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Local Synthesis of Presynaptic RNA in Squid Optic Lobe Slices

¹ University of Naples "Federico II", Naples, Italy
² NIMH, NIH, Bethesda, Maryland
³ SISSA, Trieste, Italy

The use of squid model systems has greatly contributed to the demonstration that active systems of protein synthesis are present in axons and nerve terminals. Furthermore, experiments with isolated or perfused giant axons have shown that axoplasmic RNA may originate from periaxonal glial cells, thus confirming the concept that a local system of gene expression is endowed to axons. We are now presenting evidence that local RNA synthesis may also concern the large presynaptic terminals of retinal photoreceptors. These terminals contain conspicuous aggregates of polysomes and are responsible for essentially all the protein synthetic activity of optic lobe synaptosomes. In view of the retinal location of photoreceptor cell bodies, we decided to prepare synaptosomes from optic lobe slices incubated in artificial seawater containing [³H]uridine. Under these conditions, any radiolabeled synaptosomal RNA could only originate from local sources. The radiolabeled TCA-precipitable product obtained from the incubated slices was sensitive to alkaline and RNase degradation, and its synthesis was inhibited by actinomycin D. Our data indicated that newly-synthesized RNA was present in the synaptosomal fraction in higher amounts than in the microsomal-cytosolic fraction. Its synaptosomal association was confirmed by experiments in which the incubated slices were exposed to a hypotonic medium that selectively disrupts synaptosomes. Under these conditions, essentially all radiolabeled RNA disappeared from the synaptosomal fraction. In vitro analyses supported the expected disruption of synaptosomes by showing a massive loss of synaptosomal protein synthesis induced by the hypotonic treatment. Sedimentation analyses on sucrose density gradients indicated that newly synthesized synaptosomal RNA is largely localized in light regions of the gradient, while sizable amounts sediment in gradient regions marked by ribosomal particles. Our data further support the view that axons and nerve terminals are endowed with a local gene expression system requiring the strict cooperation of glial cells.

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				A. Giuditta, J. Tai Chun, M. Eyman, C. Cefaliello, A. P. Bruno, and M. Crispino Local Gene Expression in Axons and Nerve Endings: The Glia-Neuron Unit Physiol Rev, April 1, 2008; 88(2): 515 - 555. [Abstract] [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Giuditta, A. Articles by De Stefano, R. Search for Related Content PubMed Articles by Giuditta, A. Articles by De Stefano, R.