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A tropomyosin-2 mutation suppresses a troponin I myopathy in Drosophila.

ABSTRACT: A suppressor mutation, D53, of the held-up(2) allele of the Drosophila melanogaster Troponin I (wupA) gene is described. D53, a missense mutation, S185F, of the tropomyosin-2, Tm2, gene fully suppresses all the phenotypic effects of held-up(2), including the destructive hypercontraction of the indirect flight muscles (IFMs), a lack of jumping, the progressive myopathy of the walking muscles, and reductions in larval crawling and feeding behavior. The suppressor restores normal function of the IFMs, but flight ability decreases with age and correlates with an unusual, progressive structural collapse of the myofibrillar lattice starting at the center. The S185F substitution in Tm2 is close to a troponin T binding site on tropomyosin. Models to explain suppression by D53, derived from current knowledge of the vertebrate troponin-tropomyosin complex structure and functions, are discussed. The effects of S185F are compared with those of two mutations in residues 175 and 180 of human alpha-tropomyosin 1 which cause familial hypertrophic cardiomyopathy (HCM).

SUBMITTER: Naimi B

PROVIDER: S-EPMC34603 | biostudies-literature | 2001 May

REPOSITORIES: biostudies-literature

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A tropomyosin-2 mutation suppresses a troponin I myopathy in Drosophila.

Naimi B B Harrison A A Cummins M M Nongthomba U U Clark S S Canal I I Ferrus A A Sparrow J C JC

Molecular biology of the cell 20010501 5

A suppressor mutation, D53, of the held-up(2) allele of the Drosophila melanogaster Troponin I (wupA) gene is described. D53, a missense mutation, S185F, of the tropomyosin-2, Tm2, gene fully suppresses all the phenotypic effects of held-up(2), including the destructive hypercontraction of the indirect flight muscles (IFMs), a lack of jumping, the progressive myopathy of the walking muscles, and reductions in larval crawling and feeding behavior. The suppressor restores normal function of the IF ...[more]

PMID: 11359941

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Project description:BackgroundCongenital myopathy (CM) is a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth. Currently, no definite treatment exists for CM. A de novo mutation in Tropomyosin 3-TPM3(E151G) was identified from a boy diagnosed with CM, previously TPM3(E151A) was reported to cause CM. However, the role of TPM3(E151G) in CM is unknown.MethodsHistopathological, swimming behavior, and muscle endurance were monitored in TPM3 wild-type and mutant transgenic fish, modelling CM. Gene expression profiling of muscle of the transgenic fish were studied through RNAseq, and mitochondria respiration was investigated.ResultsWhile TPM3(WT) and TPM3(E151A) fish show normal appearance, amazingly a few TPM3(E151G) fish display either no tail, a crooked body in both F0 and F1 adults. Using histochemical staining for the muscle biopsy, we found TPM3(E151G) displays congenital fiber type disproportion and TPM3(E151A) resembles nemaline myopathy. TPM3(E151G) transgenic fish dramatically swimming slower than those in TPM3(WT) and TPM3(E151A) fish measured by DanioVision and T-maze, and exhibit weaker muscle endurance by swimming tunnel instrument. Interestingly, L-carnitine treatment on TPM3(E151G) transgenic larvae significantly improves the muscle endurance by restoring the basal respiration and ATP levels in mitochondria. With RNAseq transcriptomic analysis of the expression profiling from the muscle specimens, it surprisingly discloses large downregulation of genes involved in pathways of sodium, potassium, and calcium channels, which can be rescued by L-carnitine treatment, fatty acid metabolism was differentially dysregulated in TPM3(E151G) fish and rescued by L-carnitine treatment.ConclusionsThese results demonstrate that TPM3(E151G) and TPM3(E151A) exhibit different pathogenicity, also have distinct gene regulatory profiles but the ion channels were downregulated in both mutants, and provides a potential mechanism of action of TPM3 pathophysiology. Our results shed a new light in the future development of potential treatment for TPM3-related CM.

