ENDOPLASMIC-RETICULUM TO GOLGI TRAFFICKING IN MULTINUCLEATED SKELETAL-MUSCLE FIBERS

The organization of membrane trafficking between endoplasmic reticulum and Golgi within multinucleated muscle fibers was analyzed. We found that markers for the compartment involved in endoplasmic reticulum to Golgi trafficking exhibited perinuclear as well as interfibrillar loca lization. Furthermore, these markers showed prominent colocalization w ith microtubules. To analyze membrane trafficking, we followed the tem perature controlled transport of the G protein of the mutant vesicular stomatitis virus, tsO45, in isolated myofibers. Perinuclear and cross -striated staining were seen at 39 degrees C, while at 15 degrees C a diffuse staining component appeared along a subset of interfibrillar m icrotubules. At 20 degrees C, bright Golgi spots were seen to be assoc iated with microtubules that appeared as circumnuclear rings and longi tudinal bundles. Beneath the motor end plate, however, the organizatio n of the Golgi elements and microtubules was found to be distinctive, Retrograde trafficking induced by brefeldin A resulted in the disappea rance of the Golgi spots throughout the myofibers and the appearance o f staining along microtubules. Thus, interfibrillar membranes seem to be active in protein export, and trafficking between endoplasmic retic ulum and Golgi elements occurred throughout the myofibers. The results suggest that microtubules served as tracks for the two way traffickin g between the endoplasmic reticulum and the Golgi compartment. (C) 199 7 Academic Press.