Discovering genes with localised expression in the mouse brain: cDNAs specific to the substantia nigra.

Many important phenomena of normal brain physiology and disease are likely to be related to the function of genes expressed in localised regions of the brain. We show that subtracted libraries enriched in clones corresponding to rare mRNAs, which must include genes with very localised and neuron-specific expression, can easily be produced from single-stranded directional cDNA libraries after hybridization to excess photobiotinylated opposite-stranded cDNA (or RNA) from another brain region, followed by the removal of biotinylated molecules. We also demonstrate the use of heterologous probes from anatomically precise small regions of bovine brain to identify cDNA clones that putatively represent mRNAs present at significantly higher levels in a substantia nigra mRNA population enriched for pars compacta mRNA than in the total ventral midbrain or cerebellar mRNA population. Some of these cDNAs may identify genes that play important roles in the specific molecular biology of dopaminergic neurons, including susceptibility to Parkinson's disease.