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Zebrafish models for nemaline myopathy reveal a spectrum of nemaline bodies contributing to reduced muscle function.

Sztal TE, Zhao M, Williams C, Oorschot V, Parslow AC, Giousoh A, Yuen M, Hall TE, Costin A, Ramm G, Bird PI, Busch-Nentwich EM, Stemple DL, Currie PD, Cooper ST, Laing NG, Nowak KJ, Bryson-Richardson RJ - Acta Neuropathol. (2015)

Bottom Line: Another subtype results from a reduction of actin and forms a more stable cytoplasmic body.In contrast, the final type originates at the Z-disk and is associated with myofibrillar disorganization.In addition, we show that the ACTA1(D286G) mutation causes impaired actin incorporation and localization in the sarcomere.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, Monash University, Melbourne, VIC, Australia.

ABSTRACT
Nemaline myopathy is characterized by muscle weakness and the presence of rod-like (nemaline) bodies. The genetic etiology of nemaline myopathy is becoming increasingly understood with mutations in ten genes now known to cause the disease. Despite this, the mechanism by which skeletal muscle weakness occurs remains elusive, with previous studies showing no correlation between the frequency of nemaline bodies and disease severity. To investigate the formation of nemaline bodies and their role in pathogenesis, we generated overexpression and loss-of-function zebrafish models for skeletal muscle α-actin (ACTA1) and nebulin (NEB). We identify three distinct types of nemaline bodies and visualize their formation in vivo, demonstrating these nemaline bodies not only exhibit different subcellular origins, but also have distinct pathological consequences within the skeletal muscle. One subtype is highly dynamic and upon breakdown leads to the accumulation of cytoplasmic actin contributing to muscle weakness. Examination of a Neb-deficient model suggests this mechanism may be common in nemaline myopathy. Another subtype results from a reduction of actin and forms a more stable cytoplasmic body. In contrast, the final type originates at the Z-disk and is associated with myofibrillar disorganization. Analysis of zebrafish and muscle biopsies from ACTA1 nemaline myopathy patients demonstrates that nemaline bodies also possess a different protein signature. In addition, we show that the ACTA1(D286G) mutation causes impaired actin incorporation and localization in the sarcomere. Together these data provide a novel examination of nemaline body origins and dynamics in vivo and identifies pathological changes that correlate with muscle weakness.

No MeSH data available.


Related in: MedlinePlus

Electron microscopy images of Actc1b ex 2 morphants at 2 dpf showing ii electron-dense projections emanating from the myosepta (arrowheads) as well as nemaline bodies derived from v thickened Z-disks throughout the fibers not observed in control fish (i, iii). Sections also contained broken muscle fibers iv as well as numerous mitochondria (black arrowheads; iv), compared to the uniform sarcomeres in control zebrafish skeletal muscle iii
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Fig12: Electron microscopy images of Actc1b ex 2 morphants at 2 dpf showing ii electron-dense projections emanating from the myosepta (arrowheads) as well as nemaline bodies derived from v thickened Z-disks throughout the fibers not observed in control fish (i, iii). Sections also contained broken muscle fibers iv as well as numerous mitochondria (black arrowheads; iv), compared to the uniform sarcomeres in control zebrafish skeletal muscle iii

Mentions: EM analyses revealed the presence of electron-dense projections extending from the myosepta (Fig. 12). Thickened Z-disks were clearly evident and in some cases the electron-dense region appeared to span the full width of a sarcomere (Fig. 12). We also observed disorganized and broken myofibrils surrounded by large numbers of mitochondria in the Actc1b morphant skeletal muscle compared to control skeletal muscle (Fig. 12). We performed antibody and phalloidin staining on the skeletal muscle and identified phalloidin- and Actinin2-positive nemaline bodies, concentrated near the myosepta, as well as Actinin2-positive aggregates and thickened Z-disks throughout the myofibrils in Actc1b morphants that are not present in the control skeletal muscle (Fig. 10).Fig. 12


Zebrafish models for nemaline myopathy reveal a spectrum of nemaline bodies contributing to reduced muscle function.

