MEF2: a central regulator of diverse developmental programs

Convergent Evidence From Humans and Drosophila melanogaster Implicates the Transcription Factor MEF2B/Mef2 in Alcohol Sensitivity

BACKGROUND

Self-Rating of the Effects of Alcohol (SRE) measures level of response to ethanol (EtOH) in humans. Interestingly, there is a positive relationship between the SRE and risk for abusing alcohol, suggesting mechanistic connections between SRE and alcohol abuse.

METHODS

To identify candidate genes with a role in SRE and alcohol-related behavior more generally, we coupled human genetic analyses with studies in Drosophila melanogaster. We first performed a gene-based analysis of Genomewide association studies (GWAS) summary statistics for SRE in the Avon Longitudinal Study of Parents and Children sample. Based on prior findings in humans, orthology to fly genes, and the availability of genetic reagents, we selected a subset of these genes for studies on EtOH behavior in Drosophila.

RESULTS

We found 37 genes with nominal associations in our SRE GWAS. We explored the role of 6 orthologous genes in Drosophila EtOH sedation and rapid tolerance. We found that the transcription factor Mef2 is required for normal EtOH sedation in flies. Pan-neuronal expression of 2 independent Mef2 RNAi transgenes significantly reduced Mef2 expression and made flies resistant to EtOH sedation. Additionally, flies with multiple independent mutant alleles of Mef2 were also resistant to EtOH sedation, confirming a role for Mef2 in this behavior. Altered expression of Mef2 did not change EtOH rapid tolerance or cause a net change in internal EtOH concentrations.

CONCLUSIONS

Our studies indicate that MEF2B influences SRE in humans and that Mef2 impacts EtOH sedation in Drosophila.

Epigenetics and Mechanobiology in Heart Development and Congenital Heart Disease

: Congenital heart disease (CHD) is the most common birth defect worldwide and the number one killer of live-born infants in the United States. Heart development occurs early in embryogenesis and involves complex interactions between multiple cell populations, limiting the understanding and consequent treatment of CHD. Furthermore, genome sequencing has largely failed to predict or yield therapeutics for CHD. In addition to the underlying genome, epigenetics and mechanobiology both drive heart development. A growing body of evidence implicates the aberrant regulation of these two extra-genomic systems in the pathogenesis of CHD. In this review, we describe the stages of human heart development and the heart defects known to manifest at each stage. Next, we discuss the distinct and overlapping roles of epigenetics and mechanobiology in normal development and in the pathogenesis of CHD. Finally, we highlight recent advances in the identification of novel epigenetic biomarkers and environmental risk factors that may be useful for improved diagnosis and further elucidation of CHD etiology.

Neuronal Myocyte-Specific Enhancer Factor 2D (MEF2D) Is Required for Normal Circadian and Sleep Behavior in Mice

The transcription factor, myocyte enhancer factor-2 (MEF2), is required for normal circadian behavior in Drosophila; however, its role in the mammalian circadian system has not been established. Of the four mammalian Mef2 genes, Mef2d is highly expressed in the suprachiasmatic nucleus (SCN) of the hypothalamus, a region critical for coordinating peripheral circadian clocks. Using both conventional and brain-specific Mef2d KO (Mef2d ^-/-) mouse lines, we demonstrate that MEF2D is essential for maintaining the length of the circadian free-running period of locomotor activity and normal sleep patterns in male mice. Crossing Mef2d ^-/- with Per2::luc reporter mice, we show that these behavioral changes are achieved without altering the endogenous period of the master circadian oscillator in the SCN. Together, our data suggest that alterations in behavior in Mef2d ^-/- mice may be the result of an effect on SCN output, rather than an effect on timekeeping within the SCN itself. These findings add to the growing body of evidence that MEF2 proteins play important roles in the brain.SIGNIFICANCE STATEMENT These studies are the first to show a role for MEF2 proteins in the brain outside of the hippocampus, and our findings suggest that these proteins may play diverse roles in the CNS. It is important to continue to build on our understanding of the roles of proteins acting in the SCN because SCN dysfunction underlies jet lag in humans and influences the response to shift work schedules, which are now known as risk factors for the development of cancer. Our work on MEF2D could be the basis for opening new lines of research in the development and regulation of circadian rhythms.

Seasonal temperature, the lunar cycle and diurnal rhythms interact in a combinatorial manner to modulate genomic responses to the environment in a reef-building coral

Rhythms of various periodicities drive cyclical processes in organisms ranging from single cells to the largest mammals on earth, and on scales from cellular physiology to global migrations. The molecular mechanisms that generate circadian behaviours in model organisms have been well studied, but longer phase cycles and interactions between cycles with different periodicities remain poorly understood. Broadcast spawning corals are one of the best examples of an organism integrating inputs from multiple environmental parameters, including seasonal temperature, the lunar phase and hour of the day, to calibrate their annual reproductive event. We present a deep RNA-sequencing experiment utilizing multiple analyses to differentiate transcriptomic responses modulated by the interactions between the three aforementioned environmental parameters. Acropora millepora was sampled over multiple 24-hr periods throughout a full lunar month and at two seasonal temperatures. Temperature, lunar and diurnal cycles produce distinct transcriptomic responses, with interactions between all three variables identifying a core set of genes. These core genes include mef2, a developmental master regulator, and two heterogeneous nuclear ribonucleoproteins, one of which is known to post-transcriptionally interact with mef2 and with biological clock-regulating mRNAs. Interactions between diurnal and temperature differences impacted a range of core processes ranging from biological clocks to stress responses. Genes involved with developmental processes and transcriptional regulation were impacted by the lunar phase and seasonal temperature differences. Lastly, there was a diurnal and lunar phase interaction in which genes involved with RNA-processing and translational regulation were differentially regulated. These data illustrate the extraordinary levels of transcriptional variation across time in a simple radial cnidarian in response to the environment under normal conditions.

Chemical Reprogramming of Somatic Cells in Neural Direction: Myth or Reality?

In in vitro experiments on cultures of human multipotent stem cells from the human bonearrow and dental pulp, we studied direct reprogramming towards neuro-glial lineage cells using a cocktail of small molecules. Reprogramming by the previously published protocol (with a cocktail containing β-mercaptoethanol, LIF, VPA, CHIR99021, and RepSox) and by the optimized protocol (VPA, RG108, А83-01, dorsomorphin, thiazovivin, CHIR99021, forskolin, and Isx9) allows obtaining cells with immunophenotypic and genetic signs of neural stem cells. However, neither the former, nor the optimized protocols allowed preparing neural progenitors capable of adequate terminal differentiation from both bone marrow-derived mesenchymal stem cells and nestin-positive neural crest-derived mesenchymal stem cells. Real-time PCR demonstrated the expression of some neurogenesis markers, but neural stem cell-specific expression pattern was not observed. The findings lead us to a conclusion that reprogramming with small molecules without additional factors modifying gene expression does not allow reproducible production of human neural stem cell-like progenitors that can be used as the source of neural tissue for the regenerative therapy.

