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1.  Cardiac Alpha-Myosin (MYH6) Is the Predominant Sarcomeric Disease Gene for Familial Atrial Septal Defects 
PLoS ONE  2011;6(12):e28872.
Secundum-type atrial septal defects (ASDII) account for approximately 10% of all congenital heart defects (CHD) and are associated with a familial risk. Mutations in transcription factors represent a genetic source for ASDII. Yet, little is known about the role of mutations in sarcomeric genes in ASDII etiology. To assess the role of sarcomeric genes in patients with inherited ASDII, we analyzed 13 sarcomeric genes (MYH7, MYBPC3, TNNT2, TCAP, TNNI3, MYH6, TPM1, MYL2, CSRP3, ACTC1, MYL3, TNNC1, and TTN kinase region) in 31 patients with familial ASDII using array-based resequencing. Genotyping of family relatives and control subjects as well as structural and homology analyses were used to evaluate the pathogenic impact of novel non-synonymous gene variants. Three novel missense mutations were found in the MYH6 gene encoding alpha-myosin heavy chain (R17H, C539R, and K543R). These mutations co-segregated with CHD in the families and were absent in 370 control alleles. Interestingly, all three MYH6 mutations are located in a highly conserved region of the alpha-myosin motor domain, which is involved in myosin-actin interaction. In addition, the cardiomyopathy related MYH6-A1004S and the MYBPC3-A833T mutations were also found in one and two unrelated subjects with ASDII, respectively. No mutations were found in the 11 other sarcomeric genes analyzed. The study indicates that sarcomeric gene mutations may represent a so far underestimated genetic source for familial recurrence of ASDII. In particular, perturbations in the MYH6 head domain seem to play a major role in the genetic origin of familial ASDII.
PMCID: PMC3237499  PMID: 22194935
2.  Two novel/ancient myosins in mammalian skeletal muscles: MYH14/7b and MYH15 are expressed in extraocular muscles and muscle spindles 
The Journal of Physiology  2009;588(2):353-364.
The mammalian genome contains three ancient sarcomeric myosin heavy chain (MYH) genes, MYH14/7b, MYH15 and MYH16, in addition to the two well characterized clusters of skeletal and cardiac MYHs. MYH16 is expressed in jaw muscles of carnivores; however the expression pattern of MYH14 and MYH15 is not known. MYH14 and MYH15 orthologues are present in frogs and birds, coding for chicken slow myosin 2 and ventricular MYH, respectively, whereas only MYH14 orthologues have been detected in fish. In all species the MYH14 gene contains a microRNA, miR-499. Here we report that in rat and mouse, MYH14 and miR-499 transcripts are detected in heart, slow muscles and extraocular (EO) muscles, whereas MYH15 transcripts are detected exclusively in EO muscles. However, MYH14 protein is detected only in a minor fibre population in EO muscles, corresponding to slow-tonic fibres, and in bag fibres of muscle spindles. MYH15 protein is present in most fibres of the orbital layer of EO muscles and in the extracapsular region of bag fibres. During development, MYH14 is expressed at low levels in skeletal muscles, heart and all EO muscle fibres but disappears from most fibres, except the slow-tonic fibres, after birth. In contrast, MYH15 is absent in embryonic and fetal muscles and is first detected after birth in the orbital layer of EO muscles. The identification of the expression pattern of MYH14 and MYH15 brings to completion the inventory of the MYH isoforms involved in sarcomeric architecture of skeletal muscles and provides an unambiguous molecular basis to study the contractile properties of slow-tonic fibres in mammals.
PMCID: PMC2821527  PMID: 19948655
3.  Two novel/ancient myosins in mammalian skeletal muscles: MYH14/7b and MYH15 are expressed in extraocular muscles and muscle spindles 
The Journal of Physiology  2009;588(Pt 2):353-364.
The mammalian genome contains three ancient sarcomeric myosin heavy chain (MYH) genes, MYH14/7b, MYH15 and MYH16, in addition to the two well characterized clusters of skeletal and cardiac MYHs. MYH16 is expressed in jaw muscles of carnivores; however the expression pattern of MYH14 and MYH15 is not known. MYH14 and MYH15 orthologues are present in frogs and birds, coding for chicken slow myosin 2 and ventricular MYH, respectively, whereas only MYH14 orthologues have been detected in fish. In all species the MYH14 gene contains a microRNA, miR-499. Here we report that in rat and mouse, MYH14 and miR-499 transcripts are detected in heart, slow muscles and extraocular (EO) muscles, whereas MYH15 transcripts are detected exclusively in EO muscles. However, MYH14 protein is detected only in a minor fibre population in EO muscles, corresponding to slow-tonic fibres, and in bag fibres of muscle spindles. MYH15 protein is present in most fibres of the orbital layer of EO muscles and in the extracapsular region of bag fibres. During development, MYH14 is expressed at low levels in skeletal muscles, heart and all EO muscle fibres but disappears from most fibres, except the slow-tonic fibres, after birth. In contrast, MYH15 is absent in embryonic and fetal muscles and is first detected after birth in the orbital layer of EO muscles. The identification of the expression pattern of MYH14 and MYH15 brings to completion the inventory of the MYH isoforms involved in sarcomeric architecture of skeletal muscles and provides an unambiguous molecular basis to study the contractile properties of slow-tonic fibres in mammals.
PMCID: PMC2821527  PMID: 19948655
4.  Physical Interaction between TBX5 and MEF2C Is Required for Early Heart Development▿ † 
Molecular and Cellular Biology  2009;29(8):2205-2218.
