Regulating a master regulator: establishing tissue-specific gene expression in skeletal muscle

Epigenetic control of myogenic identity of human muscle stem cells in Duchenne muscular dystrophy

In Duchenne muscular dystrophy (DMD), muscle stem cells' (MuSCs) regenerative capacities are overwhelmed leading to fibrosis. Whether MuSCs have intrinsic defects or are disrupted by their environment is unclear. We investigated cell behavior and gene expression of MuSCs from DMD or healthy human muscles. Proliferation, differentiation, and fusion were unaltered in DMD-MuSCs, but with time, they lost their myogenic identity twice as fast as healthy MuSCs. The rapid drift toward a fibroblast-like cell identity was observed at the clonal level, and resulted from altered expression of epigenetic enzymes. Re-expression of CBX3, SMC3, H2AFV, and H3F3B prevented the MuSC identity drift. Among epigenetic changes, a closing of chromatin at the transcription factor MEF2B locus caused downregulation of its expression and loss of the myogenic fate. Re-expression of MEF2B in DMD-MuSCs restored their myogenic fate. MEF2B is key in the maintenance of myogenic identity in human MuSCs, which is altered in DMD.

A novel treatment strategy targeting cellular pathways with natural products to alleviate sarcopenia

Sarcopenia is a condition marked by a significant reduction in muscle mass and strength, primarily due to the aging process, which critically impacts muscle protein dynamics, metabolic functions, and overall physical functionality. This condition leads to increased body fat and reduced daily activity, contributing to severe health issues and a lower quality of life among the elderly. Recognized in the ICD-10-CM only in 2016, sarcopenia lacks definitive treatment options despite its growing prevalence and substantial social and economic implications. Given the aging global population, addressing sarcopenia has become increasingly relevant and necessary. The primary causes include aging, cachexia, diabetes, and nutritional deficiencies, leading to imbalances in protein synthesis and degradation, mitochondrial dysfunction, and hormonal changes. Exercise remains the most effective intervention, but it is often impractical for individuals with limited mobility, and pharmacological options such as anabolic steroids and myostatin inhibitors are not FDA-approved and are still under investigation. This review is crucial as it examines the potential of natural products as a novel treatment strategy for sarcopenia, targeting multiple mechanisms involved in its pathogenesis. By exploring natural products' multi-targeted effects, this study aims to provide innovative and practical solutions for sarcopenia management. Therefore, this review indicates significant improvements in muscle mass and function with the use of specific natural compounds, suggesting promising alternatives for those unable to engage in regular physical activity.

The Molecular and Biological Function of MEF2D in Leukemia

Myocyte enhancer factor 2 (MEF2) is a key transcription factor (TF) in skeletal, cardiac, and neural tissue development and includes four isoforms: MEF2A, MEF2B, MEF2C, and MEF2D. These isoforms significantly affect embryonic development, nervous system regulation, muscle cell differentiation, B- and T-cell development, thymocyte selection, and effects on tumorigenesis and leukemia. This chapter describes the multifaceted roles of MEF2 family proteins, covering embryonic development, nervous system regulation, and muscle cell differentiation. It further elucidates the contribution of MEF2 to various blood and immune cell functions. Specifically, in B-cell precursor acute lymphoblastic leukemia (BCP-ALL), MEF2D is aberrantly expressed and forms a fusion protein with BCL9, CSF1R, DAZAP1, HNRNPUL1, and SS18. These fusion proteins are closely related to the pathogenesis of leukemia. In addition, it specifically introduces the regulatory effect of MEF2D fusion protein on the proliferation and growth of B-cell acute lymphoblastic leukemia (B-ALL) cells. Finally, we detail the positive feedback loop between MEF2D and IRF8 that significantly promotes the progression of acute myeloid leukemia (AML) and the importance of the ZMYND8-BRD4 interaction in regulating the IRF8 and MYC transcriptional programs. The MEF2D-CEBPE axis is highlighted as a key transcriptional mechanism controlling the block of leukemic cell self-renewal and differentiation in AML. This chapter starts with the structure and function of MEF2 family proteins, specifically summarizing and analyzing the role of MEF2D in B-ALL and AML, mediating the complex molecular mechanisms of transcriptional regulation and exploring their implications for human health and disease.

Vitamin D status associates with skeletal muscle loss after anterior cruciate ligament reconstruction

BACKGROUNDAlthough 25-hydroxyvitamin D [25(OH)D] concentrations of 30 ng/mL or higher are known to reduce injury risk and boost strength, the influence on anterior cruciate ligament reconstruction (ACLR) outcomes remains unexamined. This study aimed to define the vitamin D signaling response to ACLR, assess the relationship between vitamin D status and muscle fiber cross-sectional area (CSA) and bone density outcomes, and discover vitamin D receptor (VDR) targets after ACLR.METHODSTwenty-one young, healthy, physically active participants with recent ACL tears were enrolled (17.8 ± 3.2 years, BMI 26.0 ± 3.5 kg/m2). Data were collected through blood samples, vastus lateralis biopsies, dual energy x-ray bone density measurements, and isokinetic dynamometer measures at baseline, 1 week, 4 months, and 6 months after ACLR. The biopsies facilitated CSA, Western blotting, RNA-seq, and VDR ChIP-seq analyses.RESULTSACLR surgery led to decreased circulating bioactive vitamin D and increased VDR and activating enzyme expression in skeletal muscle 1 week after ACLR. Participants with less than 30 ng/mL 25(OH)D levels (n = 13) displayed more significant quadriceps fiber CSA loss 1 week and 4 months after ACLR than those with 30 ng/mL or higher (n = 8; P < 0.01 for post hoc comparisons; P = 0.041 for time × vitamin D status interaction). RNA-seq and ChIP-seq data integration revealed genes associated with energy metabolism and skeletal muscle recovery, potentially mediating the impact of vitamin D status on ACLR recovery. No difference in bone mineral density losses between groups was observed.CONCLUSIONCorrecting vitamin D status prior to ACLR may aid in preserving skeletal muscle during recovery.FUNDINGNIH grants R01AR072061, R01AR071398-04S1, and K99AR081367.

Nonsense-mediated mRNA decay suppresses injury-induced muscle regeneration via inhibiting MyoD transcriptional activity

Skeletal muscle regeneration is a crucial physiological process that occurs in response to injury or disease. As an important transcriptome surveillance system that regulates tissue development, the role of nonsense-mediated mRNA decay (NMD) in muscle regeneration remains unclear. Here, we found that NMD inhibits myoblast differentiation by targeting the phosphoinositide-3-kinase regulatory subunit 5 gene, which leads to the suppression of the transcriptional activity of myogenic differentiation (MyoD), a key regulator of myoblast differentiation. This disruption of MyoD transcriptional activity subsequently affects the expression levels of myogenin and myosin heavy chain, crucial markers of myoblast differentiation. Additionally, through up-frameshift protein 1 knockdown experiments, we observed that inhibiting NMD can accelerate muscle regeneration in vivo. These findings highlight the potential of NMD as a novel therapeutic target for the treatment of muscle-related injuries and diseases.

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.