Common Carp mef2 Genes: Evolution and Expression

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

Integrated microRNA and mRNA network analysis of the human myometrial transcriptome in the transition from quiescence to labor

We conducted integrated transcriptomics network analyses of miRNA and mRNA interactions in human myometrium to identify novel molecular candidates potentially involved in human parturition. Myometrial biopsies were collected from women undergoing primary Cesarean deliveries in well-characterized clinical scenarios: (1) spontaneous term labor (TL, n = 5); (2) term nonlabor (TNL, n = 5); (3) spontaneous preterm birth (PTB) with histologic chorioamnionitis (PTB-HCA, n = 5); and (4) indicated PTB nonlabor (PTB-NL, n = 5). RNAs were profiled using RNA sequencing, and miRNA-target interaction networks were mined for key discriminatory subnetworks. Forty miRNAs differed between TL and TNL myometrium, while seven miRNAs differed between PTB-HCA vs. PTB-NL specimens; six of these were cross-validated using quantitative PCR. Based on the combined sequencing data, unsupervised clustering revealed two nonoverlapping cohorts that differed primarily by absence or presence of uterine quiescence, rather than gestational age or original clinical cohort. The intersection of differentially expressed miRNAs and their targets predicted 22 subnetworks with enriched representation of miR-146b-5p, miR-223-3p, and miR-150-5p among miRNAs, and of myocyte enhancer factor-2C (MEF2C) among mRNAs. Of four known MEF2 transcription factors, decreased MEF2A and MEF2C expression in women with uterine nonquiescence was observed in the sequencing data, and validated in a second cohort by quantitative PCR. Immunohistochemistry localized MEF2A and MEF2C to myometrial smooth muscle cells and confirmed decreased abundance with labor. Collectively, these results suggest altered MEF2 expression may represent a previously unrecognized process through which miRNAs contribute to the phenotypic switch from quiescence to labor in human myometrium.

Regulatory pathways governing murine coronary vessel formation are dysregulated in the injured adult heart

The survival of ischaemic cardiomyocytes after myocardial infarction (MI) depends on the formation of new blood vessels. However, endogenous neovascularization is inefficient and the regulatory pathways directing coronary vessel growth are not well understood. Here we describe three independent regulatory pathways active in coronary vessels during development through analysis of the expression patterns of differentially regulated endothelial enhancers in the heart. The angiogenic VEGFA-MEF2 regulatory pathway is predominantly active in endocardial-derived vessels, whilst SOXF/RBPJ and BMP-SMAD pathways are seen in sinus venosus-derived arterial and venous coronaries, respectively. Although all developmental pathways contribute to post-MI vessel growth in the neonate, none are active during neovascularization after MI in adult hearts. This was particularly notable for the angiogenic VEGFA-MEF2 pathway, otherwise active in adult hearts and during neoangiogenesis in other adult settings. Our results therefore demonstrate a fundamental divergence between the regulation of coronary vessel growth in healthy and ischemic adult hearts.

How coronary vessels develop and respond to injury is not fully understood. Here, the authors use murine enhancer:reporter models to identify three transcriptional pathways active in different parts of coronary vasculature. These also contribute to neovascularization in the injured neonatal, but not adult, heart.

mAKAPβ signalosomes - A nodal regulator of gene transcription associated with pathological cardiac remodeling

Striated myocytes compose about half of the cells of the heart, while contributing the majority of the heart's mass and volume. In response to increased demands for pumping power, including in diseases of pressure and volume overload, the contractile myocytes undergo non-mitotic growth, resulting in increased heart mass, i.e. cardiac hypertrophy. Myocyte hypertrophy is induced by a change in the gene expression program driven by the altered activity of transcription factors and co-repressor and co-activator chromatin-associated proteins. These gene regulatory proteins are subject to diverse post-translational modifications and serve as nuclear effectors for intracellular signal transduction pathways, including those controlled by cyclic nucleotides and calcium ion. Scaffold proteins contribute to the underlying architecture of intracellular signaling networks by targeting signaling enzymes to discrete intracellular compartments, providing specificity to the regulation of downstream effectors, including those regulating gene expression. Muscle A-kinase anchoring protein β (mAKAPβ) is a well-characterized scaffold protein that contributes to the regulation of pathological cardiac hypertrophy. In this review, we discuss the mechanisms how this prototypical scaffold protein organizes signalosomes responsible for the regulation of class IIa histone deacetylases and cardiac transcription factors such as NFAT, MEF2, and HIF-1α, as well as how this signalosome represents a novel therapeutic target for the prevention or treatment of heart failure.

Dephosphorylation of HDAC4 by PP2A-Bδ unravels a new role for the HDAC4/MEF2 axis in myoblast fusion

Muscle formation is controlled by a number of key myogenic transcriptional regulators that govern stage-specific gene expression programs and act as terminal effectors of intracellular signaling pathways. To date, the role of phosphatases in the signaling cascades instructing muscle development remains poorly understood. Here, we show that a specific PP2A-B55δ holoenzyme is necessary for skeletal myogenesis. The primary role of PP2A-B55δ is to dephosphorylate histone deacetylase 4 (HDAC4) following myocyte differentiation and ensure repression of Myocyte enhancer factor 2D (MEF2D)-dependent gene expression programs during myogenic fusion. As a crucial HDAC4/MEF2D target gene that governs myocyte fusion, we identify ArgBP2, an upstream inhibitor of Abl, which itself is a repressor of CrkII signaling. Consequently, cells lacking PP2A-B55δ show upregulation of ArgBP2 and hyperactivation of CrkII downstream effectors, including Rac1 and FAK, precluding cytoskeletal and membrane rearrangements associated with myoblast fusion. Both in vitro and in zebrafish, loss-of-function of PP2A-B55δ severely impairs fusion of myocytes and formation of multinucleated muscle fibers, without affecting myoblast differentiation. Taken together, our results establish PP2A-B55δ as the first protein phosphatase to be involved in myoblast fusion and suggest that reversible phosphorylation of HDAC4 may coordinate differentiation and fusion events during myogenesis.

Transient induction of Cdk9 in the early stage of differentiation is critical for myogenesis

Cdk9 is a serine-threonine protein kinase that has been recognized as a regulator of cardiac differentiation. Recently, we have reported that transient induction of Cdk9 using noncoding RNA targeting Cdk9 sequences results in efficient cardiac differentiation. Concerning Cdk9 regulatory roles, here, we proposed whether constant overexpression of Cdk9 might influence the differentiation of myoblast C2C12 cells into myotubes. We overexpressed Cdk9 in mouse myoblast C2C12 cells to investigate its regulatory roles on myogenic differentiation. Upon Cdk9 overexpression, the expression level of myogenic regulatory factors was determined. Moreover, the expression profile of three important myomiRs consist of miR 1, 133 and 206 was examined during the differentiation process. Although Cdk9 expression is necessary for inducing differentiation in the early stage of myogenesis, continuous Cdk9 expression inhibits differentiation by modulating myomiRs and myogenic gene expression. Our results indicate that the transient induction of Cdk9 in the early stage of differentiation is critical for myogenesis.

MEF2A Regulates the MEG3-DIO3 miRNA Mega Cluster-Targeted PP2A Signaling in Bovine Skeletal Myoblast Differentiation

Understanding the molecular mechanisms of skeletal myoblast differentiation is essential for studying muscle developmental biology. In our previous study, we reported that knockdown of myocyte enhancer factor 2A (MEF2A) inhibited myoblast differentiation. Here in this study, we further identified that MEF2A controlled this process through regulating the maternally expressed 3 (MEG3)-iodothyronine deiodinase 3 (DIO3) miRNA mega cluster and protein phosphatase 2A (PP2A) signaling. MEF2A was sufficient to induce MEG3 expression in bovine skeletal myoblasts. A subset of miRNAs in the MEG3-DIO3 miRNA cluster was predicted to target PP2A subunit genes. Consistent with these observations, MEF2A regulated PP2A signaling through its subunit gene protein phosphatase 2 regulatory subunit B, gamma (PPP2R2C) during bovine myoblast differentiation. MiR-758 and miR-543 in the MEG3-DIO3 miRNA cluster were down-regulated in MEF2A-depleted myocytes. Expression of miR-758 and miR-543 promoted myoblast differentiation and repressed PPP2R2C expression. Luciferase activity assay showed that PPP2R2C was post-transcriptionally targeted by miR-758 and miR-543. Taken together, these results reveal that the MEG3-DIO3 miRNAs function at downstream of MEF2A to modulate PP2A signaling in bovine myoblast differentiation.

