The isolation, from electromotor neurone perikarya, of messenger RNAs coding for synaptic proteins

Poly(A)-containing mRNA was isolated from the electric lobe, cerebellum and forebrain of Torpedo marmorata and from cholinergic electromotor perikarya isolated from the electric lobe. All the mRNA preparations were translated by a cell-free protein-synthesizing system from rabbit reticulocytes; no brain-specific factors were required. The highest stimulation rate was found with the perikaryal mRNA suggesting that this purely neuronal mRNA is a preferred template in the protein-synthesis system; the molecular basis of this phenomenon remains to be elucidated. The translation products of the perikaryal mRNA were analysed by two-dimensional gel electrophoresis and compared with the proteins of synaptosomes derived from the electromotor nerve terminals. The majority of the synaptosomal proteins comigrated with synthesized products. More than 100 synthesized proteins were detected as individual spots in the gel pattern, among them actin, subunits of neurofilamentous proteins and a protein considered to be a specific component of electromotor synaptic vesicles. Identities were confirmed in some cases by immunochemical methods. The results suggest that protein synthesis in the perikaryon of the electromotor neurone is largely directed to the production of proteins needed to maintain synaptic integrity. A comparison of the translation products of mRNA derived from the highly cholinergic electric lobe and a brain region, the cerebellum, which is non-cholinergic, revealed, as expected, some common translation products and others which appeared to be specific for the brain regions concerned. This approach may lead to the identification of protein specific for neurones of different transmitter types.