DuVal Michèle G, Gilbert Matthew J H, Watson D Ezekiel, Zerulla Tanja C, Tierney Keith B, Allison W Ted
Department of Biological Sciences, University of Alberta, Edmonton AB, Canada.
Department of Biological Sciences, University of Alberta, Edmonton AB, Canada ; Centre for Prions and Protein Folding Disease, University of Alberta, Edmonton AB, Canada.
PLoS One. 2014 Feb 28;9(2):e89183. doi: 10.1371/journal.pone.0089183. eCollection 2014.
Mutation of Glass bottom boat, the Drosophila homologue of the bone morphogenetic protein or growth/differentiation factor (BMP/GDF) family of genes in vertebrates, has been shown to disrupt development of neuromuscular junctions (NMJ). Here we tested whether this same conclusion can be broadened to vertebrate BMP/GDF genes. This analysis was also extended to consider whether such genes are required for NMJ maintenance in post-larval stages, as this would argue that BMP genes are viable candidates for analysis in progressive neuromuscular disease. Zebrafish mutants harboring homozygous null mutations in the BMP-family gene gdf6a were raised to adulthood and assessed for neuromuscular deficits. Fish lacking gdf6a exhibited decreased endurance (∼ 50%, p = 0.005) compared to wild type, and this deficit progressively worsened with age. These fish also presented with significantly disrupted NMJ morphology (p = 0.009), and a lower abundance of spinal motor neurons (∼ 50%, p<0.001) compared to wild type. Noting the similarity of these symptoms to those of Amyotrophic Lateral Sclerosis (ALS) model mice and fish, we asked if mutations in gdf6a would enhance the phenotypes observed in the latter, i.e. in zebrafish over-expressing mutant Superoxide Dismutase 1 (SOD1). Amongst younger adult fish only bigenic fish harboring both the SOD1 transgene and gdf6a mutations, but not siblings with other combinations of these gene modifications, displayed significantly reduced endurance (75%, p<0.05) and strength/power (75%, p<0.05), as well as disrupted NMJ morphology (p<0.001) compared to wild type siblings. Bigenic fish also had lower survival rates compared to other genotypes. Thus conclusions regarding a role for BMP ligands in effecting NMJ can be extended to vertebrates, supporting conservation of mechanisms relevant to neuromuscular degenerative diseases. These conclusions synergize with past findings to argue for further analysis of GDF6 and other BMP genes as modifier loci, potentially affecting susceptibility to ALS and perhaps a broader suite of neurodegenerative diseases.
玻璃底船基因是脊椎动物中骨形态发生蛋白或生长/分化因子（BMP/GDF）基因家族在果蝇中的同源基因，其突变已被证明会破坏神经肌肉接头（NMJ）的发育。在此，我们测试了这一结论是否可推广至脊椎动物的BMP/GDF基因。该分析还进一步考虑了此类基因在幼虫后期阶段对NMJ维持是否必要，因为这表明BMP基因可能是进行性神经肌肉疾病分析的可行候选基因。将携带BMP家族基因gdf6a纯合无效突变的斑马鱼饲养至成年，并评估其神经肌肉缺陷。与野生型相比，缺乏gdf6a的鱼耐力下降（约50%，p = 0.005），且这种缺陷随年龄增长而逐渐恶化。这些鱼还表现出NMJ形态明显破坏（p = 0.009），与野生型相比，脊髓运动神经元数量减少（约50%，p<0.001）。注意到这些症状与肌萎缩侧索硬化症（ALS）模型小鼠和鱼类的症状相似，我们询问gdf6a突变是否会增强后者（即过表达突变型超氧化物歧化酶1（SOD1）的斑马鱼）所观察到的表型。在较年轻的成年鱼中，只有同时携带SOD1转基因和gdf6a突变的双基因鱼，而不是具有这些基因修饰其他组合的同胞鱼，与野生型同胞相比，表现出耐力显著降低（75%，p<0.05）、力量/功率显著降低（75%，p<0.05）以及NMJ形态破坏（p<0.001）。双基因鱼的存活率也低于其他基因型。因此，关于BMP配体在影响NMJ方面作用的结论可推广至脊椎动物，支持了与神经肌肉退行性疾病相关机制的保守性。这些结论与过去的研究结果协同，主张进一步分析GDF6和其他BMP基因作为修饰位点，它们可能影响对ALS以及或许更广泛的神经退行性疾病的易感性。
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