Characterization of CMF1 in avian skeletal muscle

This study reports the identification of the CMF1 protein in somites and embryonic limb muscle. We have previously described CMF1 in developing cardiac muscle. CMF1 is a member of the LEK family of proteins, which are involved in regulating mitosis. Our current data suggest that CMF1 expressed in skeletal and cardiac myocytes is the product of a single gene and that the two proteins are homologous or very highly conserved. Immunohistochemistry shows a dynamic subcellular localization of CMF1 in differentiating skeletal myoblasts: Early myoblasts stain positively for CMF1 antigen in the nucleus, while differentiating myoblasts stain positively in the cytoplasm. CMF1 expression precedes myosin. Later, CMF1 and myosin are detected in the cytoplasm of the same cells. Transfection analysis identifies a functional nuclear localization signal (NLS) in CMF1, whose nuclear transport capability is modified by external sequences. To characterize the function of CMF1 in skeletal muscle, we used antisense oligonucleotides to disrupt CMF1 in myoblast cultures. Expression of CMF1 in early myotubes is reduced by an average of 40% on a cell by cell basis, with a 56% reduction in anti-myosin staining. These data suggest that CMF1 is involved in induction and/or accumulation of myosin in differentiating myocytes.