Serotonergic-like progenitor cells propagated from neural stem cells in vitro: survival with SERT protein expression following implantation into brains of mice lacking SERT.

Neural stem cells (NSCs) obtained from the midbrain region of embryonic (E14) mice were initially cultured with basic fibroblast growth factor (bFGF), Sonic hedgehog, and FGF-8 in a serum-free N-2 culture medium to foster differentiation into a serotonergic-like phenotype. During the initial differentiating phase, these progenitor cells expressed En1, Pax3, and Pax5 mRNA. Subsequently, a single serotonin [5-hydroxytryptamine (5-HT)] and tryptophan hydroxylase-positive clone was isolated, which gave rise to cells that developed serotonergic properties. Sixty percent of these progenitor cells expressed the serotonin transporter (SERT), as indicated by specific ligand binding of [125I]-RTI-55. To further evaluate SERT functionality, we showed that these progenitor cells possessed specific [3H]-5-HT uptake activity. Implantation of the serotonergic-like progenitors into the hippocampus of adult mice genetically lacking SERT was followed by migration of these cells into adjacent brain regions, and survival of the cells at 8 weeks was accompanied by a gradual increase in density of SERT protein expression, which was not found in vehicle-injected, control mice. These findings suggest that this serotonergic-like NSC model will be a useful contribution to the development of cell biotechnology in regard to the expression of missing genes such as SERT in the adult brain.