circPTPN4 regulates myogenesis via the miR-499-3p/NAMPT axis

Background:Circular RNAs(circ RNAs)are a novel class of endogenous nc RNA,which widely exist in the transcriptomes of different species and tissues.Recent studies indicate important roles for circ RNAs in the regulation of gene expression by acting as competing endogenous RNAs(ce RNAs).However,the specific role of circ RNAs in myogenesis is still poorly understood.In this study,we attempted to systematically identify the circ RNAs involved in myogenesis and analyze the biological functions of circ RNAs in chicken skeletal muscle development.Results:In total,532 circ RNAs were identified as being differentially expressed between pectoralis major(PEM)and soleus(SOL)in 7-week-old Xinghua chicken.Among them,a novel circ RNA(novel_circ_002621),generated by PTPN4 gene,was named circ PTPN4 and identified.circ PTPN4 is highly expressed in skeletal muscle,and its expression level is upregulated during myoblast differentiation.circ PTPN4 facilitates the proliferation and differentiation of myoblast.Moreover,circ PTPN4 suppresses mitochondria biogenesis and activates fast-twitch muscle phenotype.Mechanistically,circ PTPN4 can function as a ce RNA to regulate NAMPT expression by sponging mi R-499-3p,thus participating in AMPK signaling.Conclusions:circ PTPN4 functions as a ce RNA to regulate NAMPT expression by sponging mi R-499-3p,thus promoting the proliferation and differentiation of myoblast,as well as activating fast-twitch muscle phenotype.

Role of Mutant TBP in Regulation of Myogenesis on Muscle Satellite Cells

In polyglutamine(PolyQ)diseases,mutant proteins cause not only neurological problems but also peripheral tissue abnormalities.Among all systemic damages,skeletal muscle dystrophy is the severest.Previously by studying knock-in(KI)mouse models of spinal cerebellar ataxia 17(SCA17),it was found that mutant TATA box binding protein(TBP)decreases its interaction with myogenic differentiation antigen,thus reducing the expression of skeletal muscle structural proteins and resulting in muscle degeneration.In this paper,the role of mutant TBP in myogenesis was investigated.Single myofibers were isolated from tibialis anterior muscles of wild type(WT)and SCA17KI mice.The 1TBP18 staining confirmed the expression of mutant TBP in muscle satellite cells in SCA17Ki mice.In the BaCl2-induced TA muscle injury,H&E cross-section staining showed no significant change in myofibril size before and after BaCl2 treatment,and there was no significant difference in centralized nuclei between WT and SCA17KI mice,suggesting that mutant TBP had no significant effect on muscle regeneration.In the cultured primary myoblasts from WT and SCA17KI mice in vitro,representative BrdU immunostaining showed no significant difference in proliferation of muscle satellite cells.The primary myoblasts were then induced to differentiate and immunostained for eMyHC,and the staining showed there was no significant difference in differentiation of primary myoblasts between WT and SCA1KI mice.Our findings confirmed that mutant TBP had no significant effect on myogenesis.

Highly Aligned Ternary Nanofiber Matrices Loaded with MXene Expedite Regeneration of Volumetric Muscle Loss

Current therapeutic approaches for volumetric muscle loss(VML)face challenges due to limited graft availability and insufficient bioactivities.To overcome these limitations,tissue-engineered scaffolds have emerged as a promising alternative.In this study,we developed aligned ternary nanofibrous matrices comprised of poly(lactide-co-ε-caprolactone)integrated with collagen and Ti_(3)C_(2)T_(x)MXene nanoparticles(NPs)(PCM matrices),and explored their myogenic potential for skeletal muscle tissue regeneration.The PCM matrices demonstrated favorable physicochemical properties,including structural uniformity,alignment,microporosity,and hydrophilicity.In vitro assays revealed that the PCM matrices promoted cellular behaviors and myogenic differentiation of C2C12 myoblasts.Moreover,in vivo experiments demonstrated enhanced muscle remodeling and recovery in mice treated with PCM matrices following VML injury.Mechanistic insights from next-generation sequencing revealed that MXene NPs facilitated protein and ion availability within PCM matrices,leading to elevated intracellular Ca^(2+)levels in myoblasts through the activation of inducible nitric oxide synthase(i NOS)and serum/glucocorticoid regulated kinase 1(SGK1),ultimately promoting myogenic differentiation via the m TOR-AKT pathway.Additionally,upregulated i NOS and increased NO–contributed to myoblast proliferation and fiber fusion,thereby facilitating overall myoblast maturation.These findings underscore the potential of MXene NPs loaded within highly aligned matrices as therapeutic agents to promote skeletal muscle tissue recovery.

