of 577 transcripts were differentially expressed (P < 0.05) which were validated by qPCR using randomly selected six lncRNA genes. The identified goat lncRNAs shared some characteristics, such as fewer exons and shorter length, with the lncRNAs in other mammals. We also found 1153 lncRNAs genes were neighbored 1455 protein-coding genes (<10 kb upstream and downstream) and functionally enriched in transcriptional regulation and development-related processes, indicating they may be in cis-regulatory relationships. Additionally, Pearson’s correlation coefficients of co-expression levels suggested 1737 lncRNAs and 19,422 mRNAs were possibly in trans-regulatory relationships (r > 0.95 or r < −0.95). These co-expressed mRNAs were enriched in development-related biological processes such as muscle system processes, regulation of cell growth, muscle cell development, regulation of transcription, and embryonic morphogenesis.

Conclusions

This study provides a catalog of goat muscle-related lncRNAs, and will contribute to a fuller understanding of the molecular mechanism underpinning muscle development in mammals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3009-3) contains supplementary material, which is available to authorized users.

Time course and side-by-side analysis of mesodermal, pre-myogenic, myogenic and differentiated cell markers in the chicken model for skeletal muscle formation

The chicken is a well-established model for amniote (including human) skeletal muscle formation because the developmental anatomy of chicken skeletal muscle matches that of mammals. The accessibility of the chicken in the egg as well as the sequencing of its genome and novel molecular techniques have raised the profile of this model. Over the years, a number of regulatory and marker genes have been identified that are suited to monitor the progress of skeletal myogenesis both in wildtype and in experimental embryos. However, in the various studies, differing markers at different stages of development have been used. Moreover, contradictory results on the hierarchy of regulatory factors are now emerging, and clearly, factors need to be able to cooperate. Thus, a reference paper describing in detail and side-by-side the time course of marker gene expression during avian myogenesis is needed. We comparatively analysed onset and expression patterns of the key markers for the chicken immature paraxial mesoderm, for muscle-competent cells, for cells committed to myogenesis and for cells entering terminal differentiation. We performed this analysis from stages when the first paraxial mesoderm is being laid down to the stage when mesoderm formation comes to a conclusion. Our data show that, although the sequence of marker gene expression is the same at the various stages of development, the timing of the expression onset is quite different. Moreover, marker gene expression in myogenic cells being deployed from the dorsomedial and ventrolateral lips of the dermomyotome is different from those being deployed from the rostrocaudal lips, suggesting different molecular programs. Furthermore, expression of Myosin Heavy Chain genes is overlapping but different along the length of a myotube. Finally, Mef2c is the most likely partner of Mrf proteins, and, in contrast to the mouse and more alike frog and zebrafish fish, chicken Mrf4 is co-expressed with MyoG as cells enter terminal differentiation.