Functionally Clustered mRNAs Are Distinctly Enriched at Cortical Astroglial Processes and Are Preferentially Affected by FMRP Deficiency

Abstract

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.