Identification of localized mRNA at neuronal synapse and the role of kinesin I in RNA transport

Abstract

Local protein synthesis is an essential mechanism for synaptic plasticity in neurons, which requires the precise regulation of RNA transport and localization. However, the characterization of local transcriptome at neuronal synapses is still largely incomplete. In this study, the relative enrichment of transcripts in synaptic fraction was examined by next-generation sequencing. Over two thousand genes were found to be enriched in the synaptoneurosome fraction, although glial cells were found to partially contribute to this enrichment. Direct visualization of selected transcripts revealed heterogeneous localization in different cell types and differential patterns for dendritic and synaptic localization. In particular, some RNA species could be co-assembled while others do not. On the other hand, Kinesin I (KIF5) is known to be responsible for RNA transport in neuron. By specific knockdown of individual protein homologs of KIF5 (KIF5A, B and C), it was demonstrated that they play non-redundant roles in neuronal RNP transport and might be involved in the regulation of granule docking. Finally, it was recently shown that synaptic mRNAs undergo extensive m6A methylation. In this study, the relationship between RNA m6A modification and dendritic function was explored. It was found that the m6A reader YTHDF1 could regulate dendritic spine morphology, indicating a functional significance of RNA modification to synapse development. In summary, this study expanded the knowledge of RNA localization at neuronal synapses and further solidified the role of kinesin in RNA transport and neuronal functions, providing directions for further investigation in specific local transcripts in the future.