Role of Nurr1 and Ret in inducing rat embryonic neural precursors to dopaminergic neurons.

BACKGROUND Nurr1, a member of the nuclear receptor superfamily of transcription factors, is highly expressed in midbrain dopaminergic (DA) neurons. Ret is a member of the receptor tyrosine kinase (RTK) superfamily and a critical signal transducing subunit of receptors for glial cell line-derived neurotrophic factor (GDNF). Both Nurr1 and Ret play important roles in the development of DA neurons. PURPOSE To investigate possible correlation between Nurr1 and Ret on inducing expression of tyrosine hydroxylase (TH) in neural precursor cells. METHODS Neural precursors isolated from rat embryonic mesencephalon (E13.5d) were transfected with vectors containing Nurr1 or Ret and treated with 9-cis-retinoic acid (RA) and/or GDNF for 3 days. RT-PCR and immunocytochemistry was used to test the expression of Nurr1 and Ret and the TH positive cells. RESULTS The number of TH positive cells was increased from 1.53 +/- 0.12 to 3.83 +/- 0.56% after the cells were transfected with Nurr1. Increased endogenous Nurr1 by RA lead to 1.8 times (2.86 +/- 0.32% versus 1.53 +/- 0.12% in the controls) increase in TH positive cells. A double inducing effect by both endogenous and exogenous Nurr1 on the expression of TH was observed by 3.3 times increase in the positive cells (from 5.03 +/- 0.76 to 1.53 +/- 0.12% in control). Ret expression was induced by overexpression of Nurr1. Overexpressed Ret had no inducing effect on the expression of Nurr1 and the number of TH positive cells. The gene of dopamine transporter (DAT) was clearly induced in the cells transfected with Ret. CONCLUSION Nurr1, required for the expression of Ret, had inducing effect on TH positive cells, and Ret may promote maturation of DA neuron by up-regulating DAT expression through its ligand. As a cooperator, Ret seems to work together with Nurr1 in the development of DA neurons.