Growth Associated Protein 43 Is Expressed in Skeletal Muscle Fibers and Is Localized in Proximity of Mitochondria and Calcium Release Units

Abstract

The neuronal Growth Associated Protein 43 (GAP43), also known as B-50 or neuromodulin, is involved in mechanisms controlling pathfinding and branching of neurons during development and regeneration. For many years this protein was classified as neuron-specific, but recent evidences suggest that a) GAP43 is expressed in the nervous system not only in neurons, but also in glial cells, and b) probably it is present also in other tissues. In particular, its expression was revealed in muscles from patients affected by various myopathies, indicating that GAP43 can no-longer considered only as a neuron-specific molecule. We have investigated the expression and subcellular localization of GAP43 in mouse satellite cells, myotubes, and adult muscle (extensor digitorum longus or EDL) using Western blotting, immuno-fluorescence combined to confocal microscopy and electron microscopy. Our in vitro results indicated that GAP43 is indeed expressed in both myoblasts and differentiating myotubes, and its cellular localization changes dramatically during maturation: in myoblasts the localization appeared to be mostly nuclear, whereas with differentiation the protein started to display a sarcomeric-like pattern. In adult fibers, GAP43 expression was evident with the protein labeling forming (in longitudinal views) a double cross striation reminiscent of the staining pattern of other organelles, such as calcium release units (CRUs) and mitochondria. Double immuno-staining and experiments done in EDL muscles fixed at different sarcomere lengths, allowed us to determine the localization, from the sarcomere Z-line, of GAP43 positive foci, falling between that of CRUs and of mitochondria. Staining of cross sections added a detail to the puzzle: GAP43 labeling formed a reticular pattern surrounding individual myofibrils, but excluding contractile elements. This work leads the way to further investigation about the possible physiological and structural role of GAP43 protein in adult fiber function and disease.

Recurrent HERV-H-Mediated 3q13.2-q13.31 Deletions Cause a Syndrome of Hypotonia and Motor, Language, and Cognitive Delays

“…In addition to its role in the SHH pathway, BOC is also a cell adhesion molecule with roles in proper myogenesis [Kang et al, 2002], making it a candidate for these phenotypes. GAP43 may play important roles in skeletal muscle development and function [Guarnieri et al, 2013], and mice lacking the orthologue demonstrated muscle incoordination, reduced strength, and altered reflexes, with heterozygotes demonstrating moderate impairments [Metz and Schwab, 2004]. Finally, the dopamine receptor Drd3 helps regulate spinal reflexes [Clemens and Hochman, 2004], so its deletion may contribute to the depressed reflexes observed.…”

Label-free microscopy and stress responses reveal the functional organization of Pseudodiaptomus marinus copepod myofibrils

“…The abrupt transition between the compressed and the extended zones in myofibrils is reminiscent of the local depolarization of mitochondria observed after the delivery by a microflow pipette of an uncoupling agent in a restricted region of the sarcolemma along a single dissociated muscle fiber (Bruton et al, 2014). These results suggest that the spacing of the actin- The model for the mouse skeletal muscle is modified from (Guarnieri et al, 2013), with mitochondria represented in red on both sides of the Z line, the sarcoplasmic reticulum in yellow. The blue compartment represents T-tubules.…”

Calcitonin-Induced Effects on Amniotic Fluid-Derived Mesenchymal Stem Cells

“…Images were acquired using a Zeiss LSM510 META system (Jena, Germany) equipped with a Zeiss Axiovert 200 inverted microscope and a Plan Neofluar oil-immersion objective (40×). Negative controls for each immunostaining assay were performed by immunolabelling a sample with only the secondary antibody [35].…”