Predominant neuronal differentiation of Olig1+ neural progenitors in forebrain cortex biased by β-catenin...

Proper neuron-glia ratio is essential for normal brain development and function. Olig1 is a basic helix-loop-helix (bHLH) transcription factor generally used as a lineage tool for oligodendrocyte research in spinal cord. Recent studies have revealed a property of Olig1-positive cells as the common progenitors of GABAergic neurons and oligodendrocytes in the forebrain during embryogenesis, and a stage-dependent regulatory role of Wnt/β-catenin signaling in the differentiation of oligodendrocytes in spinal cord. Given the neurogenic role of Wnt/β-catenin signaling in neural progenitor cells, it is unclear how β-catenin affects the differentiation of Olig1-positive progenitors in brain. In the present study, we investigated the effects of β-catenin over-expression on the differentiation of Olig1-positive progenitors in the forebrain cortex, by using Olig1-Cre:β-cateninEX3 (loxp/+):ROSA-YFP (β-cateninEX3 CKO) mice as compared to Olig1-Cre:ROSA-YFP control. The results showed that in the cortex of Olig1-Cre:ROSA-YFP mice, approximately 28.6% of YFP labeled cells are GFAP-positive, 43.7% are NG2-positive, 23.4% are CC1-positive and 3.2% are NeuN-positive, showing that Olig1-positive cells are multi-potential and mainly gliogenic. However, in the cortex of β-cateninEX3 CKO mice, the percentage of astrocytes generated from Olig1-positive cells decreased dramatically to approximately 2%, NG2-positive cells to 0.4%, and CC1-positive cells to 0.5%. In contrast, the percentage of NeuN-positive cells increased to approximately 96% of YFP-labeled cells. Taken together, our data showed that the gliogenic property of Olig1-positive progenitors in forebrain can be efficiently switched to neurogenic by over-expressing β-catenin, revealing a neurogenic effect of β-catenin in the forebrain Olig1-positive progenitors.