Visualization of Dynamics of Single Endogenous mRNA Labeled in Live Mouse

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Science  24 Jan 2014:
Vol. 343, Issue 6169, pp. 422-424
DOI: 10.1126/science.1239200

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The transcription and transport of messenger RNA (mRNA) are critical steps in regulating the spatial and temporal components of gene expression, but it has not been possible to observe the dynamics of endogenous mRNA in primary mammalian tissues. We have developed a transgenic mouse in which all β-actin mRNA is fluorescently labeled. We found that β-actin mRNA in primary fibroblasts localizes predominantly by diffusion and trapping as single mRNAs. In cultured neurons and acute brain slices, we found that multiple β-actin mRNAs can assemble together, travel by active transport, and disassemble upon depolarization by potassium chloride. Imaging of brain slices revealed immediate early induction of β-actin transcription after depolarization. Studying endogenous mRNA in live mouse tissues provides insight into its dynamic regulation within the context of the cellular and tissue microenvironment.

Observing the Messenger

In order to elucidate the dynamics of individual components in the cell, single-molecule technologies are being developed (see the Perspective by Akbalik and Schuman). Park et al. (p. 422) used a mouse expressing fluorescent β-actin messenger RNAs (mRNAs) to visualize mRNA movements in living cells and tissues. Buxbaum et al. (p. 419) showed that neurons contain β-actin mRNAs and ribosomes packaged in a dense structure, impenetrable by oligonucleotide probes. This effectively masks the mRNAs until neuronal stimulation exposes the mRNA and ribosomes briefly, presumably reflecting the local stimulation and translation involved, for example, in the generation of memories.

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