MiR-199a-3p inhibition facilitates cardiomyocyte differentiation of embryonic stem cell through promotion of MEF2C

MicroRNAs (miRNAs) is a small molecule (19-25 nucleotide) noncoding RNA that inhibits the expression of target messenger RNA (mRNA) at the posttranscriptional level as an endogenous regulator. There is an increasing evidence that miR-199a-3p has a significant effect on the development of multiple tumors. However, the specific roles of miR-199a-3p in myocardial differentiation of embryonic stem cell still need to be investigated. Method of the hanging drop was used to build the model of cardiomyocyte differentiation of stem cell and beating rate of embryoid bodies (EBs) was calculated. The levels of intracellular MEF2C, a-MHC, GATA4, Nkx2.5, and cTnT mRNA were measured by real-time quantitative polymerase chain reaction, while the expressions of miR-199a-3p were detected simultaneously. Protein levels of MEF2C, a-MHC, GATA4, Nkx2.5, and cTnT were quantified by western blot analysis. Immunoreactivities of MEF2C and cTnT were analyzed by immunofluorescence. The interaction between miR-199a-3p and its predicted target (3'-untranslated region of MEF2C mRNA) was verified by luciferase assay. MiR-199a-3p levels increased during cardiogenesis. MiR-199a-3p inhibitor increased the beating rate of EBs and promoted expressions of cardiac-specific markers (GATA4, Nkx2.5, cTnT, and a-MHC). Notably, miR-199a-3p inhibition brought upregulation of MEF2C, which is the target of miR-199a-3p that we predicted and verified experimentally. In addition, MEF2C siRNA decreased miR-199a-3p inhibitor promoted EBs beating and attenuated miR-199a-3p inhibitor-induced cTnT and MEF2C expressions. The results above showed that MEF2C was involved in the process of promoting the differentiation of stem cells into cardiac myocytes by miR-199a-3p inhibitors.

Emerging roles for MEF2 in brain development and mental disorders

The MEF2 family of transcription factors regulate large programs of gene expression important for the development and maintenance of many tissues, including the brain. MEF2 proteins are regulated by neuronal synaptic activity, and they recruit several epigenetic enzymes to influence chromatin structure and gene expression during development and throughout adulthood. Here, we provide a brief review of the recent literature reporting important roles for MEF2 during early brain development and function, and we highlight emerging roles for MEF2 as a risk factor for multiple neurodevelopmental disorders and mental illnesses, such as autism, intellectual disability, and schizophrenia.

NURR1 activation in skeletal muscle controls systemic energy homeostasis

Skeletal muscle plays a central role in the control of metabolism and exercise tolerance. Analysis of muscle enhancers activated after exercise in mice revealed the orphan nuclear receptor NURR1/NR4A2 as a prominent component of exercise-responsive enhancers. We show that exercise enhances the expression of NURR1, and transgenic overexpression of NURR1 in skeletal muscle enhances physical performance in mice. NURR1 expression in skeletal muscle is also sufficient to prevent hyperglycemia and hepatic steatosis, by enhancing muscle glucose uptake and storage as glycogen. Furthermore, treatment of obese mice with putative NURR1 agonists increases energy expenditure, improves glucose tolerance, and confers a lean phenotype, mimicking the effects of exercise. These findings identify a key role for NURR1 in governance of skeletal muscle glucose metabolism, and reveal a transcriptional link between exercise and metabolism. Our findings also identify NURR1 agonists as possible exercise mimetics with the potential to ameliorate obesity and other metabolic abnormalities.

Key nutritional factors and interactions during larval development of pikeperch (Sander lucioperca)

The effects of 8 nutritional variables (Ca/P, Eicosapentaenoic acid (20:5n-3) + Docosahexaenoic acid (22:6n − 3) (EPA + DHA), Arachidonic acid (20:4n − 6) (ARA), Se, vitamins E, C, D and A) were investigated to identify their respective importance and interactions in pikeperch larval development. In this respect, two modalities (low and high levels) of each variable were tested through a fractional factorial experimental design allowing a reduction from 256 (2⁸) to 16 (2^8 – 4) experimental units. Survival was significantly higher in larvae fed a high Ca/P diet while larval growth was significantly lower in larvae fed the same diet variant, associated with a higher incidence of kyphosis and pectoral anomalies in these larvae. Lordosis and scoliosis seemed to be mostly affected by dietary long chain polyunsaturated fatty acids (LC-PUFAs). A significant interaction was shown between n-3 LC-PUFA and vitamin C on jaw anomalies, while myocyte-specific enhancer factor 2C (mef2c) gene expression correlated positively with dietary vitamin C increment. Results also demonstrated an effect of the different nutrients and their interactions on the activity levels of digestive enzymatic activities. The results of the present study highlight the importance of the interactions between Ca/P, LC-PUFAs and vitamins C and E, suggesting their essential roles as key nutritional factors influencing pikeperch larval development.

Transcriptomic profiling identifies novel mechanisms of transcriptional regulation of the cytochrome P450 (Cyp)3a11 gene

Cytochrome P450 (CYP)3A is the most abundant CYP enzyme in the human liver, and a functional impairment of this enzyme leads to unanticipated adverse reactions and therapeutic failures; these reactions result in the early termination of drug development or the withdrawal of drugs from the market. The transcriptional regulation mechanism of the Cyp3a gene is not fully understood and requires a thorough investigation. We mapped the transcriptome of the Cyp3a gene in a mouse model. The Cyp3a gene was induced using the mPXR activator pregnenolone-16alpha-carbonitrile (PCN) and was subsequently downregulated using lipopolysaccharide (LPS). Our objective was to identify the transcription factors (TFs), epigenetic modulators and molecular pathways that are enriched or repressed by PCN and LPS based on a gene set enrichment analysis. Our analysis shows that 113 genes were significantly upregulated (by at least 1.5-fold) with PCN treatment, and that 834 genes were significantly downregulated (by at least 1.5-fold) with LPS treatment. Additionally, the targets of the 536 transcription factors were enriched by a combined treatment of PCN and LPS, and among these, 285 were found to have binding sites on Cyp3a11. Moreover, the repressed targets of the epigenetic markers HDAC1, HDAC3 and EZH2 were further suppressed by LPS treatment and were enhanced by PCN treatment. By identifying and contrasting the transcriptional regulators that are altered by PCN and LPS, our study provides novel insights into the transcriptional regulation of CYP3A in the liver.

Inflammation leads through PGE/EP3 signaling to HDAC5/MEF2-dependent transcription in cardiac myocytes

The myocyte enhancer factor 2 (MEF2) regulates transcription in cardiac myocytes and adverse remodeling of adult hearts. Activators of G protein-coupled receptors (GPCRs) have been reported to activate MEF2, but a comprehensive analysis of GPCR activators that regulate MEF2 has to our knowledge not been performed. Here, we tested several GPCR agonists regarding their ability to activate a MEF2 reporter in neonatal rat ventricular myocytes. The inflammatory mediator prostaglandin E₂ (PGE₂) strongly activated MEF2. Using pharmacological and protein-based inhibitors, we demonstrated that PGE₂ regulates MEF2 via the EP₃ receptor, the βγ subunit of G_i/o protein and two concomitantly activated downstream pathways. The first consists of Tiam1, Rac1, and its effector p21-activated kinase 2, the second of protein kinase D. Both pathways converge on and inactivate histone deacetylase 5 (HDAC5) and thereby de-repress MEF2. In vivo, endotoxemia in MEF2-reporter mice induced upregulation of PGE₂ and MEF2 activation. Our findings provide an unexpected new link between inflammation and cardiac remodeling by de-repression of MEF2 through HDAC5 inactivation, which has potential implications for new strategies to treat inflammatory cardiomyopathies.

