Whereas removal of mitogens from the culture medium induces a noncell-type-specific differentiation, addition of the factors aFGF, forskolin, TPA, and db-cAMP induces tyrosine hydroxylase (TH) expression in rat forebrain cultures and cultures of the NT2/hNT cell line, derived from human teratocarcinoma cells [29]. This evidence concerns the gene FGF1 and teratocarcinoma.