Misplaced Golgi Elements Produce Randomly Oriented Microtubules and Aberrant Cortical Arrays of Microtubules in Dystrophic Skeletal Muscle Fibers

摘要

Golgi complex and microtubules reorganize entirely during muscle differentation and maturation. The final organization is completely different from that in proliferating cells. Thousands of Golgi elements (GE), small stacks of cisternae, are positioned along nuclear membranes and along microtubules throughout the large multinucleated muscle fibers. GE serve as microtubule-organizing centers as do nuclear membranes. Disorganization of the Golgi-microtubule network in muscle diseases and in experimental conditions have pointed to factors that contribute to its regulation in muscle. Among these are the protein dystrophin that is missing in Duchenne muscular dystrophy and in the mdx mouse model of Duchenne muscular dystrophy, muscle's patterned activity, and the ?-tubulin tubb6 that is increased in Duchenne muscular dystrophy, mdx, and in an experimental muscle regeneration model. To investigate GE-microtubule network differences between wild-type and mdx muscles we have now followed GFP-tagged microtubule markers in live mdx muscle fibers and have studied recovery of their GE- microtubule network from microtubule depolymerization by nocodazole. Compared to wild-type microtubules, mdx microtubules grow modestly but significantly faster. They also show a considerably larger proportion of microtubules dissociated from GE. This does not result from a lack of GE. In both mdx and tubb6 overexpressing muscle fibers, GE are increased in number and size. The muscle-characteristic association of GE with ER exit sites is maintained in mdx and tubb6 overexpressing muscle fibers whose ER exit sites are also increased in number and size. Finally, counting the association of the cis-Golgi marker GM130 in immunostained fibers with markers of ER exit sites (Sec31), cis- and trans-Golgi (GM130 and GLUT4) and of the ER-Golgi intermediate compartment (p58) reveal that each muscle GE is a full, small, Golgi complex.