Limits...
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.

Show MeSH

Related in: MedlinePlus

NS Tms recognized by the CG3 and γ9d antibodies have distinct myofiber localization. Shown are confocal images of transverse sections (7 μm) through soleus muscles stained with γ9d (A) or CG3 (D) and costained with α-actinin (B and E). The enlarged merged images (C and F, insets) indicate that the Tms recognized by γ9d and CG3 are not colocalized with α-actinin (labels myofibrils) and therefore are located outside the myofibrils. Further transverse sections (G–I) show that CG3 and γ9d stain separate regions within the myofiber (particularly notable in the enlarged inset, I). Cross sections costained with the membrane protein dystrophin (J) and γ9d (K) also show strong staining of γ9d at the myofiber periphery beneath the membrane (L, arrow in the enlarged inset). Bars, 20 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172434&req=5

fig5: NS Tms recognized by the CG3 and γ9d antibodies have distinct myofiber localization. Shown are confocal images of transverse sections (7 μm) through soleus muscles stained with γ9d (A) or CG3 (D) and costained with α-actinin (B and E). The enlarged merged images (C and F, insets) indicate that the Tms recognized by γ9d and CG3 are not colocalized with α-actinin (labels myofibrils) and therefore are located outside the myofibrils. Further transverse sections (G–I) show that CG3 and γ9d stain separate regions within the myofiber (particularly notable in the enlarged inset, I). Cross sections costained with the membrane protein dystrophin (J) and γ9d (K) also show strong staining of γ9d at the myofiber periphery beneath the membrane (L, arrow in the enlarged inset). Bars, 20 μm.

Mentions: Studies in a number of nonmuscle systems have shown that the NS Tms are sorted to very specific intracellular locations (Gunning et al., 1998a,b). Therefore, we have stained longitudinal sections of muscle with the γ9d and CG3 antibodies to define the localization of Tm5NM1 and Tm5NM-34kd in muscle. Both antibodies produced strong striated staining that was distinct from the thin filament of the sarcomere. Specifically, both CG3 and γ9d (Fig. 5, A, D, and G, red staining) showed thin lines of staining adjacent to the Z-line (Fig. 5, B and H, green α-actinin staining) that did not correspond to the entire actin thin filament (Fig. 5 F, compare red CG3 and green phalloidin/filamentous-actin staining). The CG3 and γ9d staining is likely to represent the localization of Tm5NM-34kd and Tm5NM1, respectively, as on Western blots these were the predominant Tms detected by these antibodies in the soleus muscle (Fig. 2, A and B, respectively). On longitudinal sections the two Tms colocalized with each other in this Z-line adjacent region (Fig. 4 L, yellow staining in the merged image) and both colocalized in this region with the γ-actin antibody (Fig. 4, P–U). Costaining of sections with antibodies to γ-actin and the Z-line protein α-actinin indicates that γ-actin is at the Z-line adjacent region (Fig. 4 O) and also at the Z-line itself (indicated by the colocalized yellow signal of γ-actin and α-actinin in Fig. 4 O). The NS Tm banding pattern around the Z-line does not correspond to any known pattern of Tm staining in skeletal myofibers. Together, the data suggests that a γ-actin and these NS Tms are part of a novel cytoskeleton adjacent to the Z-line.


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)

NS Tms recognized by the CG3 and γ9d antibodies have distinct myofiber localization. Shown are confocal images of transverse sections (7 μm) through soleus muscles stained with γ9d (A) or CG3 (D) and costained with α-actinin (B and E). The enlarged merged images (C and F, insets) indicate that the Tms recognized by γ9d and CG3 are not colocalized with α-actinin (labels myofibrils) and therefore are located outside the myofibrils. Further transverse sections (G–I) show that CG3 and γ9d stain separate regions within the myofiber (particularly notable in the enlarged inset, I). Cross sections costained with the membrane protein dystrophin (J) and γ9d (K) also show strong staining of γ9d at the myofiber periphery beneath the membrane (L, arrow in the enlarged inset). Bars, 20 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig5: NS Tms recognized by the CG3 and γ9d antibodies have distinct myofiber localization. Shown are confocal images of transverse sections (7 μm) through soleus muscles stained with γ9d (A) or CG3 (D) and costained with α-actinin (B and E). The enlarged merged images (C and F, insets) indicate that the Tms recognized by γ9d and CG3 are not colocalized with α-actinin (labels myofibrils) and therefore are located outside the myofibrils. Further transverse sections (G–I) show that CG3 and γ9d stain separate regions within the myofiber (particularly notable in the enlarged inset, I). Cross sections costained with the membrane protein dystrophin (J) and γ9d (K) also show strong staining of γ9d at the myofiber periphery beneath the membrane (L, arrow in the enlarged inset). Bars, 20 μm.
Mentions: Studies in a number of nonmuscle systems have shown that the NS Tms are sorted to very specific intracellular locations (Gunning et al., 1998a,b). Therefore, we have stained longitudinal sections of muscle with the γ9d and CG3 antibodies to define the localization of Tm5NM1 and Tm5NM-34kd in muscle. Both antibodies produced strong striated staining that was distinct from the thin filament of the sarcomere. Specifically, both CG3 and γ9d (Fig. 5, A, D, and G, red staining) showed thin lines of staining adjacent to the Z-line (Fig. 5, B and H, green α-actinin staining) that did not correspond to the entire actin thin filament (Fig. 5 F, compare red CG3 and green phalloidin/filamentous-actin staining). The CG3 and γ9d staining is likely to represent the localization of Tm5NM-34kd and Tm5NM1, respectively, as on Western blots these were the predominant Tms detected by these antibodies in the soleus muscle (Fig. 2, A and B, respectively). On longitudinal sections the two Tms colocalized with each other in this Z-line adjacent region (Fig. 4 L, yellow staining in the merged image) and both colocalized in this region with the γ-actin antibody (Fig. 4, P–U). Costaining of sections with antibodies to γ-actin and the Z-line protein α-actinin indicates that γ-actin is at the Z-line adjacent region (Fig. 4 O) and also at the Z-line itself (indicated by the colocalized yellow signal of γ-actin and α-actinin in Fig. 4 O). The NS Tm banding pattern around the Z-line does not correspond to any known pattern of Tm staining in skeletal myofibers. Together, the data suggests that a γ-actin and these NS Tms are part of a novel cytoskeleton adjacent to the Z-line.

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