Analysis of mRNA localization mechanism in neuronal cells mediated by splicing-dependent complex, EJC

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It has been well accepted that steps of gene expression influence to each other in higher eukaryotes. For example, splicing not only removes intron from pre-mRNAs but also deposits exon junction complex near exon-exon junction of mRNA EJC enhances downstream events, such as translation, transport and nonsense mediated mRNA decay (NMD). Y14 and Magoh, core components of EJC, bind to mRNA in the nucleus and remain bound in the cytoplasm. This has strongly suggested that these proteins have roles in RNA localization NMD. Indeed, homologs of these proteins in Drosophila have been shown to be involved in oskar mRNA localization in oocytes. In addition, others and we also showed that these proteins participate in NMD.In this research, we hypothesized that EJC also links mRNA splicing with mRNA localization in mammalian cells, and have been investigating the molecular mechanism of mRNA localization in neuronal cells. We have identified by immunostaining that there are granules that contain nuclear cap binding complex (CBC) and Y14 in the shaft regions of neuritis. These granules are associated with microtubules and thought to be transported along them. We also found granules that contain cytoplasmic cap binding protein, eIF4E, in the branched regions of neuronal cells. By performing immunostaining, we demonstrated that both granules contain Dcp1a, which is a marker of P body. These results indicate that there are two different p body-like granules in neuronal cells; one is CBC-EJC containing transportable p body, the other is eIF4E containing anchored p body. Our findings strongly suggest a new regulatory mechanism of local translation for localized mRNAs in neurons.