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Volume 17, Number 20, Issue of October 15, 1997 pp. 7694-7702
Copyright ©1997 Society for Neuroscience

Active Polysomes Are Present in the Large Presynaptic Endings of the Synaptosomal Fraction from Squid Brain

Received May 27, 1997; revised July 24, 1997; accepted August 6, 1997.

M. Crispino¹, B. B. Kaplan², R. Martin³, J. Alvarez⁴, J. T. Chun², J. C. Benech⁵, and A. Giuditta¹

¹ Department of General and Environmental Physiology, University of Naples "Federico II," 80134 Naples, Italy, ² Western Psychiatric Institute and Clinic, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania 15213-2593, ³ Electron Microscopy Section, University of Ulm, D-89069 Ulm, Germany, ⁴ Facultad de Ciencias Biologicas, Pontificia Universidad Catolica, Santiago, Chile, and ⁵  Instituto de Investigaciones Biologicas "Clemente Estable," Montevideo 11600, Uruguay

Previous data have suggested that the large nerve terminals present in the synaptosomal fraction from squid optic lobe are capable of protein synthesis (,). We have further examined this issue by comparing the translation products of synaptosomal and microsomal polysomes. Both preparations programmed an active process of translation, which was completely abolished by their previous treatment with EDTA. After immunoabsorption of the newly synthesized neurofilament (NF) proteins, the labeling ratio of the 60 and 70 kDa NF proteins was found to differ, in agreement with comparable differences obtained with intact synaptosomes. These observations indicate that the set of mRNAs translated by synaptosomes differs from that translated by nerve cell bodies. Hence, because NF proteins are neuron-specific, they support the view that the active synaptosomal polysomes are mostly localized in the large nerve terminals that represent the most abundant neuronal component of the fraction. This hypothesis was confirmed (1) by electron spectroscopic data demonstrating the presence of ribosomes and polysomes within the large nerve endings of the synaptosomal fraction, as well as in the carrot-like nerve endings of the retinal photoreceptors that constitute the only large terminals in the optic lobe, and (2) by light and high resolution autoradiography of synaptosomal samples incubated with [³H]leucine, showing that most labeled proteins are associated with the large nerve endings. This response was abolished by cycloheximide. Taken together, the data provide the first unequivocal demonstration that presynaptic nerve terminals are capable of protein synthesis.

Key words: nerve terminals; synaptosomes; protein synthesis; polysomes; neurofilament proteins; squid

This article has been cited by other articles:

				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]

				A. Giuditta, M. Eyman, and B. B. Kaplan Gene Expression in the Squid Giant Axon: Neurotransmitter Modulation of RNA Transfer From Periaxonal Glia to the Axon Biol. Bull., October 1, 2002; 203(2): 189 - 190. [Full Text] [PDF]

				I. A. Muslimov, M. Titmus, E. Koenig, and H. Tiedge Transport of Neuronal BC1 RNA in Mauthner Axons J. Neurosci., June 1, 2002; 22(11): 4293 - 4301. [Abstract] [Full Text] [PDF]

				R Martin, B Vaida, R Bleher, M Crispino, and A Giuditta Protein synthesizing units in presynaptic and postsynaptic domains of squid neurons J. Cell Sci., January 11, 1998; 111(21): 3157 - 3166. [Abstract] [PDF]

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