Tyrosinase mRNA is expressed in human substantia nigra

Dopamine acts, under appropriate conditions, as a selective neurotoxin. This toxicity is attributed to the autoxidation of the neurotransmitter into a reactive quinone that covalently modifies cellular macromolecules (i.e. proteins and nucleic acids). The oxidation of the catecholamine to a quinone is greatly accelerated by the enzyme tyrosinase. There is controversy, however, as to whether or not tyrosinase is expressed in human brain. In the present study, RT-PCR was utilized to demonstrate the presence of tyrosinase mRNA in post-mortem human brain tissues. Using gene-specific amplification primers, specific tyrosinase amplicons were detected following analysis of RNA from substantia nigra of four individuals. Analysis of cerebellar RNA from the same individuals produced no amplification products. Control reactions performed in the absence of reverse transcriptase failed to generate PCR products for any tissue tested. Three amplicons were subjected to direct DNA sequencing and all proved to be identical with tyrosinase sequences, thus obviating the possibility of amplification of a related gene. It is clear, therefore, that the tyrosinase gene is expressed in the human substantia nigra, lending support to previous studies describing tyrosinase-like activity and immunoreactive protein in the brain. This enzyme could be central to dopamine neurotoxicity as well as contribute to the neurodegeneration associated with Parkinson's disease.