Are the enzymes of the catecholamine biosynthetic pathway locally synthesized in the axon?

Thursday, October 11, 2012 — Poster Session IV
2:00 p.m. – 4:00 p.m.	Natcher Conference Center, Building 45	NIMH	NEURO/BEHAV/SENSYS-5

* FARE Award Winner

Authors

• N.M. Gervasi
• S.N. Vohra
• M.A. MacGibeny
• A.N. Kar
• A.E. Gioio
• A.J. Makusky
• R.L. Olano
• S.P. Markey
• B.B. Kaplan

Abstract

Recent studies have shown that axons contain a heterogeneous population of mRNA, and that local protein synthesis is important for axonal function. In neurons, the enzymes involved in the synthesis of catecholamines have been reported to be synthesized in the cell soma and shipped to the axon through anterograde axonal transport. In this study, we tested the hypothesis that these enzymes can also be synthesized at the axonal level. To isolate pure axonal mRNA and protein, we cultured rat superior cervical ganglion (SCG) neurons in compartmentalized Campenot chambers. RT-PCR and fluorescence in situ hybridization analyses showed that tyrosine hydroxylase (TH) mRNA is present in axons. A significant increase in the relative abundance of TH mRNA was observed when axons were grown under conditions that led to an increase in the number of synaptic terminals. Western blot and mass spectrometric analyses of axonally synthesized proteins showed that TH protein is locally synthesized in SCG axons. Preliminary data on DOPA decarboxylase (DDC) and dopamine beta hydroxylase (DBH) suggest that they may also be locally synthesized in axons. Taken together, these results show that axonal TH mRNA is functional and suggest that multiple enzymes involved in catecholamine synthesis may be axonally synthesized.

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