Novel Functions for Neuronal RNA Processing Bodies in the Control of Axon Terminal Growth in Drosophila Melanogaster

In this thesis we first characterized neuronal functions for HPat/Pat1, a core component of RNA processing bodies or P bodies . We show that hpat mutants exhibit a strong synaptic hyperplasia at the developing and acutely stimulated Drosophila larval neuromuscular junctions (NMJs). The synaptic defects observed in hpat mutants are associated with rearrangement of the axonal microtubule cytoskeleton suggesting that HPat negatively regulates presynaptic microtubule-based growth during NMJ development. Interestingly, we also found that both pre-and postsynaptic HPat expression controlled rapid axon terminal growth in response to acute spaced synaptic stimulation. We also demonstrate that HPat interacts genetically with the catalytic subunit of the deadenylase complex (twin/CCR4) and the miRNA pathway (Argonaute 1) to control bouton formation. We propose that HPat is required to target mRNAs involved in the control of microtubule architecture and synaptic terminal growth for repression, presumably in P bodies, via both general and miRNA-mediated mechanisms. Next, we investigated whether HPat interacts with the Drosophila Fragile X Mental Retardation Protein (dFMR1), to regulate neuronal structure in a Drosophila melanogaster fragile X model. First, we demonstrated that HPat interacts biochemically with dFMRP in an RNAse independent manner. Second, we show that HPat genetically interacts with dFmr1 in the Drosophila eye although the phenotype is weak, however we did not see any interaction of hpat and dfmr1 to control synaptic structure at the NMJ. Finally, we screened additional P body components that might have function in FMRP mediated translation regulation. Interestingly, a luciferase-based translational repression tethering assays in Drosophila Schneider 2 (S2) cells showed the function of GW182 in FMRP-mediated translation regulation