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Sorting of a nonmuscle tropomyosin to a novel cytoskeletal compartment in skeletal muscle results in muscular dystrophy.

Kee AJ, Schevzov G, Nair-Shalliker V, Robinson CS, Vrhovski B, Ghoddusi M, Qiu MR, Lin JJ, Weinberger R, Gunning PW, Hardeman EC - J. Cell Biol. (2004)

Bottom Line: Tropomyosin (Tm) is a key component of the actin cytoskeleton and >40 isoforms have been described in mammals.These isoforms are excluded from the thin filament of the sarcomere and are localized to a novel Z-line adjacent structure.Our findings raise the possibility that mutations in these tropomyosin and these structures may underpin these types of myopathies.

View Article: PubMed Central - PubMed

Affiliation: Muscle Development Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, New South Wales 2145, Australia.

ABSTRACT
Tropomyosin (Tm) is a key component of the actin cytoskeleton and >40 isoforms have been described in mammals. In addition to the isoforms in the sarcomere, we now report the existence of two nonsarcomeric (NS) isoforms in skeletal muscle. These isoforms are excluded from the thin filament of the sarcomere and are localized to a novel Z-line adjacent structure. Immunostained cross sections indicate that one Tm defines a Z-line adjacent structure common to all myofibers, whereas the second Tm defines a spatially distinct structure unique to muscles that undergo chronic or repetitive contractions. When a Tm (Tm3) that is normally absent from muscle was expressed in mice it became associated with the Z-line adjacent structure. These mice display a muscular dystrophy and ragged-red fiber phenotype, suggestive of disruption of the membrane-associated cytoskeletal network. Our findings raise the possibility that mutations in these tropomyosin and these structures may underpin these types of myopathies.

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Related in: MedlinePlus

Tm5NM-34kd is expressed in slow fibers, whereas the γ9d isoforms are expressed in all major fiber types. Consecutive transverse sections (7 μm) through the soleus muscle shows that fibers that were positive for the CG3 antibody (A and B, asterisks) were slow fibers (stained with the slow myosin heavy chain (MHC) antibody in B. Sections were stained with the primary antibodies followed by peroxidase-conjugated goat/anti–mouse secondary antibodies. In contrast to CG3, γ9d stained all fibers in soleus (C) and EDL (E) muscles. Note that between them the soleus and EDL contain all adult skeletal muscle fiber types (types I, IIA, IIX, and IIB). Negative (−ve) control sections (D and F) with the secondary antibody (donkey anti–sheep Alexa 488) confirms the specificity of the staining with γ9d. Bars, 40 μm.
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fig3: Tm5NM-34kd is expressed in slow fibers, whereas the γ9d isoforms are expressed in all major fiber types. Consecutive transverse sections (7 μm) through the soleus muscle shows that fibers that were positive for the CG3 antibody (A and B, asterisks) were slow fibers (stained with the slow myosin heavy chain (MHC) antibody in B. Sections were stained with the primary antibodies followed by peroxidase-conjugated goat/anti–mouse secondary antibodies. In contrast to CG3, γ9d stained all fibers in soleus (C) and EDL (E) muscles. Note that between them the soleus and EDL contain all adult skeletal muscle fiber types (types I, IIA, IIX, and IIB). Negative (−ve) control sections (D and F) with the secondary antibody (donkey anti–sheep Alexa 488) confirms the specificity of the staining with γ9d. Bars, 40 μm.

Mentions: The novel CG3 isoform (Tm5NM-34kd) was expressed at particularly high levels in the slow-twitch soleus muscle and in other specialized muscles (Fig. 2 A, EOM and diaphragm). To examine fiber-type specific expression of this isoform we stained serial transverse sections of soleus muscles with CG3 and a slow myosin heavy chain (MHC) antibody. Only slow fibers were strongly positive for CG3 (Fig. 3, A and B) suggesting that Tm5NM-34kd is expressed predominately in slow fibers in the soleus. High levels of this novel Tm were also expressed in the diaphragm and eye muscles (EOM), muscles that only have few (5–10% of total) slow fibers in rodents (Wieczorek et al., 1985; Seward et al., 2001) suggesting that Tm5NM-34kd may also be expressed in fast fibers of the diaphragm and the specialized fibers of the eye muscles (e.g., extraocular fast and slow tonic in the EOM). In contrast, the γ9d antibody, which detects Tm5NM1 (Fig. 2 B), stained all fibers of the soleus and extensor digitorum longus (EDL) muscles (Fig. 3, C and E, respectively), indicating that Tm5NM1 is in all adult skeletal muscle fibers (types I, IIA, IIX, and IIB) in the mouse. This data is consistent with the Western blots showing similar expression of Tm5NM1 in all muscles (Fig. 2 B).


