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Regulation of the growth of multinucleated muscle cells by an NFATC2-dependent pathway.

Horsley V, Friday BB, Matteson S, Kegley KM, Gephart J, Pavlath GK - J. Cell Biol. (2001)

Bottom Line: The growth defect is intrinsic to muscle cells, since the lack of NFATC2 in primary muscle cultures results in reduced cell size and myonuclear number in myotubes.Taken together, these results implicate a novel role for NFATC2 in skeletal muscle growth.We demonstrate that during growth of multinucleated muscle cells, myoblasts initially fuse to form myotubes with a limited number of nuclei and that subsequent nuclear addition and increases in myotube size are controlled by a molecular pathway regulated by NFATC2.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Emory University, Atlanta, Georgia 30322, USA.

ABSTRACT
The nuclear factor of activated T cells (NFAT) family of transcription factors regulates the development and differentiation of several tissue types. Here, we examine the role of NFATC2 in skeletal muscle by analyzing adult NFATC2(-/)- mice. These mice exhibit reduced muscle size due to a decrease in myofiber cross-sectional area, suggesting that growth is blunted. Muscle growth was examined during regeneration after injury, wherein NFATC2- myofibers form normally but display impaired growth. The growth defect is intrinsic to muscle cells, since the lack of NFATC2 in primary muscle cultures results in reduced cell size and myonuclear number in myotubes. Retroviral-mediated expression of NFATC2 in the mutant cells rescues this cellular phenotype. Myonuclear number is similarly decreased in NFATC2(-/)- mice. Taken together, these results implicate a novel role for NFATC2 in skeletal muscle growth. We demonstrate that during growth of multinucleated muscle cells, myoblasts initially fuse to form myotubes with a limited number of nuclei and that subsequent nuclear addition and increases in myotube size are controlled by a molecular pathway regulated by NFATC2.

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Myonuclear number is reduced in NFATC2−/− myofibers. (A) A representative wild-type myofiber immunostained with an antibody against dystrophin (red) and stained with DAPI (blue) illustrates the myonuclear number assay. Arrow indicates a myonucleus within the dystrophin border, and arrowheads indicate nuclei outside the myofiber. (B) DAPI-stained nuclei within the dystrophin-positive sarcolemma were counted in soleus muscles from wild-type and NFATC2−/− mice, and the number of myonuclei was expressed per 100 myofibers. Data are mean ± standard error; n = 6 for each genotype (*P < 0.05). Bar, 20 μm.
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Figure 6: Myonuclear number is reduced in NFATC2−/− myofibers. (A) A representative wild-type myofiber immunostained with an antibody against dystrophin (red) and stained with DAPI (blue) illustrates the myonuclear number assay. Arrow indicates a myonucleus within the dystrophin border, and arrowheads indicate nuclei outside the myofiber. (B) DAPI-stained nuclei within the dystrophin-positive sarcolemma were counted in soleus muscles from wild-type and NFATC2−/− mice, and the number of myonuclei was expressed per 100 myofibers. Data are mean ± standard error; n = 6 for each genotype (*P < 0.05). Bar, 20 μm.

Mentions: The reduced number of nuclei in NFATC2−/− myotubes suggests that NFATC2−/− myofibers in vivo may also have reduced myonuclei. To determine if myonuclear number is reduced in NFATC2−/− myofibers, cross sections of soleus muscles were immunostained with dystrophin to outline the myofiber sarcolemma and stained with DAPI to label nuclei (Fig. 6 A). Nuclei inside the outline of dystrophin were counted in wild-type and NFATC2−/− soleus muscles. A 50% decrease in myonuclei is observed in NFATC2−/− soleus muscles compared with wild-type (Fig. 6 B). These data correlate with the in vitro results, showing that NFATC2−/− myotubes have fewer nuclei than wild-type myotubes. Since fusion of myoblasts and thus addition of myonuclei is required for growth of mammalian myofibers (Darr and Schultz 1989; Rosenblatt and Parry 1993; Mozdziak et al. 2000), these data also suggest that the reduced CSA of myofibers in NFATC2−/− mice results from defects in the ability of muscle cells to fuse with the myofiber and to add nuclei to the myofiber.


