Dissecting How SYNJ2 Facilitates mRNA Targeting and Translation at Neuronal Mitochondria

ABSTRACT Neurons consume a disproportionate amount of energy compared to other cell types. This heightened OXPHOS activity helps support membrane polarization and synaptic transmission. Consequently, a single neuron must maintain a mitochondrial network spread throughout the neuropil with spatiotemporal precision. One molecular mechanism to maintain local mitochondrial health is through trafficking of PINK1 mRNA. PINK1, a Ser/Thr kinase mutated in familial forms of Parkinson’s disease, accumulates on depolarized mitochondria to initiate mitophagy. The Schwarz lab has recently demonstrated that PINK1 mRNA is co-trafficked with neuronal mitochondria, including in axons. Synaptojanin2 (SYNJ2) was identified as the key RNA-binding protein (RBP) that anchors PINK1 mRNA to the outer mitochondrial membrane in neurons. Our lab has subsequently created model systems to dissect phenotypes solely dependent on the RNA-binding function of SYNJ2. Specifically, three point mutations in the RNA recognition motif of SYNJ2, which abolishes SYNJ2-mRNA interaction, have been introduced in a mouse model and human-derived iPSC neurons. My proposed fellowship research will harness these model systems to investigate the biology behind local mRNA trafficking and translation. In Specific Aim 1, I will determine cis-regulatory elements that target mRNA to mitochondria in a SYNJ2-dependent manner. I will use live mRNA imaging, RNA structure prediction, and targeted deletion of candidate sequences to achieve this. Then, in Specific Aim 2, I will determine if SYNJ2 and/or the outer mitochondrial proteome is required for local translation of PINK1 mRNA. To accomplish this, I will artificially tether PINK1 transcripts to mitochondria using viral stem loops, overriding the need for SYNJ2 trafficking. Additionally, I will mistarget PINK1 transcripts to lysosomes. Broadly, my proposed research will elucidate molecular mechanisms underlying decentralized organelle biology in neurons, with important implications for neurodegenerative disease.