Changes in protein and glycoprotein biosynthesis during differentiation of satellite cells in vitro

Inhibition of myoblast fusion by the glucosidase inhibitor N-methyl-1-deoxynojirimycin, but not by the mannosidase inhibitor 1-deoxymannojirimycin

The effects of N-linked-oligosaccharide-processing inhibitors on the fusion of rat L6 myoblasts to form myotubes were examined. The glucosidase inhibitor N-methyl-1-deoxynojirimycin (MDJN) greatly inhibited fusion, whereas the mannosidase inhibitor 1-deoxymannojirimycin (ManDJN) had relatively little effect, although both compounds prevented the formation of N-linked complex oligosaccharides. These results indicate that complex oligosaccharides on glycoproteins do not play a role in myoblast fusion. With MDJN, high-mannose oligosaccharides containing three glucose residues and seven to eight mannose residues were found at the cell surface, whereas with ManDJN, non-glucosylated high-mannose oligosaccharides with seven to nine mannose residues were obtained. These results indicate that the persistence of glucose residues on high-mannose oligosaccharides may be responsible for the inhibition of fusion. It is suggested that glucose either masks the cell-surface recognition process leading to fusion or prevents the cell-surface expression of specific glycoprotein(s) essential to the fusion process.

Acetylcholine sensitivity in replicating satellite cells

Mononucleate myogenic cells lying within skeletal muscle fiber endomysium, the so-called satellite cells (SC), isolated from adult leg muscle of normal or dystrophic mice were studied by electrophysiological techniques. Normal SC responded to iontophoretic acetylcholine (ACh) by depolarization even during the replicative phase. Acetylcholine sensitivity increased after cell fusion. Replicating SC from dystrophic muscle did not exhibit any sensitivity to ACh, and neither did embryonic myoblasts.

Differential response of satellite cells and embryonic myoblasts to a tumor promoter

Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) reversibly suppressed myotube formation and expression of acetylcholine receptors in cultures of Day 15 mouse embryo presumptive myoblasts, but was totally ineffective in cultures of adult mouse satellite cells. A subpopulation of TPA-resistant myogenic cells became apparent in cultures prepared from older embryos or newborn mice. Thus, limb presumptive myoblasts are a heterogeneous population, and part of the distinct TPA-resistant subpopulation may represent satellite cell precursors.