TBX5 is a transcription factor which plays important roles in the development of the heart and upper limbs. Mutations in this gene produce the inherited disorder Holt-Oram syndrome. Here, we report a physical interaction between TBX5 and MEF2C leading to a synergistic activation of the α-cardiac myosin heavy chain (MYH6). Mutants of TBX5, TBX5G80R, and TBX5R279X that produce severe cardiac phenotypes impair the synergy. Using fluorescence resonance energy transfer, we demonstrate the interaction of TBX5 and MEF2C in living cells. We also show that they physically associate through their DNA-binding domains to form a complex on the MYH6 promoter. Morpholino-mediated knockdowns of Tbx5 and Mef2c in zebrafish suggest that the genetic interaction of these proteins is not only required for MYH6 expression but also essential for the early stages of heart development and survival. This is the first report of a functional interaction between a T-box protein and a MADS box factor that may be crucial in cardiomyocyte differentiation.
PMCID: PMC2663302  PMID: 19204083
5.  Evolution of the myosin heavy chain gene MYH14 and its intronic microRNA miR-499: muscle-specific miR-499 expression persists in the absence of the ancestral host gene 
A novel sarcomeric myosin heavy chain gene, MYH14, was identified following the completion of the human genome project. MYH14 contains an intronic microRNA, miR-499, which is expressed in a slow/cardiac muscle specific manner along with its host gene; it plays a key role in muscle fiber-type specification in mammals. Interestingly, teleost fish genomes contain multiple MYH14 and miR-499 paralogs. However, the evolutionary history of MYH14 and miR-499 has not been studied in detail. In the present study, we identified MYH14/miR-499 loci on various teleost fish genomes and examined their evolutionary history by sequence and expression analyses.
Synteny and phylogenetic analyses depict the evolutionary history of MYH14/miR-499 loci where teleost specific duplication and several subsequent rounds of species-specific gene loss events took place. Interestingly, miR-499 was not located in the MYH14 introns of certain teleost fish. An MYH14 paralog, lacking miR-499, exhibited an accelerated rate of evolution compared with those containing miR-499, suggesting a putative functional relationship between MYH14 and miR-499. In medaka, Oryzias latipes, miR-499 is present where MYH14 is completely absent in the genome. Furthermore, by using in situ hybridization and small RNA sequencing, miR-499 was expressed in the notochord at the medaka embryonic stage and slow/cardiac muscle at the larval and adult stages. Comparing the flanking sequences of MYH14/miR-499 loci between torafugu Takifugu rubripes, zebrafish Danio rerio, and medaka revealed some highly conserved regions, suggesting that cis-regulatory elements have been functionally conserved in medaka miR-499 despite the loss of its host gene.
This study reveals the evolutionary history of the MYH14/miRNA-499 locus in teleost fish, indicating divergent distribution and expression of MYH14 and miR-499 genes in different teleost fish lineages. We also found that medaka miR-499 was even expressed in the absence of its host gene. To our knowledge, this is the first report that shows the conversion of intronic into non-intronic miRNA during the evolution of a teleost fish lineage.
PMCID: PMC3716903  PMID: 24059862
Myosin heavy chain; MYH14 (MYH7b); microRNA; miR-499; Muscle; Muscle fiber-type; Teleostei
6.  A human de novo mutation in MYH10 phenocopies the loss of function mutation in mice 
Rare Diseases  2013;1:e26144.
We used whole exome sequence analysis to investigate a possible genetic etiology for a patient with the phenotype of intrauterine growth restriction, microcephaly, developmental delay, failure to thrive, congenital bilateral hip dysplasia, cerebral and cerebellar atrophy, hydrocephalus, and congenital diaphragmatic hernia (CDH).
Whole exome sequencing identified a novel de novo c.2722G > T (p.E908X) mutation in the Myosin Heavy Chain 10 gene (MYH10) which encodes for non-muscle heavy chain II B (NMHC IIB). Mutations in MYH10 have not been previously described in association with human disease. The E908X mutation is located in the coiled-coil region of the protein and is expected to delete the tail domain and disrupt filament assembly.
Nonmuscle myosin IIs (NM IIs) are a group of ubiquitously expressed proteins, and NM II B is specifically enriched in neuronal tissue and is thought to be important in neuronal migration. It is also expressed in cardiac myocytes along with NM IIC.
Homozygous NMHC II B-/B- mouse knockouts die by embryonic day (E)14.5 with severe cardiac defects (membranous ventricular septal defect and cardiac outflow tract abnormalities) and neurodevelopmental disorders (progressive hydrocephalus and neuronal migrational abnormalities).
A heterozygous MYH10 loss of function mutation produces a severe neurologic phenotype and CDH but no apparent cardiac phenotype and suggests that MYH10 may represent a novel gene for brain malformations and/or CDH.
PMCID: PMC3927488  PMID: 25003005
whole exome sequencing; MYH10; intellectual disability; microcephaly; NMHC II B
7.  Cochlear implantation is safe and effective in patients with MYH9-related disease 
MYH9-related disease (MYH9-RD) is a rare syndromic disorder deriving from mutations in MYH9, the gene for the heavy chain of non-muscle myosin IIA. Patients present with congenital thrombocytopenia and giant platelets and have a variable risk of developing sensorineural deafness, kidney damage, presenile cataract, and liver abnormalities. Almost all MYH9-RD patients develop the hearing defect, which, in many individuals, progresses to severe to profound deafness with high impact on quality of life. These patients are potential candidates for cochlear implantation (CI), however, no consistent data are available about the risk to benefit ratio of CI in MYH9-RD. The only reported patient who received CI experienced perisurgery complications that have been attributed to concurrent platelet defects and/or MYH9 protein dysfunction.
By international co-operative study, we report the clinical outcome of 10 patients with MYH9-RD and severe to profound deafness who received a CI at 8 institutions.
Nine patients benefited from CI: in particular, eight of them obtained excellent performances with restoration of a practically normal hearing function and verbal communication abilities. One patient had a slightly worse performance that could be explained by the very long duration of severe deafness before CI. Finally, one patient did not significantly benefit from CI. No adverse events attributable to MYH9-RD syndrome were observed, in particular no perisurgery bleeding complications due to the platelet defects were seen. Patients’ perioperative management is described and discussed.