Regulation of Osteoclast Differentiation and Skeletal Maintenance by Histone Deacetylases

Bone is a dynamic tissue that must respond to developmental, repair, and remodeling cues in a rapid manner with changes in gene expression. Carefully-coordinated cycles of bone resorption and formation are essential for healthy skeletal growth and maintenance. Osteoclasts are large, multinucleated cells that are responsible for breaking down bone by secreting acids to dissolve the bone mineral and proteolytic enzymes that degrade the bone extracellular matrix. Increased osteoclast activity has a severe impact on skeletal health, and therefore, osteoclasts represent an important therapeutic target in skeletal diseases, such as osteoporosis. Progression from multipotent progenitors into specialized, terminally-differentiated cells involves carefully-regulated patterns of gene expression to control lineage specification and emergence of the cellular phenotype. This process requires coordinated action of transcription factors with co-activators and co-repressors to bring about proper activation and inhibition of gene expression. Histone deacetylases (HDACs) are an important group of transcriptional co-repressors best known for reducing gene expression via removal of acetyl modifications from histones at HDAC target genes. This review will cover the progress that has been made recently to understand the role of HDACs and their targets in regulating osteoclast differentiation and activity and, thus, serve as potential therapeutic target.

MEF2 and the Right Ventricle: From Development to Disease

Pulmonary arterial hypertension is a progressive and ultimately life-limiting disease in which survival is closely linked to right ventricular function. The right ventricle remains relatively understudied, as it is known to have key developmental and structural differences from the left ventricle. Here, we will highlight what is known about the right ventricle in normal physiology and in the disease state of pulmonary arterial hypertension. Specifically, we will explore the role of the family of MEF2 (myocyte enhancer factor 2) transcription factors in right ventricular development, its response to increased afterload, and in the endothelial dysfunction that characterizes pulmonary arterial hypertension. Finally, we will turn to review potentially novel therapeutic strategies targeting these pathways.

Protein kinase B/AKT mediates insulin-like growth factor 1-induced phosphorylation and nuclear export of histone deacetylase 5 via NADPH oxidase 4 activation in vascular smooth muscle cells

Insulin-like growth factor 1 (IGF-1) mediates the generation of reactive oxygen species (ROS) and the activation of growth promoting signaling pathways. Histone deacetylases (HDACs) regulate gene transcription by deacetylating lysine residues in histone and nonhistone proteins and a heightened HDAC activation, notably of HDAC5, is associated with vascular disorders, such as atherosclerosis. Although the contribution of IGF-1 in these pathologies is well documented, its role in HDAC phosphorylation and activation remains unexplored. Here, we examined the effect of IGF-1 on HDAC5 phosphorylation in vascular smooth muscle cells (VSMCs) and identified the signaling pathways involved in controlling HDAC5 phosphorylation and nuclear export. Treatment of A10 VSMCs with IGF-1 enhanced HDAC5 phosphorylation. Blockade of the IGF-1 receptor tyrosine kinase (TK) activity with the specific pharmacological inhibitor, AG1024, significantly inhibited IGF-1-induced HDAC5 phosphorylation, whereas the epidermal growth factor receptor (EGFR) TK antagonist, AG1478, had no effect. Inhibition of the mitogen-activated protein kinase pathway with U0126, SP600125, or SB203580, did not affect HDAC5 phosphorylation, whereas two inhibitors of the phosphoinositide 3-kinase (PI3K)/AKT pathways, wortmannin and SC66, almost completely attenuated IGF-1-induced responses as confirmed by immunoblotting of phospho-HDAC5 and by small interfering RNA (siRNA)-induced AKT silencing. Moreover, the NAD(P)H oxidase (Nox) inhibitor, diphenyleneiodonium (DPI), and Nox4 siRNA, attenuated IGF-1-induced phosphorylation of HDAC5 and AKT. The HDAC5 phosphorylation resulted in its nuclear export, which was reversed by SC66 and DPI. Our results indicate that IGF-1-induced phosphorylation and nuclear export of HDAC5 involve Nox4-dependent ROS generation and PI3K/AKT signaling pathways.

PHACTR1 gene polymorphism with the risk of coronary artery disease in Chinese Han population

BACKGROUND

Coronary artery disease (CAD) is the most frequent multifactorial disease worldwide and is characterised by endothelial injury, lipid deposition and coronary artery calcification. The purpose of this study was to determine the allelic and genotypic frequencies of two loci (rs2026458 and rs9349379) of phosphatase and actin regulator 1 (PHACTR1) to the risk of developing CAD in the Chinese Han population.

METHODS

A case-control study was conducted including 332 patients with CAD and 119 controls. Genotype analysis was performed by PCR and Sanger sequencing. Genetic model analysis was performed to evaluate the association between single nucleotide polymorphisms and CAD susceptibility using Pearson's χ² test and logistic regression analysis.

RESULTS

The GG genotype of rs9349379 represented 50% and 29% of patients with CAD and controls, respectively (p<0.001). The CC genotype of rs2026458 was more prevalent in the controls than in patients with CAD compared with TT genotype (OR=0.548, 95% CI 0.351 to 0.856, p=0.008). Logistic regression analyses revealed that PHACTR1 rs9349379 GG genotype was significantly associated with increased risk of CAD in the recessive model (OR=2.359, 95% CI 1.442 to 3.862, p=0.001), even after adjusting for age gender, hypertension, type 2 diabetes, hyperlipidaemia and smoking habit. Heterogeneity test proved that rs9349379's risk effects on CAD were more significant among women.

CONCLUSIONS

Our study indicate that the PHACTR1 rs9349379 polymorphism is associated with the increased risk for CAD in the female Chinese Han population.

Retinal-input-induced epigenetic dynamics in the developing mouse dorsal lateral geniculate nucleus

DNA methylation plays important roles in the regulation of nervous system development and in cellular responses to environmental stimuli such as light-derived signals. Despite great efforts in understanding the maturation and refinement of visual circuits, we lack a clear understanding of how changes in DNA methylation correlate with visual activity in the developing subcortical visual system, such as in the dorsal lateral geniculate nucleus (dLGN), the main retino-recipient region in the dorsal thalamus. Here, we explored epigenetic dynamics underlying dLGN development at ages before and after eye opening in wild-type mice and mutant mice in which retinal ganglion cells fail to form. We observed that development-related epigenetic changes tend to co-localize together on functional genomic regions critical for regulating gene expression, while retinal-input-induced epigenetic changes are enriched on repetitive elements. Enhancers identified in neurons are prone to methylation dynamics during development, and activity-induced enhancers are associated with retinal-input-induced epigenetic changes. Intriguingly, the binding motifs of activity-dependent transcription factors, including EGR1 and members of MEF2 family, are enriched in the genomic regions with epigenetic aberrations in dLGN tissues of mutant mice lacking retinal inputs. Overall, our study sheds new light on the epigenetic regulatory mechanisms underlying the role of retinal inputs on the development of mouse dLGN.

