A generalized model of mRNA trafficking in glia. A nascent mRNA is bound in the nucleus by an mRNA-binding protein, like hnRNP A2 in oligodendrocytes, through a 3′UTR response element. Other well-known RBPs include zipcode-binding protein ZBP1 or IMP-1 in neuronal growth cones and hippocampal dendrites; whether these signals participate in trafficking of other mRNAs than that of MBP in glia is not known, yet plausible. The mRNA–RBP complex is next shuttled out of the nucleus and assembled into messenger ribonucleoprotein (mRNP) granules in the cytoplasm. Those are transported by a motor protein, like kinesin, along microtubules toward the site of required translation, where protein can be made using localized translation machinery.