CI is safe and effective in most patients with MYH9-RD and severe to profound deafness and should be offered to these subjects, possibly as soon as they develop the criteria for candidacy.
PMCID: PMC4105151  PMID: 24980457
MYH9-related disease; Genetic deafness; Inherited thrombocytopenia; Cochlear implantation; Fetchner syndrome; Epstein syndrome; May-Hegglin anomaly; Non-muscle myosin
8.  Missense mutations in the APOL1 gene are highly associated with end stage kidney disease risk previously attributed to the MYH9 gene 
Human Genetics  2010;128(3):345-350.
MYH9 has been proposed as a major genetic risk locus for a spectrum of nondiabetic end stage kidney disease (ESKD). We use recently released sequences from the 1000 Genomes Project to identify two western African-specific missense mutations (S342G and I384M) in the neighboring APOL1 gene, and demonstrate that these are more strongly associated with ESKD than previously reported MYH9 variants. The APOL1 gene product, apolipoprotein L-1, has been studied for its roles in trypanosomal lysis, autophagic cell death, lipid metabolism, as well as vascular and other biological activities. We also show that the distribution of these newly identified APOL1 risk variants in African populations is consistent with the pattern of African ancestry ESKD risk previously attributed to MYH9.
Mapping by admixture linkage disequilibrium (MALD) localized an interval on chromosome 22, in a region that includes the MYH9 gene, which was shown to contain African ancestry risk variants associated with certain forms of ESKD (Kao et al. 2008; Kopp et al. 2008). MYH9 encodes nonmuscle myosin heavy chain IIa, a major cytoskeletal nanomotor protein expressed in many cell types, including podocyte cells of the renal glomerulus. Moreover, 39 different coding region mutations in MYH9 have been identified in patients with a group of rare syndromes, collectively termed the Giant Platelet Syndromes, with clear autosomal dominant inheritance, and various clinical manifestations, sometimes also including glomerular pathology and chronic kidney disease (Kopp 2010; Sekine et al. 2010). Accordingly, MYH9 was further explored in these studies as the leading candidate gene responsible for the MALD signal. Dense mapping of MYH9 identified individual single nucleotide polymorphisms (SNPs) and sets of such SNPs grouped as haplotypes that were found to be highly associated with a large and important group of ESKD risk phenotypes, which as a consequence were designated as MYH9-associated nephropathies (Bostrom and Freedman 2010). These included HIV-associated nephropathy (HIVAN), primary nonmonogenic forms of focal segmental glomerulosclerosis, and hypertension affiliated chronic kidney disease not attributed to other etiologies (Bostrom and Freedman 2010). The MYH9 SNP and haplotype associations observed with these forms of ESKD yielded the largest odds ratios (OR) reported to date for the association of common variants with common disease risk (Winkler et al. 2010). Two specific MYH9 variants (rs5750250 of S-haplotype and rs11912763 of F-haplotype) were designated as most strongly predictive on the basis of Receiver Operating Characteristic analysis (Nelson et al. 2010). These MYH9 association studies were then also extended to earlier stage and related kidney disease phenotypes and to population groups with varying degrees of recent African ancestry admixture (Behar et al. 2010; Freedman et al. 2009a, b; Nelson et al. 2010), and led to the expectation of finding a functional African ancestry causative variant within MYH9. However, despite intensive efforts including re-sequencing of the MYH9 gene no suggested functional mutation has been identified (Nelson et al. 2010; Winkler et al. 2010). This led us to re-examine the interval surrounding MYH9 and to the detection of novel missense mutations with predicted functional effects in the neighboring APOL1 gene, which are significantly more associated with ESKD than all previously reported SNPs in MYH9.
Electronic supplementary material
The online version of this article (doi:10.1007/s00439-010-0861-0) contains supplementary material, which is available to authorized users.
PMCID: PMC2921485  PMID: 20635188
9.  Six Homeoproteins and a linc-RNA at the Fast MYH Locus Lock Fast Myofiber Terminal Phenotype 
PLoS Genetics  2014;10(5):e1004386.
Thousands of long intergenic non-coding RNAs (lincRNAs) are encoded by the mammalian genome. However, the function of most of these lincRNAs has not been identified in vivo. Here, we demonstrate a role for a novel lincRNA, linc-MYH, in adult fast-type myofiber specialization. Fast myosin heavy chain (MYH) genes and linc-MYH share a common enhancer, located in the fast MYH gene locus and regulated by Six1 homeoproteins. linc-MYH in nuclei of fast-type myofibers prevents slow-type and enhances fast-type gene expression. Functional fast-sarcomeric unit formation is achieved by the coordinate expression of fast MYHs and linc-MYH, under the control of a common Six-bound enhancer.
Author Summary
Adult skeletal muscles are classified into fast-type and slow-type, which display different resistance to muscle atrophy and metabolic protection against obesity. We identify in this manuscript a new mechanism controlling in vivo adult muscle fiber-type specification implicating a long intergenic non-coding RNA, linc-MYH. We demonstrate a three-element genetic partnership, where an enhancer under the control of the myogenic homeoprotein Six1 functions as a regulatory hub to control fibre phenotype. In this partnership, the enhancer controls positively the expression of both the adjacent fast myosin heavy chain (MYH) gene cluster and of linc-MYH. linc-MYH is present only in adult fast type skeletal myofibers and controls their phenotype by suppressing slow-type gene expression. The regulation of linc-MYH could provide a lead for new therapeutic approaches or drug development.
PMCID: PMC4031048  PMID: 24852826
10.  Noncompaction of the Ventricular Myocardium Is Associated with a De Novo Mutation in the β-Myosin Heavy Chain Gene 
PLoS ONE  2007;2(12):e1362.