A Transcriptomic Analysis of Physiological Significance of Hypoxia-inducible Factor-1α in Myogenesis and Carbohydrate Metabolism of Genioglossus in Mice

Background： Chronic intermittent hypoxia is the most remarkable feature of obstructive sleep apnea/hypopnea syndrome and it can induce the change of hypoxia-inducible factor-1α （H IF-1α） expression and contractile properties in the genioglossus. To clarify the role of HIF-lot in contractile properties of the genioglossus, this study generated and compared high-throughput RNA-sequencing data from genioglossus between HIF-1α conditional knockout （KO） mice and littermate wild-type （WT） mice. Methods： KO mice were generated with cre-loxP strategy. Gene expression profile analysis was performed using gene enrichment analysis. Gene ontology （GO） and Kyoto Encyclopedia of Genes and Genomes （KEGG） pathway analyses of differently expressed messenger RNAs were performed to identify the related pathways and biological lhnctions. Six differentially expressed genes （DEGs） were validated by qualitative reverse transcription polymerase chain reaction. Results： A total of 142 （77 upregulated and 65 downregulated） transcripts were found to exhibit statistically significant difference between the HIF-la-KO and WT mice. GO and KEGG analyses indicated that DEGs included genes involved in ＂skeletal muscle cell differentiation,＂ ＂muscle organ development,＂ ＂glucose metabolic process,＂ ＂glycogen biosynthetic and metabolic process,＂ etc. Conclusion： This study might provide evidence that H IF-lot affects the expression of multiple genes involved in the myogenesis, muscle developrnent, and carbohydrate metabolism through transcriptome analysis in conditional HIE-1α-KO mice.

Coordinated transcriptional and post-transcriptional epigenetic regulation during skeletal muscle development and growth in pigs

Background:N6-methyladenosine(m^(6)A)and DNA 5-methylcytosine(5mC)methylation plays crucial roles in diverse biological processes,including skeletal muscle development and growth.Recent studies unveiled a potential link between these two systems,implicating the potential mechanism of coordinated transcriptional and post-transcrip-tional regulation in porcine prenatal myogenesis and postnatal skeletal muscle growth.Methods:Immunofluorescence and co-IP assays were carried out between the 5mC writers and m^(6)A writers to investigate the molecular basis underneath.Large-scale in-house transcriptomic data were compiled for applying weighted correlation network analysis(WGCNA)to identify the co-expression patterns of m^(6)A and 5mC regulators and their potential role in pig myogenesis.Whole-genome bisulfite sequencing(WGBS)and methylated RNA immu-noprecipitation sequencing(MeRIP-seq)were performed on the skeletal muscle samples from Landrace pigs at four postnatal growth stages(days 30,60,120 and 180).Results:Significantly correlated expression between 5mC writers and m^(6)A writers and co-occurrence of 5mC and m^(6)A modification were revealed from public datasets of C2C12 myoblasts.The protein-protein interactions between the DNA methylase and the m^(6)A methylase were observed in mouse myoblast cells.Further,by analyzing tran-scriptome data comprising 81 pig skeletal muscle samples across 27 developmental stages,we identified a 5mC/m^(6)A epigenetic module eigengene and decoded its potential functions in pre-or post-transcriptional regulation in postnatal skeletal muscle development and growth of pigs.Following integrative multi-omics analyses on the WGBS methylome data and MeRIP-seq data for both m^(6)A and gene expression profiles revealed a genome/transcriptome-wide correlated dynamics and co-occurrence of 5mC and m^(6)A modifications as a consequence of 5mC/m^(6)A crosstalk in the postnatal myogenesis progress of pigs.Last,we identified a group of myogenesis-related genes collaboratively regulated by both 5mC and m^(6)A modifications in postnatal skeletal muscle growth in pigs.Conclusions:Our study discloses a potential epigenetic mechanism in skeletal muscle development and provides a novel direction for animal breeding and drug development of related human muscle-related diseases.

