Cholinergic differentiation of neural progenitors in adult mouse motor facial nucleus

Environmental cues are critical determinants of the fate of neural progenitors (NPs) upon transplantation into the central nervous system. In the present study, we assessed the differentiation potential of NPs implanted in a cholinergic environment of the adult mouse brain. Neurospheres containing NPs issued from fetal ganglionic eminences of transgenic mice expressing the green fluorescent protein (GFP) were transplanted either inside or outside the mouse cholinergic facial motor nucleus. In some mice, a pre-degenerated nerve releasing trophic factors was grafted into this nucleus to favor NP survival and improve axonal growth into the graft. The fate of NPs was analyzed 6 to 9 days or 2 months post-transplantation by immunofluorescence under confocal microscopy. Transplanted NPs were observed both inside and outside the facial nucleus after 6 to 9 days, but almost exclusively inside after 2 months regardless of the presence of a pre-degenerated nerve. NPs expressed markers of undifferentiated cells, astrocytes, oligodendrocytes, neurons, or cholinergic cells. The cholinergic phenotype of NPs engrafted inside the facial nucleus increased with time and the presence of a pre-degenerated nerve. Large GFP cholinergic somata and abundant long cholinergic GFP axons projecting into the nerve graft were also observed. Our results show that NPs, isolated from fetal mouse brain and transplanted into the non-neurogenic environment of the adult mouse facial nucleus, differentiate into cholinergic cells capable to project axons. This environment and the nerve graft favored NP differentiation into cholinergic neurons.