15 June 2011 00:00 hrs.
Subcellular Compartmentation of Neuronal Protein Synthesis: New Insights into the Biology of the Neuron.

Dr. Barry Kaplan, Section on Molecular Neurobiology, National Institute of Mental Health, National Institutes of Health, bethesda, USA


Prof. Hans van Bokhoven, dept. of Human Genetics, RUNMC and Dr. Armaz Aschrafi, Donders Institute Nijmegen

15-06-2011 00:00:00Europe/AmsterdamSubcellular Compartmentation of Neuronal Protein Synthesis: New Insights into the Biology of the Neuron.

Remarks / more information:

Barry-KaplanBackground: It is now well recognized that the axon contains a heterogeneous population of nuclear-encoded mitochondrial mRNAs and a local protein synthetic system. Several of these mRNAs code for proteins which play a key role in oxidative phosphorylation, such as Cytochrome c Oxidase Subunit Four (COXIV) and ATP synthase (ATP5G1). In this talk, an overview is provided of the results derived from the investigation into the regulation of the axonal expression of these mRNAs by microRNA (miRNA) and the affects of the modulation of the local synthesis of these nuclear-encoded mitochondrial proteins on axonal function and growth.

Methods: All experiments were conducted using primary sympathetic neurons obtained from superior cervical ganglion of 3 d-old rats. Neurons were cultured in Campenot chambers in serum-free media containing NGF. RNA and protein levels were assessed in SCG neurons after 3-7 DIV, using qRT-PCR and western analysis, respectively.

Results: Sequence analysis of the 3'UTRs of both these mRNAs revealed a nucleotide stem-loop structure which contained a targeting motif (i.e.,cis-acting regulatory element) for miRNA-338, a brain-specific miRNA. Transfection of the precursor of miRNA-338 directly into the axons of SCG neurons resulted in a marked decrease in the levels of these mRNAs and their cognate proteins, which were followed by decreases in local ATP levels, elevation in axonal ROS levels, and attenuation in the rate of axonal growth. Conversely, the introduction into the axon of synthetic oligonucleotides that inhibit miRNA-338 binding to the 3'UTR increased the relative abundance of these mRNAs, elevated local ATP levels, decreased ROS production, and enhanced the rate of axonal growth. Similar to the findings obtain from the miRNA studies, knock-down of axonal COXIV and ATP synthase mRNAs levels using siRNA transfection methodology also diminished local energy metabolism and inhibited the growth of the axon.

Conclusion: These findings establish that the local expression of nuclear-encoded mitochondrial mRNAs such as COXIV and ATP5G1 can be regulated by miRNAs and that the miRNA-mediated modulation of their local translation can significantly alter the metabolic activity of the axon and its growth.

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