Increasing Skeletal Muscle Mass in Mice by Non-Invasive Intramuscular Delivery of Myostatin Inhibitory Peptide by Iontophoresis

Sarcopenia is a major public health issue that affects older adults. Myostatin inhibitory-D-peptide-35 (MID-35) can increase skeletal muscle and is a candidate therapeutic agent, but a non-invasive and accessible technology for the intramuscular delivery of MID-35 is required. Recently, we succeeded in the intradermal delivery of various macromolecules, such as siRNA and antibodies, by iontophoresis (ItP), a non-invasive transdermal drug delivery technology that uses weak electricity. Thus, we expected that ItP could deliver MID-35 non-invasively from the skin surface to skeletal muscle. In the present study, ItP was performed with a fluorescently labeled peptide on mouse hind leg skin. Fluorescent signal was observed in both skin and skeletal muscle. This result suggested that the peptide was effectively delivered to skeletal muscle from skin surface by ItP. Then, the effect of MID-35/ItP on skeletal muscle mass was evaluated. The skeletal muscle mass increased 1.25 times with ItP of MID-35. In addition, the percentage of new and mature muscle fibers tended to increase, and ItP delivery of MID-35 showed a tendency to induce alterations in the levels of mRNA of genes downstream of myostatin. In conclusion, ItP of myostatin inhibitory peptide is a potentially useful strategy for treating sarcopenia.

Contribution of muscle satellite cells to sarcopenia

Sarcopenia, a disorder characterized by age-related muscle loss and reduced muscle strength, is associated with decreased individual independence and quality of life, as well as a high risk of death. Skeletal muscle houses a normally mitotically quiescent population of adult stem cells called muscle satellite cells (MuSCs) that are responsible for muscle maintenance, growth, repair, and regeneration throughout the life cycle. Patients with sarcopenia are often exhibit dysregulation of MuSCs homeostasis. In this review, we focus on the etiology, assessment, and treatment of sarcopenia. We also discuss phenotypic and regulatory mechanisms of MuSC quiescence, activation, and aging states, as well as the controversy between MuSC depletion and sarcopenia. Finally, we give a multi-dimensional treatment strategy for sarcopenia based on improving MuSC function.

Histone-lysine N-methyltransferase 2 (KMT2) complexes - a new perspective

Histone H3 Lys4 (H3K4) methylation is catalyzed by the Histone-Lysine N-Methyltransferase 2 (KMT2) protein family, and its members are required for gene expression control. In vertebrates, the KMT2s function in large multisubunit complexes known as COMPASS or COMPASS-like complexes (COMplex of Proteins ASsociated with Set1). The activity of these complexes is critical for proper development, and mutation-induced defects in their functioning have frequently been found in human cancers. Moreover, inherited or de novo mutations in KMT2 genes are among the etiological factors in neurodevelopmental disorders such as Kabuki and Kleefstra syndromes. The canonical role of KMT2s is to catalyze H3K4 methylation, which results in a permissive chromatin environment that drives gene expression. However, current findings described in this review demonstrate that these enzymes can regulate processes that are not dependent on methylation: noncatalytic functions of KMT2s include DNA damage response, cell division, and metabolic activities. Moreover, these enzymes may also methylate non-histone substrates and play a methylation-dependent function in the DNA damage response. In this review, we present an overview of the new, noncanonical activities of KMT2 complexes in a variety of cellular processes. These discoveries may have crucial implications for understanding the functions of these methyltransferases in developmental processes, disease, and epigenome-targeting therapeutic strategies in the future.

mRNP granule proteins Fmrp and Dcp1a differentially regulate mRNP complexes to contribute to control of muscle stem cell quiescence and activation

Background

During skeletal muscle regeneration, satellite stem cells use distinct pathways to repair damaged myofibers or to self-renew by returning to quiescence. Cellular/mitotic quiescence employs mechanisms that promote a poised or primed state, including altered RNA turnover and translational repression. Here, we investigate the role of mRNP granule proteins Fragile X Mental Retardation Protein (Fmrp) and Decapping protein 1a (Dcp1a) in muscle stem cell quiescence and differentiation.

Methods

Using isolated single muscle fibers from adult mice, we established differential enrichment of mRNP granule proteins including Fmrp and Dcp1a in muscle stem cells vs. myofibers. We investigated muscle tissue homeostasis in adult Fmr1-/- mice, analyzing myofiber cross-sectional area in vivo and satellite cell proliferation ex vivo. We explored the molecular mechanisms of Dcp1a and Fmrp function in quiescence, proliferation and differentiation in a C2C12 culture model. Here, we used polysome profiling, imaging and RNA/protein expression analysis to establish the abundance and assembly status of mRNP granule proteins in different cellular states, and the phenotype of knockdown cells.

Results

Quiescent muscle satellite cells are enriched for puncta containing the translational repressor Fmrp, but not the mRNA decay factor Dcp1a. MuSC isolated from Fmr1^-/- mice exhibit defective proliferation, and mature myofibers show reduced cross-sectional area, suggesting a role for Fmrp in muscle homeostasis. Expression and organization of Fmrp and Dcp1a varies during primary MuSC activation on myofibers, with Fmrp puncta prominent in quiescence, but Dcp1a puncta appearing during activation/proliferation. This reciprocal expression of Fmrp and Dcp1a puncta is recapitulated in a C2C12 culture model of quiescence and activation: consistent with its role as a translational repressor, Fmrp is enriched in non-translating mRNP complexes abundant in quiescent myoblasts; Dcp1a puncta are lost in quiescence, suggesting stabilized and repressed transcripts. The function of each protein differs during proliferation; whereas Fmrp knockdown led to decreased proliferation and lower cyclin expression, Dcp1a knockdown led to increased cell proliferation and higher cyclin expression. However, knockdown of either Fmrp or Dcp1a led to compromised differentiation. We also observed cross-regulation of decay versus storage mRNP granules; knockdown of Fmrp enhances accumulation of Dcp1a puncta, whereas knockdown of Dcp1a leads to increased Fmrp in puncta.

Conclusions

Taken together, our results provide evidence that the balance of mRNA turnover versus utilization is specific for distinct cellular states.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13395-021-00270-9.

Epigenetic regulation of satellite cell fate during skeletal muscle regeneration

In response to muscle injury, muscle stem cells integrate environmental cues in the damaged tissue to mediate regeneration. These environmental cues are tightly regulated to ensure expansion of muscle stem cell population to repair the damaged myofibers while allowing repopulation of the stem cell niche. These changes in muscle stem cell fate result from changes in gene expression that occur in response to cell signaling from the muscle environment.

Integration of signals from the muscle environment leads to changes in gene expression through epigenetic mechanisms. Such mechanisms, including post-translational modification of chromatin and nucleosome repositioning, act to make specific gene loci more, or less, accessible to the transcriptional machinery. In youth, the muscle environment is ideally structured to allow for coordinated signaling that mediates efficient regeneration. Both age and disease alter the muscle environment such that the signaling pathways that shape the healthy muscle stem cell epigenome are altered. Altered epigenome reduces the efficiency of cell fate transitions required for muscle repair and contributes to muscle pathology. However, the reversible nature of epigenetic changes holds out potential for restoring cell fate potential to improve muscle repair in myopathies.