Myostatin gene promoter:structure,conservation and importance as a target for muscle modulation

Myostatin(MSTN) is one of the key factors regulating myogenesis. Because of its role as a negative regulator of muscle mass deposition, much interest has been given to its protein and, in recent years, several studies have analysed MSTN gene regulation. This review discusses the MSTN gene promoter, focusing on its structure in several animal species, both vertebrate and invertebrate. We report the important binding sites considering their degree of phylogenetic conservation and roles they play in the promoter activity. Finally, we discuss recent studies focusing on MSTN gene regulation via promoter manipulation and the potential applications they have both in medicine and agriculture.

Neonatal vitamin A injection promotes cattle muscle growth and increases oxidative muscle fibers

Background: Vitamin A and its metabolite,retinoic acid(RA),are important regulators of cell differentiation and organ morphogenesis.Its impact on beef cattle muscle growth remains undefined.Method: Angus steer calves were administrated with 0(control) or 150,000 IU vitamin A(retinyl palmitate in glycerol,i.m.) per calf at birth and 1 month of age.At 2 months of age,a biopsy of the Biceps femoris muscle was obtained to analyze the immediate effects of vitamin A injection on myogenic capacity of muscle cells.The resulting steers were harvested at 14 months of age.Results: Vitamin A administration increased cattle growth at 2 months.At 2 months of age,Vitamin A increased PAX7 positive satellite cells and the expression of myogenic marker genes including PAX7,MYF5,MYOD and MYOG.Muscle derived mononuclear cells were further isolated and induced myogenesis in vitro.More myotubes and a higher degree of myogenesis was observed in vitamin A groups.Consistently,vitamin A increased Latissimus dorsi(LD) muscle fiber size at harvest.In addition,vitamin A increased the ratio of oxidative type I and type IIA fibers and reduced the glycolic type IIX fibers.Furthermore,we found that RA,a key bioactive metabolite of vitamin A,activated PPARGC1 A promoter,which explains the upregulated expression of PPARGC1 A in skeletal muscle.Conclusion: Vitamin A administration to neonatal calves enhanced postnatal muscle growth by promoting myogenesis and increasing satellite cell density,accompanied with a shift to oxidative muscle fibers.

Stem cell transplantation for treating Duchenne muscular dystrophy A Web of Science-based literature analysis

OBJECTIVE： To identify global research trends in stem cell transplantation for treating Duchenne muscular dystrophy using a bibliometric analysis of Web of Science. DATA RETRIEVAL： We performed a bibliometric analysis of studies on stem cell transplantation for treating Duchenne muscular dystrophy from 2002 to 2011 retrieved from Web of Science. SELECTION CRITERIA： Inclusion criteria： （a） peer-reviewed published articles on stem cell transplantation for treating Duchenne muscular dystrophy indexed in Web of Science; （b） original research articles, reviews, meeting abstracts, proceedings papers, book chapters, editorial material, and news items; and （c） publication between 2002 and 2011. Exclusion criteria： （a） articles that required manual searching or telephone access; （b） documents that were not published in the public domain; and （c） corrected papers. MAIN OUTCOME MEASURES： （1）Annual publication output; （2） distribution according to subject areas; （3） distribution according to journals; （4） distribution according to country; （5） distribution according to institution; （6） distribution according to institution in China; （7） distribution according to institution that cooperated with Chinese institutions; （8） top-cited articles from 2002 to 2006; （9） top-cited articles from 2007 to 2011. RESULTS： A total of 318 publications on stem cell transplantation for treating Duchenne muscular dystrophy were retrieved from Web of Science from 2002 to 2011, of which almost half derived from American authors and institutes. The number of publications has gradually increased over the past 10 years. Most papers appeared in journals with a focus on gene and molecular research, such as Molecular Therapy, Neuromuscular Disorders, and PLoS One. The 10 most-cited papers from 2002 to 2006 were mostly about different kinds of stem cell transplantation for muscle regeneration, while the 10 most-cited papers from 2007 to 2011 were mostly about new techniques of stem cell transplantation for treating Duchenne muscular dystrophy. CONCLUSION： The publications on stem cell transplantation for treating Duchenne muscular dystrophy were relatively few. It also needs more research to confirm that stem cell therapy is a reliable treatment for Duchenne muscular dystrophy.

