Mature protoplasmic astroglia in the mammalian CNS uniquely possess a large number of fine processes that have been considered primary sites to mediate astroglia to neuron synaptic signaling. However, localized mechanisms for regulating interactions between astroglial processes and synapses, especially for regulating the expression of functional surface proteins at these fine processes, are largely unknown. Previously, we showed that the loss of the RNA binding protein FMRP in astroglia disrupts astroglial mGluR5 signaling and reduces expression of the major astroglial glutamate transporter GLT1 and glutamate uptake in the cortex of Fmr1 conditional deletion mice. In the current study, by examining ribosome localization using electron microscopy and identifying mRNAs enriched at cortical astroglial processes using synaptoneurosome/translating ribosome affinity purification and RNA-Seq in WT and FMRP-deficient male mice, our results reveal interesting localization-dependent functional clusters of mRNAs at astroglial processes. We further showed that the lack of FMRP preferentially alters the subcellular localization and expression of process-localized mRNAs. Together, we defined the role of FMRP in altering mRNA localization and expression at astroglial processes at the postnatal development (P30-P40) and provided new candidate mRNAs that are potentially regulated by FMRP in cortical astroglia.

SIGNIFICANCE STATEMENT Localized mechanisms for regulating interactions between astroglial processes and synapses, especially for regulating the expression of functional surface proteins at these fine processes, are largely unknown. Previously, we showed that the loss of the RNA binding protein FMRP in astroglia disrupts expression of several astroglial surface proteins, such as mGluR5 and major astroglial glutamate transporter GLT1 in the cortex of FMRP-deficient mice. Our current study examined ribosome localization using electron microscopy and identified mRNAs enriched at cortical astroglial processes in WT and FMRP-deficient mice. These results reveal interesting localization-dependent functional clusters of mRNAs at astroglial processes and demonstrate that the lack of FMRP preferentially alters the subcellular localization and expression of process-localized mRNAs.

哺乳动物中枢神经系统中成熟的原生质星形胶质细胞独特地拥有大量精细过程，这些过程被认为是介导星形胶质细胞与神经元突触信号传导的主要部位。然而，调节星形胶质细胞过程和突触之间相互作用的局部机制，特别是调节这些精细过程中功能性表面蛋白的表达，在很大程度上是未知的。此前，我们发现星形胶质细胞中 RNA 结合蛋白 FMRP 的缺失会破坏星形胶质细胞 mGluR5 信号传导，并减少主要星形胶质细胞谷氨酸转运蛋白 GLT1 的表达以及 Fmr1 条件缺失小鼠皮层中谷氨酸的摄取。在当前的研究中，通过使用电子显微镜检查核糖体定位，并使用突触神经体/翻译核糖体亲和纯化和 RNA-Seq 鉴定在 WT 和 FMRP 缺陷雄性小鼠中皮质星形胶质细胞过程中富集的 mRNA，我们的结果揭示了有趣的依赖于定位的功能簇星形胶质细胞过程中的 mRNA。我们进一步表明，FMRP 的缺乏优先改变过程定位 mRNA 的亚细胞定位和表达。我们共同定义了 FMRP 在改变出生后发育 (P30-P40) 星形胶质细胞过程中 mRNA 定位和表达的作用，并提供了皮质星形胶质细胞中可能受 FMRP 调节的新候选 mRNA。

意义声明调节星形胶质细胞突起和突触之间相互作用的局部机制，特别是调节这些精细突起的功能性表面蛋白的表达，在很大程度上是未知的。此前，我们发现星形胶质细胞中 RNA 结合蛋白 FMRP 的缺失会破坏 FMRP 缺陷小鼠皮质中几种星形胶质细胞表面蛋白的表达，例如 mGluR5 和主要星形胶质细胞谷氨酸转运蛋白 GLT1。我们目前的研究使用电子显微镜检查了核糖体定位，并鉴定了 WT 和 FMRP 缺陷小鼠的皮质星形胶质细胞过程中富集的 mRNA。这些结果揭示了星形胶质细胞突起中有趣的依赖于定位的 mRNA 功能簇，并证明缺乏 FMRP 会优先改变突起定位 mRNA 的亚细胞定位和表达。