Anacardic acid attenuates pressure-overload cardiac hypertrophy through inhibiting histone acetylases

Cardiac hypertrophy has become a major cardiovascular problem wordwide and is considered the early stage of heart failure. Treatment and prevention strategies are needed due to the suboptimal efficacy of current treatment methods. Recently, many studies have demonstrated the important role of histone acetylation in myocardium remodelling along with cardiac hypertrophy. A Chinese herbal extract containing anacardic acid (AA) is known to possess strong histone acetylation inhibitory effects. In previous studies, we demonstrated that AA could reverse alcohol‐induced cardiac hypertrophy in an animal model at the foetal stage. Here, we investigated whether AA could attenuate cardiac hypertrophy through the modulation of histone acetylation and explored its potential mechanisms in the hearts of transverse aortic constriction (TAC) mice. This study showed that AA attenuated hyperacetylation of acetylated lysine 9 on histone H3 (H3K9ac) by inhibiting the expression of p300 and p300/CBP‐associated factor (PCAF) in TAC mice. Moreover, AA normalized the transcriptional activity of the heart nuclear transcription factor MEF2A. The high expression of cardiac hypertrophy‐linked genes (ANP, β‐MHC) was reversed through AA treatment in the hearts of TAC mice. Additionally, we found that AA improved cardiac function and survival rate in TAC mice. The current results further highlight the mechanism by which histone acetylation is controlled by AA treatment, which may help prevent and treat hypertrophic cardiomyopathy.

Long non-coding RNA EPIC1 inhibits viability and invasion of osteosarcoma cells by promoting MEF2D ubiquitylation

BACKGROUND

Long non-coding RNAs (lncRNAs) can modulate gene expression through different mechanisms, but the fundamental molecular mechanism behind EPIC1 and osteosarcoma (OS) was poorly understood.

METHODS

Bone tumor tissues and the matched normal tissues were obtained from 36 OS patients who received tumor resection from 2014 to 2018. The expression of EPIC1 and MEF2D was determined by quantitative real-Time PCR and western blotting. Cell viability and invasion were evaluated by MTT assay and transwell assay. The animal xenograft model was also established.

RESULTS

EPIC1 was down-regulated, but MEF2D was up-regulated in OS tissues and OS cell lines. Overexpression of EPIC1 inhibited cell viability and invasion of OS cells. Targeting relationship between EPIC1 and MEF2D was confirmed by RNA pull-down and RNA immunoprecipitation (RIP). The MEF2D protein binding to ubiquitin was significantly increased in OS cells overexpressing EPIC1. The co-transfection with pcDNA-EPIC1 and pcDNA-MEF2D rescued the inhibition of cell viability and invasion caused by the overexpression of EPIC1. Overexpression of EPIC1 suppressed tumor growth in the OS xenograft model.

CONCLUSION

Our findings indicated that overexpression of EPIC1 inhibited cell viability and invasion of OS cells by promoting MEF2D ubiquitylation, which provided innovative lncRNA and protein targets for treating OS.

Protein kinase A mediates novel serine-584 phosphorylation of HDAC4

Given the well-established diversified signaling pathways for histone deacetylase 4 (HDAC4) and the regulation of HDAC4 by several post-translational modifications (PTMs), including phosphorylation, sumoylation, and ubiquitination, an unbiased and detailed analysis of HDAC4 PTMs is needed. In this study, we used matrix-assisted laser desorption/ionization time of flight (MALDI-TOF/TOF) to describe phosphorylation at serine 584 (Ser584) along with already-known dual phosphorylation at serines 265 and 266 (Ser265/266), that together regulate HDAC4 activity. Overexpression of site-specific HDAC4 mutants (S584A, S265/266A) in HEK 293T cells, followed by HDAC activity assays, revealed the mutants to be less active than the wild-type protein. In vitro kinase assays have established that Ser584 and Ser265/266 are phosphorylated by protein kinase A (PKA). Luciferase assays driven by the myocyte enhancer factor 2 (MEF2) promoter and real-time PCR analysis of the MEF2 target genes show that the S584A and S265/266A mutants are less repressive than the wild-type. Furthermore, treatment with PKA activators such as 8-Bromo-cAMP and forskolin, and silencing either by shRNA or its inhibitor H-89 in a mouse myoblast cell line (C2C12) and in a non-muscle human cell line (K562), confirmed in vivo phosphorylation of HDAC4 in C2C12 but not in K562 cells, indicating the specific functional significance of HDAC4 phosphorylation in muscle cells. Thus, we identified PKA-induced Ser584 phosphorylation of HDAC4 as a yet unknown regulatory mechanism of the HDAC4-MEF2 axis.

Combining Developmental and Perturbation-Seq Uncovers Transcriptional Modules Orchestrating Neuronal Remodeling

Developmental neuronal remodeling is an evolutionarily conserved mechanism required for precise wiring of nervous systems. Despite its fundamental role in neurodevelopment and proposed contribution to various neuropsychiatric disorders, the underlying mechanisms are largely unknown. Here, we uncover the fine temporal transcriptional landscape of Drosophila mushroom body γ neurons undergoing stereotypical remodeling. Our data reveal rapid and dramatic changes in the transcriptional landscape during development. Focusing on DNA binding proteins, we identify eleven that are required for remodeling. Furthermore, we sequence developing γ neurons perturbed for three key transcription factors required for pruning. We describe a hierarchical network featuring positive and negative feedback loops. Superimposing the perturbation-seq on the developmental expression atlas highlights a framework of transcriptional modules that together drive remodeling. Overall, this study provides a broad and detailed molecular insight into the complex regulatory dynamics of developmental remodeling and thus offers a pipeline to dissect developmental processes via RNA profiling.

Inferring the Molecular Mechanisms of Noncoding Alzheimer's Disease-Associated Genetic Variants

Most of the loci identified by genome-wide association studies (GWAS) for late-onset Alzheimer's disease (LOAD) are in strong linkage disequilibrium (LD) with nearby variants all of which could be the actual functional variants, often in non-protein-coding regions and implicating underlying gene regulatory mechanisms. We set out to characterize the causal variants, regulatory mechanisms, tissue contexts, and target genes underlying these associations. We applied our INFERNO algorithm to the top 19 non-APOE loci from the IGAP GWAS study. INFERNO annotated all LD-expanded variants at each locus with tissue-specific regulatory activity. Bayesian co-localization analysis of summary statistics and eQTL data was performed to identify tissue-specific target genes. INFERNO identified enhancer dysregulation in all 19 tag regions analyzed, significant enrichments of enhancer overlaps in the immune-related blood category, and co-localized eQTL signals overlapping enhancers from the matching tissue class in ten regions (ABCA7, BIN1, CASS4, CD2AP, CD33, CELF1, CLU, EPHA1, FERMT2, ZCWPW1). In several cases, we identified dysregulation of long noncoding RNA (lncRNA) transcripts and applied the lncRNA target identification algorithm from INFERNO to characterize their downstream biological effects. We also validated the allele-specific effects of several variants on enhancer function using luciferase expression assays. By integrating functional genomics with GWAS signals, our analysis yielded insights into the regulatory mechanisms, tissue contexts, genes, and biological processes affected by noncoding genetic variation associated with LOAD risk.

Lipin1 is required for skeletal muscle development by regulating MEF2c and MyoD expression

KEY POINTS

Lipin1 is critical for skeletal muscle development. Lipin1 regulates MyoD and myocyte-specific enhancer factor 2C (MEF2c) expression via the protein kinase C (PKC)/histone deacetylase 5-mediated pathway. Inhibition of PKCμ activity suppresses myoblast differentiation by inhibiting MyoD and MEF2c expression.