In this review, we will describe the current knowledge of the mechanisms allowing muscle stem cell fate transitions during regeneration and how it is altered in muscle disease. In addition, we provide some examples of how epigenetics could be harnessed therapeutically to improve regeneration in various muscle pathologies.

Aberrant Activity of Histone-Lysine N-Methyltransferase 2 (KMT2) Complexes in Oncogenesis

KMT2 (histone-lysine N-methyltransferase subclass 2) complexes methylate lysine 4 on the histone H3 tail at gene promoters and gene enhancers and, thus, control the process of gene transcription. These complexes not only play an essential role in normal development but have also been described as involved in the aberrant growth of tissues. KMT2 mutations resulting from the rearrangements of the KMT2A (MLL1) gene at 11q23 are associated with pediatric mixed-lineage leukemias, and recent studies demonstrate that KMT2 genes are frequently mutated in many types of human cancers. Moreover, other components of the KMT2 complexes have been reported to contribute to oncogenesis. This review summarizes the recent advances in our knowledge of the role of KMT2 complexes in cell transformation. In addition, it discusses the therapeutic targeting of different components of the KMT2 complexes.

Master regulator genes and their impact on major diseases

Master regulator genes (MRGs) have become a hot topic in recent decades. They not only affect the development of tissue and organ systems but also play a role in other signal pathways by regulating additional MRGs. Because a MRG can regulate the concurrent expression of several genes, its mutation often leads to major diseases. Moreover, the occurrence of many tumors and cardiovascular and nervous system diseases are closely related to MRG changes. With the development in omics technology, an increasing amount of investigations will be directed toward MRGs because their regulation involves all aspects of an organism’s development. This review focuses on the definition and classification of MRGs as well as their influence on disease regulation.

Dietary Complex and Slow Digestive Carbohydrates Prevent Fat Deposits During Catch-Up Growth in Rats

A nutritional growth retardation study, which closely resembles the nutritional observations in children who consumed insufficient total energy to maintain normal growth, was conducted. In this study, a nutritional stress in weanling rats placed on restricted balanced diet for 4 weeks is produced, followed by a food recovery period of 4 weeks using two enriched diets that differ mainly in the slow (SDC) or fast (RDC) digestibility and complexity of their carbohydrates. After re-feeding with the RDC diet, animals showed the negative effects of an early caloric restriction: an increase in adiposity combined with poorer muscle performance, insulin resistance and, metabolic inflexibility. These effects were avoided by the SDC diet, as was evidenced by a lower adiposity associated with a decrease in fatty acid synthase expression in adipose tissue. The improved muscle performance of the SDC group was based on an increase in myocyte enhancer factor 2D (MEF2D) and creatine kinase as markers of muscle differentiation as well as better insulin sensitivity, enhanced glucose uptake, and increased metabolic flexibility. In the liver, the SDC diet promoted glycogen storage and decreased fatty acid synthesis. Therefore, the SDC diet prevents the catch-up fat phenotype through synergistic metabolic adaptations in adipose tissue, muscle, and liver. These coordinated adaptations lead to better muscle performance and a decrease in the fat/lean ratio in animals, which could prevent long-term negative metabolic alterations such as obesity, insulin resistance, dyslipidemia, and liver fat deposits later in life.

Hierarchical and Dynamic Regulation of Defense-Responsive Specialized Metabolism by WRKY and MYB Transcription Factors

The plant kingdom produces hundreds of thousands of specialized bioactive metabolites, some with pharmaceutical and biotechnological importance. Their biosynthesis and function have been studied for decades, but comparatively less is known about how transcription factors with overlapping functions and contrasting regulatory activities coordinately control the dynamics and output of plant specialized metabolism. Here, we performed temporal studies on pathogen-infected intact host plants with perturbed transcription factors. We identified WRKY33 as the condition-dependent master regulator and MYB51 as the dual functional regulator in a hierarchical gene network likely responsible for the gene expression dynamics and metabolic fluxes in the camalexin and 4-hydroxy-indole-3-carbonylnitrile (4OH-ICN) pathways. This network may have also facilitated the regulatory capture of the newly evolved 4OH-ICN pathway in Arabidopsis thaliana by the more-conserved transcription factor MYB51. It has long been held that the plasticity of plant specialized metabolism and the canalization of development should be differently regulated; our findings imply a common hierarchical regulatory architecture orchestrated by transcription factors for specialized metabolism and development, making it an attractive target for metabolic engineering.

Linking aberrant chromatin features in chronic lymphocytic leukemia to transcription factor networks

In chronic lymphocytic leukemia (CLL), a diverse set of genetic mutations is embedded in a deregulated epigenetic landscape that drives cancerogenesis. To elucidate the role of aberrant chromatin features, we mapped DNA methylation, seven histone modifications, nucleosome positions, chromatin accessibility, binding of EBF1 and CTCF, as well as the transcriptome of B cells from CLL patients and healthy donors. A globally increased histone deacetylase activity was detected and half of the genome comprised transcriptionally downregulated partially DNA methylated domains demarcated by CTCF CLL samples displayed a H3K4me3 redistribution and nucleosome gain at promoters as well as changes of enhancer activity and enhancer linkage to target genes. A DNA binding motif analysis identified transcription factors that gained or lost binding in CLL at sites with aberrant chromatin features. These findings were integrated into a gene regulatory enhancer containing network enriched for B-cell receptor signaling pathway components. Our study predicts novel molecular links to targets of CLL therapies and provides a valuable resource for further studies on the epigenetic contribution to the disease.

Activation of PASK by mTORC1 is required for the onset of the terminal differentiation program

During skeletal muscle regeneration, muscle stem cells (MuSCs) respond to multiple signaling inputs that converge onto mammalian target of rapamycin complex 1 (mTORC1) signaling pathways. mTOR function is essential for establishment of the differentiation-committed progenitors (early stage of differentiation, marked by the induction of myogenin expression), myotube fusion, and, ultimately, hypertrophy (later stage of differentiation). While a major mTORC1 substrate, p70S6K, is required for myotube fusion and hypertrophy, an mTORC1 effector for the induction of myogenin expression remains unclear. Here, we identified Per-Arnt-Sim domain kinase (PASK) as a downstream phosphorylation target of mTORC1 in MuSCs during differentiation. We have recently shown that the PASK phosphorylates Wdr5 to stimulate MuSC differentiation by epigenetically activating the myogenin promoter. We show that phosphorylation of PASK by mTORC1 is required for the activation of myogenin transcription, exit from self-renewal, and induction of the myogenesis program. Our studies reveal that mTORC1-PASK signaling is required for the rise of myogenin-positive committed myoblasts (early stage of myogenesis), whereas mTORC1-S6K signaling is required for myoblast fusion (later stage of myogenesis). Thus, our discoveries allow molecular dissection of mTOR functions during different stages of the myogenesis program driven by two different substrates.

Polycomb/Trithorax Antagonism: Cellular Memory in Stem Cell Fate and Function

Stem cells are continuously challenged with the decision to either self-renew or adopt a new fate. Self-renewal is regulated by a system of cellular memory, which must be bypassed for differentiation. Previous studies have identified Polycomb group (PcG) and Trithorax group (TrxG) proteins as key modulators of cellular memory. In this Perspective, we draw from embryonic and adult stem cell studies to discuss the complex roles played by PcG and TrxG in maintaining cell identity while allowing for microenvironment-mediated alterations in cell fate. Finally, we discuss the potential for targeting these proteins as a therapeutic approach in cancer.

