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Loss of Tropomodulin4 in the zebrafish mutant träge causes cytoplasmic rod formation and muscle weakness reminiscent of nemaline myopathy.

Berger J, Tarakci H, Berger S, Li M, Hall TE, Arner A, Currie PD - Dis Model Mech (2014)

Bottom Line: Accordingly, although actin monomers polymerize to form thin filaments in the skeletal muscle of tmod4(trg) mutants, thin filaments often appeared to be dispersed throughout myofibres.Myofibrils of tmod4(trg) mutants often featured thin filaments of various lengths, widened Z-disks, undefined H-zones and electron-dense aggregations of various shapes and sizes.Importantly, Gomori trichrome staining and the lattice pattern of the detected cytoplasmic rods, together with the reactivity of rods with phalloidin and an antibody against actinin, is reminiscent of nemaline rods found in nemaline myopathy, suggesting that misregulation of thin filament length causes cytoplasmic rod formation in tmod4(trg) mutants.

View Article: PubMed Central - PubMed

Affiliation: Australian Regenerative Medicine Institute, Monash University, Clayton, VIC 3800, Australia Joachim.Berger@monash.edu.

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Related in: MedlinePlus

Cytoplasmic rod formation in tmod4trg. (A) Transmission electron micrographs of skeletal muscle from siblings at 3 dpf display the typical myofibril striation and well-aligned sarcomeres. (A′) In contrast, the myofibrils of tmod4trg mutants appear non-uniform, and filaments are misoriented. Sarcomere H-zones are less defined (arrowhead) and Z-disks are widened with electron-dense inclusions of various sizes and shapes. (B,B′) Magnified views of the respective boxes in A and A′ reveal the lattice pattern of the cytoplasmic rods (arrow) that is typical for nemaline rods of individuals with NM. (C) In addition to abnormal sarcomeres (arrowhead), organised sarcomeres (arrows) rarely form in tmod4trg, and filaments are often scattered throughout myofibres (asterisk). (D) Brackets mark the various lengths of thin filaments of tmod4trg from short (0.60 μm) to long (0.75 μm). In organised myofibrils, thin filaments are of lengths comparable to those of siblings (0.68 μm). Indistinct H-zones are marked by arrowheads. (E–H) At 3 dpf, labelling of F-actin with phalloidin (red) and actinin using an antibody (green) shows the typical myofibril striation in siblings. (G,H) Merged images, H shows magnification of the boxed area indicated in G. (E′-H′) In tmod4trg mutants, actinin and actin colocalize in cytoplasmic aggregations. In contrast to the internal fast myofibres that show abundant cytoplasmic rods (arrowheads), the superficial slow muscle fibres, which in zebrafish form a single layer on the lateral outline of the somites, do not display cytoplasmic rods (arrows). (G′,H′) Merged images, H′ shows magnification of the boxed area indicated in G′. (I,I′) On cross sections at 5 dpf, Gomori trichrome staining indicates the presence of cytoplasmic rods in tmod4trg that are reminiscent of nemaline rods. (J,J′) Magnifications of boxes indicated in I and I′, respectively. Arrowheads mark nemaline-like cytoplasmic rods.
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f4-0071407: Cytoplasmic rod formation in tmod4trg. (A) Transmission electron micrographs of skeletal muscle from siblings at 3 dpf display the typical myofibril striation and well-aligned sarcomeres. (A′) In contrast, the myofibrils of tmod4trg mutants appear non-uniform, and filaments are misoriented. Sarcomere H-zones are less defined (arrowhead) and Z-disks are widened with electron-dense inclusions of various sizes and shapes. (B,B′) Magnified views of the respective boxes in A and A′ reveal the lattice pattern of the cytoplasmic rods (arrow) that is typical for nemaline rods of individuals with NM. (C) In addition to abnormal sarcomeres (arrowhead), organised sarcomeres (arrows) rarely form in tmod4trg, and filaments are often scattered throughout myofibres (asterisk). (D) Brackets mark the various lengths of thin filaments of tmod4trg from short (0.60 μm) to long (0.75 μm). In organised myofibrils, thin filaments are of lengths comparable to those of siblings (0.68 μm). Indistinct H-zones are marked by arrowheads. (E–H) At 3 dpf, labelling of F-actin with phalloidin (red) and actinin using an antibody (green) shows the typical myofibril striation in siblings. (G,H) Merged images, H shows magnification of the boxed area indicated in G. (E′-H′) In tmod4trg mutants, actinin and actin colocalize in cytoplasmic aggregations. In contrast to the internal fast myofibres that show abundant cytoplasmic rods (arrowheads), the superficial slow muscle fibres, which in zebrafish form a single layer on the lateral outline of the somites, do not display cytoplasmic rods (arrows). (G′,H′) Merged images, H′ shows magnification of the boxed area indicated in G′. (I,I′) On cross sections at 5 dpf, Gomori trichrome staining indicates the presence of cytoplasmic rods in tmod4trg that are reminiscent of nemaline rods. (J,J′) Magnifications of boxes indicated in I and I′, respectively. Arrowheads mark nemaline-like cytoplasmic rods.

