RESUMEN
It has been proposed that microtubules (MTs) participate in skeletal muscle cell differentiation. However, it is still unclear how this happens. To examine whether MTs could participate directly in the organization of thick and thin filaments into sarcomeres, we observed the concomitant reorganization and dynamics of MTs with the behavior of sarcomeric actin and myosin by time-lapse confocal microscopy. Using green fluorescent protein (GFP)-EB1 protein to label MT plus ends, we determined that MTs become organized into antiparallel arrays along fusing myotubes. Their dynamics and orientation was found to be different across the thickness of the myotubes. We observed fast movements of Dsred-myosin along GFP-MTs. Comparison of GFP-EB1 and Dsred-myosin dynamics revealed that myosin moved toward MT plus ends. Immuno-electron microscopy experiments confirmed that myosin was actually associated with MTs in myotubes. Finally, we confirmed that MTs were required for the stabilization of myosin-containing elements prior to incorporation into mature sarcomeres. Collectively, our results strongly suggest that MTs become organized into a scaffold that provides directional cues for the positioning and organization of myosin filaments during sarcomere formation.
Asunto(s)
Diferenciación Celular , Microtúbulos/fisiología , Músculo Esquelético/citología , Miosinas/metabolismo , Sarcómeros/ultraestructura , Actinas/metabolismo , Actinas/ultraestructura , Genes Reporteros , Proteínas Fluorescentes Verdes/análisis , Proteínas Fluorescentes Verdes/genética , Microscopía Confocal , Microscopía Fluorescente , Microscopía Inmunoelectrónica , Microtúbulos/ultraestructura , Modelos Biológicos , Fibras Musculares Esqueléticas/química , Fibras Musculares Esqueléticas/ultraestructura , Músculo Esquelético/metabolismo , Músculo Esquelético/ultraestructura , Miosinas/ultraestructura , Transporte de Proteínas , Tubulina (Proteína)/análisisRESUMEN
Spinal muscular atrophies (SMA) are characterized by degeneration of lower motor neurons associated with muscle paralysis and atrophy. Childhood SMA is a frequent recessive autosomal disorder and represents one of the most common genetic causes of death in childhood. Mutations of the SMN1 gene are responsible for SMA. The knowledge of the genetic basis of SMA, a better understanding of SMN function, and the recent generation of SMA mouse models represent major advances in the field of SMA. These are starting points towards understanding the pathophysiology of SMA and developing therapeutic strategies for this devastating neurodegenerative disease, for which no curative treatment is known so far.