Project description:Purpose: Congenital myopathies (CM) are a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth. Currently, no definite treatment exists for CM. A novel and de novo mutation in tropomyosin 3 [TPM3(E151G)] was identified from a 7-year-old boy with clinically diagnosed CM. TPM3(E151A) mutation was previously reported as causing CM. In this study, we created transgenic zebrafish to investigate the pathogenicity and find potential treatment. The goals of this study are to describe the RNA contents in muscle specimens derived from TPM3(WT), TPM3(E151A), TPM3(E152G) at embryos and adult stages and to compare the differences TPM3(E151A), TPM3(E151G) mutants and TPM3(WT). The biological function of L-carnitine treatment TPM3(E151G) versus without treatment are also predicted and evaluated. Methods: Muscle mRNA profiles of 6 months adult zebrafish from TPM3(WT), TPM3(E151A) and TPM3(E151G) were extracted and performed deep sequencing, in duplicate, using Illumina Novaseq6000. We also obtained the muscle mRNA profiles of 2 day's zebrafish embryos from TPM3(WT), TPM3(E151A), TPM3(E151G) and TPM3(E151G) treated with L-carnitine. RNA profiles of adult and embryos were generated by deep sequencing, using Illumina NovaSeq 6000. Results: After acquiring of clean reads, we mapped about 40 million sequence reads per sample to the zebrafish genome (GRCz11). Saturation rate analysis was then performed evaluating the gene coverage rate along with read depth increase. The transcripts mapping to difference functional region of the genome was then analyzed. Circos software was used to map the consistency of samples with zebrafish genome on a chromosomal level. The quantification of transcript intensity was analyzed using Fragments Per Kilobase of exon modelper Million mapped fragments (FPKM). Conclusions: Our study represents the first detailed analysis of zebrafish muscle transcriptomes, with biologic replicates, generated by RNA-seq technology. The optimized data analysis workflows reported here should provide a framework for comparative investigations of expression profiles between TPM3(WT), TPM3(E151A) and TPM3(E151G) and L-carnitine treatment. Our results show that NGS offers a comprehensive and more accurate quantitative and qualitative evaluation of mRNA content within a cell or tissue. We conclude that RNA-seq based transcriptome characterization would expedite genetic network analyses and permit the dissection of complex biologic functions.

Project description:Complete description of thin filament conformational transitions accompanying muscle regulation requires ready access to atomic structures of actin-bound tropomyosin-troponin. To date, several molecular-docking protocols have been employed to identify troponin interactions on actin-tropomyosin because high-resolution experimentally determined structures of filament-associated troponin are not available. However, previously published all-atom models of the thin filament show chain separation and corruption of components during our molecular dynamics simulations of the models, implying artifactual subunit organization, possibly due to incorporation of unorthodox tropomyosin-TnT crystal structures and complex FRET measurements during model construction. For example, the recent Williams et al. (2016) atomistic model of the thin filament displays a paucity of salt bridges and hydrophobic complementarity between the TnT tail (TnT1) and tropomyosin, which is difficult to reconcile with the high, 20 nM Kd binding of TnT onto tropomyosin. Indeed, our molecular dynamics simulations show the TnT1 component in their model partially dissociates from tropomyosin in under 100 ns, whereas actin-tropomyosin and TnT1 models themselves remain intact. We therefore revisited computational work aiming to improve TnT1-thin filament models by employing unbiased docking methodologies, which test billions of trial rotations and translations of TnT1 over three-dimensional grids covering end-to-end bonded tropomyosin alone or tropomyosin on F-actin. We limited conformational searches to the association of well-characterized TnT1 helical domains and either isolated tropomyosin or actin-tropomyosin yet avoided docking TnT domains that lack known or predicted structure. The docking programs PIPER and ClusPro were used, followed by interaction energy optimization and extensive molecular dynamics. TnT1 docked to either side of isolated tropomyosin but uniquely onto one location of actin-bound tropomyosin. The antiparallel interaction with tropomyosin contained abundant salt bridges and intimately integrated hydrophobic networks joining TnT1 and the tropomyosin N-/C-terminal overlapping domain. The TnT1-tropomyosin linkage yields well-defined molecular crevices. Interaction energy measurements strongly favor this TnT1-tropomyosin design over previously proposed models.

Dataset Information

A tropomyosin-2 mutation suppresses a troponin I myopathy in Drosophila.

Publications

A tropomyosin-2 mutation suppresses a troponin I myopathy in Drosophila.

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