Sorting of a nonmuscle tropomyosin to a novel cytoskeletal compartment in skeletal muscle results in muscular dystrophy.

Kee AJ, Schevzov G, Nair-Shalliker V, Robinson CS, Vrhovski B, Ghoddusi M, Qiu MR, Lin JJ, Weinberger R, Gunning PW, Hardeman EC - J. Cell Biol. (2004)

Tm5NM-34kd is expressed in slow fibers, whereas the γ9d isoforms are expressed in all major fiber types. Consecutive transverse sections (7 μm) through the soleus muscle shows that fibers that were positive for the CG3 antibody (A and B, asterisks) were slow fibers (stained with the slow myosin heavy chain (MHC) antibody in B. Sections were stained with the primary antibodies followed by peroxidase-conjugated goat/anti–mouse secondary antibodies. In contrast to CG3, γ9d stained all fibers in soleus (C) and EDL (E) muscles. Note that between them the soleus and EDL contain all adult skeletal muscle fiber types (types I, IIA, IIX, and IIB). Negative (−ve) control sections (D and F) with the secondary antibody (donkey anti–sheep Alexa 488) confirms the specificity of the staining with γ9d. Bars, 40 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172434&req=5

fig3: Tm5NM-34kd is expressed in slow fibers, whereas the γ9d isoforms are expressed in all major fiber types. Consecutive transverse sections (7 μm) through the soleus muscle shows that fibers that were positive for the CG3 antibody (A and B, asterisks) were slow fibers (stained with the slow myosin heavy chain (MHC) antibody in B. Sections were stained with the primary antibodies followed by peroxidase-conjugated goat/anti–mouse secondary antibodies. In contrast to CG3, γ9d stained all fibers in soleus (C) and EDL (E) muscles. Note that between them the soleus and EDL contain all adult skeletal muscle fiber types (types I, IIA, IIX, and IIB). Negative (−ve) control sections (D and F) with the secondary antibody (donkey anti–sheep Alexa 488) confirms the specificity of the staining with γ9d. Bars, 40 μm.
Mentions: The novel CG3 isoform (Tm5NM-34kd) was expressed at particularly high levels in the slow-twitch soleus muscle and in other specialized muscles (Fig. 2 A, EOM and diaphragm). To examine fiber-type specific expression of this isoform we stained serial transverse sections of soleus muscles with CG3 and a slow myosin heavy chain (MHC) antibody. Only slow fibers were strongly positive for CG3 (Fig. 3, A and B) suggesting that Tm5NM-34kd is expressed predominately in slow fibers in the soleus. High levels of this novel Tm were also expressed in the diaphragm and eye muscles (EOM), muscles that only have few (5–10% of total) slow fibers in rodents (Wieczorek et al., 1985; Seward et al., 2001) suggesting that Tm5NM-34kd may also be expressed in fast fibers of the diaphragm and the specialized fibers of the eye muscles (e.g., extraocular fast and slow tonic in the EOM). In contrast, the γ9d antibody, which detects Tm5NM1 (Fig. 2 B), stained all fibers of the soleus and extensor digitorum longus (EDL) muscles (Fig. 3, C and E, respectively), indicating that Tm5NM1 is in all adult skeletal muscle fibers (types I, IIA, IIX, and IIB) in the mouse. This data is consistent with the Western blots showing similar expression of Tm5NM1 in all muscles (Fig. 2 B).

Bottom Line: Tropomyosin (Tm) is a key component of the actin cytoskeleton and >40 isoforms have been described in mammals.These isoforms are excluded from the thin filament of the sarcomere and are localized to a novel Z-line adjacent structure.Our findings raise the possibility that mutations in these tropomyosin and these structures may underpin these types of myopathies.

View Article: PubMed Central - PubMed

Affiliation: Muscle Development Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, New South Wales 2145, Australia.

ABSTRACT
Tropomyosin (Tm) is a key component of the actin cytoskeleton and >40 isoforms have been described in mammals. In addition to the isoforms in the sarcomere, we now report the existence of two nonsarcomeric (NS) isoforms in skeletal muscle. These isoforms are excluded from the thin filament of the sarcomere and are localized to a novel Z-line adjacent structure. Immunostained cross sections indicate that one Tm defines a Z-line adjacent structure common to all myofibers, whereas the second Tm defines a spatially distinct structure unique to muscles that undergo chronic or repetitive contractions. When a Tm (Tm3) that is normally absent from muscle was expressed in mice it became associated with the Z-line adjacent structure. These mice display a muscular dystrophy and ragged-red fiber phenotype, suggestive of disruption of the membrane-associated cytoskeletal network. Our findings raise the possibility that mutations in these tropomyosin and these structures may underpin these types of myopathies.

Show MeSH
Related in: MedlinePlus