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Published online 28 May 2001. doi:10.1083/jcb.153.5.985
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© The Rockefeller University Press, 0021-9525/2001//985 $5.00
The Journal of Cell Biology, Volume 153, Number 5, , 2001 985-998

Original Article

The Small Muscle-Specific Protein Csl Modifies Cell Shape and Promotes Myocyte Fusion in an Insulin-like Growth Factor 1–Dependent Manner



Steve Palmera, Nicola Grovesa, Aaron Schindelera, Thomas Yeoha, Christine Bibena, Cheng-Chun Wanga, Duncan B. Sparrowa, Louise Barnettb, Nancy A. Jenkinsc, Neal G. Copelandc, Frank Koentgenb, Tim Mohund, and Richard P. Harveya,e

a Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia
b Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia
c Mouse Cancer Genetics Program, National Cancer Institute-Frederick, Frederick, Maryland 21702
d Medical Research Council Institute for Medical Research, London NW7 1AA, United Kingdom
e Faculties of Medicine and Life Sciences, University of New South Wales, Kensington, NSW 2051, Australia
Victor Chang Cardiac Research Institute, 384 Victoria St., Darlinghurst 2010, NSW, Australia.61-2-9295-852861-2-9295-8520

r.harvey{at}victorchang.unsw.edu.au

We have isolated a murine cDNA encoding a 9-kD protein, Chisel (Csl), in a screen for transcriptional targets of the cardiac homeodomain factor Nkx2-5. Csl transcripts were detected in atria and ventricles of the heart and in all skeletal muscles and smooth muscles of the stomach and pulmonary veins. Csl protein was distributed throughout the cytoplasm in fetal muscles, although costameric and M-line localization to the muscle cytoskeleton became obvious after further maturation. Targeted disruption of Csl showed no overt muscle phenotype. However, ectopic expression in C2C12 myoblasts induced formation of lamellipodia in which Csl protein became tethered to membrane ruffles. Migration of these cells was retarded in a monolayer wound repair assay. Csl-expressing myoblasts differentiated and fused normally, although in the presence of insulin-like growth factor (IGF)-1 they showed dramatically enhanced fusion, leading to formation of large dysmorphogenic "myosacs." The activities of transcription factors nuclear factor of activated T cells (NFAT) and myocyte enhancer–binding factor (MEF)2, were also enhanced in an IGF-1 signaling–dependent manner. The dynamic cytoskeletal localization of Csl and its dominant effects on cell shape and behavior and transcription factor activity suggest that Csl plays a role in the regulatory network through which muscle cells coordinate their structural and functional states during growth, adaptation, and repair.

Key Words: costameres • heart • lamellipodia • Nkx2-5 • skeletal muscle

© 2001 The Rockefeller University Press

F. Koentgen's present address is Ozgene, Australian Gene Targeting Center, Nedlands 6009, Australia.

S. Palmer's present address is The Institute of Cancer Research, London SW 36JB, UK.

C.-C. Wang's present address is Institute of Molecular and Cell Biology, Singapore 117609.

Abbreviations used in this paper: CsA, cyclosporine A; Csl, Chisel; GFP, green fluorescent protein; GST, glutathione S-transferase; hPAP, human placental alkaline phosphatase; IGF, insulin-like growth factor; MEF, myocyte enhancer–binding factor; MLC, myosin light chain; NFAT, nuclear factor of activated T cells; PFA, paraformaldehyde.


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