Functional recovery of troponin I in a Drosophila heldup mutant after a second site mutation.

Prado, Antonio; Canal, Inmaculada; Barbas, Julio A.; Molloy, Justin E.; Ferrús, Alberto

doi:10.1091/mbc.6.11.1433

Cited by 26 publications

(30 citation statements)

References 25 publications

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“…held-up 2 (hdp 2 ) a missense mutation of the TnI gene, produces a fully penetrant raised wing phenotype. Six dominant suppressors of hdp 2 , including D53, were recovered (Prado et al, 1995). Here we show that D53 is a missense mutation, S185F, of the Tm2 tropomyosin gene and characterize the functional and structural effects of the suppression.…”

Section: Introductionmentioning

confidence: 77%

A Tropomyosin-2 Mutation Suppresses a Troponin I Myopathy inDrosophila

Naïmi

Harrison

Cummins

et al. 2001

MBoC

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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 ␣-tropomyosin 1 which cause familial hypertrophic cardiomyopathy (HCM).

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Section: Introductionmentioning

confidence: 77%

A Tropomyosin-2 Mutation Suppresses a Troponin I Myopathy inDrosophila

Naïmi

Harrison

Cummins

et al. 2001

MBoC

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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: 99%

“…Df(1)23437 and the point mutations hdp 2 and hdp 3 were described previously (Beall and Fyrberg, 1991;Barbas et al, 1993;Prado et al, 1995Prado et al, , 1999. Regulatory mutants PL87 and PG31 were provided by H.M.…”

Section: Fly Strains and Crossesmentioning

confidence: 99%

“…In that context, we tested for transvection in heterozygotes between the three rearrangements, and between these and two point mutations in TnI. The latter correspond to wupA hdp2 , a A116V change in a constitutive exon (Beall and Fyrberg, 1991;Prado et al, 1995), and to wupA hdp3 , a single nucleotide change at the splice acceptor site for exon 6d (Barbas et al, 1993). In effect, allele hdp3 can be considered a regulatory mutation because it leads to the absence of a subfamily of TnI isoforms, whereas allele hdp2 is a structural mutation that does not interfere with transcription levels.…”

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confidence: 99%

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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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“…In humans, mutations in TNNI2 and TNNI3 cause distal arthrogryposis type 2B (Sung et al, 2003) and familial hypertrophic cardiomyopathy (Kimura et al, 1997), respectively. In Drosophila, viable mutations in the single gene expressing TnI, wings up A (wupA) [also known as held up (hdp)], result in hypercontraction and degeneration of the indirect flight muscles of the thorax due to recessive hypomorphic point mutations (Prado et al, 1995). However, studies on lack of function mutations for this gene have been hampered by the fact that null alleles are dominant lethals (Prado et al, 1999).…”

Section: Introductionmentioning

confidence: 99%