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Abstract:
A common mechanism of cell polarisation is the transport of specific RNAs to distinct intra-cellular compartments, where they are locally translated afterwards. In neurons specific RNAs are dendritically localised, but detailed information is still missing. In Dendrites ribonucleo-protein complexes showing a microtubule-dependent transport and containing the mammalian homolog of the D. melanogaster Staufen protein have been described. The aim of the present study was, to isolate such Staufen-containing complexes biochemically and to characterise them. The cellular distribution of both mammalian homologs Staufen1 and Staufen2 was firstly exa-mined and afterwards the Staufen-containing complexes were biochemically isolated. Both Staufen proteins are present within the cell body and the dendrites of fully polarised neu-rons. In the soma they colocalise with the ER, whereas in dendrites they are present in distinct complexes, distributed in fine particles. Staufen is forming different kinds of soluble high molecular complexes with a molecular weight of 440 kDa to over 2 MDa. The 700 kDa Staufen1 particles are ribonucleoprotein com-plexes, which are disrupted partially, if the RNA is removed. In gel filtration experiments, the complexes cofractionate specifically with two dendritic-localised RNAs, brain cytoplasmic RNA 1 and Calcium/Calmodulin kinase II-alpha, as well as with kinesin heavy chain, a micro-tubule-associated motor protein. Both Staufen proteins are present in different isoforms in rat brain tissue and neurons, which interact partially RNA mediated whith their partners. Whereas Staufen163 and Staufen252 are mainly found in soluble complexes, Staufen155, Staufen259 und Staufen262 are associated with rER and polyribosomes. With the within this thesis established isolation of the Staufen containing ribonucleoprotein complexes from rat brain, it was, for the first time, possible to identify two dendritic-localised RNAs, which could be recognized by Staufen specifically. The present data suggest, that a kinesin motor mediates the transport of the ribonucleoprotein particles.