Dietary isoleucine improved flesh quality,muscle antioxidant capacity,and muscle growth associated with AKT/TOR/S6K1 and AKT/FOXO3a signaling in hybrid bagrid catfish(Pelteobagrus vachelli♀×Leiocassis longirostris♂)

Background:Muscle is the complex and heterogeneous tissue,which comprises the primary edible part of the trunk of fish and mammals.Previous studies have shown that dietary isoleucine(Ile)exerts beneficial effects on growth in aquatic animals.However,there were limited studies regarding the benefits of Ile on fish muscle and their effects on flesh quality and muscle growth.Thus,this study was conducted to explore whether dietary Ile had affected flesh quality and muscle growth in hybrid bagrid catfish(Pelteobagrus vachelli♀×Leiocassis longirostris♂).Methods:A total of 630 hybrid fish,with an initial average body weight of 33.11±0.09 g,were randomly allotted into seven experimental groups with three replicates each,and respectively fed seven diets with 5.0,7.5,10.0,12.5,15.0,17.5,and 20.0 g Ile/kg diets for 8 weeks.Results:In the present study,we demonstrated that Ile significantly:(1)increased muscle protein and lipid contents and the frequency distribution of myofibers with≤20μm and≥50μm of diameter;(2)improved pH value,shear force,cathepsin B and L activities,hydroxyproline content,resilience,cohesiveness,and decreased cooking loss,lactate content,hardness,springiness,gumminess,and chewiness;(3)decreased reactive oxygen species(ROS),malondialdehyde(MDA),and protein carbonyl(PC)contents,GCLC and Keap1 mRNA levels,and up-regulated CuZnSOD,CAT,GPX1a,GST,and Nrf2 mRNA levels;(4)up-regulated the insulin-like growth factor 1,2(IGF-1,IGF-2),insulin-like growth factor 1 receptor(IGF-1R),proliferating cell nuclear antigen(PCNA),Myf5,Myod,Myog,Mrf4,and MyHC mRNA levels,and decreased MSTN mRNAlevel;(5)increased muscle protein deposition by activating AKT-TOR-S6K1 and AKT-FOXO3a signaling pathways.Conclusion:These results revealed that dietary Ile improved flesh quality,which might be due to increasing nutritional content,physicochemical,texture parameters,and antioxidant ability;promoting muscle growth by affecting myocytes hyperplasia and hypertrophy,and muscle protein deposition associated with protein synthesis and degradation signaling pathways.Finally,the quadratic regression analysis of chewiness,ROS,and protein contents against dietary Ile levels suggested that the optimal dietary Ile levels for hybrid bagrid catfish was estimated to be 14.19,12.36,and 12.78 g/kg diet,corresponding to 36.59,31.87,and 32.96 g/kg dietary protein,respectively.

Transgene expression and differentiation of baculovirus-transduced adipose-derived stem cells from dystrophin-utrophin double knock-out mouse

In this study, recombinant baculovirus carrying the microdystrophin and β-catenin genes was used to infect adipose-derived stem cells from a dystrophin-utrophin double knock-out mouse. Results showed that, after baculovirus transgene infection, microdystrophin and β-catenin genes were effectively expressed in adipose-derived stem cells from the dystrophin-utrophin double knock-out mouse. Furthermore, this transgenic expression promoted adipose-derived stem cell differentiation into muscle cells, but inhibited adipogenic differentiation. In addition, protein expression related to the microdystrophin and Wnt/β-catenin signaling pathway was upregulated. Our experimental findings indicate that baculovirus can successfully deliver the microdystrophin and β-catenin genes into adipose-derived stem cells, and the microdystrophin and Wnt/β-catenin signaling pathway plays an important role in myogenesis of adipose-derived stem cells in the dystrophin-utrophin double knock-out mouse.

Developmental Dynamics of the Larval Muscle System of Bay Scallop(Argopecten irradians)

Though the larval development of bivalves has been extensively studied for commercial purposes,the dynamic development of larval muscle system remains largely unknown.In this study,we characterized the larval muscle system at different developmental stages(D-shaped veligers,umbo veligers and spats)in the bay scallop(Argopecten irradians)by phalloidin staining and under a confocal microscopy.The functional muscles are initially established at the early stage of veligers,which have four pairs of velar retractors and one anterior adductor.At the veliger stage,the velum and posterior retractor muscles are functionally important for velar contractility but undergo an irreversible shrink until they disappear at the end of the larval stage.During metamorphosis,three crucial modifications take place in the larval muscle system.The metamorphosis process involves the gradual degeneration of velum retractors,mantle margin development from an unfolded to a three-fold state,and remodeling of the adductor muscle system from dimyarian(two adductors)to monomyarian condition(one adductor)as in juveniles/adults.All retractor muscles are composed of striated muscle,but both anterior and posterior adductors have smooth and striated components.These findings highlight that the morphological changes at different stages are typical features of myogenesis in scallops.The present knowledge on the developmental dynamics of myogenesis in the bay scallop will not only improve our understanding of phenotypic diversity of larval myoanatomy in bivalves,but also provide useful information on the larval culture in hatcheries.

