Local synthesis of nuclear‐encoded mitochondrial proteins in the presynaptic nerve terminal

Abstract

One of the central tenets in neuroscience has been that the protein constituents of distal compartments of the neuron (e.g., the axon and nerve terminal) are synthesized in the nerve cell body and are subsequently transported to their ultimate sites of function. In contrast to this postulate, we have established previously that a heterogeneous population of mRNAs and biologically active polyribosomes exist in the giant axon and presynaptic nerve terminals of the photoreceptor neurons in squid. We report that these mRNA populations contain mRNAs for nuclear-encoded mitochondrial proteins to include: cytochrome oxidase subunit 17, propionyl-CoA carboxylase (EC 6.4.1.3), dihydrolipoamide dehydrogenase (EC 1.8.1.4), and coenzyme Q subunit 7. The mRNA for heat shock protein 70, a chaperone protein known to be involved in the import of proteins into mitochondria, has also been identified. Electrophoretic gel analysis of newly synthesized proteins in the synaptosomal fraction isolated from the squid optic lobe revealed that the large presynaptic terminals of the photoreceptor neuron contain a cytoplasmic protein synthetic system. Importantly, a significant amount of the cycloheximide resistant proteins locally synthesized in the terminal becomes associated with mitochondria. PCR analysis of RNA from synaptosomal polysomes establishes that COX17 and CoQ7 mRNAs are being actively translated. Taken together, these findings indicate that proteins required for the maintenance of mitochondrial function are synthesized locally in the presynaptic nerve terminal, and call attention to the intimacy of the relationship between the terminal and its energy generating system. J. Neurosci. Res. 64:447-453, 2001. Published 2001 Wiley-Liss, Inc.

Local Gene Expression in Axons and Nerve Endings: The Glia-Neuron Unit

“…The low level of contaminating structures was confirmed by light and EM autoradiographic analyses, which also demonstrated the nearly exclusive localization of newly synthesized proteins in large synaptosomes (58). Polysomes purified from optic lobe synaptosomes incubated with [ 35 S]methionine were shown to contain nascent peptide chains (57), and to be free from microsomal polysomes (110). Polysomes were likewise identified in the large optic lobe synaptosomes using ESI (Fig.…”

“…RT-PCR analyses of synaptosomal polysomes have led to the identification of mRNAs coding for cytoskeletal and ribosomal proteins, translation factors and, most notably, mitochondrial proteins encoded by nuclear DNA (110,111). The association of these mRNAs with purified polysomes indicates that the corresponding proteins are synthesized in presynaptic synaptosomes.…”

Differential Transport and Local Translation of Cytoskeletal, Injury-Response, and Neurodegeneration Protein mRNAs in Axons

“…Localized synthesis of HSP70 has been shown in presynaptic nerve terminals from squid optic lobe (Gioio et al, 2001;Jimenez et al, 2002), and the mRNA of Hsc70, a constitutively expressed HSP70 family member, has been detected in dendrites (Foster and Brown, 1996). Localized synthesis of other HSPs has not been reported previously.…”

The axonal transport of mitochondria

“…However, almost all the genes that encode mitochondrial proteins reside in the nuclear genome within the cell body, so full biogenesis in the axon would require anterograde axonal transport of hundreds of different mitochondrial proteins, or their mRNAs. Axoplasm has a modest translation capacity (Lee and Hollenbeck, 2003) and some mitochondrial protein synthesis can occur there (Gioio et al, 2001;Martin et al, 1998;Sotelo-Silveira et al, 2006). Axonal mRNA microarray analysis and quantitative PCR have shown that axons can contain many mitochondrial mRNAs, some at concentrations as high as 10% of their levels measured in the cell body (Taylor et al, 2009).…”