Abstract
Decades of work have demonstrated that messenger RNAs (mRNAs) are localized and translated within neuronal dendrites and axons to provide proteins for remodeling and maintaining growth cones or synapses. It remains unknown, however, whether specific forms of plasticity differentially regulate the dynamics and translation of individual mRNA species. To address this, we targeted three individual synaptically localized mRNAs, CamkIIa, β-actin, Psd95, and used molecular beacons to track endogenous mRNA movements. We used reporters and CRISPR/Cas9 gene editing to track mRNA translation in cultured neurons. We found alterations in mRNA dynamic properties occurred during two forms of synaptic plasticity, long-term potentiation (cLTP) and depression (mGluR-LTD). Changes in mRNA dynamics following either form of plasticity resulted in an enrichment of mRNA in the vicinity of dendritic spines. Both the reporters and tagging of endogenous proteins revealed the transcript-specific stimulation of protein synthesis following cLTP or mGluR-LTD. As such, the plasticity-induced enrichment of mRNA near synapses could be uncoupled from its translational status. The enrichment of mRNA in the proximity of spines allows for localized signaling pathways to decode plasticity milieus and stimulate a specific translational profile, resulting in a customized remodeling of the synaptic proteome.
Highlights
Coupling observations of messenger RNAs (mRNAs) dynamics with live imaging of endogenous protein synthesis dynamics, we found that alterations in mRNA movements occur independently of their translational state, indicating a multistep mechanism of capture and decoding of an mRNA to determine when translation occurs
To assess endogenous mRNA dynamics, we focused on Camk2a, β-actin, and Psd95 as they are abundant in neuronal dendrites [28] and are translationally regulated by plasticity [18, 22, 29, 30]
We examined how mRNA dynamics were altered during two forms of protein synthesis-dependent plasticity, chemically induced LTP (cLTP) [38] and mGluR-LTD [39] (SI Appendix, Fig. S3 A and B). cLTP induction (Materials and Methods) was performed by a 5-min incubation in magnesium-free buffer supplemented with glycine and picrotoxin, whereas as mGluR-LTD was induced with 100 μM (S)-3,5-Dihydroxyphenylglycine hydrate (S-DHPG) for 5 min
Summary
Decades of work have demonstrated that messenger RNAs (mRNAs) are localized and translated within neuronal dendrites and axons to provide proteins for remodeling and maintaining growth cones or synapses It remains unknown, whether specific forms of plasticity differentially regulate the dynamics and translation of individual mRNA species. Changes in mRNA dynamics following either form of plasticity resulted in an enrichment of mRNA in the vicinity of dendritic spines Both the reporters and tagging of endogenous proteins revealed the transcript-specific stimulation of protein synthesis following cLTP or mGluR-LTD. We found that induction of either chemically induced LTP (cLTP) or metabotropic glutamate receptor LTD (mGluR-LTD) resulted in a widespread attenuation of mRNA motility and led to an enrichment of mRNA near dendritic spines These altered mRNA dynamics and availability near synapses was accompanied for some, but not all, mRNAs by enhanced translation of either a reporter or a CRISPR/Cas9tagged endogenous protein. Given the capacity for protein synthesis in distal compartments, a fundamental question is how dendritically and axonally localized mRNAs become recruited near synapses and translationally regulated locally during plasticity
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