Filamin C plays an essential role in the maintenance of the structural integrity of cardiac and skeletal muscles, revealed by the medaka mutant zacro.
Filamin C is an actin-crosslinking protein that is specifically expressed in cardiac and skeletal muscles. Although mutations in the filamin C gene cause human myopathy with cardiac involvement, the function of filamin C in vivo is not yet fully understood. Here we report a medaka mutant, zacro (zac), that displayed an enlarged heart, caused by rupture of the myocardiac wall, and progressive skeletal muscle degeneration in late embryonic stages. We identified zac to be a homozygous nonsense mutation in the filamin C (flnc) gene. The medaka filamin C protein was found to be localized at myotendinous junctions, sarcolemma, and Z-disks in skeletal muscle, and at intercalated disks in the heart. zac embryos showed prominent myofibrillar degeneration at myotendinous junctions, detachment of myofibrils from sarcolemma and intercalated disks, and focal Z-disk destruction. Importantly, the expression of γ-actin, which we observed to have a strong subcellular localization at myotendinous junctions, was specifically reduced in zac mutant myotomes. Inhibition of muscle contraction by anesthesia alleviated muscle degeneration in the zac mutant. These results suggest that filamin C plays an indispensable role in the maintenance of the structural integrity of cardiac and skeletal muscles for support against mechanical stress.
Department of Biological Information, Tokyo Institute of Technology, 4259-B-33 Nagatsuta, Yokohama 226-8501, Japan.
Misato
M
Fujita
Hiroaki
H
Mitsuhashi
Sumio
S
Isogai
Takahiro
T
Nakata
Atsushi
A
Kawakami
Ikuya
I
Nonaka
Satoru
S
Noguchi
Yukiko K
YK
Hayashi
Ichizo
I
Nishino
Akira
A
Kudo
D000199:Actins / Q000378:metabolism; D000818:Animals; D001718:Birefringence; D006332:Cardiomegaly / Q000235:genetics*; D003001:Cloning, Molecular; D018389:Codon, Nonsense / Q000235:genetics; D003285:Contractile Proteins / Q000235:genetics* / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D064448:Filamins; D005455:Fluorescent Antibody Technique; D017403:In Situ Hybridization; D008840:Microfilament Proteins / Q000235:genetics* / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D018482:Muscle, Skeletal / Q000378:metabolism*; D020966:Muscular Disorders, Atrophic / Q000235:genetics*; D009206:Myocardium / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000235:genetics; D009990:Oryzias / Q000196:embryology* / Q000235:genetics; D012150:Polymorphism, Restriction Fragment Length / Q000235:genetics; D012508:Sarcolemma / Q000473:pathology
D000199:Actins; D018389:Codon, Nonsense; D003285:Contractile Proteins; D017931:DNA Primers; C578661:FLNC protein, human; D064448:Filamins; D008840:Microfilament Proteins; D016376:Oligonucleotides, Antisense