טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGolani Adi
SubjectRNA Localization as a Mechanism to Maintain Mitochondria
Availability and Function in Neuronal Axons
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisors Professor Yoav Arava
Professor Emeritus Yeshayahu Talmon


Abstract

Mitochondria are cellular organelles that facilitate diverse cellular functions, most importantly energy production. To perform these functions, mitochondria host hundreds of proteins and enzymes and these must be replenished throughout mitochondria life-time. This process is farther complicated in polarized cells, specifically in neuronal axons, where mitochondria and proteins must travel long distances to reach distal synapses. This geographical gap can be bridged by localized translation - a process by which proteins are synthesized at their target site, enabling rapid and efficient response to local needs.

In this thesis, we explored several aspects of mitochondria function and distribution in axons from a localized translation point of view. First, we addressed the hypothesis that proteins are synthesized near mitochondria by examining two key indicators of local translation - ribosomes and mRNA. Ribosomes were explored by applying a variety of electron microscopy methodologies. Ribosomes were detected at the mitochondria vicinity in both muscle and nerve tissues, yet their physical association to mitochondria was not conclusive. mRNA was examined by a biochemical approach in which mitochondria with associated mRNA were isolated from neuronal axon, and mRNA was subjected to RT-qPCR. This analysis revealed an association of nuclear encoded mitochondrial transcripts to mitochondria.

Since 20-50% of neuronal mitochondria are mobile, we next investigated whether transcripts involved in mitochondria trafficking are locally translated in axons to maintain a stable mitochondria trafficking-protein supply. By applying a plethora of methods, from in vivo imaging to biochemical fractionation, we found that mitochondria-trafficking transcripts, including these encoding Kinesin-1 family motors and Trak adaptor proteins, are highly enriched in axons. Interestingly, the axonal localization of these mRNAs appears to be achieved by their selective stability rather than transport. This suggests a novel mechanism that underlies local synthesis of proteins in neurons. Overall, this work expands our understanding of localized synthesis of mitochondrial proteins in axons, and provides molecular insights into the mechanism of mitochondria distribution in neuronal cells.