PubMed · 8646850
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S J Winder, M P Walsh. 1996. Calponin.. https://doi.org/10.1016/s0070-2137(96)80002-1
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Myoblast fusion is crucial for the formation, growth, maintenance and regeneration of healthy skeletal muscle. Unfortunately, the molecular machinery, cell behaviors, and membrane and cytoskeletal remodeling events that govern fusion and myofiber formation remain poorly understood. Using time-lapse imaging approaches on mouse C2C12 myoblasts, we identify discrete and specific molecular events at myoblast membranes during fusion and myotube formation. These events include rearrangement of cell shape from fibroblast to spindle-like morphologies, changes in lamellipodial and filopodial extensions during different periods of differentiation, and changes in membrane alignment and organization during fusion. We find that actin-cytoskeleton remodeling is crucial for these events: pharmacological inhibition of F-actin polymerization leads to decreased lamellipodial and filopodial extensions and to reduced myoblast fusion. Additionally, shRNA-mediated inhibition of Nap1, a member of the WAVE actin-remodeling complex, results in accumulations of F-actin structures at the plasma membrane that are concomitant with a decrease in myoblast fusion. Our data highlight distinct and essential roles for actin cytoskeleton remodeling during mammalian myoblast fusion, provide a platform for cellular and molecular dissection of the fusion process, and suggest a functional conservation of Nap1-regulated actin-cytoskeleton remodeling during myoblast fusion between mammals and Drosophila.
In order to define the role of cyclin D1 in the progression of malignant glioma, cells over-expressing cyclin D1 were constructed (a-1 cells). They exhibited significantly increased invasiveness as compared with mock-transfected cells. Since cellular invasion is thought to depend on extracellular-matrix degradation, we determined whether cyclin-D1 expression modifies the activity of matrix metalloproteinases (MMPs). Increased gelatinolytic activity of latent type MMP-2 (proMMP-2) and active MMP-2 was observed in a-1 cells. Moreover, cyclin-D1 expression was associated with increased activation of proMMP-9 through MMP-3. Wound assays showed an increase of cell motility in a-1 cells. Cyclin-D1 expression was found to be associated with up-regulation of Rac1, which modulates the formation of ruffling membranes and cell motility. Our results show that cyclin D1 may modulate invasive ability by increasing MMP activity and cell motility, and suggests a novel function of cyclin D1 in the progression of malignant gliomas.
To identify a protein histidine methyltransferase from Saccharomyces cerevisiae, we examined purified actin for the presence of the highly conserved 3-methylhistidine residue at position 73 by amino acid analysis of the whole protein and by amino acid analysis and mass spectrometry of the corresponding tryptic fragment. Surprisingly, we found that His-73 is not modified. A similar lack of modification was also found in actin from the yeast Candida albicans, while rabbit muscle actin revealed the expected 3-methylhistidine residue. Phylogenetic analysis of actin sequences suggests that this modification was introduced in evolution after the divergence of yeast from higher eukaryotic organisms, including unicellular eukaryotes such as Acanthamoeba, Dictyostelium, and Physarum, whose actins contain 3-methylhistidine. Our methodology for the analytical determination of 3-methylhistidine in actin offers an improved approach for investigating histidine methylation in proteins.