Epigenetics Variation and Pathogenesis in Diabetes

PURPOSE OF REVIEW

Great strides have recently been made in elucidating the role of genetic sequence variation in diabetes pathogenesis. Increasingly, studies are focusing on other factors that may contribute to the pathogenesis of diabetes, such as epigenetics, a term "traditionally" encompassing changes to the DNA that do not alter sequence and are heritable (primary methylation and histone modification) but often expanded to include microRNAs. This review summarizes latest findings on the role of epigenetics in diabetes pathogenesis.

RECENT FINDINGS

Recent studies illustrate roles for methylation changes, histone modification, imprinting, and microRNAs across several diabetes types and complications. Notably, methylation changes in the human leukocyte antigen (HLA) region have been found to precede the development of type 1 diabetes. In type 2 diabetes, lifestyle factors appear to interact with epigenetic mechanisms in pathogenesis. Emerging technologies have allowed increasingly comprehensive descriptive analysis of the role of epigenetic mechanisms in diabetes pathogenesis which have yielded meaningful insights into effects on expression of relevant genes. These findings have the potential to inform future development of predictive testing to enable primary prevention and further work to uncover the complex pathogenesis of diabetes.

Gold and gold-silver alloy nanoparticles enhance the myogenic differentiation of myoblasts through p38 MAPK signaling pathway and promote in vivo skeletal muscle regeneration

Under the severe trauma condition, the skeletal muscles regeneration process is inhibited by forming fibrous scar tissues. Understanding the interaction between bioactive nanomaterials and myoblasts perhaps has important effect on the enhanced skeletal muscle tissue regeneration. Herein, we investigate the effect of monodispersed gold and gold-silver nanoparticles (AuNPs and Au-AgNPs) on the proliferation, myogenic differentiation and associated molecular mechanism of myoblasts (C2C12), as well as the in vivo skeletal muscle tissue regeneration. Our results showed that AuNPs and Au-AgNPs could support myoblast attachment and proliferation with negligible cytotoxicity. Under various incubation conditions (normal and differentiation medium), AuNPs and Au-AuNPs significantly enhanced the myogenic differentiation of myoblasts by upregulating the expressions of myosin heavy chain (MHC) protein and myogenic genes (MyoD, MyoG and Tnnt-1). The further analysis demonstrated that AuNPs and Au-AgNPs could activate the p38α mitogen-activated protein kinase pathway (p38α MAPK) signaling pathway and enhance the myogenic differentiation. Additionally, the AuNPs and Au-AgNPs significantly promote the in vivo skeletal muscle regeneration in a tibialis anterior muscle defect model of rat. This study may provide a nanomaterials-based strategy to improve the skeletal muscle repair and regeneration.

Congenital Hyperinsulinism in Infants with Turner Syndrome: Possible Association with Monosomy X and KDM6A Haploinsufficiency

BACKGROUND

Previous case reports have suggested a possible association of congenital hyperinsulinism with Turner syndrome.

OBJECTIVE

We examined the clinical and molecular features in girls with both congenital hyperinsulinism and Turner syndrome seen at The Children's Hospital of Philadelphia (CHOP) between 1974 and 2017.

METHODS

Records of girls with hyperinsulinism and Turner syndrome were reviewed. Insulin secretion was studied in pancreatic islets and in mouse islets treated with an inhibitor of KDM6A, an X chromosome gene associated with hyperinsulinism in Kabuki syndrome.

RESULTS

Hyperinsulinism was diagnosed in 12 girls with Turner syndrome. Six were diazoxide-unresponsive; 3 had pancreatectomies. The incidence of Turner syndrome among CHOP patients with hyperinsulinism (10 of 1,050 from 1997 to 2017) was 48 times more frequent than expected. The only consistent chromosomal anomaly in these girls was the presence of a 45,X cell line. Studies of isolated islets from 1 case showed abnormal elevated cytosolic calcium and heightened sensitivity to amino acid-stimulated insulin release; similar alterations were demonstrated in mouse islets treated with a KDM6A inhibitor.

CONCLUSION

These results demonstrate a higher than expected frequency of Turner syndrome among children with hyperinsulinism. Our data suggest that haploinsufficiency for KDM6A due to mosaic X chromosome monosomy may be responsible for hyperinsulinism in Turner syndrome.

Identification of novel KMT2D mutations in two Chinese children with Kabuki syndrome: a case report and systematic literature review

Background

Kabuki syndrome (KS) is a rare pediatric congenital disorder with multiple congenital anomalies and intellectual disabilities, which is inherited in an autosomal dominant manner. Mutations in KMT2D and KDM6A have been proven to be the primary cause in most cases of KS.

Case presentation

Here we report two Chinese boys with clinical features of KS referred to our hospital for clinical diagnosis. Next-generation sequencing was performed on MiSeq to analyze the genetic mutations in both patients. In both, two novel de novo mutations in KMT2D gene (c.5235delA, p.(A1746Lfs*39) and c.7048G > A, p.(Q2350*)) were detected, both of which were subsequently confirmed by the two-generation pedigree analysis based on Sanger sequencing. A systematic literature review of previously reported mutational spectrum of KMT2D was also conducted.

Conclusions

Two novel de novo mutations in KMT2D gene were identified and considered to be pathogenic in both of KS patients. Our data adds information to the growing knowledge on the mutational spectrum of KS.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0545-5) contains supplementary material, which is available to authorized users.

To roll the eyes and snap a bite - function, development and evolution of craniofacial muscles

Craniofacial muscles, muscles that move the eyes, control facial expression and allow food uptake and speech, have long been regarded as a variation on the general body muscle scheme. However, evidence has accumulated that the function of head muscles, their developmental anatomy and the underlying regulatory cascades are distinct. This article reviews the key aspects of craniofacial muscle and muscle stem cell formation and discusses how this differs from the trunk programme of myogenesis; we show novel RNAseq data to support this notion. We also trace the origin of head muscle in the chordate ancestors of vertebrates and discuss links with smooth-type muscle in the primitive chordate pharynx. We look out as to how the special properties of head muscle precursor and stem cells, in particular their competence to contribute to the heart, could be exploited in regenerative medicine.

