Who Needs Microtubules? Myogenic Reorganization of MTOC, Golgi Complex and ER Exit Sites Persists Despite Lack of Normal Microtubule Tracks

University of Colorado, Boulder, United States of America
PLoS ONE (Impact Factor: 3.23). 12/2011; 6(12):e29057. DOI: 10.1371/journal.pone.0029057
Source: PubMed


A wave of structural reorganization involving centrosomes, microtubules, Golgi complex and ER exit sites takes place early during skeletal muscle differentiation and completely remodels the secretory pathway. The mechanism of these changes and their functional implications are still poorly understood, in large part because all changes occur seemingly simultaneously. In an effort to uncouple the reorganizations, we have used taxol, nocodazole, and the specific GSK3-β inhibitor DW12, to disrupt the dynamic microtubule network of differentiating cultures of the mouse skeletal muscle cell line C2. Despite strong effects on microtubules, cell shape and cell fusion, none of the treatments prevented early differentiation. Redistribution of centrosomal proteins, conditional on differentiation, was in fact increased by taxol and nocodazole and normal in DW12. Redistributions of Golgi complex and ER exit sites were incomplete but remained tightly linked under all circumstances, and conditional on centrosomal reorganization. We were therefore able to uncouple microtubule reorganization from the other events and to determine that centrosomal proteins lead the reorganization hierarchy. In addition, we have gained new insight into structural and functional aspects of the reorganization of microtubule nucleation during myogenesis.

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    • "Interestingly, in short-time MT regrowth experiments, new MTs not only formed at the perinuclear ring but also appeared as asters growing from cytoplasmic nucleating sites. More than 85% of these MT regrowth foci were identified as Golgi elements that in fused myotubes not only surrounded nuclei but also extended between them [83–85]. "
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    • "Accordingly, in addition to labeling the endogenous Yip1B protein with the polyclonal antibody we generated, we stained muscle fast fibers from the tibialis anterior and slow fibers from soleus muscles with a monoclonal antibody against the GM130, used as cis-Golgi marker. Confocal analysis revealed the cis-Golgi protein GM130 as trains of spots along the fiber in the slow-twitch soleus muscle and in pairs of spots in the fast-twitch tibialis anterior muscle, as expected (Zaal et al. 2011). Staining of the same muscles with Yip1B revealed spots resembling the GM130 pattern (Fig. 3). "
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    • "During muscle differentiation the MTOC redistributes from centrosomes to nuclear membranes (Tassin et al., 1985a; Lu et al., 2001; Bugnard et al., 2005; Zaal et al., 2011). EB3-GFP and immobile, highlighting a frame that remains unchanged for minutes (Fig. 1 D1 and Video 3); the color-coded projections are mostly white (Fig. 1 D2). "
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