Specific Myosin Heavy Chain Mutations Suppress Troponin I Defects in <i>Drosophila</i> Muscles

Kronert, William A.; Acebes, Ángel; Ferrús, Alberto; Bernstein, Sanford I.

doi:10.1083/jcb.144.5.989

Cited by 37 publications

(45 citation statements)

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“…The slow, progressive retraction of IFM in canB2 mutants is reminiscent of the hypercontracted IFM phenotype observed in myosin heavy chain mutants (25) and the troponin I mutant heldup 2 (26). Muscle contraction is known to be a result of numerous protein-protein interactions and conformational changes that allow for the relative movement of thin and thick filaments, leading to sarcomere shortening.…”

Section: Discussionmentioning

confidence: 99%

Requirement of the calcineurin subunit gene canB2 for indirect flight muscle formation in Drosophila

Gajewski

Wang

Molkentin

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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Calcineurin is a calcium-activated protein phosphatase involved in multiple aspects of cardiac and skeletal muscle development and disease. Genes encoding calcineurin subunit proteins are highly conserved among animal species. Toward the goal of identifying new calcineurin-interacting loci that function in myogenic processes, we expressed an activated form of mouse calcineurin A in Drosophila and screened for suppressors of the phosphataseinduced lethality. Here, we demonstrate that a mutation in the canB2 gene, which encodes a regulatory subunit of Drosophila calcineurin, can suppress a pupal developmental arrest phenotype to adult viability. As canB2 is an essential gene and rare homozygous escapers are flightless, we further analyzed canB2 expression and function in pupae and adults. The gene is expressed in the forming indirect flight muscles and central nervous system during pupal development. A canA gene is comparably expressed in these tissues. Consistent with the observed muscle expression, canB2 mutants exhibit severe defects in the organization of their indirect flight muscles, a phenotype that is likely caused by muscle hypercontractility. Together, these findings demonstrate a vital role for the phosphatase in this specific facet of Drosophila myogenesis and show conserved fly and vertebrate calcineurin genes contribute prominently to fundamental processes of muscle formation and function.

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Section: Discussionmentioning

confidence: 99%

Requirement of the calcineurin subunit gene canB2 for indirect flight muscle formation in Drosophila

Gajewski

Wang

Molkentin

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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“…15, March 2004mutation in TnI, hdp 2 , is coupled to either a second structural mutation (Leu188Phe) in TnI, D3 or to an independent structural mutation (2-base pair insertion at exon 7) in the myosin heavy chain, D41. These second mutations suppress almost completely the functional defects of hdp 2 and show normal levels of gene expression (Prado et al, 1995;Kronert et al, 1999). In both genotypes, Z discs can be found with subtle abnormalities, including failures in their ordered alignment or failure to anchor all thin filaments from a sarcomere (Figure 10, C-F).…”

Section: Table 2 Reporter Expression From D-mef2 Mutated Ire Fragmentsmentioning

confidence: 98%

Transcription ofDrosophilaTroponin I Gene Is Regulated by Two Conserved, Functionally Identical, Synergistic Elements

Marín

Toledo-Rodriguez

Ferrús

2004

MBoC

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The Drosophila wings-up A gene encodes Troponin I. Two regions, located upstream of the transcription initiation site (upstream regulatory element) and in the first intron (intron regulatory element), regulate gene expression in specific developmental and muscle type domains. Based on LacZ reporter expression in transgenic lines, upstream regulatory element and intron regulatory element yield identical expression patterns. Both elements are required for full expression levels in vivo as indicated by quantitative reverse transcription-polymerase chain reaction assays. Three myocyte enhancer factor-2 binding sites have been functionally characterized in each regulatory element. Using exon specific probes, we show that transvection is based on transcriptional changes in the homologous chromosome and that Zeste and Suppressor of Zeste 3 gene products act as repressors for wings-up A. Critical regions for transvection and for Zeste effects are defined near the transcription initiation site. After in silico analysis in insects (Anopheles and Drosophila pseudoobscura) and vertebrates (Ratus and Coturnix), the regulatory organization of Drosophila seems to be conserved. Troponin I (TnI) is expressed before muscle progenitors begin to fuse, and sarcomere morphogenesis is affected by TnI depletion as Z discs fail to form, revealing a novel developmental role for the protein or its transcripts. Also, abnormal stoichiometry among TnI isoforms, rather than their absolute levels, seems to cause the functional muscle defects. INTRODUCTIONContractile protein systems are widely represented in most cell types as a force generator device (Davison et al., 2000). In muscles, troponin I (TnI) is a key element in the protein complex that regulates sliding of thin over thick filaments (Farah and Reinach, 1995;Geeves and Lehrer, 1998;Squire and Morris, 1998;Maytum et al., 2003). Several TnI protein isoforms are generated, either from transcription of independent genes (e.g., vertebrates) or from differential splicing of a single gene primary transcript (e.g., Drosophila). Amino acid substitutions in constitutive or alternatively spliced exons in TnI can lead to pathological conditions such as familial hypertrophic cardiomyopathy (Carrier et al., 1993;Coonar and McKenna, 1997) and distal arthrogryposis (Sung et al., 2003), due to abnormal interactions with other sarcomere components. Also, TnI is a relevant indicator of heart failure (Lewinter and Vanburen, 2002) and a potent angiogenesis inhibitor through its interaction with polycystin-2 (Li et al., 2003). The potential applications that this knowledge could provide, however, are handicapped by the scant information on the regulatory mechanisms of TnI gene expression. This issue is particularly relevant in the context of future gene therapy strategies and justifies this in vivo study of the regulatory mechanism of the Drosophila homologue. In addition, this study takes advantage of the fact that TnI in Drosophila is encoded by a single gene, wings up A (wupA), and that isoform replacem...

