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J. Cell Biol.,
Volume 140, Number 5, March 9, 1998 1101-1111
Department of Anatomy, University of Oulu, FIN-90220 Oulu, Finland
Exocytic organelles undergo profound reorganization during myoblast differentiation and fusion.
Here, we analyzed whether glycoprotein processing
and targeting changed during this process by using vesicular stomatitis virus (VSV) G protein and influenza virus hemagglutinin (HA) as models. After the induction of differentiation, the maturation and transport of
the VSV G protein changed dramatically. Thus, only
half of the G protein was processed and traveled
through the Golgi, whereas the other half remained unprocessed. Experiments with the VSV tsO45 mutant indicated that the unprocessed form folded and trimerized normally and then exited the ER. It did not,
however, travel through the Golgi since brefeldin A recalled it back to the ER. Influenza virus HA glycoprotein, on the contrary, acquired resistance to endoglycosidase H and insolubility in Triton X-100, indicating
passage through the Golgi. Biochemical and morphological assays indicated that the HA appeared at the
myotube surface. A major fraction of the Golgi-processed VSV G protein, however, did not appear at the
myotube surface, but was found in intracellular vesicles
that partially colocalized with the regulatable glucose transporter. Taken together, the results suggest that,
during early myogenic differentiation, the VSV G protein was rerouted into developing, muscle-specific
membrane compartments. Influenza virus HA, on the
contrary, was targeted to the myotube surface.
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