Embryonic stem cell-derived neurogenesis - Retinoic acid induction and lineage selection of neuronal cells

Embryonic stem (ES) cells are able to differentiate in vitro into endoderma l, mesodermal, and ectodermal cell types. However, the spontaneous developm ent of neuronal cells from ES cells is rather limited. Therefore, specific protocols to increase the differentiation of neuronal cells have been estab lished, such as retinoic acid (RA) induction and lineage selection of neuro nal cells. High concentrations of RA resulted in efficient neuronal differe ntiation paralleled by the expression of tissue-specific genes, proteins, i on channels, and receptors in a developmentally controlled manner. Because the developmental pattern and survival capacity of RA-induced neuronal cell s were limited, specific differentiation protocols by lineage selection of neuronal cells have been established using growth and extracellular matrix factors. After formation of cells of the three primary germ layers, mesoder mal differentiation was inhibited by serum depletion, and neural precursor cells were generated by addition of basic fibroblast growth factor, followe d by differentiation induction by neuronal differentiation factors. Further application of survival-promoting factors such as neurotrophic factors and cytokines at terminal stages resulted in a significant increase, survival, and maintenance of dopaminergic neurons. In the future, these cellular sys tems will be applicable: (1) for studying commitment and neuronal specifica tion in vitro, (2) as pharmacological assays for drug screening, and (3) fo r the selective isolation of differentiated neuronal cells which may be use d as a source for cell and tissue grafts.