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“…Drosophila age in weeks, and they share common mechanisms that determine aging rates and longevity with higher organisms (Parkes et al, 1999;Finch and Ruvkun, 2001;Tatar et al, 2003;Wessells and Bodmer, 2007). Thus, the fly is an extremely powerful model for studying the progression of myosin-related skeletal and cardiac muscle dysfunction.Two myosin point mutations in the Drosophila Mhc gene, D45 and Mhc 5 , were localized in proximity to coding regions for loops and linkers of the transducer (Kronert et al, 1999;Montana and Littleton, 2004). These mutations are in Mhc constitutive exons 5 and 4, respectively.…”

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confidence: 99%

Myosin Transducer Mutations Differentially Affect Motor Function, Myofibril Structure, and the Performance of Skeletal and Cardiac Muscles

Cammarato

Dambacher

Knowles

et al. 2008

MBoC

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116

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Striated muscle myosin is a multidomain ATP-dependent molecular motor. Alterations to various domains affect the chemomechanical properties of the motor, and they are associated with skeletal and cardiac myopathies. The myosin transducer domain is located near the nucleotide-binding site. Here, we helped define the role of the transducer by using an integrative approach to study how Drosophila melanogaster transducer mutations D45 and Mhc 5 affect myosin function and skeletal and cardiac muscle structure and performance. We found D45 (A261T) myosin has depressed ATPase activity and in vitro actin motility, whereas Mhc 5 (G200D) myosin has these properties enhanced. Depressed D45 myosin activity protects against age-associated dysfunction in metabolically demanding skeletal muscles. In contrast, enhanced Mhc 5 myosin function allows normal skeletal myofibril assembly, but it induces degradation of the myofibrillar apparatus, probably as a result of contractile disinhibition. Analysis of beating hearts demonstrates depressed motor function evokes a dilatory response, similar to that seen with vertebrate dilated cardiomyopathy myosin mutations, and it disrupts contractile rhythmicity. Enhanced myosin performance generates a phenotype apparently analogous to that of human restrictive cardiomyopathy, possibly indicating myosin-based origins for the disease. The D45 and Mhc 5 mutations illustrate the transducer's role in influencing the chemomechanical properties of myosin and produce unique pathologies in distinct muscles. Our data suggest Drosophila is a valuable system for identifying and modeling mutations analogous to those associated with specific human muscle disorders. INTRODUCTIONThe myosin molecular motor of striated muscle is a hexameric molecule composed of two myosin heavy chains (MHCs) and four light chains. The N-terminal globular motor domain is a product inhibited ATPase comprised of several communicating domains and functional units (reviewed by Holmes, 1999, 2005;. Alterations to the various domains dramatically affect the biochemical and mechanical properties of the motor in vitro, and mutations that diminish or enhance the molecular performance of myosin in vivo are associated with the pathogenesis of both skeletal and cardiac myopathies (reviewed by Sellers, 1999;Redowicz, 2002;Oldfors et al., 2004;Chang and Potter, 2005;Laing and Nowak, 2005;Tardiff, 2005;Oldfors, 2007). Central to an understanding of myosinbased myopathies is a fundamental appreciation for how depressed or enhanced molecular motor function differentially affects diverse striated muscles.Among the communicating functional units of myosin is the recently described transducer region (Coureux et al., 2004). Myosin V crystal structures reveal the transducer's central location within the motor domain near the nucleotide binding site. The transducer includes the last three strands of a seven-stranded ␤-sheet, which undergoes distortion essential for rearrangements within the nucleotide pocket during the ATPase cycle, and the loops an...

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Specific Myosin Heavy Chain Mutations Suppress Troponin I Defects in Drosophila Muscles

Cited by 37 publications

References 50 publications

Requirement of the calcineurin subunit gene canB2 for indirect flight muscle formation in Drosophila

Requirement of the calcineurin subunit gene canB2 for indirect flight muscle formation in Drosophila

Transcription ofDrosophilaTroponin I Gene Is Regulated by Two Conserved, Functionally Identical, Synergistic Elements

Myosin Transducer Mutations Differentially Affect Motor Function, Myofibril Structure, and the Performance of Skeletal and Cardiac Muscles

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