Defective maturation of a viral glycoprotein and partial loss of the Golgi stack structure during in vitro myogenesis.

In the present study, the functional and structural reorganization of the Golgi compartment shortly after the fusion of rat L6 myoblasts into multinucleated muscle cells was examined. When we followed the maturation and the transport of a bulk flow marker protein, the vesicular stomatitis virus G glycoprotein, in the fused cells, we found that only about half of the newly synthesized G protein acquired endo H resistance within the Golgi prior to its transport to the cell surface. The other half of the G protein remained endo H-sensitive and was retarded intracellularly. Our immunofluorescence and cell fractionation data indicated that this maturation defect did not result from the inefficient transport of the G protein into the Golgi, but rather from the functional impairment of the Golgi compartment in the fused cells. In accordance with this view, electron microscopy revealed that the majority of the Golgi-derived elements in the fused cells were structurally abnormal and consisted of large tubulovesicular "Golgi clusters." Our results support the view that reorganization of the Golgi complex during myogenesis involves at least a partial loss of both Golgi structure and function.