RESUMEN
Neural Precursor Cells (NPCs) generate complex stereotypic arrays of neuronal subtypes in the brain. This process involves the integration of patterning cues that progressively restrict the fate of specific NPCs. Yet the capacity of NPCs to interpret foreign microenvironments during development remains poorly defined. The aim of this work was to test the competence of mouse telencephalic NPCs to respond to the dopaminergic niche of the mesencephalon. Telencephalic NPCs isolated from midgestation mouse embryos (E10.5) and transplanted to age-matched mesencephalic explants efficiently differentiated into neurons but were largely unable to produce midbrain dopaminergic (mDA) neurons. Instead, E10.5 telencephalic NPCs behaved as restricted gabaergic progenitors that maintained ectopic expression of Foxg1 and Pax6. In contrast, E8.5 telencephalic NPCs were able to differentiate into Lmx1a(+)/Foxa2(+)/TH(+) neurons in the dopaminergic niche of the mesencephalic explants. In addition, these early telencephalic NPCs showed region-dependent expression of Nkx6.1, Nkx2.2 and site-specific differentiation into gabaergic neurons within the mesencephalic tissue. Significant dopaminergic differentiation of E8.5 telencephalic NPCs was not observed after transplantation to E12.5 mesencephalic explants, suggesting that inductive signals in the dopaminergic niche rapidly decay after midgestation. Moreover, we employed transplantation of embryonic stem cells-derived precursors to demonstrate that extinction of inductive signals within the telencephalon lags behind the commitment of residing NPCs. Our data indicate that the plasticity to interpret multiple instructive niches is an early and ephemeral feature of the telencephalic neural lineage.
Asunto(s)
Tipificación del Cuerpo/fisiología , Diferenciación Celular/fisiología , Dopamina/metabolismo , Mesencéfalo/embriología , Células-Madre Neurales/metabolismo , Neurogénesis , Telencéfalo/citología , Animales , Proteínas del Ojo/metabolismo , Factores de Transcripción Forkhead/metabolismo , Factor Nuclear 3-beta del Hepatocito/metabolismo , Proteína Homeobox Nkx-2.2 , Proteínas de Homeodominio/metabolismo , Proteínas con Homeodominio LIM , Ratones , Microscopía Fluorescente , Proteínas del Tejido Nervioso/metabolismo , Células-Madre Neurales/trasplante , Factor de Transcripción PAX6 , Factores de Transcripción Paired Box/metabolismo , Proteínas Represoras/metabolismo , Factores de TranscripciónRESUMEN
Specific neuronal differentiation of Embryonic Stem Cells (ESCs) depends on their capacity to interpret environmental cues. At present, it is not clear at which stage of differentiation ESCs become competent to produce multiple neuronal lineages in response to the niche of the embryonic brain. To unfold the developmental potential of ESC-derived precursors, we transplanted these cells into the embryonic midbrain explants, where neurogenesis occurs as in normal midbrain development. Using this experimental design, we show that the transition from ESCs to Embryoid Body (EB) precursors is necessary to differentiate into Lmx1a(+)/Ptx3(+)/TH(+) dopaminergic neurons around the ventral midline of the midbrain. In addition, EB cells placed at other dorsal-ventral levels of the midbrain give rise to Nkx6.1(+) red nucleus (RN) neurons, Nkx2.2(+) ventral interneurons and Pax7(+) dorsal neurons at the correct positions. Notably, differentiation of ESCs into Neural Precursor Cells (NPCs) prior to transplantation markedly reduces specification at the Lmx1a, Nkx6.1 and Pax7 expression domains, without affecting neuronal differentiation. Finally, exposure to Fgf8 and Shh in vitro promotes commitment of some ESC-derived NPCs to differentiate into putative Lmx1a(+) dopaminergic neurons in the midbrain. Our data demonstrate intrinsic developmental potential differences among ESC-derived precursor populations.