Induced differentiation of human embryonic stem cells toward motor neurons
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The understanding of mammalian cellular differentiation and cell fate specification are progressing intensively using an in vitro system, comprised of embryonic stem cells. Research on the cell fate specification in the central nervous system (CNS) is of enormous interest given the therapeutic potential in neuronal repair strategies. The main focus of this study was to derive motor neurons from human embryonic stem cells (hESC). For this main purpose, first study involved derivation and proliferation of neuroepithelial stem cells (NEP) which are the earliest multipotent neural stem cells from hESC. Embryonic stem cells cultured in serum-deprived defined medium developed a distinct canal structure which could be isolated either by dissociation or physical feeder separation. Dissociated cells formed colonies comprised of cells characterized as NEP in MEDII medium (HepG2 cell conditioned medium) dependent manner. However, cells isolated by feeder separation maintained adherence and developed enriched NEP like cells independent of exposure to MEDII. Further characterization indicates that these cells have a phenotype profile and differentiation potential of NEP. To proliferate NEP, ideal cell culture conditions were established and cells have been proliferated successfully in this condition for over six months, maintaining stable karyotype and without loss of their multipotent neural stem cell characteristics. After successful derivation and proliferation of NEP, studies were conducted to differentiate them into specific type of neurons. To differentiate NEP into motor neurons, specific morphogens that have been demonstrated as important in development were introduced to short and long term cultured NEPs. First, freshly isolated (< one month, early) and propagated (> three months, late) cultures of NEP were characterized and both populations were exposed to inductive signals for the stimulation into motor neuron. Increased motor neuron gene expression was shown in both early and late NEP by retinoic acid and additional effect of sonic hedgehog was observed in early NEP. Finally, a spinal motor neuron phenotype was demonstrated in early and late NEPs. The acquired efficient neural induction, long term culture of NEP and subsequently derived motor neuron would serve as a great in vitro model to understand developmental cues and to overcome diseases related to motor neurons.