Double Stranded RNA-Binding Protein Staufen and Cytoplasmic RNA Transport in Oligodendrocytes

MARTINEZ TOSAR LJ; THOMAS, MG; BOCCACCIO, GL

Viena, Austria

Congreso; (th Annual Meeting of the RNA Society; 2003

RNA Society

Double Stranded RNA-Binding Protein Staufen and Cytoplasmic RNA Transport in Oligodendrocytes L.J.Martinez Tosar, M.G.Thomas and G.L.Boccaccio. Fundación Instituto Leloir; IIB FCEyN-University of Buenos Aires, IIB-BA-CONICET Buenos Aires, Argentina. RNA sorting is a widespread molecular strategy involved in a number of phenomena including cell differentiation, synaptic plasticity, and definition of subcellular compartments and cell polarity. The double-stranded RNA-binding protein Staufen was initially described in maternal RNA sorting in Drosophila and recently found to be expressed in many other organisms, including rodents and humans. We have cloned several alternatively spliced Staufen isoforms from mouse brain. One of these variants encodes for a modified C-terminal domain of unknown function. Analysis of Staufen sequence predicts two nuclear localization signals putatively involved in nucleo-cytoplasmic shuttling of ribonucleoparticle complexes. Accordingly, we observed Staufen localization to the nucleus -and presumably nucleolus- in a number of transfected cells. Nuclear export of the protein appears to be CRM-1 and exportin 5 independent. In oligodendrocytes, mRNAs encoding Myelin Basic Protein are localized to the cellular processes to structure the myelin sheath. Immunostaining experiments show Staufen granules located at the cell body and myelinating processes, and a fraction of them colocalizes with MBP mRNA. Colocalization with ribosomes is also evident. Granule distribution upon puromycin treatment suggests that Staufen is associated to translationally active ribosomes in the cell body, while peripheral granules are insensitive to the drug. Sucrose density gradient analysis shows two Staufen containing fractions likely related to the two types of granules observed in puromycin treated cells. siRNA-mediated inhibition of Staufen expression followed by immunostaining and western blot analysis suggests that the protein is remarkably stable.