Mef2 and the skeletal muscle differentiation program

Mef2 is a conserved and significant transcription factor in the control of muscle gene expression. In cell culture Mef2 synergises with MyoD-family members in the activation of gene expression and in the conversion of fibroblasts into myoblasts. Amongst its in vivo roles, Mef2 is required for both Drosophila muscle development and mammalian muscle regeneration. Mef2 has functions in other cell-types too, but this review focuses on skeletal muscle and surveys key findings on Mef2 from its discovery, shortly after that of MyoD, up to the present day. In particular, in vivo functions, underpinning mechanisms and areas of uncertainty are highlighted. We describe how Mef2 sits at a nexus in the gene expression network that controls the muscle differentiation program, and how Mef2 activity must be regulated in time and space to orchestrate specific outputs within the different aspects of muscle development. A theme that emerges is that there is much to be learnt about the different Mef2 proteins (from different paralogous genes, spliced transcripts and species) and how the activity of these proteins is controlled.

miRNA-223 upregulated by MYOD inhibits myoblast proliferation by repressing IGF2 and facilitates myoblast differentiation by inhibiting ZEB1

Skeletal muscle differentiation can be regulated by various transcription factors and non-coding RNAs. In our previous work, miR-223 is differentially expressed in the skeletal muscle of chicken with different growth rates, but its role, expression and action mechanism in muscle development still remains unknown. Here, we found that MYOD transcription factor can upregulate miR-223 expression by binding to an E-box region of the gga-miR-223 gene promoter during avian myoblast differentiation. IGF2 and ZEB1 are two target genes of miR-223. The target inhibition of miR-223 on IGF2 and ZEB1 are dynamic from proliferation to differentiation of myoblast. miR-223 inhibits IGF2 expression only in the proliferating myoblast, whereas it inhibits ZEB1 mainly in the differentiating myoblast. The inhibition of IGF2 by miR-223 resulted in the repression of myoblast proliferation. During myoblast differentiation, miR-223 would be upregulated owing to the promoting effect of MYOD, and the upregulation of miR-223 would inhibit ZEB1 to promote myoblast differentiation. These results not only demonstrated that the well-known muscle determination factor MYOD can promote myoblast differentiation by upregulate miR-223 transcription, but also identified that miR-223 can influence myoblast proliferation and differentiation by a dynamic manner regulates the expression of its target genes.

Epigenetic Regulation of Adult Myogenesis

Skeletal muscle regeneration is an efficient stem cell-based repair system that ensures healthy musculature. For this repair system to function continuously throughout life, muscle stem cells must contribute to the process of myofiber repair as well as repopulation of the stem cell niche. The decision made by the muscle stem cells to commit to the muscle repair or to remain a stem cell depends upon patterns of gene expression, a process regulated at the epigenetic level. Indeed, it is well accepted that dynamic changes in epigenetic landscapes to control DNA accessibility and expression is a critical component during myogenesis for the effective repair of damaged muscle. Changes in the epigenetic landscape are governed by various posttranslational histone tail modifications, nucleosome repositioning, and DNA methylation events which collectively allow the control of changes in transcription networks during transitions of satellite cells from a dormant quiescent state toward terminal differentiation. This chapter focuses upon the specific epigenetic changes that occur during muscle stem cell-mediated regeneration to ensure myofiber repair and continuity of the stem cell compartment. Furthermore, we explore open questions in the field that are expected to be important areas of exploration as we move toward a more thorough understanding of the epigenetic mechanism regulating muscle regeneration.

Function analysis of Mef2c promoter in muscle differentiation

Regeneration of adult skeletal muscle following injury occurs through the activation of satellite cells that proliferates, differentiates, and fuses with injured myofibers. Myocyte enhancer factor 2 (MEF2) proteins are reported to have the potential contributions to adult muscle regeneration. To further understand Mef2c gene, the promoter of pig Mef2c gene was analyzed in this paper. Quantitative real-time PCR (qRT-PCR) revealed the expression pattern of Mef2c gene in muscle of eight tissues. The Mef2c promoter had the higher transcriptional activity in differentiated C2C12 cells than that in proliferating C2C12 cells, which was accompanied by the upregulation of mRNA expression of Mef2c gene. Function deletion and mutation analyses showed that MyoD and MEF2 binding sites within the Mef2c promoter were responsible for the regulation of Mef2c transcription. MEF2C could upregulate the transcriptional activities of Mef2c promoter constructs, which contained a 3'-end nucleotide sequence with p300 binding site. The electrophoretic mobility shift assays and chromatin immunoprecipitation assays determined the MyoD binding site in Mef2c promoter. These results advanced our knowledge of the promoter of the pig Mef2c gene, and the study of Mef2c promoter regulator elements helped to elucidate the regulation mechanisms of Mef2c in muscle differentiation or muscle repair and regeneration.

p38 MAPK activation and H3K4 trimethylation is decreased by lactate in vitro and high intensity resistance training in human skeletal muscle

Exercise induces adaptation of skeletal muscle by acutely modulating intracellular signaling, gene expression, protein turnover and myogenic activation of skeletal muscle stem cells (Satellite cells, SCs). Lactate (La)-induced metabolic stimulation alone has been shown to modify SC proliferation and differentiation. Although the mechanistic basis remains elusive, it was demonstrated that La affects signaling via p38 mitogen activated protein kinase (p38 MAPK) which might contribute to trimethylation of histone 3 lysine 4 (H3K4me3) known to regulate satellite cell proliferation and differentiation. We investigated the effects of La on p38 MAPK and H3K4me3 in a model of activated SCs. Differentiating C2C12 myoblasts were treated with La (20 mM) and samples analysed using qRT-PCR, immunofluorescence, and western blotting. We determined a reduction of p38 MAPK phosphorylation, decreased H3K4me3 and reduced expression of Myf5, myogenin, and myosin heavy chain (MHC) leading to decreased differentiation of La-treated C2C12 cells after 5 days of repeated La treatment. We further investigated whether this regulatory pathway would be affected in human skeletal muscle by the application of two different resistance exercise regimes (RE) associated with distinct metabolic demands and blood La accumulation. Muscle biopsies were obtained 15, 30 min, 1, 4, and 24 h post exercise after moderate intensity RE (STD) vs. high intensity RE (HIT). Consistent with in vitro results, reduced p38 phosphorylation and blunted H3K4me3 were also observed upon metabolically demanding HIT RE in human skeletal muscle. Our data provide evidence that La-accumulation acutely affects p38 MAPK signaling, gene expression and thereby cell differentiation and adaptation in vitro, and likely in vivo.

Malat1 regulates myogenic differentiation and muscle regeneration through modulating MyoD transcriptional activity

Malat1 is one of the most abundant long non-coding RNAs in various cell types; its exact cellular function is still a matter of intense investigation. In this study we characterized the function of Malat1 in skeletal muscle cells and muscle regeneration. Utilizing both in vitro and in vivo assays, we demonstrate that Malat1 has a role in regulating gene expression during myogenic differentiation of myoblast cells. Specifically, we found that knockdown of Malat1 accelerates the myogenic differentiation in cultured cells. Consistently, Malat1 knockout mice display enhanced muscle regeneration after injury and deletion of Malat1 in dystrophic mdx mice also improves the muscle regeneration. Mechanistically, in the proliferating myoblasts, Malat1 recruits Suv39h1 to MyoD-binding loci, causing trimethylation of histone 3 lysine 9 (H3K9me3), which suppresses the target gene expression. Upon differentiation, the pro-myogenic miR-181a is increased and targets the nuclear Malat1 transcripts for degradation through Ago2-dependent nuclear RNA-induced silencing complex machinery; the Malat1 decrease subsequently leads to the destabilization of Suv39h1/HP1β/HDAC1-repressive complex and displacement by a Set7-containing activating complex, which allows MyoD trans-activation to occur. Together, our findings identify a regulatory axis of miR-181a-Malat1-MyoD/Suv39h1 in myogenesis and uncover a previously unknown molecular mechanism of Malat1 action in gene regulation.