Mentions: As tropomodulins play a major role in thin filament length and dynamics (Gokhin and Fowler, 2013; Littlefield et al., 2001), thin filament organisation was analysed in greater detail. In line with the analysis in animals carrying transgenic Tg(acta1:lifeact-GFP), transmission electron micrographs confirmed that monomeric actin polymerises to form thin filaments in tmod4trg mutants (Fig. 4A,A′). However, filaments were often scattered throughout the myoplasm and rarely assembled into organised myofibrils (Fig. 4C). Instead, most myofibrils appeared disorganised in tmod4trg mutants with undefined H-bands and widened Z-disks (Fig. 4D). Electron-dense aggregations of various sizes and shapes were often detected with a clearly documented lattice pattern, all features of nemaline rods documented in muscle biopsies of NM patients (Fig. 4A,A′). The rare organised myofibrils evident in tmod4trg mutants contained sarcomeres and thin filaments of similar length compared with those of siblings (tmod4trg, 1.75±0.03 μm; siblings, 0.68±0.01 μm). However, thin filaments of different lengths were measured in misorganised myofibrils. Assuming that, in misorganised myofibrils, thin filaments stretch from Z-disk to the rim of the H-zone, thin filaments of various lengths, including 0.6 μm (short) and 0.75 μm (long), were measured (Fig. 4D).


Loss of Tropomodulin4 in the zebrafish mutant träge causes cytoplasmic rod formation and muscle weakness reminiscent of nemaline myopathy.

Berger J, Tarakci H, Berger S, Li M, Hall TE, Arner A, Currie PD - Dis Model Mech (2014)