ABSTRACT

Our previous characterization of global lipin1-deficient (fld) mice demonstrated that lipin1 played a novel role in skeletal muscle (SM) regeneration. The present study using cell type-specific Myf5-cre;Lipin1^fl/fl conditional knockout mice (Lipin1^Myf5cKO ) shows that lipin1 is a major determinant of SM development. Lipin1 deficiency induced reduced muscle mass and myopathy. Our results from lipin1-deficient myoblasts suggested that lipin1 regulates myoblast differentiation via the protein kinase Cμ (PKCμ)/histone deacetylase 5 (HDAC5)/myocyte-specific enhancer factor 2C (MEF2c):MyoD-mediated pathway. Lipin1 deficiency leads to the suppression of PKC isoform activities, as well as inhibition of the downstream target of PKCμ, class II deacetylase HDAC5 nuclear export, and, consequently, inhibition of MEF2c and MyoD expression in the SM of lipin1^Myf5cKO mice. Restoration of diacylglycerol-mediated signalling in lipin1 deficient myoblasts by phorbol 12-myristate 13-acetate transiently activated PKC and HDAC5, and upregulated MEF2c expression. Our findings provide insights into the signalling circuitry that regulates SM development, and have important implications for developing intervention aimed at treating muscular dystrophy.

Muscle A-kinase-anchoring protein-β-bound calcineurin toggles active and repressive transcriptional complexes of myocyte enhancer factor 2D

Myocyte enhancer factor 2 (MEF2) transcription factors are key regulators of the development and adult phenotype of diverse tissues, including skeletal and cardiac muscles. Controlled by multiple post-translational modifications, MEF2D is an effector for the Ca²⁺/calmodulin-dependent protein phosphatase calcineurin (CaN, PP2B, and PPP3). CaN-catalyzed dephosphorylation promotes the desumoylation and acetylation of MEF2D, increasing its transcriptional activity. Both MEF2D and CaN bind the scaffold protein muscle A-kinase-anchoring protein β (mAKAPβ), which is localized to the nuclear envelope, such that C2C12 skeletal myoblast differentiation and neonatal rat ventricular myocyte hypertrophy are inhibited by mAKAPβ signalosome targeting. Using immunoprecipitation and DNA-binding assays, we now show that the formation of mAKAPβ signalosomes is required for MEF2D dephosphorylation, desumoylation, and acetylation in C2C12 cells. Reduced MEF2D phosphorylation was coupled to a switch from type IIa histone deacetylase to p300 histone acetylase binding that correlated with increased MEF2D-dependent gene expression and ventricular myocyte hypertrophy. Together, these results highlight the importance of mAKAPβ signalosomes for regulating MEF2D activity in striated muscle, affirming mAKAPβ as a nodal regulator in the myocyte intracellular signaling network.

Oxytocin alters the morphology of hypothalamic neurons via the transcription factor myocyte enhancer factor 2A (MEF-2A)

Oxytocin (OT) has gained attention not only as anxiolytic drug and as potential treatment option for autistic children; it also acts as a growth and differentiation factor in neuronal cells. While behavioral effects of OT have been studied in detail, knowledge about the cellular effects of OT is relatively sparse. In this study, we present evidence for three hypotheses: 1) OT leads to neurite retraction in hypothalamic neurons via the OT receptor (OTR) 2) The transcription factor MEF-2A is a central regulator of OT-induced neurite retraction, and 3) The MAPK pathway is critical for OT-induced MEF-2A activation. Incubation of rat hypothalamic H32 cells with 10 nM to 1 μM OT, vasopressin, and the specific OTR agonist TGOT, over the course of 12 h resulted in a time-dependent, significant retraction of neurites. In addition, the size of the nuclear compartment increased, whereas the overall cell size remained unchanged. OT treatment for 10 h increased the cellular viability significantly, and this effect could be blocked by a specific OTR antagonist, providing evidence for a specific and pro-active effect of OT on neurite retraction, and not as an unspecific side effect of apoptosis. The molecular mechanism that controls OT-induced neurite retraction includes a reduced phosphorylation of the transcription factor MEF-2A at Serine 408 (S408). This dephosphorylation is under the control of the OTR-coupled MAPK pathway, as blocking MEK1/2 by U0126 inhibited MEF-2A activation and subsequent neurite retraction. The siRNA-mediated knockdown of MEF-2A prevented the OT-induced neurite retraction, providing direct evidence for a role of MEF-2A in morphological alterations induced by OT treatment. In summary, the present study reveals a previously unknown OTR-coupled MAPK-MEF-2A pathway, which is responsible for OT-induced neurite retraction of hypothalamic neurons.

MEF2 plays a significant role in the tumor inhibitory mechanism of encapsulated RENCA cells via EGF receptor signaling in target tumor cells

Background

Agarose encapsulated murine renal adenocarcinoma cells (RENCA macrobeads) are currently being investigated in clinical trials as a treatment for therapy-resistant metastatic colorectal cancer. We have previously demonstrated the capacity of RENCA macrobeads to produce diffusible substances that markedly inhibit the proliferation of epithelial-derived tumor cells outside the macrobead environment. This study examined the molecular mechanisms underlying the observed inhibition in targeted tumor cells exposed to RENCA macrobeads.

Methods

We evaluated changes in transcription factor responses, participating intracellular signaling pathways and the involvement of specific cellular receptors in targeted tumor cells exposed to RENCA macrobeads.

Results

Factors secreted by RENCA macrobeads significantly up-regulated the activity of the MEF2 transcription factor as well as altered the transcription of MEF2b and MEF2d isoforms in targeted tumor cells. Suppression of individual or multiple MEF2 isoforms in target tumor cells markedly reduced the growth inhibitory effects of RENCA macrobeads. Furthermore, these effects were linked to the activation of the EGF receptor as attenuation of EGFR resulted in a substantial reduction of the cancer cell growth-inhibitory effect.

Conclusions

Since interruption of the EGFR signaling cascade did not eliminate RENCA macrobead-induced growth control, our data suggests that RENCA macrobeads exert their full growth inhibitory effects through the simultaneous activation of multiple signaling pathways. In contrast to a precision medicine approach targeting single molecular abnormalities, the RENCA macrobead functions as a biological-systems therapy to re-establish regulation in a highly dysfunctional and dysregulated cancer system.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-5128-5) contains supplementary material, which is available to authorized users.

Cardiovascular development and survival require Mef2c function in the myocardial but not the endothelial lineage

MEF2C is a member of the highly conserved MEF2 family of transcription factors and is a key regulator of cardiovascular development. In mice, Mef2c is expressed in the developing heart and vasculature, including the endothelium. Loss of Mef2c function in germline knockout mice leads to early embryonic demise and profound developmental abnormalities in the cardiovascular system. Previous attempts to uncover the cause of embryonic lethality by specifically disrupting Mef2c function in the heart or vasculature failed to recapitulate the global Mef2c knockout phenotype and instead resulted in relatively minor defects that did not compromise viability or result in significant cardiovascular defects. However, previous studies examined the requirement of Mef2c in the myocardial and endothelial lineages using Cre lines that begin to be expressed after the expression of Mef2c has already commenced. Here, we tested the requirement of Mef2c in the myocardial and endothelial lineages using conditional knockout approaches in mice with Cre lines that deleted Mef2c prior to onset of its expression in embryonic development. We found that deletion of Mef2c in the early myocardial lineage using Nkx2-5^Cre resulted in cardiac and vascular abnormalities that were indistinguishable from the defects in the global Mef2c knockout. In contrast, early deletion of Mef2c in the vascular endothelium using an Etv2::Cre line active prior to the onset of Mef2c expression resulted in viable offspring that were indistinguishable from wild type controls with no overt defects in vascular development, despite nearly complete early deletion of Mef2c in the vascular endothelium. Thus, these studies support the idea that the requirement of MEF2C for vascular development is secondary to its requirement in the heart and suggest that the observed failure in vascular remodeling in Mef2c knockout mice results from defective heart function.

