RNA-silencing foci regulate local translation at the neuronal synapse

THOMAS MG; PASCUAL M; HABIF M; MASCHI D; LUCHELLI L; BAEZ MV; BOCCACCIO GL

Kyoto, Japon

Congreso; RNA Society; 2011

Smaug is an mRNA repressor that defines a novel family of RNA-binding proteins. Both Drosophila Smaug and mammalian Smaug 1 repress the translation of reporter mRNAs carrying specific motifs termed Smaug-Recognition-Element (SRE) (Baez and Boccaccio, JBC 2005). Here we show that Smaug1 is restricted to mature neurons, and that Smaug1 knockdown affects synaptogenesis, provokes the presence of immature synapses, and impairs the response to synaptic stimulation. Smaug 1 forms silencing foci (S-foci) located at post-synaptic sites of cultured hippocampal neurons. S-foci are distinct from Stress Granules (SGs) and P-bodies (PBs), and from other neuronal RNA granules hitherto described. Synaptic S-foci are usually static under basal conditions, and highly dynamic upon neuron stimulation. NMDA receptor activation and PI3K signalling induce S-foci dissolution, thus allowing mRNA release and translation. Other neuronal RNA granules, such as those containing Fragile X Mental Retardation Protein (FMRP), do not respond to NMDA, and dissolve upon the activation of distinct synaptic receptors. Finally, we found that Smaug 1 aggregation is independent of its activity as mRNA repressor, and requires a conserved region at the N-terminus. S-foci are in contact with PBs. RNAi strategies against key PB components indicate that Smaug 1 aggregation does not require PB integrity. In contrast, Smaug1-mediated mRNA repression induces PB assembly. This work suggests an important role for a novel translational regulation pathway that involves Smaug 1 and PBs on mammalian synaptogenesis. Furthermore, it highlights the selective use of distinct mRNA silencing foci for the fine-tuning of local protein synthesis at the synapse.