Quiñones-Frías Mónica C, Ocken Dina M, Rodal Avital
Department of Biology, Brandeis University, Waltham, MA.
bioRxiv. 2025 Feb 15:2023.09.01.555994. doi: 10.1101/2023.09.01.555994.
The endoplasmic reticulum (ER) extends throughout neurons and regulates many neuronal functions, including neurite outgrowth, neurotransmission, and synaptic plasticity. Mutations in proteins that control ER shape are linked to the neurodegenerative disorder Hereditary Spastic Paraplegia (HSP), yet the ultrastructure and dynamics of neuronal ER remain largely unexplored, especially at presynaptic terminals. Using super-resolution and live imaging in larval motor neurons, we investigated ER structure at presynaptic terminals of wild-type animals and null mutants of the ER shaping protein and HSP-linked gene, Atlastin. Previous studies using an ER luminal marker reported diffuse localization at mutant presynaptic terminals, which was attributed to ER fragmentation. However, using an ER membrane marker, we discovered that mutant ER forms robust networks with only mild defects in structural dynamics, indicating the primary defect is functional rather than architectural. We demonstrate that mutants progressively displace overexpressed luminal ER proteins to the cytosol during larval development, specifically at synapses, while these proteins remain correctly localized in cell bodies, axons, and muscles. This synaptic-specific displacement phenotype, previously unreported in non-neuronal cells, emphasizes the importance of studying neurons to understand HSP pathogenesis.
内质网（ER）贯穿神经元并调节许多神经元功能，包括神经突生长、神经传递和突触可塑性。控制内质网形态的蛋白质突变与神经退行性疾病遗传性痉挛性截瘫（HSP）有关，但神经元内质网的超微结构和动力学在很大程度上仍未得到探索，尤其是在突触前终末。利用幼虫运动神经元的超分辨率和实时成像技术，我们研究了野生型动物以及内质网塑形蛋白和与HSP相关基因Atlastin的无效突变体的突触前终末的内质网结构。先前使用内质网腔标记物的研究报道，在突变体突触前终末内质网呈弥漫性定位，这被归因于内质网碎片化。然而，使用内质网膜标记物，我们发现突变体的内质网形成了强大的网络，结构动力学仅存在轻微缺陷，这表明主要缺陷是功能性的而非结构性的。我们证明，在幼虫发育过程中，特别是在突触处，突变体逐渐将过表达的内质网腔蛋白转移到细胞质中，而这些蛋白在细胞体、轴突和肌肉中仍正确定位。这种突触特异性转移表型，此前在非神经元细胞中未被报道，强调了研究神经元对于理解HSP发病机制的重要性。
