The Mammalian Staufen Protein Localizes to the Somatodendritic Domain of Cultured Hippocampal Neurons: Implications for Its Involvement in mRNA Transport

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Abstract
In hippocampal neurons, certain mRNAs have been found in dendrites (Steward, 1997), and their localization and translation have been implicated in synaptic plasticity (Martin et al., 1997). One attractive candidate to achieve transport of mRNAs into dendrites is Staufen (Stau), a double-stranded RNA-binding protein, which plays a pivotal role in mRNA transport, localization, and translation inDrosophila(St. Johnston, 1995). Using antibodies raised against a peptide located in the RNA-binding domain IIa and a polyclonal antibody raised against a recently cloned human Staufen homolog, we identify a 65 kDa rat homolog in cultured rat hippocampal neurons. In agreement with the exclusive somatodendritic localization of mRNAs in these cells, we find that Staufen is restricted to the same domain. By immunoelectron microscopy, we show enrichment of the mammalian homolog of Stau (mStau) in the vicinity of smooth endoplasmic reticulum and microtubules near synaptic contacts. Finally, the association of the mStau with neuronal mRNAs is suggested by the colocalization with ribonucleoprotein particles specifically in distal dendrites known to contain mRNA, ribosomes, and translation factors (Knowles et al., 1996). These results suggest a role for mStau in the polarized transport and localization of mRNAs in mammalian neurons.