Messenger RNA is Present in the Axoplasm of Squid Giant Axons
Using a translation assay it has been shown that the axoplasm extruded from the squid giant axon contains mRNA. The translation pattern of axoplasmic mRNA, as resolved on SDS-polyacrylamide gels, is different from the translation patterns of stellate nerve and giant fibre lobe (nerve cell bodies) RNA, although many protein bands are the same in axoplasm and the nerve cell bodies, as might be expected. Comparison of the axoplasmic proteins reveals a significant degree of correspondence. Axoplasmic mRNA is associated with the “microsomal” fraction of the axoplasm. Using reverse transcriptase, axoplasmic RNA can be transcribed into cDNA. The results of hybridization kinetics of axoplasmic cDNA with its template RNA show that the diversity of axo- plasmic RNA is considerable higher than indicated by the translation assays. On the other hand, the complexity of axoplasmic RNA is about 30-fold lower than that of total giant fibre lobe RNA and about 150-fold lower than that of optic lobe polysomal poly(A)+ mRNA. The latter results strongly supports the view that the high complexity of brain mRNA reflects the marked cellular and subcellular heterogeneity of the tissue.
KeywordsTranslation Product Optic Lobe Nerve Cell Body Giant Axon Rabbit Reticulocyte Lysate
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