Department of Biotechnology, University of Kashmir, Srinagar, Jammu and Kashmir 190006, India.
Department of Biological Sciences, Laboratory of Neurogenetics, IISER-Bhopal, Bhopal, Madhya Pradesh, 462066, India.
Hum Mol Genet. 2021 Aug 28;30(18):1677-1692. doi: 10.1093/hmg/ddab087.
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disease that develops in some premutation (PM) carriers of the FMR1 gene with alleles bearing 55-200 CGG repeats. The discovery of a broad spectrum of clinical and cell-developmental abnormalities among PM carriers with or without FXTAS and in model systems suggests that neurodegeneration seen in FXTAS could be the inevitable end-result of pathophysiological processes set during early development. Hence, it is imperative to trace early PM-induced pathological abnormalities. Previous studies have shown that transgenic Drosophila carrying PM-length CGG repeats are sufficient to cause neurodegeneration. Here, we used the same transgenic model to understand the effect of CGG repeats on the structure and function of the developing nervous system. We show that presynaptic expression of CGG repeats restricts synaptic growth, reduces the number of synaptic boutons, leads to aberrant presynaptic varicosities, and impairs synaptic transmission at the larval neuromuscular junctions. The postsynaptic analysis shows that both glutamate receptors and subsynaptic reticulum proteins were normal. However, a high percentage of boutons show a reduced density of Bruchpilot protein, a key component of presynaptic active zones required for vesicle release. The electrophysiological analysis shows a significant reduction in quantal content, a measure of total synaptic vesicles released per excitation potential. Together, these findings suggest that synapse perturbation caused by riboCGG (rCGG) repeats mediates presynaptically during larval neuromuscular junction development. We also suggest that the stress-activated c-Jun N-terminal kinase protein Basket and CIDE-N protein Drep-2 positively mediate Bruchpilot active zone defects caused by rCGG repeats.
脆性 X 相关震颤/共济失调综合征 (FXTAS) 是一种迟发性神经退行性疾病，发生在携带 FMR1 基因等位基因中有 55-200 个 CGG 重复的前突变 (PM) 携带者中。在有或没有 FXTAS 的 PM 携带者和模型系统中发现广泛的临床和细胞发育异常，表明 FXTAS 中所见的神经退行性变可能是早期发育过程中病理生理过程的必然结果。因此，追踪早期 PM 诱导的病理异常至关重要。先前的研究表明，携带 PM 长度 CGG 重复的转基因果蝇足以引起神经退行性变。在这里，我们使用相同的转基因模型来了解 CGG 重复对发育中神经系统的结构和功能的影响。我们表明，CGG 重复的突触前表达限制了突触生长，减少了突触小泡的数量，导致了异常的突触前膨体，并损害了幼虫神经肌肉接头的突触传递。突触后分析表明谷氨酸受体和突触下网状蛋白均正常。然而，很大比例的末梢显示 Bruchpilot 蛋白密度降低，Bruchpilot 蛋白是囊泡释放所必需的突触前活性区的关键组成部分。电生理分析表明量子含量显著减少，量子含量是每个激发电位释放的总突触小泡的量度。综上所述，这些发现表明由 rCGG (rCGG) 重复引起的突触扰动在幼虫神经肌肉接头发育过程中是突触前介导的。我们还表明，应激激活的 c-Jun N 端激酶蛋白 Basket 和 CIDE-N 蛋白 Drep-2 积极介导 rCGG 重复引起的 Bruchpilot 活性区缺陷。
