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MicroRNA-338 regulates local cytochrome c oxidase IV mRNA levels and oxidative phosphorylation in the axons of sympathetic neurons.

ABSTRACT: MicroRNAs (miRs) are evolutionarily conserved, noncoding RNA molecules of approximately 21 nt that regulate the expression of genes that are involved in various biological processes, such as cell proliferation and differentiation. Previously, we reported the presence of a heterogeneous population of mRNAs present in the axons and nerve terminals of primary sympathetic neurons to include the nuclear-encoded mitochondrial mRNA coding for COXIV. Sequence analysis of the 3'UTR of this mRNA revealed the presence of a putative binding site for miR-338, a brain-specific microRNA. Transfection of precursor miR-338 into the axons of primary sympathetic neurons decreases COXIV mRNA and protein levels and results in a decrease in mitochondrial activity, as measured by the reduction of ATP levels. Conversely, the transfection of synthetic anti-miR oligonucleotides that inhibit miR-338 increases COXIV levels, and results in a significant increase in oxidative phosphorylation and also norepinephrine uptake in the axons. Our results point to a molecular mechanism by which this microRNA participates in the regulation of axonal respiration and function by modulating the levels of COXIV, a protein which plays a key role in the assembly of the mitochondrial cytochrome c oxidase complex IV.

SUBMITTER: Aschrafi A

PROVIDER: S-EPMC3496265 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The subcellular localization of specific mRNAs is an evolutionary conserved mechanism that underlies the establishment of cellular polarity and specialized cell functions. In neurons, mRNA trafficking and local protein translation in dendrites provides an important mechanism that mediates synaptic development and plasticity. The significance of mRNA targeting and protein synthesis in axons, however, is still unclear. Only a small number of transcripts have been identified in axons to date, and their contribution to axon growth and neuronal survival remains largely unknown. Here, we report the results of a novel screen that allowed the separate identification of mRNAs localized in cell bodies and in axons of developing neurons. Using compartmentalized cultures of sympathetic neurons and Sequential Analysis of Gene Expression (SAGE), the screen identified more than 200 axonal mRNAs, including ones that encode cytoskeletal proteins and proteins that function in neural development and signal transduction. Importantly, several classes of transcripts were selectively enriched in axons, indicating that an active process drives the targeting of specific mRNAs from the cell bodies to the axons. This study is the first comprehensive and unbiased analysis of mRNA localization in subcellular domains of any neuronal cell type. We used compartmentalized chambers to culture neonatal rat sympathetic neurons (Campenot, 1977). In these cultures, the cell bodies are separated from the distal axons by a 1 mm wide Teflon divider, which maintains the cell bodies and axon terminals in separate fluid compartments. Primary rat sympathetic neurons are especially suitable for compartmentalized culture because they can be grown as a highly homogeneous population without glial cells. Neurons were seeded in the central compartment with nerve growth factor (NGF), and after a few days, the NGF was lowered in this compartment and supplied only to the peripheral compartment to stimulate axon growth. The anti-mitotic agent cytosine arabinoside C (Ara-C) was added to both compartments to remove non-neuronal cells. mRNA was then isolated after 12 days in culture (DIV) from cell body or axon compartments. As the initial mRNA content in axons was not sufficient to perform the SAGE analysis, both axon and cell body mRNAs were subjected to two rounds of linear amplification to obtain antisense RNA (aRNA). The amplified aRNA was then reverse transcribed and second strand synthesis was performed to proceed with the SAGE assay using the LongSAGE kit (Invitrogen) according to the manufacturer’s protocol.

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MicroRNA-338 regulates local cytochrome c oxidase IV mRNA levels and oxidative phosphorylation in the axons of sympathetic neurons.

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