Regulation of the growth of multinucleated muscle cells by an NFATC2-dependent pathway.

Horsley V, Friday BB, Matteson S, Kegley KM, Gephart J, Pavlath GK - J. Cell Biol. (2001)

Myonuclear number is reduced in NFATC2−/− myofibers. (A) A representative wild-type myofiber immunostained with an antibody against dystrophin (red) and stained with DAPI (blue) illustrates the myonuclear number assay. Arrow indicates a myonucleus within the dystrophin border, and arrowheads indicate nuclei outside the myofiber. (B) DAPI-stained nuclei within the dystrophin-positive sarcolemma were counted in soleus muscles from wild-type and NFATC2−/− mice, and the number of myonuclei was expressed per 100 myofibers. Data are mean ± standard error; n = 6 for each genotype (*P < 0.05). Bar, 20 μm.
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Related In: Results  -  Collection

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Figure 6: Myonuclear number is reduced in NFATC2−/− myofibers. (A) A representative wild-type myofiber immunostained with an antibody against dystrophin (red) and stained with DAPI (blue) illustrates the myonuclear number assay. Arrow indicates a myonucleus within the dystrophin border, and arrowheads indicate nuclei outside the myofiber. (B) DAPI-stained nuclei within the dystrophin-positive sarcolemma were counted in soleus muscles from wild-type and NFATC2−/− mice, and the number of myonuclei was expressed per 100 myofibers. Data are mean ± standard error; n = 6 for each genotype (*P < 0.05). Bar, 20 μm.
Mentions: The reduced number of nuclei in NFATC2−/− myotubes suggests that NFATC2−/− myofibers in vivo may also have reduced myonuclei. To determine if myonuclear number is reduced in NFATC2−/− myofibers, cross sections of soleus muscles were immunostained with dystrophin to outline the myofiber sarcolemma and stained with DAPI to label nuclei (Fig. 6 A). Nuclei inside the outline of dystrophin were counted in wild-type and NFATC2−/− soleus muscles. A 50% decrease in myonuclei is observed in NFATC2−/− soleus muscles compared with wild-type (Fig. 6 B). These data correlate with the in vitro results, showing that NFATC2−/− myotubes have fewer nuclei than wild-type myotubes. Since fusion of myoblasts and thus addition of myonuclei is required for growth of mammalian myofibers (Darr and Schultz 1989; Rosenblatt and Parry 1993; Mozdziak et al. 2000), these data also suggest that the reduced CSA of myofibers in NFATC2−/− mice results from defects in the ability of muscle cells to fuse with the myofiber and to add nuclei to the myofiber.

Bottom Line: The growth defect is intrinsic to muscle cells, since the lack of NFATC2 in primary muscle cultures results in reduced cell size and myonuclear number in myotubes.Taken together, these results implicate a novel role for NFATC2 in skeletal muscle growth.We demonstrate that during growth of multinucleated muscle cells, myoblasts initially fuse to form myotubes with a limited number of nuclei and that subsequent nuclear addition and increases in myotube size are controlled by a molecular pathway regulated by NFATC2.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Emory University, Atlanta, Georgia 30322, USA.

ABSTRACT
The nuclear factor of activated T cells (NFAT) family of transcription factors regulates the development and differentiation of several tissue types. Here, we examine the role of NFATC2 in skeletal muscle by analyzing adult NFATC2(-/)- mice. These mice exhibit reduced muscle size due to a decrease in myofiber cross-sectional area, suggesting that growth is blunted. Muscle growth was examined during regeneration after injury, wherein NFATC2- myofibers form normally but display impaired growth. The growth defect is intrinsic to muscle cells, since the lack of NFATC2 in primary muscle cultures results in reduced cell size and myonuclear number in myotubes. Retroviral-mediated expression of NFATC2 in the mutant cells rescues this cellular phenotype. Myonuclear number is similarly decreased in NFATC2(-/)- mice. Taken together, these results implicate a novel role for NFATC2 in skeletal muscle growth. We demonstrate that during growth of multinucleated muscle cells, myoblasts initially fuse to form myotubes with a limited number of nuclei and that subsequent nuclear addition and increases in myotube size are controlled by a molecular pathway regulated by NFATC2.

Show MeSH
Related in: MedlinePlus