Cytoplasmic rod formation in tmod4trg. (A) Transmission electron micrographs of skeletal muscle from siblings at 3 dpf display the typical myofibril striation and well-aligned sarcomeres. (A′) In contrast, the myofibrils of tmod4trg mutants appear non-uniform, and filaments are misoriented. Sarcomere H-zones are less defined (arrowhead) and Z-disks are widened with electron-dense inclusions of various sizes and shapes. (B,B′) Magnified views of the respective boxes in A and A′ reveal the lattice pattern of the cytoplasmic rods (arrow) that is typical for nemaline rods of individuals with NM. (C) In addition to abnormal sarcomeres (arrowhead), organised sarcomeres (arrows) rarely form in tmod4trg, and filaments are often scattered throughout myofibres (asterisk). (D) Brackets mark the various lengths of thin filaments of tmod4trg from short (0.60 μm) to long (0.75 μm). In organised myofibrils, thin filaments are of lengths comparable to those of siblings (0.68 μm). Indistinct H-zones are marked by arrowheads. (E–H) At 3 dpf, labelling of F-actin with phalloidin (red) and actinin using an antibody (green) shows the typical myofibril striation in siblings. (G,H) Merged images, H shows magnification of the boxed area indicated in G. (E′-H′) In tmod4trg mutants, actinin and actin colocalize in cytoplasmic aggregations. In contrast to the internal fast myofibres that show abundant cytoplasmic rods (arrowheads), the superficial slow muscle fibres, which in zebrafish form a single layer on the lateral outline of the somites, do not display cytoplasmic rods (arrows). (G′,H′) Merged images, H′ shows magnification of the boxed area indicated in G′. (I,I′) On cross sections at 5 dpf, Gomori trichrome staining indicates the presence of cytoplasmic rods in tmod4trg that are reminiscent of nemaline rods. (J,J′) Magnifications of boxes indicated in I and I′, respectively. Arrowheads mark nemaline-like cytoplasmic rods.
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f4-0071407: Cytoplasmic rod formation in tmod4trg. (A) Transmission electron micrographs of skeletal muscle from siblings at 3 dpf display the typical myofibril striation and well-aligned sarcomeres. (A′) In contrast, the myofibrils of tmod4trg mutants appear non-uniform, and filaments are misoriented. Sarcomere H-zones are less defined (arrowhead) and Z-disks are widened with electron-dense inclusions of various sizes and shapes. (B,B′) Magnified views of the respective boxes in A and A′ reveal the lattice pattern of the cytoplasmic rods (arrow) that is typical for nemaline rods of individuals with NM. (C) In addition to abnormal sarcomeres (arrowhead), organised sarcomeres (arrows) rarely form in tmod4trg, and filaments are often scattered throughout myofibres (asterisk). (D) Brackets mark the various lengths of thin filaments of tmod4trg from short (0.60 μm) to long (0.75 μm). In organised myofibrils, thin filaments are of lengths comparable to those of siblings (0.68 μm). Indistinct H-zones are marked by arrowheads. (E–H) At 3 dpf, labelling of F-actin with phalloidin (red) and actinin using an antibody (green) shows the typical myofibril striation in siblings. (G,H) Merged images, H shows magnification of the boxed area indicated in G. (E′-H′) In tmod4trg mutants, actinin and actin colocalize in cytoplasmic aggregations. In contrast to the internal fast myofibres that show abundant cytoplasmic rods (arrowheads), the superficial slow muscle fibres, which in zebrafish form a single layer on the lateral outline of the somites, do not display cytoplasmic rods (arrows). (G′,H′) Merged images, H′ shows magnification of the boxed area indicated in G′. (I,I′) On cross sections at 5 dpf, Gomori trichrome staining indicates the presence of cytoplasmic rods in tmod4trg that are reminiscent of nemaline rods. (J,J′) Magnifications of boxes indicated in I and I′, respectively. Arrowheads mark nemaline-like cytoplasmic rods.
Mentions: As tropomodulins play a major role in thin filament length and dynamics (Gokhin and Fowler, 2013; Littlefield et al., 2001), thin filament organisation was analysed in greater detail. In line with the analysis in animals carrying transgenic Tg(acta1:lifeact-GFP), transmission electron micrographs confirmed that monomeric actin polymerises to form thin filaments in tmod4trg mutants (Fig. 4A,A′). However, filaments were often scattered throughout the myoplasm and rarely assembled into organised myofibrils (Fig. 4C). Instead, most myofibrils appeared disorganised in tmod4trg mutants with undefined H-bands and widened Z-disks (Fig. 4D). Electron-dense aggregations of various sizes and shapes were often detected with a clearly documented lattice pattern, all features of nemaline rods documented in muscle biopsies of NM patients (Fig. 4A,A′). The rare organised myofibrils evident in tmod4trg mutants contained sarcomeres and thin filaments of similar length compared with those of siblings (tmod4trg, 1.75±0.03 μm; siblings, 0.68±0.01 μm). However, thin filaments of different lengths were measured in misorganised myofibrils. Assuming that, in misorganised myofibrils, thin filaments stretch from Z-disk to the rim of the H-zone, thin filaments of various lengths, including 0.6 μm (short) and 0.75 μm (long), were measured (Fig. 4D).

Bottom Line: Accordingly, although actin monomers polymerize to form thin filaments in the skeletal muscle of tmod4(trg) mutants, thin filaments often appeared to be dispersed throughout myofibres.Myofibrils of tmod4(trg) mutants often featured thin filaments of various lengths, widened Z-disks, undefined H-zones and electron-dense aggregations of various shapes and sizes.Importantly, Gomori trichrome staining and the lattice pattern of the detected cytoplasmic rods, together with the reactivity of rods with phalloidin and an antibody against actinin, is reminiscent of nemaline rods found in nemaline myopathy, suggesting that misregulation of thin filament length causes cytoplasmic rod formation in tmod4(trg) mutants.

View Article: PubMed Central - PubMed

Affiliation: Australian Regenerative Medicine Institute, Monash University, Clayton, VIC 3800, Australia Joachim.Berger@monash.edu.

Show MeSH
Related in: MedlinePlus