Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
G3 (Bethesda). 2022 Nov 4;12(11). doi: 10.1093/g3journal/jkac239.
MicroRNAs are enriched in neurons and play important roles in dendritic spine development and synaptic plasticity. MicroRNA activity is controlled by a wide range of RNA-binding proteins. FMRP, a highly conserved RNA-binding protein, has been linked to microRNA-mediated gene regulation in axonal development and dendritic spine formation. FMRP also participates in dendritic arbor morphogenesis, but whether and how microRNAs contribute to its function in this process remains to be elucidated. Here, using Drosophila larval sensory neurons, we show that a FMRP-associated microRNA, miR-276, functions in FMRP-mediated space-filling dendrite morphogenesis. Using EGFP microRNA sensors, we demonstrate that FMRP likely acts by regulating miR-276a RNA targeting rather than by modulating microRNA levels. Supporting this conclusion, miR-276a coimmunoprecipitated with FMRP and this association was dependent on the FMRP KH domains. By testing putative targets of the FMRP-miR-276a regulatory axis, we identified nejire as a FMRP-associated mRNA and, using EGFP reporters, showed that the nejire 3' untranslated region is a target of miR-276a in vivo. Genetic analysis places nejire downstream of the FMRP-miR-276a pathway in regulating dendrite patterning. Together, our findings support a model in which FMRP facilitates miR-276a-mediated control of nejire for proper dendrite space-filling morphology and shed light on microRNA-dependent dendrite developmental pathology of fragile X syndrome.
微 RNA 富含于神经元中，在树突棘发育和突触可塑性中发挥重要作用。微 RNA 的活性受到广泛的 RNA 结合蛋白的调控。FMRP 是一种高度保守的 RNA 结合蛋白，已与轴突发育和树突棘形成过程中的微 RNA 介导的基因调控有关。FMRP 还参与树突分支形态发生，但微 RNA 是否以及如何有助于其在该过程中的功能仍有待阐明。在这里，我们使用果蝇幼虫感觉神经元表明，与 FMRP 相关的 microRNA，miR-276，在 FMRP 介导的空间填充树突形态发生中发挥作用。使用 EGFP microRNA 传感器，我们证明 FMRP 可能通过调节 miR-276a RNA 靶向而不是通过调节 microRNA 水平来发挥作用。支持这一结论，miR-276a 与 FMRP 共免疫沉淀，这种关联依赖于 FMRP KH 结构域。通过测试 FMRP-miR-276a 调控轴的假定靶标，我们鉴定出 nejire 作为与 FMRP 相关的 mRNA，并使用 EGFP 报告器表明，nejire 的 3'非翻译区是体内 miR-276a 的靶标。遗传分析将 nejire 置于 FMRP-miR-276a 通路下游，调节树突模式。总之，我们的研究结果支持了这样一种模型，即 FMRP 促进 miR-276a 介导的 nejire 调控，以实现适当的树突空间填充形态，并阐明脆性 X 综合征中微 RNA 依赖性树突发育病理学。
