Final Report Summary - TRAFFIC IN SKM (Study of the involvement of secretory pathway in skeletal muscle differentiation)
Skeletal muscle (SKM) cell differentiation and remodeling requires synthesis and transport of proteins addressed to build up the contractile apparatus, the SR and the sarcolemma. This process most probably requires an important involvement of endoplasmic reticulum (ER), ER exit sites (ERES), Golgi Complex (GC), or early secretory pathway components, and vesicular traffic in general.
Despite the wide knowledge on the SKM specific organelles organization and functioning, the early secretory pathway components have not been studied deeply in this tissue. In terminally differentiated SKM early secretory pathway components are regularly arranged; the GC is organized in a unique fashion, fiber-type dependent and, formed by very small GC elements, still formed by cisternae, which are localized around the nucleus and in all the fiber. Interestingly, in mature myotubes GC elements are always found associated to ERES. Whether GC reorganization consists in fragmentation or de-novo biogenesis is not known, and whether its co-localization with ERES is the result of relocalization of ERES at minus end of microtubules, structural hindrance by the myofibrils and membrane systems, or depends on interaction mechanisms has not been explained.
Aiming at a better understanding how GC and ERES achieve their mature structure and what is their role during SKM differentiation, the two main aims of the project are:
1- Study how specialized domains, as sarcoplasmic reticulum (SR), ER, GC and vesicles, reciprocally organize during skeletal muscle differentiation;
2- Analyze the impact of the down regulation of proteins of the secretory pathway on differentiation, and on specialized domains assembly in skeletal muscle cells.
By developing the above reported aims, the results obtained lead to propose that:
1- during SKM differentiation GC and ERES undergo dramatic morphological changes that result in an increased ER to GC traffic efficiency;
2- GC morphology modification in differentiating cells seems to be due to a pre-existing membrane modification more than de novo biogenesis process, as previously reported;
3- GC integrity is essential for the ERES organization in differentiating SKM cells.
Altogether these results propose an active role of GC during SKM differentiation.
Moreover, these data together with the technological and methodological achievements, lay the groundwork to study the role of early secretory pathway in SKM differentiation and open new research perspectives in the field. Going to detail, it will be interesting to investigate the proteins and the mechanisms responsible of the characteristic association of GC and ERES, and their role in SKM differentiation. In this context a new line of research could be oriented on the importance of the cytoskeleton (microtubules, intermediated filaments and contractile proteins) in the modification of early secretory pathway components.
Despite the wide knowledge on the SKM specific organelles organization and functioning, the early secretory pathway components have not been studied deeply in this tissue. In terminally differentiated SKM early secretory pathway components are regularly arranged; the GC is organized in a unique fashion, fiber-type dependent and, formed by very small GC elements, still formed by cisternae, which are localized around the nucleus and in all the fiber. Interestingly, in mature myotubes GC elements are always found associated to ERES. Whether GC reorganization consists in fragmentation or de-novo biogenesis is not known, and whether its co-localization with ERES is the result of relocalization of ERES at minus end of microtubules, structural hindrance by the myofibrils and membrane systems, or depends on interaction mechanisms has not been explained.
Aiming at a better understanding how GC and ERES achieve their mature structure and what is their role during SKM differentiation, the two main aims of the project are:
1- Study how specialized domains, as sarcoplasmic reticulum (SR), ER, GC and vesicles, reciprocally organize during skeletal muscle differentiation;
2- Analyze the impact of the down regulation of proteins of the secretory pathway on differentiation, and on specialized domains assembly in skeletal muscle cells.
By developing the above reported aims, the results obtained lead to propose that:
1- during SKM differentiation GC and ERES undergo dramatic morphological changes that result in an increased ER to GC traffic efficiency;
2- GC morphology modification in differentiating cells seems to be due to a pre-existing membrane modification more than de novo biogenesis process, as previously reported;
3- GC integrity is essential for the ERES organization in differentiating SKM cells.
Altogether these results propose an active role of GC during SKM differentiation.
Moreover, these data together with the technological and methodological achievements, lay the groundwork to study the role of early secretory pathway in SKM differentiation and open new research perspectives in the field. Going to detail, it will be interesting to investigate the proteins and the mechanisms responsible of the characteristic association of GC and ERES, and their role in SKM differentiation. In this context a new line of research could be oriented on the importance of the cytoskeleton (microtubules, intermediated filaments and contractile proteins) in the modification of early secretory pathway components.