Sztal TE, Zhao M, Williams C, Oorschot V, Parslow AC, Giousoh A, Yuen M, Hall TE, Costin A, Ramm G, Bird PI, Busch-Nentwich EM, Stemple DL, Currie PD, Cooper ST, Laing NG, Nowak KJ, Bryson-Richardson RJ - Acta Neuropathol. (2015)

Electron microscopy images of Actc1b ex 2 morphants at 2 dpf showing ii electron-dense projections emanating from the myosepta (arrowheads) as well as nemaline bodies derived from v thickened Z-disks throughout the fibers not observed in control fish (i, iii). Sections also contained broken muscle fibers iv as well as numerous mitochondria (black arrowheads; iv), compared to the uniform sarcomeres in control zebrafish skeletal muscle iii
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4541704&req=5

Fig12: Electron microscopy images of Actc1b ex 2 morphants at 2 dpf showing ii electron-dense projections emanating from the myosepta (arrowheads) as well as nemaline bodies derived from v thickened Z-disks throughout the fibers not observed in control fish (i, iii). Sections also contained broken muscle fibers iv as well as numerous mitochondria (black arrowheads; iv), compared to the uniform sarcomeres in control zebrafish skeletal muscle iii
Mentions: EM analyses revealed the presence of electron-dense projections extending from the myosepta (Fig. 12). Thickened Z-disks were clearly evident and in some cases the electron-dense region appeared to span the full width of a sarcomere (Fig. 12). We also observed disorganized and broken myofibrils surrounded by large numbers of mitochondria in the Actc1b morphant skeletal muscle compared to control skeletal muscle (Fig. 12). We performed antibody and phalloidin staining on the skeletal muscle and identified phalloidin- and Actinin2-positive nemaline bodies, concentrated near the myosepta, as well as Actinin2-positive aggregates and thickened Z-disks throughout the myofibrils in Actc1b morphants that are not present in the control skeletal muscle (Fig. 10).Fig. 12

Bottom Line: Another subtype results from a reduction of actin and forms a more stable cytoplasmic body.In contrast, the final type originates at the Z-disk and is associated with myofibrillar disorganization.In addition, we show that the ACTA1(D286G) mutation causes impaired actin incorporation and localization in the sarcomere.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, Monash University, Melbourne, VIC, Australia.

ABSTRACT
Nemaline myopathy is characterized by muscle weakness and the presence of rod-like (nemaline) bodies. The genetic etiology of nemaline myopathy is becoming increasingly understood with mutations in ten genes now known to cause the disease. Despite this, the mechanism by which skeletal muscle weakness occurs remains elusive, with previous studies showing no correlation between the frequency of nemaline bodies and disease severity. To investigate the formation of nemaline bodies and their role in pathogenesis, we generated overexpression and loss-of-function zebrafish models for skeletal muscle α-actin (ACTA1) and nebulin (NEB). We identify three distinct types of nemaline bodies and visualize their formation in vivo, demonstrating these nemaline bodies not only exhibit different subcellular origins, but also have distinct pathological consequences within the skeletal muscle. One subtype is highly dynamic and upon breakdown leads to the accumulation of cytoplasmic actin contributing to muscle weakness. Examination of a Neb-deficient model suggests this mechanism may be common in nemaline myopathy. Another subtype results from a reduction of actin and forms a more stable cytoplasmic body. In contrast, the final type originates at the Z-disk and is associated with myofibrillar disorganization. Analysis of zebrafish and muscle biopsies from ACTA1 nemaline myopathy patients demonstrates that nemaline bodies also possess a different protein signature. In addition, we show that the ACTA1(D286G) mutation causes impaired actin incorporation and localization in the sarcomere. Together these data provide a novel examination of nemaline body origins and dynamics in vivo and identifies pathological changes that correlate with muscle weakness.

No MeSH data available.


Related in: MedlinePlus