MEF2 transcription factors: developmental regulators and emerging cancer genes

The MEF2 transcription factors have roles in muscle, cardiac, skeletal, vascular, neural, blood and immune system cell development through their effects on cell differentiation, proliferation, apoptosis, migration, shape and metabolism. Altered MEF2 activity plays a role in human diseases and has recently been implicated in the development of several cancer types. In particular, MEF2B, the most divergent and least studied protein of the MEF2 family, has a role unique from its paralogs in non-Hodgkin lymphomas. The use of genome-scale technologies has enabled comprehensive MEF2 target gene sets to be identified, contributing to our understanding of MEF2 proteins as nodes in complex regulatory networks. This review surveys the molecular interactions of MEF2 proteins and their effects on cellular and organismal phenotypes. We include a discussion of the emerging roles of MEF2 proteins as oncogenes and tumor suppressors of cancer. Throughout this article we highlight similarities and differences between the MEF2 family proteins, including a focus on functions of MEF2B.

Master regulators in development: Views from the Drosophila retinal determination and mammalian pluripotency gene networks

Among the mechanisms that steer cells to their correct fate during development, master regulatory networks are unique in their sufficiency to trigger a developmental program outside of its normal context. In this review we discuss the key features that underlie master regulatory potency during normal and ectopic development, focusing on two examples, the retinal determination gene network (RDGN) that directs eye development in the fruit fly and the pluripotency gene network (PGN) that maintains cell fate competency in the early mammalian embryo. In addition to the hierarchical transcriptional activation, extensive positive transcriptional feedback, and cooperative protein-protein interactions that enable master regulators to override competing cellular programs, recent evidence suggests that network topology must also be dynamic, with extensive rewiring of the interactions and feedback loops required to navigate the correct sequence of developmental transitions to reach a final fate. By synthesizing the in vivo evidence provided by the RDGN with the extensive mechanistic insight gleaned from the PGN, we highlight the unique regulatory capabilities that continual reorganization into new hierarchies confers on master control networks. We suggest that deeper understanding of such dynamics should be a priority, as accurate spatiotemporal remodeling of network topology will undoubtedly be essential for successful stem cell based therapeutic efforts.

P/CAF mediates PAX3-FOXO1-dependent oncogenesis in alveolar rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) is an aggressive paediatric cancer of skeletal muscle with poor prognosis. A PAX3-FOXO1 fusion protein acts as a driver of malignancy in ARMS by disrupting tightly coupled but mutually exclusive pathways of proliferation and differentiation. While PAX3-FOXO1 is an attractive therapeutic target, no current treatments are designed to block its oncogenic activity. The present work shows that the histone acetyltransferase P/CAF (KAT2B) is overexpressed in primary tumours from ARMS patients. Interestingly, in fusion-positive ARMS cell lines, P/CAF acetylates and stabilizes PAX3-FOXO1 rather than MyoD, a master regulator of muscle differentiation. Silencing P/CAF, or pharmacological inhibition of its acetyltransferase activity, down-regulates PAX3-FOXO1 levels concomitant with reduced proliferation and tumour burden in xenograft mouse models. Our studies identify a P/CAF-PAX3-FOXO1 signalling node that promotes oncogenesis and may contribute to MyoD dysfunction in ARMS. This work exemplifies the therapeutic potential of targeting chromatin-modifying enzymes to inhibit fusion oncoproteins that are a frequent event in sarcomas. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

miRNA targeted signaling pathway in the early stage of denervated fast and slow muscle atrophy

Denervation often results in skeletal muscle atrophy. Different mechanisms seem to be involved in the determination between denervated slow and fast skeletal muscle atrophy. At the epigenetic level, miRNAs are thought to be highly involved in the pathophysiological progress of denervated muscles. We used miRNA microarrays to determine miRNA expression profiles from a typical slow muscle (soleus muscle) and a typical fast muscle (tibialis anterior muscle) at an early denervation stage in a rat model. Results showed that miR-206, miR-195, miR-23a, and miR-30e might be key factors in the transformation process from slow to fast muscle in denervated slow muscles. Additionally, certain miRNA molecules (miR-214, miR-221, miR-222, miR-152, miR-320, and Let-7e) could be key regulatory factors in the denervated atrophy process involved in fast muscle. Analysis of signaling pathway networks revealed the miRNA molecules that were responsible for regulating certain signaling pathways, which were the final targets (e.g., p38 MAPK pathway; Pax3/Pax7 regulates Utrophin and follistatin by HDAC4; IGF1/PI3K/Akt/mTOR pathway regulates atrogin-1 and MuRF1 expression via FoxO phosphorylation). Our results provide a better understanding of the mechanisms of denervated skeletal muscle pathophysiology.

p38α MAPK disables KMT1A-mediated repression of myogenic differentiation program

BACKGROUND

Master transcription factor MyoD can initiate the entire myogenic gene expression program which differentiates proliferating myoblasts into multinucleated myotubes. We previously demonstrated that histone methyltransferase KMT1A associates with and inhibits MyoD in proliferating myoblasts, and must be removed to allow differentiation to proceed. It is known that pro-myogenic signaling pathways such as PI3K/AKT and p38α MAPK play critical roles in enforcing associations between MyoD and transcriptional activators, while removing repressors. However, the mechanism which displaces KMT1A from MyoD, and the signals responsible, remain unknown.

METHODS

To investigate the role of p38α on MyoD-mediated differentiation, we utilized C2C12 myoblast cells as an in vitro model. p38α activity was either augmented via overexpression of a constitutively active upstream kinase or blocked via lentiviral delivery of a specific p38α shRNA or treatment with p38α/β inhibitor SB203580. Overexpression of KMT1A in these cells via lentiviral delivery was also used as a system wherein terminal differentiation is impeded by high levels of KMT1A.

RESULTS

The association of KMT1A and MyoD persisted, and differentiation was blocked in C2C12 myoblasts specifically after pharmacologic or genetic blockade of p38α. Conversely, forced activation of p38α was sufficient to activate MyoD and overcome the differentiation blockade in KMT1A-overexpressing C2C12 cells. Consistent with this finding, KMT1A phosphorylation during C2C12 differentiation correlated strongly with the activation of p38α. This phosphorylation was prevented by the inhibition of p38α. Biochemical studies further revealed that KMT1A can be a direct substrate for p38α. Importantly, chromatin immunoprecipitation (ChIP) studies show that the removal of KMT1A-mediated transcription repressive histone tri-methylation (H3K9me3) from the promoter of the Myogenin gene, a critical regulator of muscle differentiation, is dependent on p38α activity in C2C12 cells. Elevated p38α activity was also sufficient to remove this repressive H3K9me3 mark. Moreover, ChIP studies from C2C12 cells show that p38α activity is necessary and sufficient to establish active H3K9 acetylation on the Myogenin promoter.

CONCLUSIONS

Activation of p38α displaces KMT1A from MyoD to initiate myogenic gene expression upon induction of myoblasts differentiation.

