Howard Hughes Medical Institute, Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, Oregon, United States of America.
PLoS One. 2011;6(11):e27146. doi: 10.1371/journal.pone.0027146. Epub 2011 Nov 3.
Vesicle fusion contributes to the maintenance of synapses in the nervous system by mediating synaptic transmission, release of neurotrophic factors, and trafficking of membrane receptors. N-ethylmaleimide-sensitive factor (NSF) is indispensible for dissociation of the SNARE-complex following vesicle fusion. Although NSF function has been characterized extensively in vitro, the in vivo role of NSF in vertebrate synaptogenesis is relatively unexplored. Zebrafish possess two nsf genes, nsf and nsfb. Here, we examine the function of either Nsf or Nsfb in the pre- and postsynaptic cells of the zebrafish lateral line organ and demonstrate that Nsf, but not Nsfb, is required for maintenance of afferent synapses in hair cells. In addition to peripheral defects in nsf mutants, neurodegeneration of glutamatergic synapses in the central nervous system also occurs in the absence of Nsf function. Expression of an nsf transgene in a null background indicates that stabilization of synapses requires Nsf function in both hair cells and afferent neurons. To identify potential targets of Nsf-mediated fusion, we examined the expression of genes implicated in stabilizing synapses and found that transcripts for multiple genes including brain-derived neurotrophic factor (bdnf) were significantly reduced in nsf mutants. With regard to trafficking of BDNF, we observed a striking accumulation of BDNF in the neurites of nsf mutant afferent neurons. In addition, injection of recombinant BDNF protein partially rescued the degeneration of afferent synapses in nsf mutants. These results establish a role for Nsf in the maintenance of synaptic contacts between hair cells and afferent neurons, mediated in part via the secretion of trophic signaling factors.
囊泡融合通过介导突触传递、神经递质释放和膜受体运输，有助于维持神经系统中的突触。N-乙基马来酰亚胺敏感因子（NSF）对于囊泡融合后 SNARE 复合物的解离是必不可少的。尽管 NSF 的功能已在体外得到广泛研究，但 NSF 在脊椎动物突触发生中的体内作用相对未知。斑马鱼拥有两个 nsf 基因，nsf 和 nsfb。在这里，我们研究了 Nsf 或 Nsfb 在斑马鱼侧线器官的前突触和后突触细胞中的功能，并证明 Nsf（而不是 Nsfb）对于维持毛细胞中的传入突触是必需的。除了 nsf 突变体的外周缺陷外，中枢神经系统中谷氨酸能突触的神经退行性变也发生在缺乏 NSF 功能的情况下。在缺失背景下表达一个 nsf 转基因表明，稳定突触需要 Nsf 在毛细胞和传入神经元中的功能。为了确定 NSF 介导的融合的潜在靶点，我们研究了稳定突触的相关基因的表达，发现包括脑源性神经营养因子（BDNF）在内的多个基因的转录本在 nsf 突变体中显著减少。关于 BDNF 的运输，我们观察到 nsf 突变体传入神经元的神经突中 BDNF 的积累明显增加。此外，注射重组 BDNF 蛋白部分挽救了 nsf 突变体中传入突触的退化。这些结果确立了 NSF 在毛细胞和传入神经元之间维持突触接触中的作用，部分通过分泌营养信号因子介导。