Noncompaction of the ventricular myocardium (NVM) is the morphological hallmark of a rare familial or sporadic unclassified heart disease of heterogeneous origin. NVM results presumably from a congenital developmental error and has been traced back to single point mutations in various genes. The objective of this study was to determine the underlying genetic defect in a large German family suffering from NVM. Twenty four family members were clinically assessed using advanced imaging techniques. For molecular characterization, a genome-wide linkage analysis was undertaken and the disease locus was mapped to chromosome 14ptel-14q12. Subsequently, two genes of the disease interval, MYH6 and MYH7 (encoding the α- and β-myosin heavy chain, respectively) were sequenced, leading to the identification of a previously unknown de novo missense mutation, c.842G>C, in the gene MYH7. The mutation affects a highly conserved amino acid in the myosin subfragment-1 (R281T). In silico simulations suggest that the mutation R281T prevents the formation of a salt bridge between residues R281 and D325, thereby destabilizing the myosin head. The mutation was exclusively present in morphologically affected family members. A few members of the family displayed NVM in combination with other heart defects, such as dislocation of the tricuspid valve (Ebstein's anomaly, EA) and atrial septal defect (ASD). A high degree of clinical variability was observed, ranging from the absence of symptoms in childhood to cardiac death in the third decade of life. The data presented in this report provide first evidence that a mutation in a sarcomeric protein can cause noncompaction of the ventricular myocardium.
PMCID: PMC2137931  PMID: 18159245
11.  Distribution of histone3 lysine4 trimethylation at T3-responsive loci in the heart during reversible changes in gene expression 
Gene expression  2012;15(4):183-198.
Expression in the adult heart of a number of cardiac genes, including the two genes comprising the cardiac Myosin heavy chain locus (Myh), is controlled by thyroid hormone (T3) levels, but there is minimal information concerning the epigenetic status of the genes when their expressions change. We fed mice normal chow or a Propyl thio uracil (PTU, an inhibitor of T3 production)-diet for 6 weeks, or the PTU diet for 6 weeks followed by normal chow for a further two weeks. Heart ventricles from these groups were then used for ChIP-seq analyses with an antibody to H3K4me3, a well documented epigenetic marker of gene activation. The resulting data show that, at the Myh7 locus, H3K4me3 modifications are induced primarily at 5’ transcribed region in parallel with increased expression of beta myosin heavy chain (MHC). At the Myh6 locus, decreases in H3K4me3 modifications occurred at the promoter and 5’ transcribed region. Extensive H3K4me3 modifications also occurred at the intergenic region between the two Myh genes which extended into the 3’ transcribed region of Myh7. The PTU-induced changes in H3K4me3 levels are, for the most part, reversible but are not invariably complete. We found full restoration of Myh6 gene expression upon PTU withdrawal, however the H3K4me3 pattern was only partially restored at Myh6, suggesting that full re-expression of Myh6 does not require that the H3K4me3 modifications return fully to the untreated conditions. Together, our data show that the H3K4me3 modification is an epigenetic marker closely associated with changes in Myh gene expression.
PMCID: PMC3607203  PMID: 22783727
Myosin heavy chain; epigenetic; ChIP-seq; Thyroid Hormone; Heart; histone methylation
12.  The fraction of strongly bound cross-bridges is increased in mice that carry the myopathy-linked myosin heavy chain mutation MYH4L342Q 
Disease Models & Mechanisms  2013;6(3):834-840.
Myosinopathies have emerged as a new group of diseases and are caused by mutations in genes encoding myosin heavy chain (MyHC) isoforms. One major hallmark of these diseases is skeletal muscle weakness or paralysis, but the underlying molecular mechanisms remain unclear. Here, we have undertaken a detailed functional study of muscle fibers from Myh4arl mice, which carry a mutation that provokes an L342Q change within the catalytic domain of the type IIb skeletal muscle myosin protein MYH4. Because homozygous animals develop rapid muscle-structure disruption and lower-limb paralysis, they must be killed by postnatal day 13, so all experiments were performed using skeletal muscles from adult heterozygous animals (Myh4arl/+). Myh4arl/+ mice contain MYH4L342Q expressed at 7% of the levels of the wild-type (WT) protein, and are overtly and histologically normal. However, mechanical and X-ray diffraction pattern analyses of single membrane-permeabilized fibers revealed, upon maximal Ca2+ activation, higher stiffness as well as altered meridional and equatorial reflections in Myh4arl/+ mice when compared with age-matched WT animals. Under rigor conditions, by contrast, no difference was observed between Myh4arl/+ and WT mice. Altogether, these findings prove that, in adult MYH4L342Q heterozygous mice, the transition from weak to strong myosin cross-bridge binding is facilitated, increasing the number of strongly attached myosin heads, thus enhancing force production. These changes are predictably exacerbated in the type IIb fibers of homozygous mice, in which the embryonic myosin isoform is fully replaced by MYH4L342Q, leading to a hypercontraction, muscle-structure disruption and lower-limb paralysis. Overall, these findings provide important insights into the molecular pathogenesis of skeletal myosinopathies.
PMCID: PMC3634666  PMID: 23335206
13.  Expression Patterns of Cardiac Myofilament Proteins – Genomic and Protein Analysis of Surgical Myectomy Tissue from Patients with Obstructive Hypertrophic Cardiomyopathy 
Circulation. Heart failure  2009;2(4):325-333.
Mutations in myofilament proteins, most commonly MYBPC3-encoded myosin binding protein C and MYH7-encoded β-myosin heavy chain, can cause hypertrophic cardiomyopathy (HCM). Despite significant advances in structure-function relationships pertaining to the cardiac sarcomere, there is limited knowledge of how a mutation leads to clinical HCM. We therefore set out to study expression and localization of myofilament proteins in left ventricular tissue of patients with HCM.
