A Tropomyosin-2 Mutation Suppresses a Troponin I Myopathy inDrosophila

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

Aberrant Splicing of an Alternative Exon in the Drosophila Troponin-T Gene Affects Flight Muscle Development

“…Jumping ability of up 1 /1 heterozygotes remained constant for at least 15 days after eclosion. up 1 has no effects on walking ability, unlike the up 101 allele (Naimi et al 2001). All flies, including Canton-S and up 1 /1 heterozygotes, could climb the 10.5-cm height of the measuring system in 6-14 sec; larval crawling was not affected (data not shown).…”

“…Behavioral experiments: Walking and larval crawling experiments were performed as described by Naimi et al (2001). For jump tests, flies, with their wings removed, were placed on a 2-mm ruled grid; jumps were induced by lightly touching the dorsal thorax with a paintbrush and 8-10 jumps observed for each fly.…”

“…Overall, the behavioral data suggest that the up 1 phenotype is restricted to the IFM and TDT. on other muscle mutants that this character is not a reliable indicator of IFM structure or function (Naimi et al 2001;Nongthomba et al 2003).…”

“…The IFM-and TDT-specific TnT isoform, the smallest, is encoded by an mRNA made only from constitutive exons (Fyrberg et al 1990;Benoist et al 1998). All up mutants were recovered by their effects on the IFM (absence of flight or wing position), but most, such as up 101 (Fyrberg et al 1990) are due to mutations in constitutive exons and show behavioral defects associated with myopathy in other muscle groups (Naimi et al 2001). However, the effects of the up 2 and up 3 mutations are restricted to the flight and jump muscles.…”

Paramyosin phosphorylation site disruption affects indirect flight muscle stiffness and power generation in Drosophila melanogaster

“…The flight index for each line was determined by using the formula: 6 ϫ U͞T ϩ 4 ϫ H͞T ϩ 2 ϫ D͞T ϩ 0 ϫ N͞T, where U, H, D, and N are the number of flies in each category of flight ability, and T is the total number of flies tested for that line (22). Crawling speed of third-instar larvae was assayed as the number of 0.5-cm grid boxes crossed in 5 min (40). Fibers were split in half lengthwise (to Ϸ100 m diameter) to reduce the cross-sectional area to facilitate quicker diffusion of solutions.…”