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- Materials and Methods
Neural precursors (NPs) derived from ventral mesencephalon (VM) normally generate dopaminergic (DA) neurons in vivo but lose their potential to differentiate into DA neurons during mitogenic expansion in vitro, hampering their efficient use as a transplantable and experimental cell source. Because embryonic stem (ES) cell-derived NPs (ES NP) do not go through the same maturation process during in vitro expansion, we hypothesized that expanded ES NPs may maintain their potential to differentiate into DA neurons. To address this, we expanded NPs derived from mouse embryonic day-12.5 (E12.5) VM or ES cells and compared their developmental properties. Interestingly, expanded ES NPs fully sustain their ability to differentiate to the neuronal as well as to the DA fate. In sharp contrast, VM NPs almost completely lost their ability to become neurons and tyrosine hydroxylase-positive (TH+) neurons after expansion. Expanded ES NP-derived TH+ neurons coexpressed additional DA markers such as dopa decarboxylase and DAT (dopamine transporter). Furthermore, they also expressed other midbrain DA markers, including Nurr1 and Pitx3, and released significant amounts of DA. We also found that these ES NPs can be cryopreserved without losing their proliferative and developmental potential. Finally, we tested the in vivo characteristics of the expanded NPs derived from J1 ES cells with low passage number. When transplanted into the mouse striatum, the expanded NPs as well as control NPs efficiently generated DA neurons expressing mature DA markers, with approximately 10% tumor formation in both cases. We conclude that ES NPs maintain their developmental potential during in vitro expansion, whereas mouse E12.5 VM NPs do not.