Improvement of Duchenne muscular dystrophy phenotype following obestatin treatment

BACKGROUND

This study was performed to test the therapeutic potential of obestatin, an autocrine anabolic factor regulating skeletal muscle repair, to ameliorate the Duchenne muscular dystrophy (DMD) phenotype.

METHODS AND RESULTS

Using a multidisciplinary approach, we characterized the ageing-related preproghrelin/GPR39 expression patterns in tibialis anterior (TA) muscles of 4-, 8-, and 18-week-old mdx mice (n = 3/group) and established the effects of obestatin administration at this level in 8-week-old mdx mice (n = 5/group). The findings were extended to in vitro effects on human immortalized DMD myotubes. An analysis of TAs revealed an age-related loss of preproghrelin expression, as precursor of obestatin, in mdx mice. Administration of obestatin resulted in a significant increase in tetanic specific force (33.0% ± 1.5%, P < 0.05), compared with control mdx mice. Obestatin-treated TAs were characterized by reduction of fibres with centrally located nuclei (10.0% ± 1.2%, P < 0.05) together with an increase in the number of type I fibres (25.2% ± 1.7%, P < 0.05) associated to histone deacetylases/myocyte enhancer factor-2 and peroxisome proliferator-activated receptor-gamma coactivator 1α axis, and down-regulation of ubiquitin E3-ligases by inactivation of FoxO1/4, indexes of muscle atrophy. Obestatin reduced the level of contractile damage and tissue fibrosis. These observations correlated with decline in serum creatine kinase (58.8 ± 15.2, P < 0.05). Obestatin led to stabilization of the sarcolemma by up-regulation of utrophin, α-syntrophin, β-dystroglycan, and α7β1-integrin proteins. These pathways were also operative in human DMD myotubes.

CONCLUSIONS

These results highlight the potential of obestatin as a peptide therapeutic for preserving muscle integrity in DMD, thus allowing a better efficiency of gene or cell therapy in a combined therapeutic approach.

Chromosomal translocation-mediated evasion from miRNA induces strong MEF2D fusion protein expression, causing inhibition of PAX5 transcriptional activity

MEF2D fusion genes are newly discovered recurrent gene abnormalities that are detected in approximately 5% of acute lymphoblastic leukemia cases. We previously demonstrated that the vector-driven expression of MEF2D fusion proteins was markedly stronger than that of wild-type MEF2D; however, the underlying mechanisms and significance of this expression have yet to be clarified. We herein showed that the strong expression of MEF2D fusion proteins was caused by the loss of the target site of miRNA due to gene translocation. We identified the target region of miRNA located in the coding region and selected miR-122 as a candidate of the responsible miRNA. Mutations at a putative binding site of miR-122 increased MEF2D expression, while the transfection of its miRNA mimic reduced the expression of wild-type MEF2D, but not MEF2D fusion proteins. We also found that MEF2D fusion proteins inhibited the transcriptional activity of PAX5, a B-cell differentiation regulator in a manner that depended on fusion-specific strong expression and an association with histone deacetylase 4, which may lead to the differentiation disorders of B cells. Our results provide novel insights into the mechanisms underlying leukemia development by MEF2D fusion genes and the involvement of the deregulation of miRNA-mediated repression in cancer development.

Novel MEF2C point mutations in Chinese patients with Rett (-like) syndrome or non-syndromic intellectual disability: insights into genotype-phenotype correlation

BACKGROUND

MEF2C (Myocyte-specific enhancer factor 2C) has been associated with neurodevelopmental disorders. This study aimed at delineating the clinical profiles of MEF2C gene mutations.

METHODS

In total, 112 Chinese patients with intellectual disability (ID) were recruited, including 44 patients presented with Rett syndrome (RTT) or RTT-like syndrome, and 68 patients with non-syndromic ID. Targeted next-generation sequencing (NGS) was performed. Detailed clinical information was collected.

RESULTS

Five heterozygous MEF2C gene mutations were identified, of which three were novel. The MEF2C mutant rate was 4.5% (5/112) in total, and 6.8% (3/44) in the RTT (-like) cohort. All patients with MEF2C gene mutation presented with cognitive impairment, gross motor delay, speech disorder and autistic features. Four patients had epilepsy, which responded well to antiepileptic drugs. One female was diagnosed with classical RTT, two females with RTT-like syndrome, and two males with non-syndromic ID. Generally, the phenotype of two males with relatively downstream mutations (c.565C > T, p.Arg 189*; c.766C > T, p.Arg 256*) was milder than that of three females with upstream mutations (c.48C > G, p.Asn16Lys; c.334G > T, p.Glu112* and c.403-1G > T).

CONCLUSIONS

Our findings expanded the current understanding of the consequences of MEF2C dysfunctions, especially MEF2C point mutations. MEF2C mutations are associated with a broad clinical spectrum, ranged from classical RTT to non-syndromic ID. Through our study, it can be inferred that there is correlation between the phenotype and MEF2C-genotype, the mutation site. Overall, the MEF2C gene mutational analysis should be performed in ID cohort, especially in patients with features overlapped with RTT.

A temporal transcriptome and methylome in human embryonic stem cell-derived cardiomyocytes identifies novel regulators of early cardiac development

Stem cell-based cardiogenesis has become a powerful tool to enhance our understanding of cardiac development and test novel therapeutics for cardiovascular diseases. However, transcriptional and epigenetic regulation of multiple transitional stages from pluripotent cells to committed cardiomyocytes has not yet been fully characterized. To characterize how transcription factors, lincRNAs and DNA methylation change at temporal developmental stages, and identify potential novel regulators during cardiogenesis. We utilized a previously reported protocol that yields human cardiomyocytes (hCM) with more than 90% purity from human Embryonic Stem Cells (hESC). Leveraging the purity of cells resulting from this protocol, we systematically examined how gene expression and DNA methylation programs change at temporal developmental stages during cardiogenesis. Our results provide a comprehensive view of expression changes during cardiogenesis that extend previous studies, allowing us to identify key transcription factors as well as lincRNAs that are strongly associated with cardiac differentiation. Moreover, we incorporated a simple but powerful method to screen for novel regulators of cardiogenesis solely based on expression changes and found four novel cardiac-related transcription factors, i.e., SORBS2, MITF, DPF3, and ZNF436, which have no or few prior literature reports and we were able to validate using siRNA. Our strategy of identifying novel regulators of cardiogenesis can also be easily implemented in other stem cell-based systems. Our results provide a valuable resource for understanding cardiogenesis that extends previous findings by leveraging the purity of our cell lines, which allowed us to identify four novel cardiac-related regulators.

Myocyte Enhancer Factor 2c Regulates Dendritic Complexity and Connectivity of Cerebellar Purkinje Cells

Mef2c haploinsufficiency is implicated in behavioral deficits related to autism, schizophrenia, and intellectual disability. Although perturbations in the cerebellum, notably Purkinje cells, have been linked to these neurological disorders, the underlying mechanisms remain poorly understood. In this study, we investigated the roles of Mef2c in cerebellar Purkinje cells during the first three weeks of postnatal development. Our analysis revealed that in comparison to other members of the Mef2 family, Mef2c expression is limited to postnatal Purkinje cells. Because the role of Mef2c has not been assessed in GABAergic neurons, we set out to determine the functional significance of Mef2c by knocking down the expression of Mef2c selectively in Purkinje cells. We found that the loss of Mef2c expression during the first and second postnatal week results in an increase in dendritic arborization without impact on the general growth and migration of Purkinje cells. The influence of Mef2c on dendritic arborization persists throughout the first three weeks, but is most prominent during the first postnatal week suggesting a critical period of Mef2c activity. Additionally, the loss of Mef2c expression results in an increase in the number of spines accompanied by an increase in Gad67 and vGluT1 puncta and decrease in vGluT2 puncta. Thus, our results reveal the specific expression and functional relevance of Mef2c in developing Purkinje cells and offer insight to how disruption of the expression of Mef2c in a GABAergic neuronal subtype may lead to pathogenesis of cerebellar-associated disorders.