Methods and Results
Frozen surgical myectomy specimens from 47 patients with HCM were examined and genotyped for mutations involving 8 myofilament-encoding genes. Myofilament protein levels were quantified by western blot with localization graded from immunohistochemical staining of tissue sections. Overall, 25/47 (53%) patients had myofilament-HCM including 12 with MYBPC3-HCM and 9 with MYH7-HCM. Compared to healthy heart tissue, levels of myofilament proteins were increased in patients manifesting a mutation in either gene. Patients with a frameshift mutation predicted to truncate MYBPC3 exhibited marked disturbances in protein localization as compared to missense mutations in either MYBPC3 or MYH7.
In this first expression study in human HCM tissue, increased myofilament protein levels in patients with either MYBPC3 or MYH7-mediated HCM suggest a poison peptide mechanism. Specifically, the mechanism of dysfunction may vary according to the genetic subgroup suggested by a distinctly abnormal distribution of myofilament proteins in patients manifesting a truncation mutation in MYBPC3.
PMCID: PMC2765062  PMID: 19808356
Cardiomyopathy; Hypertrophy; Genetics; Protein
14.  Myosinopathies: pathology and mechanisms 
Acta Neuropathologica  2012;125(1):3-18.
The myosin heavy chain (MyHC) is the molecular motor of muscle and forms the backbone of the sarcomere thick filaments. Different MyHC isoforms are of importance for the physiological properties of different muscle fiber types. Hereditary myosin myopathies have emerged as an important group of diseases with variable clinical and morphological expression depending on the mutated isoform and type and location of the mutation. Dominant mutations in developmental MyHC isoform genes (MYH3 and MYH8) are associated with distal arthrogryposis syndromes. Dominant or recessive mutations affecting the type IIa MyHC (MYH2) are associated with early-onset myopathies with variable muscle weakness and ophthalmoplegia as a consistent finding. Myopathies with scapuloperoneal, distal or limb-girdle muscle weakness including entities, such as myosin storage myopathy and Laing distal myopathy are the result of usually dominant mutations in the gene for slow/β cardiac MyHC (MYH7). Protein aggregation is part of the features in some of these myopathies. In myosin storage myopathy protein aggregates are formed by accumulation of myosin beneath the sarcolemma and between myofibrils. In vitro studies on the effects of different mutations associated with myosin storage myopathy and Laing distal myopathy indicate altered biochemical and biophysical properties of the light meromyosin, which is essential for thick filament assembly. Protein aggregates in the form of tubulofilamentous inclusions in association with vacuolated muscle fibers are present at late stage of dominant myosin IIa myopathy and sometimes in Laing distal myopathy. These protein aggregates exhibit features indicating defective degradation of misfolded proteins. In addition to protein aggregation and muscle fiber degeneration some of the myosin mutations cause functional impairment of the molecular motor adding to the pathogenesis of myosinopathies.
PMCID: PMC3535372  PMID: 22918376
Myopathy; Myosin; Myosin heavy chain; Mutation; Myosin storage myopathy; Laing distal myopathy; Protein aggregate
15.  The UNC-45 Chaperone Is Critical for Establishing Myosin-Based Myofibrillar Organization and Cardiac Contractility in the Drosophila Heart Model 
PLoS ONE  2011;6(7):e22579.
UNC-45 is a UCS (UNC-45/CRO1/She4P) class chaperone necessary for myosin folding and/or accumulation, but its requirement for maintaining cardiac contractility has not been explored. Given the prevalence of myosin mutations in eliciting cardiomyopathy, chaperones like UNC-45 are likely to be equally critical in provoking or modulating myosin-associated cardiomyopathy. Here, we used the Drosophila heart model to examine its role in cardiac physiology, in conjunction with RNAi-mediated gene silencing specifically in the heart in vivo. Analysis of cardiac physiology was carried out using high-speed video recording in conjunction with movement analysis algorithms. unc-45 knockdown resulted in severely compromised cardiac function in adults as evidenced by prolonged diastolic and systolic intervals, and increased incidence of arrhythmias and extreme dilation; the latter was accompanied by a significant reduction in muscle contractility. Structural analysis showed reduced myofibrils, myofibrillar disarray, and greatly decreased cardiac myosin accumulation. Cardiac unc-45 silencing also dramatically reduced life-span. In contrast, third instar larval and young pupal hearts showed mild cardiac abnormalities, as severe cardiac defects only developed during metamorphosis. Furthermore, cardiac unc-45 silencing in the adult heart (after metamorphosis) led to less severe phenotypes. This suggests that UNC-45 is mostly required for myosin accumulation/folding during remodeling of the forming adult heart. The cardiac defects, myosin deficit and decreased life-span in flies upon heart-specific unc-45 knockdown were significantly rescued by UNC-45 over-expression. Our results are the first to demonstrate a cardiac-specific requirement of a chaperone in Drosophila, suggestive of a critical role of UNC-45 in cardiomyopathies, including those associated with unfolded proteins in the failing human heart. The dilated cardiomyopathy phenotype associated with UNC-45 deficiency is mimicked by myosin knockdown suggesting that UNC-45 plays a crucial role in stabilizing myosin and possibly preventing human cardiomyopathies associated with functional deficiencies of myosin.
PMCID: PMC3143160  PMID: 21799905
16.  Molecular basis of hypertrophic and dilated cardiomyopathy. 
Texas Heart Institute Journal  1994;21(1):6-15.
