Staufen 1 and 2 form distinct RNA Granules in mature oligodendrocyte processes

THOMAS MG; MARTINEZ TOSAR LJ; BULLOJ, A; KINDLER, S.; BOCCACCIO, GL

San Francisco USA

Congreso; ASCB -American Society for Cell Biology 43rdAnnual Meeting; 2003

American Society for Cell Biology 43rdAnnual Meeting

 “Staufen 1 and 2 form distinct RNA Granules in mature oligodendrocyte processes” Cytoplasmic mRNA granules are considered to be the functional unit for a variety of cellular events such as mRNA transport, silencing, activation and degradation. The double-stranded RNA-binding protein Staufen emerges as a quite ubiquitous RNA granule-forming protein. It is involved in asymmetric distribution of mRNAs in Drosophila developing CNS and oocytes. In vertebrates, two highly homologous genes with alternative splicing transcripts exist, Staufen1 and 2. We cloned a minor Staufen1 splicing variant encoding a polypeptide with a novel C-terminal domain. We raised specific antibodies against Staufen1 and 2 and showed that both proteins form granules in myelinating oligodendrocyte processes. The interaction with cytoskeleton filaments, RER vesicles and components of the translational machinery was analyzed by imaging and biochemical approaches. Staufen1 has two nuclear localization signals and showed nuclear-cytoplasmic localization. In transiently transfected cells nuclear export of the protein appears to be CRM-1 and exportin 5 independent. We evaluated the colocalization of Staufen with the prototype targeted MBP mRNAs at the myelinating cell processes. The majority of MBP mRNA granules (80%) were not positive for Staufen molecules. In addition, Staufen1 and 2 do not colocalize, suggesting the existence of different kinds of RNA granules at the distal processes. Sucrose density gradient analysis showed that Staufen1 comigrates mostly with polysomes. Accordingly, upon treatment of cultured oligodendrocytes with puromycin, Staufen1 granules partially coalesced in larger structures indicating its association to actively translating polysomes. Our results suggest that both Staufen homologues may participate in mRNA transport, anchoring or translation in mature oligodendrocyte processes, having redundant or specific functions. RNA interference experiments against the distinct Staufen molecules are being carried out to address these topics.