Craig Lab Publications


Fast skeletal muscle regulatory light chain is required for fast and slow skeletal muscle development

UMMS Affiliation

Department of Cell Biology

Publication Date


Document Type



Animals; Animals, Newborn; Crosses, Genetic; Female; Fetal Heart; Gene Expression Regulation, Developmental; Genes, Lethal; Genotype; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Myocardium; Myosin Light Chains; Polymerase Chain Reaction


Cell Biology


In skeletal muscle, the myosin molecule contains two sets of noncovalently attached low molecular weight proteins, the regulatory (RLC) and essential (ELC) light chains. To assess the functional and developmental significance of the fast skeletal isoform of the RLC (RLC-f), the murine fast skeletal RLC gene (Mylpf) was disrupted by homologous recombination. Heterozygotes containing an intronic neo cassette (RLC-/+) had approximately one-half of the amount of the RLC-f mRNA compared to wild-type (WT) mice but their muscles were histologically normal in both adults and neonates. In contrast, homozygous mice (RLC-/-) had no RLC-f mRNA or protein and completely lacked both fast and slow skeletal muscle. This was likely due to interference with mRNA processing in the presence of the neo cassette. These RLC-f null mice died immediately after birth, presumably due to respiratory failure since their diaphragms lacked skeletal muscle. The body weight of newborn RLC-f null mice was decreased 30% compared to heterozygous or WT newborn mice. The lack of skeletal muscle formation in the null mice did not affect the development of other organs including the heart. In addition, we found that WT mice did not express the ventricular/slow skeletal RLC isoform (RLC-v/s) until after birth, while it was expressed normally in the embryonic heart. The lack of skeletal muscle formation observed in RLC-f null mice indicates the total dependence of skeletal muscle development on the presence of RLC-f during embryogenesis. This observation, along with the normal function of the RLC-v/s in the heart, implicates a coupled, diverse pathway for RLC-v/s and RLC-f during embryogenesis, where RLC-v/s is responsible for heart development and RLC-f is necessary for skeletal muscle formation. In conclusion, in this study we demonstrate that the Mylpf gene is critically important for fast and slow skeletal muscle development.

DOI of Published Version



FASEB J. 2007 Jul;21(9):2205-14. Epub 2007 Mar 13. Link to article on publisher's site

Journal/Book/Conference Title

The FASEB journal : official publication of the Federation of American Societies for Experimental Biology

Related Resources

Link to Article in PubMed

PubMed ID