Wood Jonathan D, Landers Jennifer A, Bingley Megan, McDermott Christopher J, Thomas-McArthur Vickie, Gleadall Lisa J, Shaw Pamela J, Cunliffe Vincent T
MRC Centre Development for Developmental and Biomedical Genetics, Department of Biomedical Science, University of Sheffield, UK.
Hum Mol Genet. 2006 Sep 15;15(18):2763-71. doi: 10.1093/hmg/ddl212. Epub 2006 Aug 7.
Hereditary spastic paraplegia (HSP) is a collection of neurological disorders characterized by developmental failure or degeneration of motor axons in the corticospinal tract and progressive lower limb spasticity. SPG4 mutations are the most common cause of autosomal dominant HSP and Spastin (the SPG4 gene product) is a microtubule severing protein that shares homology with katanin, the microtubule severing activity of which promotes axon growth in cultured neurons. Given the sequence and functional similarity between spastin and katanin, we hypothesized that spastin promotes the dynamic disassembly and remodelling of microtubules required for robust, properly directed motor axon outgrowth. To investigate this hypothesis, we cloned the zebrafish spg4 orthologue and used morpholino antisense oligonucleotides directed against the translation start site and the intron 7-8 splice donor site to knock down spastin function in the developing zebrafish embryo. Reduced spg4 function caused dramatic defects in motor axon outgrowth without affecting the events driving the initial specification of motor neurones. Other neuronal subtypes also exhibited a requirement for spg4 function, since spg4 knock down caused both widespread defects in neuronal connectivity and extensive CNS-specific apoptosis. Our results reveal a critical requirement for spastin to promote axonal outgrowth during embryonic development, and they validate the zebrafish embryo as a novel model system to dissect the pathogenetic mechanisms underlying HSP. Taken together with other recent studies, our findings suggest that axon outgrowth defects may be a common feature of childhood SPG3A and SPG4 cases.
遗传性痉挛性截瘫（HSP）是一组神经系统疾病，其特征为皮质脊髓束运动轴突发育失败或退化以及进行性下肢痉挛。SPG4突变是常染色体显性HSP最常见的病因，痉挛蛋白（SPG4基因产物）是一种微管切断蛋白，与katanin具有同源性，后者的微管切断活性可促进培养神经元中的轴突生长。鉴于痉挛蛋白和katanin之间的序列和功能相似性，我们推测痉挛蛋白可促进微管的动态拆卸和重塑，这对于强劲、正确定向的运动轴突生长是必需的。为了研究这一假设，我们克隆了斑马鱼spg4直系同源物，并使用针对翻译起始位点和内含子7-8剪接供体位点的吗啉代反义寡核苷酸，在发育中的斑马鱼胚胎中敲低痉挛蛋白的功能。spg4功能降低导致运动轴突生长出现严重缺陷，但不影响驱动运动神经元初始特化的事件。其他神经元亚型也表现出对spg4功能的需求，因为敲低spg4会导致神经元连接广泛缺陷和广泛的中枢神经系统特异性凋亡。我们的结果揭示了痉挛蛋白在胚胎发育过程中促进轴突生长的关键需求，并验证了斑马鱼胚胎作为剖析HSP潜在致病机制的新型模型系统。与其他近期研究一起，我们的发现表明轴突生长缺陷可能是儿童SPG3A和SPG4病例的共同特征。