MEF2B Instructs Germinal Center Development and Acts as an Oncogene in B Cell Lymphomagenesis

The gene encoding the MEF2B transcription factor is mutated in germinal center (GC)-derived B cell lymphomas, but its role in GC development and lymphomagenesis is unknown. We demonstrate that Mef2b deletion reduces GC formation in mice and identify MEF2B transcriptional targets in GC, with roles in cell proliferation, apoptosis, GC confinement, and differentiation. The most common lymphoma-associated MEF2B mutant (MEF2B^D83V) is hypomorphic, yet escapes binding and negative regulation by components of the HUCA complex and class IIa HDACs. Mef2b^D83V expression in mice leads to GC enlargement and lymphoma development, a phenotype that becomes fully penetrant in combination with BCL2 de-regulation, an event associated with human MEF2B mutations. These results identify MEF2B as a critical GC regulator and a driver oncogene in lymphomagenesis.

Morphology regulation in vascular endothelial cells

Morphological change in endothelial cells is an initial and crucial step in the process of establishing a functional vascular network. Following or associated with differentiation and proliferation, endothelial cells elongate and assemble into linear cord-like vessels, subsequently forming a perfusable vascular tube. In vivo and in vitro studies have begun to outline the underlying genetic and signaling mechanisms behind endothelial cell morphology regulation. This review focuses on the transcription factors and signaling pathways regulating endothelial cell behavior, involved in morphology, during vascular development.

Drosophila mef2 is essential for normal mushroom body and wing development

MEF2 (myocyte enhancer factor 2) transcription factors are found in the brain and muscle of insects and vertebrates and are essential for the differentiation of multiple cell types. We show that in the fruit fly Drosophila, MEF2 is essential for the formation of mushroom bodies in the embryonic brain and for the normal development of wings in the adult. In embryos mutant for mef2, there is a striking reduction in the number of mushroom body neurons and their axon bundles are not detectable. The onset of MEF2 expression in neurons of the mushroom bodies coincides with their formation in the embryo and, in larvae, expression is restricted to post-mitotic neurons. In flies with a mef2 point mutation that disrupts nuclear localization, we find that MEF2 is restricted to a subset of Kenyon cells that project to the α/β, and γ axonal lobes of the mushroom bodies, but not to those forming the α’/β’ lobes.

Summary:Drosophila mef2 expression is restricted to subsets of mushroom body neurons, from the time of their differentiation to adulthood, and is essential for mushroom body formation.

Hypercapnia increases airway smooth muscle contractility via caspase-7-mediated miR-133a-RhoA signaling

The elevation of carbon dioxide (CO2) in tissues and the bloodstream (hypercapnia) occurs in patients with severe lung diseases, including chronic obstructive pulmonary disease (COPD). Whereas hypercapnia has been recognized as a marker of COPD severity, a role for hypercapnia in disease pathogenesis remains unclear. We provide evidence that CO2 acts as a signaling molecule in mouse and human airway smooth muscle cells. High CO2 activated calcium-calpain signaling and consequent smooth muscle cell contraction in mouse airway smooth muscle cells. The signaling was mediated by caspase-7-induced down-regulation of the microRNA-133a (miR-133a) and consequent up-regulation of Ras homolog family member A and myosin light-chain phosphorylation. Exposure of wild-type, but not caspase-7-null, mice to hypercapnia increased airway contraction and resistance. Deletion of the Caspase-7 gene prevented hypercapnia-induced airway contractility, which was restored by lentiviral transfection of a miR-133a antagonist. In a cohort of patients with severe COPD, hypercapnic patients had higher airway resistance, which improved after correction of hypercapnia. Our data suggest a specific molecular mechanism by which the development of hypercapnia may drive COPD pathogenesis and progression.

Crystal Structure of Apo MEF2B Reveals New Insights in DNA Binding and Cofactor Interaction

The myocyte enhancer factor 2 (MEF2) family of transcription factors plays important roles in developmental processes and adaptive responses. Although MEF2 proteins are known to bind DNA in the nucleus to regulate specific gene expression, there are reports that show that MEF2 also functions in the cytoplasm. Previous structural studies of MEF2 focused exclusively on DNA-bound MEF2 with and without various corepressors or coactivators. While these studies have established a comprehensive structural model of DNA recognition and cofactor recruitment by MEF2, the structure of MEF2 not bound to DNA, which include cytoplasmic MEF2 and free MEF2 in the nucleus, is unknown. Here we determined the structure of the MADS-box/MEF2 domain of MEF2B without DNA nor cofactor. The Apo structure of MEF2B reveals a largely preformed DNA binding interface that may be important for recognizing the shape of DNA from the minor groove side. In addition, our structure also reveals that the C-terminal helix of the MEF2-specific domain could flip up to bind to the hydrophobic groove that serves as the binding sites of MEF2 transcription cofactors. These observations shed new insights into DNA binding and cofactor interaction by MEF2 proteins.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

MEF2 and the tumorigenic process, hic sunt leones

While MEF2 transcription factors are well known to cooperate in orchestrating cell fate and adaptive responses during development and adult life, additional studies over the last decade have identified a wide spectrum of genetic alterations of MEF2 in different cancers. The consequences of these alterations, including triggering and maintaining the tumorigenic process, are not entirely clear. A deeper knowledge of the molecular pathways that regulate MEF2 expression and function, as well as the nature and consequences of MEF2 mutations are necessary to fully understand the many roles of MEF2 in malignant cells. This review discusses the current knowledge of MEF2 transcription factors in cancer.

Diacylglycerol kinase δ controls down-regulation of cyclin D1 for C2C12 myogenic differentiation

Diacylglycerol kinase (DGK) is a lipid-metabolizing enzyme that phosphorylates diacylglycerol (DG) to produce phosphatidic acid (PA). DGKδ is highly expressed in the skeletal muscle, and a decrease in DGKδ expression increases the severity of type 2 diabetes. However, the role of DGKδ in myogenic differentiation is still unknown. The present study demonstrated that DGKδ expression was down-regulated in the early stage of C2C12 myogenic differentiation almost concurrently with a decrease in cyclin D1 expression. The knockdown of DGKδ by DGKδ-specific siRNAs significantly increased the levels of cyclin D1 expression at 48 h after C2C12 myogenic differentiation. In contrast, at the same time, the knockdown of DGKδ decreased the levels of myogenin expression and the number of myosin heavy chain (MHC)-positive cells. These results indicate that DGKδ regulates the early differentiation of C2C12 myoblasts via controlling the down-regulation of cyclin D1 expression. Moreover, the suppression of DGKδ expression increased the phosphorylation levels of conventional and novel protein kinase Cs (cnPKCs). Furthermore, DGKδ suppression increased the levels of cyclin D1 and phospho-cnPKCs even at the first 24 h of myogenic differentiation. These results suggest that DGKδ controls the down-regulation of cyclin D1 expression by attenuating the PKC signaling pathway for C2C12 myogenic differentiation.