Hypertrophic cardiomyopathy is a heterogeneous disease with autosomal dominant Mendelian inheritance. In 1989, the 1st locus for hypertrophic cardiomyopathy was mapped to cardiac myosin genes located on chromosome 14q1. Soon, several mutations that cosegregated with inheritance of the disease were identified in the beta-myosin heavy chain gene, or MHY7. More than 30 missense mutations and 1 deletion mutation in the beta-myosin heavy chain gene have since been described. Recently, expression of both the mutant beta-myosin heavy chain mRNA and the mutant protein has been shown in the cardiac and skeletal muscles of individuals with hypertrophic cardiomyopathy. Characterization of the clinical features of beta-myosin heavy chain mutations has shown that certain mutations, such as Arg403Gln and Arg719Trp mutations, are associated with high rate of sudden cardiac death. In addition to the beta-myosin heavy chain gene, 3 new loci for hypertrophic cardiomyopathy have recently been described, but the candidate genes have not yet been identified. Dilated cardiomyopathy can be inherited as an autosomal dominant, autosomal recessive, and X-linked disease. The familial form of dilated cardiomyopathy comprises approximately 20% of the cases of idiopathic cardiomyopathy. Echocardiographic abnormalities such as left ventricular enlargement are present in 10% of asymptomatic relatives. No gene for familial dilated cardiomyopathy has been identified, but linkage studies using polymorphic, short-tandem repeat markers are ongoing. Dilated cardiomyopathy is a common manifestation of Duchenne/Becker muscular dystrophy. Heart failure is a common cause of death in the affected individuals. The gene responsible for this disease is the dystrophin gene located on X chromosome. There have been reports in these patients of several dystrophin-gene deletion mutations, which result in a decrease in the expression of the dystrophin protein in the cardiac and skeletal tissues. X-linked cardiomyopathy, in which the disease is restricted to the heart, has also been linked to the dystrophin gene. Myotonic dystrophy is an autosomal dominant disease that commonly involves the myocardium and the conduction tissue, resulting in conduction defects and heart failure. Sudden cardiac death is the most common cause of mortality in patients with myotonic dystrophy. Recently, the myotonin protein kinase gene located on chromosome 19 was identified as the gene responsible for this disease. Expansion of the number of trinucleotide repeats in the myotonin protein kinase gene results in myotonic dystrophy. Mutations in mitochondrial DNA have been associated with hypertrophic and dilated cardiomyopathy. The inheritance of mitochondrial cardiomyopathy is maternal and the disease is associated with certain systemic disorders.
PMCID: PMC325126  PMID: 8180512
17.  Reduced Expression of Androgen Receptor and Myosin Heavy Chain mRNA in Cremaster Muscle of Boys with Nonsyndromic Cryptorchidism 
The Journal of urology  2012;188(4 Suppl):1411-1416.
To better define developmental mechanisms of nonsyndromic cryptorchidism (NSC), we measured expression of hormone receptor and muscle type-specific mRNAs in target tissues of boys with and without NSC.
Materials and Methods
Prospectively collected cremaster muscle and/or hernia sac tissues from boys with congenital (n=79) or acquired (n=66) NSC and hernia/hydrocele (controls, n=84) were analyzed for hormone receptor (RXFP2, AR, ESR1, ESR2) and myosin heavy chain-specific (MYH1, MYH2, MYH7) mRNA expression using real time RT-PCR. Log-transformed mRNA, phenotype and feeding history data were statistically analyzed using Pearson’s correlation, ANOVA and 2-sample T tests.
AR mRNA expression was higher in cremaster than sac, and significantly lower in both congenital and acquired NSC relative to controls (p<0.01). Type 1 (slow/cardiac) MYH7 mRNA expression was also significantly reduced in both NSC groups (p≤0.002) while a reduction in type 2 (fast) MYH2 expression was more modest and significant only for the congenital group (p<0.05). Cremasteric MYH7 and AR levels were strongly correlated (r2 = .751, p<0.001). MYH7 and ESR1 mRNA levels were higher and lower, respectively, in soy formula-fed boys with NSC. Expression of other genes was not measurable.
Our data suggest that boys with congenital and acquired NSC differentially express AR and slow twitch-specific MYH7 mRNA in cremaster and that MYH7 expression is correlated with AR levels and soy formula use. These differences in gene expression may reflect aberrant hormonal signaling and/or innervation during development with the potential for secondary functional effects and failed testicular descent.
PMCID: PMC3601375  PMID: 22906643
Cryptorchidism; androgen; estrogen; myosin; cremaster
18.  Digenic mutational inheritance of the integrin alpha 7 and the myosin heavy chain 7B genes causes congenital myopathy with left ventricular non-compact cardiomyopathy 
We report an Italian family in which the proband showed a severe phenotype characterized by the association of congenital fiber type disproportion (CFTD) with a left ventricular non-compaction cardiomyopathy (LVNC). This study was focused on the identification of the responsible gene/s.
Methods and results
Using the whole-exome sequencing approach, we identified the proband homozygous missense mutations in two genes, the myosin heavy chain 7B (MYH7B) and the integrin alpha 7 (ITGA7). Both genes are expressed in heart and muscle tissues, and both mutations were predicted to be deleterious and were not found in the healthy population.
The R890C mutation in the MYH7B gene segregated with the LVNC phenotype in the examined family. It was also found in one unrelated patient affected by LVNC, confirming a causative role in cardiomyopathy.
The E882K mutation in the ITGA7 gene, a key component of the basal lamina of muscle fibers, was found only in the proband, suggesting a role in CFTD.
This study identifies two novel disease genes. Mutation in MYH7B causes a classical LVNC phenotype, whereas mutation in ITGA7 causes CFTD. Both phenotypes represent alterations of skeletal and cardiac muscle maturation and are usually not severe. The severe phenotype of the proband is most likely due to a synergic effect of these two mutations.
This study provides new insights into the genetics underlying Mendelian traits and demonstrates a role for digenic inheritance in complex phenotypes.
PMCID: PMC3695851  PMID: 23800289
Left ventricular noncompact cardiomyopathy; Congenital type fiber disproportion; Integrin alpha 7 (ITGA7); Myosin heavy chain 7B (MYH7B); Whole exome sequencing
19.  Mice expressing mutant myosin heavy chains are a model for familial hypertrophic cardiomyopathy. 
Molecular Medicine  1996;2(5):556-567.