CAT7 and cat7l Long Non-coding RNAs Tune Polycomb Repressive Complex 1 Function during Human and Zebrafish Development

The essential functions of polycomb repressive complex 1 (PRC1) in development and gene silencing are thought to involve long non-coding RNAs (lncRNAs), but few specific lncRNAs that guide PRC1 activity are known. We screened for lncRNAs, which co-precipitate with PRC1 from chromatin and found candidates that impact polycomb group protein (PcG)-regulated gene expression in vivo A novel lncRNA from this screen, CAT7, regulates expression and polycomb group binding at the MNX1 locus during early neuronal differentiation. CAT7 contains a unique tandem repeat domain that shares high sequence similarity to a non-syntenic zebrafish analog, cat7l Defects caused by interference of cat7l RNA during zebrafish embryogenesis were rescued by human CAT7 RNA, enhanced by interference of a PRC1 component, and suppressed by interference of a known PRC1 target gene, demonstrating cat7l genetically interacts with a PRC1. We propose a model whereby PRC1 acts in concert with specific lncRNAs and that CAT7/cat7l represents convergent lncRNAs that independently evolved to tune PRC1 repression at individual loci.

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.

De novo exonic deletion of KDM6A in a Chinese girl with Kabuki syndrome: A case report and brief literature review

Kabuki syndrome (KS) is a rare condition with multiple congenital anomalies and mental retardation. Exonic deletions, disrupting the lysine (K)-specific demethylase 6A (KDM6A) gene have been demonstrated as rare cause of KS. Here, we report a de novo 227-kb deletion in chromosome Xp11.3 of a 7-year-old Chinese girl with KS. Besides the symptoms of KS, the patient also presented with skin allergic manifestations, which were considered to be a new, rare feature of the phenotypic spectrum. The deletion includes the upstream region and exons 1-2 of KDM6A and potentially causes haploinsuffiency of the gene. We also discuss the mutation spectrum of KDM6A and clinical variability of patients with KDM6A deletion through a literature review. © 2016 Wiley Periodicals, Inc.

Regulation of Skeletal Muscle Stem Cell Quiescence by Suv4-20h1-Dependent Facultative Heterochromatin Formation

Skeletal muscle stem cells (MuSCs) are required for regeneration of adult muscle following injury, a response that demands activation of mainly quiescent MuSCs. Despite the need for dynamic regulation of MuSC quiescence, relatively little is known about the determinants of this property. Here, we show that Suv4-20h1, an H4K20 dimethyltransferase, controls MuSC quiescence by promoting formation of facultative heterochromatin (fHC). Deletion of Suv4-20h1 reduces fHC and induces transcriptional activation and repositioning of the MyoD locus away from the heterochromatic nuclear periphery. These effects promote MuSC activation, resulting in stem cell depletion and impaired long-term muscle regeneration. Genetic reduction of MyoD expression rescues fHC formation and lost MuSC quiescence, restoring muscle regeneration capacity in Suv4-20h1 mutants. Together, these findings reveal that Suv4-20h1 actively regulates MuSC quiescence via fHC formation and control of the MyoD locus, thereby guarding and preserving the stem cell pool over a lifetime.

Changes in calsequestrin, TNF-α, TGF-β and MyoD levels during the progression of skeletal muscle dystrophy in mdx mice: a comparative analysis of the quadriceps, diaphragm and intrinsic laryngeal muscles

In Duchenne muscular dystrophy (DMD), the search for new biomarkers to follow the evolution of the disease is of fundamental importance in the light of the evolving gene and pharmacological therapies. In addition to the lack of dystrophin, secondary events including changes in calcium levels, inflammation and fibrosis greatly contribute to DMD progression and the molecules involved in these events may represent potential biomarkers. In this study, we performed a comparative evaluation of the progression of dystrophy within muscles that are differently affected by dystrophy (diaphragm; DIA and quadriceps; QDR) or spared (intrinsic laryngeal muscles) using the mdx mice model of DMD. We assessed muscle levels of calsequestrin (calcium-related protein), tumour necrosis factor (TNF-α; pro-inflammatory cytokine), tumour growth factor (TGF-β; pro-fibrotic factor) and MyoD (muscle proliferation) vs. histopathology at early (1 and 4 months of age) and late (9 months of age) stages of dystrophy. Fibrosis was the primary feature in the DIA of mdx mice (9 months: 32% fibrosis), which was greater than in the QDR (9 months: 0.6% fibrosis). Muscle regeneration was the primary feature in the QDR (9 months: 90% of centrally nucleated fibres areas vs. 33% in the DIA). The QDR expressed higher levels of calsequestrin than the DIA. Laryngeal muscles showed normal levels of TNF-α, TGF-β and MyoD. A positive correlation between histopathology and cytokine levels was observed only in the diaphragm, suggesting that TNF-α and TGF-β serve as markers of dystrophy primarily for the diaphragm.

MEF2B mutations in non-Hodgkin lymphoma dysregulate cell migration by decreasing MEF2B target gene activation

Myocyte enhancer factor 2B (MEF2B) is a transcription factor with mutation hotspots at K4, Y69 and D83 in diffuse large B-cell lymphoma (DLBCL). To provide insight into the regulatory network of MEF2B, in this study, we analyse global gene expression and DNA-binding patterns. We find that candidate MEF2B direct target genes include RHOB, RHOD, CDH13, ITGA5 and CAV1, and that indirect target genes of MEF2B include MYC, TGFB1, CARD11, MEF2C, NDRG1 and FN1. MEF2B overexpression increases HEK293A cell migration and epithelial-mesenchymal transition, and decreases DLBCL cell chemotaxis. K4E, Y69H and D83V MEF2B mutations decrease the capacity of MEF2B to activate transcription and decrease its' effects on cell migration. The K4E and D83V mutations decrease MEF2B DNA binding. In conclusion, our map of the MEF2B regulome connects MEF2B to drivers of oncogenesis.

Long-Term Therapy With Omega-3 Ameliorates Myonecrosis and Benefits Skeletal Muscle Regeneration in Mdx Mice

In Duchenne muscle dystrophy (DMD) and in the mdx mouse model of DMD, a lack of dystrophin leads to myonecrosis and cardiorespiratory failure. Several lines of evidence suggest a detrimental role of the inflammatory process in the dystrophic process. Previously, we demonstrated that short-term therapy with eicosapentaenoic acid (EPA), at early stages of disease, ameliorated dystrophy progression in the mdx mouse. In the present study, we evaluated the effects of a long-term therapy with omega-3 later in dystrophy progression. Three-month-old mdx mice received omega-3 (300 mg/kg) or vehicle by gavage for 5 months. The quadriceps and diaphragm muscles were removed and processed for histopathology and Western blot. Long-term therapy with omega-3 increased the regulatory protein MyoD and muscle regeneration and reduced markers of inflammation (TNF-α and NF-kB) in both muscles studied. The present study supports the long-term use of omega-3 at later stages of dystrophy as a promising option to be investigated in DMD clinical trials.

Hijacked in cancer: the KMT2 (MLL) family of methyltransferases

Histone-lysine N-methyltransferase 2 (KMT2) family proteins methylate lysine 4 on the histone H3 tail at important regulatory regions in the genome and thereby impart crucial functions through modulating chromatin structures and DNA accessibility. Although the human KMT2 family was initially named the mixed-lineage leukaemia (MLL) family, owing to the role of the first-found member KMT2A in this disease, recent exome-sequencing studies revealed KMT2 genes to be among the most frequently mutated genes in many types of human cancers. Efforts to integrate the molecular mechanisms of KMT2 with its roles in tumorigenesis have led to the development of first-generation inhibitors of KMT2 function, which could become novel cancer therapies.

