Constitutive overexpression of the transcription factor Nurr1 in pluripotent embryonic stem (ES) cells enhances the development of tyrosine hydroxylase (TH) pos. midbrain dopaminergic (DA) neurons in vitro (S. Chung, SFN 2001 mtg. abstr.#14452). To determine the effects of Nurr1 expression at different stages of cell differentiation, we generated inducible Nurr1-expressing J1-rtTA ES cell clones, which express the reverse transactivator (rtTA) of the Tet-System from the ROSA26 locus and characterized them in in vitro differentitation assays. We found that the rtTA-recombinant J1 cells developed into fewer neurons including the TH+ subtype when compared to naïve J1 ES cells. However, the pattern of marker gene expression specific for early CNS (Otx1, Otx2, GBX2, En-1), germlayers (CK-17, GATA4, HNF-4, Brachyury) and midbrain DA (Pitx3, AADC, Calbindin, DAT) were similar between the J1 ES cells analyzed. In this system, the induction of Nurr1 expression at different stages during cell differentiation led to ...