The expression,function,and coding potential of circular RNA circEDC3 in chicken skeletal muscle development

As an emerging class of non-coding transcripts,circular RNAs(circRNAs)are proved to participate in the complex process of myogenesis in diverse species.A previous study has identified circular RNA EDC3(circEDC3)as a typical covalently closed circular RNA abundant in chicken skeletal muscle.This study found that circEDC3 is a conservative circular RNA and performed functional analysis to investigate the role of circEDC3 in chicken muscle growth.The results indicated that circEDC3 could inhibit(P<0.05)chicken skeletal muscle satellite cells(SMSCs)proliferation and differentiation but had no significant influence on SMSCs apoptosis.Additionally,bioinformatics analysis showed that circEDC3 had promising coding potential.The open reading frames(ORF)were found in circEDC3 in this study.Furthermore,this study predicted that circEDC3 had internal ribosome entry sites(IRES)and N6-methyladenosine(m6A)motifs in different species,implying that circEDC3 might be translatable.This study revealed that circEDC3 might be a negative regulator in chicken muscle development and suggested it has protein-coding potential in different species.

Multiple Isoforms of Olive Flounder (Paralichthys olivaceus) Pax3a and Pax3b Display Differential Regulations on Myogenic Differentiation

Paired box 3(Pax3)is a critical upstream regulator of the onset of myogenesis.We have previously identified two spliced isoforms of pax3a(pax3a-1 and pax3a-2)and three spliced isoforms of pax3b(pax3b-1,pax3b-2,and pax3b-3)in olive flounder,but their roles in myogenesis are unknown.In this study,we investigated their cellular localization,transcriptional activity on myod gene regulation,and roles in myogenesis.Different Pax3a and Pax3b isoforms revealed various subcellular localizations,which were related to their corresponding protein structures.Pax3a-1,Pax3a-2,and Pax3b-1 promoted the transcriptional activity of myod to dif-ferent degrees,whereas Pax3b-2 and Pax3b-3 had a slight inhibitory or no effect.The pairwise interaction analysis demonstrated the synergistic effect of Pax3b-1 and Pax3b-3 on myod transcriptional activity.The overexpression of different pax3a and pax3b isoforms differentially altered the spatial expression patterns of myod and differentially regulated the expression levels of their target genes(myod,myf5,and c-met)in zebrafish embryonic myogenesis.In addition,the different flounder myod promoter-driven pax3a/3b isoform expression vectors were successfully introduced into the skeletal muscles of juvenile flounder by electroporation.How-ever,none of them could change the mRNA expression levels of mstn,myf5,myod,myogenin,pax7a,and pax7b in the electroporated muscles.These results suggest that different Pax3a and Pax3b isoforms may precisely and collaboratively regulate embryonic myogenesis,but their roles in juvenile myogenesis are uncertain.

Effect of Androstenedione on Adipogenesis in Murine C3H10T1/2 Mesenchymal Cells

Clinical trials of weak androgen androstenedione (AD) administered at a high concentration, showed an increase in muscle mass in men like strong androgens testosterone (T) and dihydrotestosterone (DHT), but did not show any inhibitory effect on fat mass unlike strong androgens. This observation prompted us to check the in-vitro effect of AD on adipogenesis using mouse mesenchymal multipotent cells (C3H10T1/2), which can differentiate into both myoblasts and adipocytes. Results indicated that AD inhibited adipogenesis at 10 nM, 100 nM and 1 μM concentrations, but not at 10 μM concentration. AD did not inhibit adipogenesis at 10 μM concentration and also did not inhibitmyogenesis at 10 μM concentration. Addition of bicalutamide, an androgen receptor (AR) antagonist decreased myogenesis and increased adipogenesis, indicating that the effect of AD was mediated through AR. Another weak androgen dehydroepiandrosterone (DHEA) also showed the same pattern of adipogenesis in 10T1/2 cells. AD also showed a similar pattern of adipogenesis in 3T3-L1 preadipocyte cells. Thus, the in-vitro results of AD on adipogenesis correlated with the in-vivo results of AD on fat-mass from clinical trials and suggested a possible difference in biological action between weak androgens (AD, DHEA) and strong androgens (T, DHT) on adipogenesis. Since the biological action of AD was mediated through AR, this physiological difference onadipogenesis could be due to the nature (partial agonist/antagonist) of AD binding to AR.