A KAP1 phosphorylation switch controls MyoD function during skeletal muscle differentiation

The transcriptional activator MyoD serves as a master controller of myogenesis. Singh et al. identify KAP1/TRIM28 as a key regulator of MyoD function. In myoblasts, KAP1 is present with MyoD and Mef2 at many muscle genes, where it acts as a scaffold to recruit not only coactivators such as p300 and LSD1 but also corepressors such as G9a and HDAC1, with promoter silencing as the net outcome. Upon differentiation, MSK1-mediated phosphorylation of KAP1 releases the corepressors from the scaffold, unleashing transcriptional activation by MyoD/Mef2 and their positive cofactors.

The transcriptional activator MyoD serves as a master controller of myogenesis. Often in partnership with Mef2 (myocyte enhancer factor 2), MyoD binds to the promoters of hundreds of muscle genes in proliferating myoblasts yet activates these targets only upon receiving cues that launch differentiation. What regulates this off/on switch of MyoD function has been incompletely understood, although it is known to reflect the action of chromatin modifiers. Here, we identify KAP1 (KRAB [Krüppel-like associated box]-associated protein 1)/TRIM28 (tripartite motif protein 28) as a key regulator of MyoD function. In myoblasts, KAP1 is present with MyoD and Mef2 at many muscle genes, where it acts as a scaffold to recruit not only coactivators such as p300 and LSD1 but also corepressors such as G9a and HDAC1 (histone deacetylase 1), with promoter silencing as the net outcome. Upon differentiation, MSK1-mediated phosphorylation of KAP1 releases the corepressors from the scaffold, unleashing transcriptional activation by MyoD/Mef2 and their positive cofactors. Thus, our results reveal KAP1 as a previously unappreciated interpreter of cell signaling, which modulates the ability of MyoD to drive myogenesis.

High-wire act: the poised genome and cellular memory

Emerging evidence aided by genome-wide analysis of chromatin and transcriptional states has shed light on the mechanisms by which stem cells achieve cellular memory. The epigenetic and transcriptional plasticity governing stem cell behavior is highlighted by the identification of 'poised' genes, which permit cells to maintain readiness to undertake alternate developmental fates. This review focuses on two crucial mechanisms of gene poising: bivalent chromatin marks and RNA polymerase II stalling. We provide the context for these mechanisms by exploring the current consensus on the regulation of chromatin states, especially in quiescent adult stem cells, where poised genes are critical for recapitulating developmental choices, leading to regenerative function.

Extracellular deposition of matrilin-2 controls the timing of the myogenic program during muscle regeneration

Here, we identify a role for the matrilin-2 (Matn2) extracellular matrix protein in controlling the early stages of myogenic differentiation. We observed Matn2 deposition around proliferating, differentiating and fusing myoblasts in culture and during muscle regeneration in vivo. Silencing of Matn2 delayed the expression of the Cdk inhibitor p21 and of the myogenic genes Nfix, MyoD and Myog, explaining the retarded cell cycle exit and myoblast differentiation. Rescue of Matn2 expression restored differentiation and the expression of p21 and of the myogenic genes. TGF-β1 inhibited myogenic differentiation at least in part by repressing Matn2 expression, which inhibited the onset of a positive-feedback loop whereby Matn2 and Nfix activate the expression of one another and activate myoblast differentiation. In vivo, myoblast cell cycle arrest and muscle regeneration was delayed in Matn2(-/-) relative to wild-type mice. The expression levels of Trf3 and myogenic genes were robustly reduced in Matn2(-/-) fetal limbs and in differentiating primary myoblast cultures, establishing Matn2 as a key modulator of the regulatory cascade that initiates terminal myogenic differentiation. Our data thus identify Matn2 as a crucial component of a genetic switch that modulates the onset of tissue repair.

The interaction of MYC with the trithorax protein ASH2L promotes gene transcription by regulating H3K27 modification

The appropriate expression of the roughly 30,000 human genes requires multiple layers of control. The oncoprotein MYC, a transcriptional regulator, contributes to many of the identified control mechanisms, including the regulation of chromatin, RNA polymerases, and RNA processing. Moreover, MYC recruits core histone-modifying enzymes to DNA. We identified an additional transcriptional cofactor complex that interacts with MYC and that is important for gene transcription. We found that the trithorax protein ASH2L and MYC interact directly in vitro and co-localize in cells and on chromatin. ASH2L is a core subunit of KMT2 methyltransferase complexes that target histone H3 lysine 4 (H3K4), a mark associated with open chromatin. Indeed, MYC associates with H3K4 methyltransferase activity, dependent on the presence of ASH2L. MYC does not regulate this methyltransferase activity but stimulates demethylation and subsequently acetylation of H3K27. KMT2 complexes have been reported to associate with histone H3K27-specific demethylases, while CBP/p300, which interact with MYC, acetylate H3K27. Finally WDR5, another core subunit of KMT2 complexes, also binds directly to MYC and in genome-wide analyses MYC and WDR5 are associated with transcribed promoters. Thus, our findings suggest that MYC and ASH2L-KMT2 complexes cooperate in gene transcription by controlling H3K27 modifications and thereby regulate bivalent chromatin.

Identification of KMT2D and KDM6A mutations by exome sequencing in Korean patients with Kabuki syndrome

Kabuki syndrome (KS) (OMIM#147920) is a multiple congenital anomaly/mental retardation syndrome. Recently, pathogenic variants in KMT2D and KDM6A were identified as the causes of KS in 55.8-80.0% of patients. To elucidate further the molecular characteristics of Korean patients with KS, we screened a cohort of patients with clinically defined KS for mutations in KMT2D and KDM6A. Whole-exome sequencing and direct sequencing for validation were performed in 12 patients with a clinical suspicion of KS. KMT2D and KDM6A mutations were identified in 11 (91.7%) patients. No recurrent mutation was observed, and 10 out of the 11 mutations found were novel. KMT2D mutations were detected in 10 patients, including four small deletions or insertions and four nonsense and two missense mutations. One girl had a novel splice-site mutation in KDM6A. Each patient had a unique individual mutation. This is the first report of mutational analysis via exome sequencing in Korean patients with KS. Because the mutation-detection rate was high in this study, rigorous mutation analysis of KMT2D and KDM6A may be an important tool for the early diagnosis and genetic counseling of Korean patients with KS.

A three generation X-linked family with Kabuki syndrome phenotype and a frameshift mutation in KDM6A

Kabuki syndrome is a rare malformation syndrome characterized by a typical facial appearance, skeletal anomalies, cardiac malformation, and mild to moderate intellectual disability. In 55-80% of patients with Kabuki syndrome, a mutation in MLL2 is identified. Recently, eight patients with Kabuki syndrome and a mutation in KDM6A were described. In this report, we describe two brothers with a mutation in KDM6A inherited from their mother and maternal grandmother. The two boys have Kabuki-like phenotypes whereas the mother and grandmother present with attenuated phenotypes. This family represents the first instance of hereditary X-linked Kabuki syndrome. We present a short literature review of the patients described with a mutation in KDM6A.