Amplified MS2 labeling reveals heterogeneous dynamics of RNA granules in the live murine brain

Dynamics of messenger ribonucleic acids (mRNAs) and the complexes with associated proteins (RNPs), also known as RNA granules, provide post-transcriptional control of gene expression. This regulation is crucial for cell-type diversity and activity-dependent plasticity of the mammalian central nervous system (CNS). However, elucidating the physiological significance of RNA granules has been hampered by the lack of technologies for probing them in live mouse brain. Here, we describe a novel method to visualize RNA granules in native CNS tissues in vivo. To amplify the fluorescence signal from single mRNAs incorporating MS2 stem loops, MS2 capsid protein (MCP) was conjugated with 4 tandem superfolder green fluorescent proteins (sfGFPs). Using MCP-4xsfGFP, a significant population of RNPs could be detected in specific cells of the CNS, enabling new findings, e.g., remarkable heterogeneity of Actb mRNA dynamics across neurons and glial cells. The highly sensitive in vivo RNA imaging could be useful for illuminating the regulation of the dynamics of RNA granules in naive and diseased animals. SignificanceRNA granules, complexes of RNAs and binding proteins, play a vital role in regulating gene expression and mRNA dynamics. Despite the importance, monitoring their behavior in functional neural tissue has proven technically challenging, in part due to optical turbidity and weak fluorescent tags. In this study, we present a new approach to better observe RNA granules in specific cells of murine brain through the use of amplified fluorescent signals and advanced imaging techniques. Our method provides a powerful means to analyze the properties of RNA granules within neurons and glial cells in vivo, offering valuable insights into healthy and neurodegenerative brains.