Biology of Hippo signaling pathway:Skeletal muscle development and beyond

Global demand for farm animals and their meat products i.e.,pork,chicken and other livestock meat,is steadily incresing.With the ongoing life science research and the rapid development of biotechnology,it is a great opportunity to develop advanced molecular breeding markers to efficiently improve animal meat production traits.Hippo is an important study subject because of its crucial role in the regulation of organ size.In recent years,with the increase of research on Hippo signaling pathway,the integrative application of multi-omics technologies such as genomics,transcriptomics,proteomics,and metabolomics can help promote the in-depth involvement of Hippo signaling pathway in skeletal muscle development research.The Hippo signaling pathway plays a key role in many biological events,including cell division,cell migration,cell proliferation,cell differentiation,cell apoptosis,as well as cell adhesion,cell polarity,homeostasis,maintenance of the face of mechanical overload,etc.Its influence on the development of skeletal muscle has important research value for enhancing the efficiency of animal husbandry production.In this study,we traced the origin of the Hippo pathway,comprehensively sorted out all the functional factors found in the pathway,deeply analyzed the molecular mechanism of its function,and classified it from a novel perspective based on its main functional domain and mode of action.Our aim is to systematically explore its regulatory role throughout skeletal muscle development.We specifically focus on the Hippo signaling pathway in embryonic stem cell development,muscle satellite cell fate determination,myogenesis,skeletal muscle meat production and organ size regulation,muscle hypertrophy and atrophy,muscle fiber formation and its transformation between different types,and cardiomyocytes.The roles in proliferation and regeneration are methodically summarized and analyzed comprehensively.The summary and prospect of the Hippo signaling pathway within this article will provide ideas for further improving meat production and muscle deposition and developing new molecular breeding technologies for livestock and poultry,which will be helpful for the development of animal molecular breeding.

Vitamin A injection at birth improves muscle growth in lambs

Vitamin A and its metabolite,retinoic acid(RA)play important roles in regulating skeletal muscle development.This study was conducted to investigate the effects of early intramuscular vitamin A injection on the muscle growth of lambs.A total of 16 newborn lambs were given weekly intramuscular injections of corn oil(control group,n=8)or 7,500 IU vitamin A palmitate(vitamin A group,n=8)from birth to 3 wk of age(4 shots in total).At 3 wk of age and weaning,biceps femoris muscle samples were taken to analyze the effects of vitamin A on the myogenic capacity of skeletal muscle cells.All lambs were slaughtered at 8 months of age.The results suggest that vitamin A treatment accelerated the growth rate of lambs and increased the loin eye area(P<0.05).Consistently,vitamin A increased the diameter of myofibers in longissimus thoracis muscle(P<0.01)and increased the final body weight of lambs(P<0.05).Vitamin A injection did not change the protein kinase B/mammalian target of rapamycin and myostatin signaling(P>0.05).Moreover,vitamin A upregulated the expression of PAX7(P<0.05)and the myogenic marker genes including MYOD and MYOG(P<0.01).The skeletal muscle-derived mononuclear cells from vitamin A-treated lambs showed higher expression of myogenic genes(P<0.05)and formed more myotubes(P<0.01)when myogenic differentiation was induced in vitro.In addition,in vitro analysis showed that RA promoted myogenic differentiation of the skeletal muscle-derived mononuclear cells in the first 3 d(P<0.05)but not at the later stage(P>0.05)as evidenced by myogenic gene expression and fusion index.Taken together,neonatal intramuscular vitamin A injection promotes lamb muscle growth by promoting the myogenic potential of satellite cells.

