Neuroscience Research Center, Chang Gung Memorial Hospital, Linkou, Taoyuan, Taiwan; College of Medicine, Chang Gung University, Taoyuan, Taiwan; Section of Movement Disorders, Department of Neurology, Chang Gung Memorial Hospital at Linkou Medical Center, Taoyuan, Taiwan; Department of Neurology, Taipei Medical University Hospital, Taipei, Taiwan; School of Medicine, Taipei Medical University, Taipei, Taiwan.
College of Medicine, Chang Gung University, Taoyuan, Taiwan; Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
Exp Neurol. 2018 Jun;304:114-124. doi: 10.1016/j.expneurol.2018.03.002. Epub 2018 Mar 6.
Hexanucleotide repeat expansions in the C9orf72 gene are a common genetic cause of familial and sporadic amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, the function of C9orf72 in neural development and the pathogenic mechanism underlying neurodegeneration are unknown. We found that disrupting C9orf72 expression by using C9orf72 constructs that lack the complete DENN domain result in reduced GTPase activity in zebrafish embryos, demonstrating the indispensability of the complete DENN domain. This effect was phenocopied by knocking down endogenous C9orf72 expression by using morpholinos. C9orf72-deficient zebrafish embryos exhibited impaired axonogenesis and motility defects. The C9orf72 deficiency upregulated the expression of tp53 and caused neuronal apoptosis. Knockdown Tp53 in the C9orf72-deficient embryos rescued only the apoptotic phenotype but not the phenotype with axonal and motility defects. The C9orf72 deficiency also induced ccng1 (encodes Cyclin G1) mRNA expression, and injection of a dominant-negative Cyclin G1 construct rescued the axonal impairment, apoptosis, and motility defects in the C9orf72-deficient embryos. Our results revealed the GTPase activity of C9orf72 and demonstrated that Cyclin G1 is an essential downstream mediator for C9orf72 in neural development and motility. Furthermore, downregulating Cyclin G1 was sufficient to rescue all the defects caused by C9orf72 deficiency. In summary, we revealed a novel regulatory mechanism underlying the role of C9orf72 in neurological and motility defects. This result facilitates understanding the function of the C9orf72 gene in the developing nervous system and provides a potential mechanism underlying the pathogenesis of ALS-FTD.
C9orf72 基因中的六核苷酸重复扩增是家族性和散发性肌萎缩侧索硬化症（ALS）和额颞叶痴呆（FTD）的常见遗传原因。然而，C9orf72 在神经发育中的功能和神经退行性变的致病机制尚不清楚。我们发现，使用缺乏完整 DENN 结构域的 C9orf72 构建体破坏 C9orf72 的表达会导致斑马鱼胚胎中的 GTPase 活性降低，这表明完整的 DENN 结构域是必不可少的。这种效应被使用 morpholino 敲低内源性 C9orf72 表达所模拟。C9orf72 缺陷型斑马鱼胚胎表现出轴突发生受损和运动缺陷。C9orf72 缺陷导致 tp53 表达上调并引起神经元凋亡。在 C9orf72 缺陷型胚胎中敲低 Tp53 仅挽救了凋亡表型，而没有挽救轴突和运动缺陷的表型。C9orf72 缺陷还诱导了 ccng1（编码细胞周期蛋白 G1）mRNA 的表达，并且注射显性负性细胞周期蛋白 G1 构建体挽救了 C9orf72 缺陷型胚胎中的轴突损伤、凋亡和运动缺陷。我们的结果揭示了 C9orf72 的 GTPase 活性，并表明细胞周期蛋白 G1 是 C9orf72 在神经发育和运动中的必需下游介质。此外，下调细胞周期蛋白 G1 足以挽救 C9orf72 缺陷引起的所有缺陷。总之，我们揭示了 C9orf72 在神经和运动缺陷中的作用的新的调节机制。这一结果有助于理解 C9orf72 基因在发育中神经系统中的功能，并为 ALS-FTD 的发病机制提供了潜在的机制。
