Dynamics of tyrosine hydroxylase promoter activity during midbrain dopaminergic neuron development

Dopamine (DA)-producing neurons in the ventral midbrain are generated from a specified neuronal lineage and form selective axonal pathways that mediate multiple CNS functions. Expression of the gene encoding tyrosine hydroxylase (TH), which is a key enzyme of catecholamine biosynthesis, is regulated during the development of midbrain DA neurons. In the present study, we report the developmental regulation and cell type specificity of TH gene promoter in the ventral midbrain by using a green fluorescent protein (GFP) reporter system. Transgenic mice were generated that express GFP in the majority of midbrain DA neurons under the control of the 9-kb upstream region of the rat TH gene. At an early embryonic stage, GFP expression was induced in the developing DA neurons, and the expression was then markedly down-regulated at later embryonic stages. However, the expression was reactivated and approached the adult levels during early post-natal development. These developmental changes in GFP expression patterns suggest the presence of multistep regulatory mechanisms for TH gene expression during DA neuron development. The TH promoter appears to possess transcriptional elements at least necessary for the induction of TH expression at the early embryonic stage and its reactivation during the post-natal development.