BACKGROUND: Familial hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease characterized by ventricular hypertrophy, myocellular disarray, arrhythmias, and sudden death. Mutations in several contractile proteins, including cardiac myosin heavy chains, have been described in families with this disease, leading to the hypothesis that HCM is a disease of the sarcomere. MATERIALS AND METHODS: A mutation in the myosin heavy chain (Myh) predicted to interfere strongly with myosin's binding to actin was designed and used to create an animal model for HCM. Five independent lines of transgenic mice were produced with cardiac-specific expression of the mutant Myh. RESULTS: Although the mutant Myh represents a small proportion (1-12%) of the heart's myosin, the mice exhibit the cardiac histopathology seen in HCM patients. Histopathology is absent from the atria and primarily restricted to the left ventricle. The line exhibiting the highest level of mutant Myh expression demonstrates ventricular hypertrophy by 12 weeks of age, but the further course of the disease is strongly affected by the sex of the animal. Hypertrophy increases with age in female animals while the hearts of male show severe dilation by 8 months of age, in the absence of increased mass. CONCLUSIONS: The low levels of the transgene protein in the presence of the phenotypic features of HCM suggest that the mutant protein acts as a dominant negative. In addition, the distinct phenotypes developed by aging male or female transgenic mice suggest that extragenic factors strongly influence the development of the disease phenotype.
PMCID: PMC2230192  PMID: 8898372
20.  Abnormal blood pressure response to exercise occurs more frequently in hypertrophic cardiomyopathy patients with the R92W troponin T mutation than in those with myosin mutations 
Heart Rhythm  2009;6(11):S18-S24.
Abnormal blood pressure response to exercise is reported to occur in up to a third of hypertrophic cardiomyopathy (HCM) cases and is associated with an increased risk of death, particularly in the young, but it is not known whether the HCM-causing mutation influences blood pressure response to exercise. The purpose of this article is to ascertain whether the blood pressure response to exercise differs among carriers of the R92W mutation in the cardiac troponin T gene (TNNT2), which has been associated with an increased risk of sudden cardiac death in young males; carriers of mutations in the cardiac β-myosin heavy chain gene (MYH7); and their noncarrier relatives. Thirty R92WTNNT2 carriers, 51 MYH7 mutation carriers, and 68 of their noncarrier relatives were subjected to bicycle ergonometric exercise testing to assess blood pressure response to, as well as heart rate recovery after, exercise. Additional echocardiographic and demographic details were documented for all participants. R92WTNNT2 carriers demonstrated significantly more abnormal blood pressure responses to exercise (P = .021; odds ratio 3.03; confidence interval 1.13–8.12) and smaller increases in systolic blood pressure than MYH7 mutation carriers or related noncarrier control individuals. Although abnormal blood pressure response occurred at similar frequencies in males in all groups (23%–26%), the percentage of R92WTNNT2 females with abnormal blood pressure response was 64%, compared with 25% for MYH7 and 22% for noncarriers. Therefore, these results show that blood pressure response to exercise is influenced by genotype and gender in patients with HCM.
PMCID: PMC2773911  PMID: 19880069
Hypertrophic cardiomyopathy; Abnormal blood pressure response; Survival; Troponin T; Beta-myosin; Genetic mutation; Ca2+, calcium; CR, chronotropic response; DBP, diastolic blood pressure; ECG, electrocardiogram; HCM, hypertrophic cardiomyopathy; HR, heart rate; LV, left ventricle; LVM, left ventricular mass; maxLVWT, maximum left ventricular wall thickness; METs, metabolic equivalents; MYH7, beta cardiac myosin heavy chain gene; SBP, systolic blood pressure; SCD, sudden cardiac death; TNNT2, cardiac troponin T gene
21.  Myostatin facilitates slow and inhibits fast myosin heavy chain expression during myogenic differentiation 
Skeletal muscles in the limb and body trunk are composed of heterogeneous myofibers expressing different isoforms of myosin heavy chain (Myh), including type I (slow, Myh7), IIA (intermediate, Myh2), IIX (fast, Myh1) and IIB (very fast, Myh4). While the contraction force and speed of a muscle are known to be determined by the relative abundance of myofibers expressing each Myh isoform, it is unclear how specific combinations of myofiber types are formed and regulated at the cellular and molecular level. We report here that myostatin (Mstn) positively regulates slow but negatively regulates fast Myh isoforms. Mstn was expressed at higher levels in the fast muscle myoblasts and myofibers than in the slow muscle counterparts. Interestingly, Mstn knockout led to a shift of Myh towards faster isoforms, suggesting an inhibitory role of Mstn in fast Myh expression. Consistently, when induced to differentiate, Mstn null myoblasts formed myotubes preferentially expressing fast Myh. Conversely, treatment of myoblasts with a recombinant Mstn protein upregulated Myh7 but downregulated Myh4 gene expression in newly formed myotubes. Importantly, both Mstn antibody and soluble activin type 2B receptor inhibited slow Myh7 and promoted fast Myh4 expression, indicating that myostatin acts through canonical activin receptor to regulate the expression of Myh genes. These results demonstrate a role of myostatin in the specification of myofiber types during myogenic differentiation.
PMCID: PMC3483024  PMID: 22910409
Myostatin (Mstn); satellite cells; myofiber; myosin heavy chain; TGFβ
22.  Lampreys Have a Single Gene Cluster for the Fast Skeletal Myosin Heavy Chain Gene Family 
PLoS ONE  2013;8(12):e85500.
