Nd. Stull et L. Iacovitti, Sonic hedgehog and FGF8: Inadequate signals for the differentiation of a dopamine phenotype in mouse and human neurons in culture, EXP NEUROL, 169(1), 2001, pp. 36-43
Embryonic mouse striatal neurons and human neurons derived from the NT2/hNT
stem cell line can be induced, in culture, to express the dopaminergic (DA
) biosynthetic enzyme tyrosine hydroxylase (TH). The novel expression of TH
in these cells is signaled by the synergistic interaction of factors prese
nt in the media, such as fibroblast growth factor 1 (FGF1) and one of sever
al possible coactivators [DA, phorbol 12-myris-tate 13-acetate (TPA), isobu
tylmethylxanthine (IBMX), or forskolin]. Similarly, in vivo it has recently
been reported that the expression of TH in the developing midbrain is medi
ated by the synergy of FGF8 and the patterning molecule sonic hedgehog (Shh
). In the present study, we examined whether the putative in vivo DA differ
entiation factors can similarly signal TH in our in vitro cell systems. We
found that FGF8 and Shh induced TH expression in fewer than 2% of NT2/ hNT
cells and less than 5% of striatal neurons. The latter could be amplified t
o as much as 30% by increasing the concentration of growth factor 10-fold o
r by the addition of other competent coactivators (IBMX/ forskolin, TPA, an
d DA). Additivity/inhibitor experiments indicated that FGF8 worked through
traditional tyrosine kinase-initiated MAP/MEK signaling pathways. However,
the Shh signal transduction cascade remained unclear. These data suggest th
at cues effective in vivo may be less successful in promoting the different
iation of a DA phenotype in mouse and human neurons in culture. Thus, our a
bility to generate DA neurons from different cell lines, for use in the tre
atment of Parkinson's disease, will depend on the identification of appropr
iate differentiation signals for each cell type under investigation. (C) 20
01 Academic Press.