Cox7c mRNA co-transport with mitochondria along axons via coding-region dependent mechanism
2Sackler Faculty of Medicine, Tel Aviv University, Israel
Neurons are cells with high energetic demands. As such, they are enriched in mitochondria. The mitochondria contain hundreds of proteins, most of them derived from nucleus-transcribed mRNAs, and need to be transported to distant mitochondria. It is hypothesized that these mitochondria rely on local translation of nuclear-encoded mRNAs for their maintenance. Accordingly, mRNAs, ribosomes, and translation factors need to be transported to neuronal extremities to allow such local synthesis. The transport mechanisms of these elements are largely unknown. We propose that transport of these elements occurs through association with moving mitochondria.
Here we show by fractionation analysis that mRNAs of nuclear-encoded mitochondrial genes are associated with mitochondria, in both a neural-like cell line and motor neuron axons. Furthermore, by applying the MS2 mRNA visualization system we show that one of these mRNAs, Cox7c, is not only associated but also co-transported with mitochondria along neurites. We examined the importance of different Cox7c mRNA regions and found that the coding sequence, rather than the 3’UTR, had a greater contribution to co-localization and co-transport. Specifically, the predicted N-terminal 15 amino acids mitochondrial targeting sequence (MTS) is important for localization. These results reveal that mRNAs encoding mitochondrial proteins are associated and transported with mitochondria in a manner that might involve translation.
Next, to identify additional factors that may be involved in this process, we set up an mRNA-Protein isolation protocol based on the MS2 system. This allows us to further investigate the role of Cox7c mRNA-associated proteins in its transport.