Studies on the role of Pur α in BC1 RNA transport in neuronal dendrites

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Pur alpha, which is involved in diverse aspects of cellular functions, is strongly expressed in neuronal cytoplasm. Previously, we have reported that this protein controls BC1 RNA expression and its subsequent distribution within dendrites, and that pur alpha is associated with polyribosomes. Here, we report that, following treatment with EDTA, pur alpha was released from polyribosomes in mRNA/ protein complexes (mRNPs), which also contained mStaufen, Fragile X Mental Retardation Protein (FMRP), myosin Va and other proteins with unknown functions. As the coimmunoprecipitation of these proteins by an anti-pur alpha antibody was abolished by Rnase treatment, pur alpha may assist mRNP assembly in an RNA-dependent manner, and be involved in targeting mRNPs to polyribosomes in cooperation with other RNA-binding proteins. The immunoprecipitation of mStaufen- and FMRP-containing mRNPs provided additional evidence that the anti-pur alpha detected structurally or functionally related mRNA subsets which are distributed in the somatodendritic compartment. Furthermore, mRNPs appear to reside on rough endoplasmic reticulum (rER) equipped with a kinesin motor. Based on our present findings, we propose that this rER structure may form the molecular machinery that mediates and regulates multi-step transport of polyribosomes along microtubules and actin filaments, as well as localized translation in the somatodendritic compartment.More recently, studies on protein components of the mRNPs revealed that number of proteins implicated in metabolism of mRNAs or mRNA transport and translation were included. Moreover, several dendritic mRNAs were also associated with these complexes. It would be intriguing to further study the biological roles of pur alpha protein, together with other proteins, played in the process of mRNA transport in the neuronal dendrites.