Analysis of differentiation system in cerebral GABAergic neuron and oligodendrocyte progenitors.

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GABAergic neurons and oligodendrocyte share many characters in the forebrain development. Both cell types have been reported to originate in the medial ganglionic eminence and migrate to the neocortex. Previously, it has been reported that GABAergic neuron progenitors express not only of GABAergic neuron markers but also ones of oligodendrocytes progenitors, such as NG2 and CNP (Belachew et al., 2003 ; Aguirre et al., 2004 ; Dayer, et al., 2005). Moreover, NG2/Olig2 positive glial progenitors generate both oligodendrocyte and astrocyte in the developing forebrain using NG2creBAC transgenic mouse (Zhu et al., 2008) and Olig2-CreER knock-in mouse (Ono et al., 2008). These previous data raise a possibility that some GABAergic neuron progenitors produce glial cells in the developing forebrain. To test this possibility, here we have performed immunohistochemistry, single-cell RT-PCR, single-cell microarray analysis and immunocytochemistry analyses with glial markers in GAD67-GFP positive cells from GAD67-GFP knock-in mouse brain. As a result, we found that the neuronal markers and glial markers are co-localized in the GAD67-GFP-positive cells at mRNA and protein level. To further investigate cell lineage(s) from GABAergic neuron progenitors in vivo and in vitro, we utilized GAD67-Cre knock-in mice and Z/EG reporter mice. As a result, we found that the neuronal markers and glial markers are co-localized in the GAD67-GFP-positive cells at mRNA and protein level. Finally, to investigate GAD67 lineage in vivo and in vitro, we utilized GAD67-Cre knock-in mice and Z/EG reporter mice. We observed the most of recombined GFP positive cells were GABAergic neuron, but a few cells were oligodendrocyte and astrocyte. At present, we can not completely rule out the possibility that leaky or weak expression of GAD67 gene occur in the small subset of glial progenitors during cell-type specification.