Department of Neuroscience and Imaging (DNI), University G. d'Annunzio, Chieti, Italy.
PLoS One. 2013;8(1):e53267. doi: 10.1371/journal.pone.0053267. Epub 2013 Jan 7.
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.
神经元生长相关蛋白 43（GAP43），也称为 B-50 或神经调节素，参与控制神经元在发育和再生过程中的路径寻找和分支的机制。多年来，这种蛋白质被归类为神经元特异性，但最近的证据表明：a）GAP43不仅在神经元中，而且在神经胶质细胞中表达，b）它可能存在于其他组织中。特别是，它在患有各种肌病的患者的肌肉中表达，表明 GAP43不再仅仅被认为是神经元特异性分子。我们使用 Western blot、免疫荧光结合共聚焦显微镜和电子显微镜研究了 GAP43 在小鼠卫星细胞、肌管和成年肌肉（伸趾长肌或 EDL）中的表达和亚细胞定位。我们的体外结果表明，GAP43确实在成肌细胞和分化的肌管中表达，其细胞定位在成熟过程中发生了巨大变化：在成肌细胞中，定位似乎主要在核内，而随着分化，蛋白质开始呈现出类似于肌节的模式。在成年纤维中，GAP43 的表达明显，蛋白标记形成（在纵向上）类似于其他细胞器（如钙释放单位（CRUs）和线粒体）的双交叉条纹。双重免疫染色和在不同肌节长度固定的 EDL 肌肉中进行的实验使我们能够确定从肌节 Z 线开始的 GAP43 阳性焦点的定位，该焦点位于 CRUs 和线粒体之间。横切染色为这个难题增添了一个细节：GAP43 标记形成了围绕单个肌原纤维的网状图案，但不包括收缩元件。这项工作为进一步研究 GAP43 蛋白在成年纤维功能和疾病中的可能生理和结构作用奠定了基础。