Master regulators of skeletal muscle lineage development and pluripotent stem cells differentiation

In vertebrates, the skeletal muscles of the body and their associated stem cells originate from muscle progenitor cells,during development. The specification of the muscles of the trunk, head and limbs, relies on the activity of distinctgenetic hierarchies. The major regulators of trunk and limb muscle specification are the paired-homeobox transcriptionfactors PAX3 and PAX7. Distinct gene regulatory networks drive the formation of the different muscles of thehead. Despite the redeployment of diverse upstream regulators of muscle progenitor differentiation, the commitmenttowards the myogenic fate requires the expression of the early myogenic regulatory factors MYF5, MRF4, MYOD andthe late differentiation marker MYOG. The expression of these genes is activated by muscle progenitors throughoutdevelopment, in several waves of myogenic differentiation, constituting the embryonic, fetal and postnatal phases ofmuscle growth. In order to achieve myogenic cell commitment while maintaining an undifferentiated pool of muscleprogenitors, several signaling pathways regulate the switch between proliferation and differentiation of myoblasts.The identification of the gene regulatory networks operating during myogenesis is crucial for the development ofin vitro protocols to differentiate pluripotent stem cells into myoblasts required for regenerative medicine.

Canonical NF-κB signaling regulates satellite stem cell homeostasis and function during regenerative myoge nesis

Skeletal muscle regeneration in adults is attributed to the presence of satellite stem cells that proliferate,differentiate,and eventually fuse with injured myofibers.However,the signaling mechanisms that regulate satellite cell homeostasis and function remain less understood.While IKKp-mediated canonical NF-κB signaling has been implicated in the regulation of myogenesis and skeletal muscle mass,its role in the regulation of satellite cell function during muscle regeneration has not been fully elucidated.Here,we report that canonical NF-κB signaling is induced in skeletal muscle upon injury.Satellite cell-specific inducible ablation of IKKβattenuates skeletal muscle regeneration in adult mice.Targeted ablation of IKKβalso reduces the number of satellite cells in injured skeletal muscle of adult mice,potentially through inhibiting their proliferation and survival.We also demonstrate that the inhibition of specific components of the canonical NF-κB pathway causes precocious differentiation of cultured satellite cells both ex vivo and in vitro.Finally,our results highlight that the constitutive activation of canonical NF-κB signaling in satellite cells also attenuates skeletal muscle regeneration following injury in adult mice.Collectively,our study demonstrates that the proper regulation of canonical NF-κB signaling is important for the regeneration of adult skeletal muscle.

Characterization and developmental expression of AmphiMef2 gene in amphioxus

Myocyte enhancer factor 2 proteins are members of MADS family of transcription factors, which can control the expression of muscle-specific genes in vertebrates. However, not all Mef2 genes are es-sential for muscle development in invertebrates. Here we have isolated a full-length cDNA from am-phioxus, designated AmphiMef2. The predicted amino acid sequence has highly conserved MADS and MEF2 domains, showing higher identity with the corresponding regions of its homologues in verte-brates than those in invertebrates. Results from whole-mount in situ hybridization show that the ex-pression of AmphiMef2 initially appears in the presomitic mesoderm at early neurula stage, then the transcripts are detected in both the somites and the unsegmented presomitic mesoderm. At 36 h larval stage, the expression is only detected in the posterior somites. By 48 h larval stage, the expression is shifted to the preoral pit (a homologous organ to the vertebrate adenohypophysis) and persists until at least 72 h larval stage. The results suggest that AmphiMef2 may be not only involved in the myogenesis but also the development or function of the preoral pit in amphioxus.

Bio-printing of aligned GelMa-based cell-laden structure for muscle tissue regeneration

Volumetric muscle loss(VML)is associated with a severe loss of muscle tissue that overwhelms the regenerative potential of skeletal muscles.Tissue engineering has shown promise for the treatment of VML injuries,as evidenced by various preclinical trials.The present study describes the fabrication of a cell-laden GelMa muscle construct using an in situ crosslinking(ISC)strategy to improve muscle functionality.To obtain optimal biophysical properties of the muscle construct,two UV exposure sources,UV exposure dose,and wall shear stress were evaluated using C2C12 myoblasts.Additionally,the ISC system showed a significantly higher degree of uniaxial alignment and myogenesis compared to the conventional crosslinking strategy(post-crosslinking).To evaluate the in vivo regenerative potential,muscle constructs laden with human adipose stem cells were used.The VML defect group implanted with the bio-printed muscle construct showed significant restoration of functionality and muscular volume.The data presented in this study suggest that stem cell-based therapies combined with the modified bioprinting process could potentially be effective against VML injuries.