Muscle tissues contain the most classic sarcomeric myosin, called myosin II, which consists of 2 heavy chains (MYHs) and 4 light chains. In the case of humans (tetrapod), a total of 6 fast skeletal-type MYH genes (MYHs) are clustered on a single chromosome. In contrast, torafugu (teleost) contains at least 13 fast skeletal MYHs, which are distributed in 5 genomic regions; the MYHs are clustered in 3 of these regions. In the present study, the evolutionary relationship among fast skeletal MYHs is elucidated by comparing the MYHs of teleosts and tetrapods with those of cyclostome lampreys, one of two groups of extant jawless vertebrates (agnathans). We found that lampreys contain at least 3 fast skeletal MYHs, which are clustered in a head-to-tail manner in a single genomic region. Although there was apparent synteny in the corresponding MYH cluster regions between lampreys and tetrapods, phylogenetic analysis indicated that lamprey and tetrapod MYHs have independently duplicated and diversified. Subsequent transgenic approaches showed that the 5′-flanking sequences of Japanese lamprey fast skeletal MYHs function as a regulatory sequence to drive specific reporter gene expression in the fast skeletal muscle of zebrafish embryos. Although zebrafish MYH promoters showed apparent activity to direct reporter gene expression in myogenic cells derived from mice, promoters from Japanese lamprey MYHs had no activity. These results suggest that the muscle-specific regulatory mechanisms are partially conserved between teleosts and tetrapods but not between cyclostomes and tetrapods, despite the conserved synteny.
PMCID: PMC3869912  PMID: 24376886
23.  Cardiomyopathy in Irx4-Deficient Mice Is Preceded by Abnormal Ventricular Gene Expression 
Molecular and Cellular Biology  2001;21(5):1730-1736.
To define the role of Irx4, a member of the Iroquois family of homeobox transcription factors in mammalian heart development and function, we disrupted the murine Irx4 gene. Cardiac morphology in Irx4-deficient mice (designated Irx4Δex2/Δex2) was normal during embryogenesis and in early postnatal life. Adult Irx4Δex2/Δex2 mice developed a cardiomyopathy characterized by cardiac hypertrophy and impaired contractile function. Prior to the development of cardiomyopathy, Irx4Δex2/Δex2 hearts had abnormal ventricular gene expression: Irx4-deficient embryos exhibited reduced ventricular expression of the basic helix-loop-helix transcription factor eHand (Hand1), increased Irx2 expression, and ventricular induction of an atrial chamber-specific transgene. In neonatal hearts, ventricular expression of atrial natriuretic factor and α-skeletal actin was markedly increased. Several weeks subsequent to these changes in embryonic and neonatal gene expression, increased expression of hypertrophic markers BNP and β-myosin heavy chain accompanied adult-onset cardiac hypertrophy. Cardiac expression of Irx1, Irx2, and Irx5 may partially compensate for loss of Irx4 function. We conclude that Irx4 is not sufficient for ventricular chamber formation but is required for the establishment of some components of a ventricle-specific gene expression program. In the absence of genes under the control of Irx4, ventricular function deteriorates and cardiomyopathy ensues.
PMCID: PMC86719  PMID: 11238910
24.  Somatic mutation analysis of MYH11 in breast and prostate cancer 
BMC Cancer  2008;8:263.
MYH11 (also known as SMMHC) encodes the smooth-muscle myosin heavy chain, which has a key role in smooth muscle contraction. Inversion at the MYH11 locus is one of the most frequent chromosomal aberrations found in acute myeloid leukemia. We have previously shown that MYH11 mutations occur in human colorectal cancer, and may also be associated with Peutz-Jeghers syndrome. The mutations found in human intestinal neoplasia result in unregulated proteins with constitutive motor activity, similar to the mutant myh11 underlying the zebrafish meltdown phenotype characterized by disrupted intestinal architecture. Recently, MYH1 and MYH9 have been identified as candidate breast cancer genes in a systematic analysis of the breast cancer genome.
The aim of this study was to investigate the role of somatic MYH11 mutations in two common tumor types; breast and prostate cancers. A total of 155 breast cancer and 71 prostate cancer samples were analyzed for those regions in MYH11 (altogether 8 exons out of 42 coding exons) that harboured mutations in colorectal cancer in our previous study.
In breast cancer samples only germline alterations were observed. One prostate cancer sample harbored a frameshift mutation c.5798delC, which we have previously shown to result in a protein with unregulated motor activity.
Little evidence for a role of somatic MYH11 mutations in the formation of breast or prostate cancers was obtained in this study.
PMCID: PMC2562392  PMID: 18796164
25.  Coordinate changes in Myosin heavy chain isoform gene expression are selectively associated with alterations in dilated cardiomyopathy phenotype. 
Molecular Medicine  2002;8(11):750-760.
BACKGROUND: The most common cause of chronic heart failure in the US is secondary or primary dilated cardiomyopathy (DCM). The DCM phenotype exhibits changes in the expression of genes that regulate contractile function and pathologic hypertrophy. However, it is unclear if any of these alterations in gene expression are disease producing or modifying. MATERIALS AND METHODS: One approach to providing evidence for cause-effect of a disease-influencing gene is to quantitatively compare changes in phenotype to changes in gene expression by employing serial measurements in a longitudinal experimental design. We investigated the quantitative relationships between changes in gene expression and phenotype n 47 patients with idiopathic DCM. In endomyocardial biopsies at baseline and 6 months later, we measured mRNA expression of genes regulating contractile function (beta-adrenergic receptors, sarcoplasmic reticulum Ca(2) + ATPase, and alpha- and beta-myosin heavy chain isoforms) or associated with pathologic hypertrophy (beta-myosin heavy chain and atrial natriuretic peptide), plus beta-adrenergic receptor protein expression. Left ventricular phenotype was assessed by radionuclide ejection fraction. RESULTS: Improvement in DCM phenotype was directly related to a coordinate increase in alpha- and a decrease in beta-myosin heavy chain mRNA expression. In contrast, modification of phenotype was unrelated to changes in the expression of beta(1)- or beta(2)-adrenergic receptor mRNA or protein, or to the mRNA expression of sarcoplasmic reticulum Ca(2) + ATPase and atrial natriuretic peptide. CONCLUSION: We conclude that in human DCM, phenotypic modification is selectively associated with myosin heavy chain isoform changes. These data support the hypothesis that myosin heavy chain isoform changes contribute to disease progression in human DCM.
PMCID: PMC2039952  PMID: 12520092

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