Smaug, a novel RNA binding protein and its role in postranscriptional regulation in the postsynapsis

MV BAEZ; GL BOCCACCIO

Iguazú, Argentina

Congreso; XL SAIB; 2004

Cytoplasmic events contribute to the fine-tuning of gene expression. These mechanisms depend on several families of RNA binding proteins (RBPs) that are less known than transcription factors, in spite of their comparable importance in regulating gene expression. SAM-containing RBPs constitute a novel family that function as post-transcriptional regulators. The SAM domain in these proteins binds a sequence motif known as SRE (Smaug Recognition Element). Drosophila Smaug is involved in translational repression of maternal mRNAs, contributing to define embryo polarity. In contrast, the yeast member, Vts1, stimulates degradation of SRE-containing messengers. Two homologous genes are present in the mammalian genome. Here we show that one of the Smaug homologue (mSmaug1) is expressed in the CNS and is abundant in synaptoneurosomes, where translation is tightly regulated. Biochemical analysis indicated that mSmaug1 forms small RNPs, and is absent from polysomes. When expressed in non-neural cell lines, Smaug1 forms cytoplasmic granules that contain polyA+ mRNAs. Smaug1 granules are in dynamic equilibrium with polysomes and can be converted into stress granules upon induction of cellular stress. Our results suggest a role for mammalian Smaug in translation regulation at post-synaptic sites.