TYROSINASE MESSENGER-RNA IS EXPRESSED IN HUMAN SUBSTANTIA-NIGRA

Dopamine acts, under appropriate conditions, as a selective neurotoxin . This toxicity is attributed to the autoxidation of the neurotransmit ter into a reactive quinone that covalently modifies cellular macromol ecules (i.e. proteins and nucleic acids). The oxidation of the catecho lamine to a quinone is greatly accelerated by the enzyme tyrosinase. T here is controversy, however, as to whether or not tyrosinase is expre ssed in human brain. In the present study, RT-PCR was utilized to demo nstrate the presence of tyrosinase mRNA in post-mortem human brain tis sues. Using gene-specific amplification primers, specific tyrosinase a mplicons were detected following analysis of RNA from substantia nigra of four individuals. Analysis of cerebellar RNA from the same individ uals produced no amplification products. Control reactions performed i n the absence of reverse transcriptase failed to generate PCR products for any tissue tested. Three amplicons were subjected to direct DNA s equencing and all proved to be identical with tyrosinase sequences, th us 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 tyros inase-like activity and immunoreactive protein in the brain. This enzy me could be central to dopamine neurotoxicity as well as contribute to the neurodegeneration associated with Parkinson's disease.