Department of Medical Genetics, University of Alberta Faculty of Medicine and Dentistry, Edmonton, Alberta, Canada.
PLoS One. 2013 Jul 24;8(7):e69194. doi: 10.1371/journal.pone.0069194. Print 2013.
Duchenne muscular dystrophy (DMD), one of the most common and lethal genetic disorders, and the mdx mouse myopathies are caused by a lack of dystrophin protein. These dystrophic muscles contain sporadic clusters of dystrophin-expressing revertant fibers (RFs), as detected by immunohistochemistry. RFs are known to arise from muscle precursor cells with spontaneous exon skipping (alternative splicing) and clonally expand in size with increasing age through the process of muscle degeneration/regeneration. The expansion of revertant clusters is thought to represent the cumulative history of muscle regeneration and proliferation of such precursor cells. However, the precise mechanisms by which RFs arise and expand are poorly understood. Here, to test the effects of mutation types and aging on RF expansion and muscle regeneration, we examined the number of RFs in mdx mice (containing a nonsense mutation in exon 23) and mdx52 mice (containing deletion mutation of exon 52) with the same C57BL/6 background at 2, 6, 12, and 18months of age. Mdx mice displayed a significantly higher number of RFs compared to mdx52 mice in all age groups, suggesting that revertant fiber expansion largely depends on the type of mutation and/or location in the gene. A significant increase in the expression and clustering levels of RFs was found beginning at 6months of age in mdx mice compared with mdx52 mice. In contrast to the significant expansion of RFs with increasing age, the number of centrally nucleated fibers and embryonic myosin heavy chain-positive fibers (indicative of cumulative and current muscle regeneration, respectively) decreased with age in both mouse strains. These results suggest that mutation types and aging differently affect revertant fiber expansion in mdx and mdx52 mice.
杜氏肌营养不良症（DMD）是最常见和最致命的遗传疾病之一，mdx 小鼠肌病是由于缺乏肌营养不良蛋白引起的。这些营养不良的肌肉中含有散在的肌营养不良蛋白表达的回复纤维（RFs）簇，通过免疫组织化学检测到。RFs 已知源自具有自发外显子跳跃（选择性剪接）的肌肉前体细胞，并随着年龄的增长通过肌肉退化/再生过程逐渐克隆性扩大。RF 簇的扩大被认为代表了肌肉再生和前体细胞增殖的累积历史。然而，RF 产生和扩大的确切机制仍知之甚少。在这里，为了测试突变类型和衰老对 RF 扩展和肌肉再生的影响，我们检查了具有相同 C57BL/6 背景的 mdx 小鼠（含有外显子 23 中的无义突变）和 mdx52 小鼠（含有外显子 52 的缺失突变）在 2、6、12 和 18 月龄时的 RF 数量。在所有年龄组中，mdx 小鼠的 RF 数量明显高于 mdx52 小鼠，这表明回复纤维的扩展在很大程度上取决于突变类型和/或基因中的位置。与 mdx52 小鼠相比，mdx 小鼠在 6 月龄时开始发现 RFs 的表达和聚类水平显著增加。与 RFs 随年龄显著增加形成鲜明对比的是，两种小鼠品系的中心核纤维和胚胎肌球蛋白重链阳性纤维（分别代表累积和当前的肌肉再生）的数量随着年龄的增长而减少。这些结果表明，突变类型和衰老以不同的方式影响 mdx 和 mdx52 小鼠中 RF 的扩展。
