α-Taxilin has been identified as a binding partner of syntaxin family members and thus has been proposed to function in syntaxin-mediated intracellular vesicle trafficking. However, the lack of detailed information concerning the cellular and subcellular localization of α-taxilin impedes an understanding of the role of this protein. In the present study, we characterized α-taxilin-expressing cells in the rat CNS with a specific antibody. During embryonic development, α-taxilin was prominently expressed in nestin-positive neural stem cells in vivo and in vitro. As CNS development proceeded, the α-taxilin expression level was rapidly down-regulated. In the post-natal CNS, α-taxilin expression was almost confined to the neuronal lineage, with the highest levels of expression in motor neurons within the brainstem nuclei and spinal cord and in primary sensory neurons in mesencephalic trigeminal nucleus. At the cellular level, α-taxilin was preferentially located in Nissl substance-like structures with a tigroid or globular morphology within the soma and proximal to dendrites, but it was excluded from terminals. Combined staining with propidium iodide demonstrated that α-taxilin distribution overlapped with the cytoplasmic compartment enriched in RNA species, suggesting a close association of α-taxilin with actively translating ribosomes or polysomes in neurons. In agreement with this, a recent study indicated the preferential binding of α-taxilin to the nascent polypeptide-associated complex (αNAC), a dynamic component of the ribosomal exit tunnel in eukaryotic cells. Taken together, these findings suggest that α-taxilin plays multiple roles in the generation and maintenance of neurons through modulation of the NAC-mediated translational machinary and/or the syntaxin-mediated vesicle traffic in the soma.
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