Expression of flavin-containing monooxygenases in the human brain

Flavin-containing Monooxygenases (FMOs) were found in the human brain basal-ganglia, an area affected by neurodegenerative disorders. Full length radiolabelled cDNA probes encoding each of the five known FMOs were used in northern blot hybridisation. FMO3 and FMO4 mRNAs were detected in thalamus, substantia nigra, subthalamic nucleus and corpus callosum regions. In-situ hybridisation analysis of brain sections from normal and Parkinsons disease individuals was carried out using cRNA FMO3 and FMO4 probes. Both mRNAs were detected in dopaminergic neurons of the substantia nigra and red nucleus, neurons of the subthalamic nucleus, neurons of the thalamus and pyramidal cells of Ammons horn. Neither mRNA was found in the crus cerebre, internal capsule or superior colliculus of mid brain, or the internal capsule, putamen, dentate gyrus of the hippocampus. FMO3 was detected in higher levels than FMO4. Immunocytochemistry confirmed FMO3 is present in the same neuronal types as its mRNA. To confirm expression in human brain (and not other cross-reacting FMO mRNAs), RT-PCR of RNA from the thalamus of human subjects was undertaken. Each of the five known FMO DNA sequences were amplified using specific primers. Neither FMO1 or FMO2 sequences were amplified. The PCR product for FMO3 was of the expected size. Restriction digestion analysis and Southern blotting confirmed FMO3 is expressed in human brain. FMO5 gave a positive result which was an RT-PCR of RNA from human subthalamic nucleus. Due to the species difference in FMO expression it was of interest to see if other primates express FMO3 in brain. Substantia nigra, thalamus, midbrain and central brain regions were dissected from Orang-utan and Gorilla brain and RNA prepared. Each FMO sequence was amplified using RT-PCR reactions. No amplification products were observed for FMO1, FMO2 or FMO5. However, FMO3 amplification products were detected and a faint amplification product for FMO4 was observed