Squid giant axon contains neurofilament protein mRNA but does not synthesize neurofilament proteins

Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Cellular and Molecular Neurobiology 37 (2017): 475-486, doi:10.1007/s10571-016-0382-z.When isolated squid giant axons are incubated in radioactive amino acids, abundant newly synthesized proteins are found in the axoplasm. These proteins are translated in the adaxonal Schwann cells and subsequently transferred into the giant axon. The question as to whether any de novo protein synthesis occurs in the giant axon itself is difficult to resolve because the small contribution of the proteins possibly synthesized intra-axonally is not easily distinguished from the large amounts of the proteins being supplied from the Schwann cells. In this paper we reexamine this issue by studying the synthesis of endogenous neurofilament (NF) proteins in the axon. Our laboratory previously showed that NF mRNA and protein is present in the squid giant axon, but not in the surrounding adaxonal glia. Therefore, if the isolated squid axon could be shown to contain newly synthesized NF protein de novo, it could not arise from the adaxonal glia. The results of experiments in this paper show that abundant 3H-labeled NF protein is synthesized in the squid giant fiber lobe containing the giant axon’s neuronal cell bodies, but despite the presence of NF mRNA in the giant axon, no labeled NF protein is detected in the giant axon. This lends support to the Glia-Axon Protein Transfer Hypothesis which posits that the squid giant axon obtains newly synthesized protein by Schwann cell transfer and not through intra-axonal protein synthesis, and further suggests that the NF mRNA in the axon is in a translationally repressed state.This research was supported by the Intramural Research Program of the NIH2017-05-2

Expression of dihydropyridine-sensitive brain calcium channels in the rat central nervous system

AbstractWe have localized dihydropyridine (DHP)-sensitive calcium channels in rat brain by in situ hybridization and immunohistochemistry. The mRNA for the dihydropyridine-sensitive calcium channel α1 subunit (DHPR-B) is prominently localized in neuronal cells in the olfactory bulb, dentate gyrus, hippocampus, arcuate nucleus, paraventricular nucleus, ventromedial nucleus, cerebral cortex, superior colliculus and the cerebellar Purkinje cell layer. Strong expression of DHPR-B mRNA was also found in the pituitary and pineal glands. DHP-sensitive calcium channel α1 subunit distribution has also been examined immunohistochemically with polyclonal antibodies raised against synthetic peptides specific for the DHPR-B α1 subunit protein. The results from immunohistochemistry were in good agreement with those from in situ hybridization. Thus, regional distribution and localization of DHPR-B mRNA and α1 subunit protein in rat brain suggest that this type of DHP-sensitive brain calcium channel may play an important role in excitation-secretion coupling functions in the neuroendocrine system