As another molecular hallmark for reactive astrocytes, nestin did not appear in the cerebral cortex in control mice, but was observed throughout the brain of Mlc1-ErbB2V664E mice and colocalized well with GFAP+ cells (Figure 4f). Similarly, Olig2+ nuclei increased in various brain regions of Mlc1-ErbB2V664E mice (Supplementary Figure S8c), with many localized in GFAP+ cells (Figure 4g). An increased proportion of Olig2+ cells was correlated with an increase in GFAP+ cells (Figure 4h). As in our experiments using the injury model, we observed that many Olig2+ cells were positive for Ki67 in the brains of Mlc1-ErbB2V664E mice (Supplementary Figure S8d), indicating an actively proliferating status. Further, the percentage of Olig2+ cells positive for Ki67 was close to the percentage positive for GFAP (Figure 4i), suggesting that proliferative Olig2+ cells were mainly astrocytes in Mlc1-ErbB2V664E mice. A similar colocalization pattern was observed for Olig2 and nestin in Mlc1-ErbB2V664E mice (Supplementary Figure S8e). We examined the mRNA levels of a series of genes , and did not reveal a typical transcriptional pattern of subtype A1 or A2 for the reactive astrocytes in Mlc1-ErbB2V664E mice (Supplementary Figure S8f). Both A1 and A2 subtype-specific genes were actively transcribed, suggesting reactive astrocytes induced in the brain of Mlc1-ErbB2V664E mice were phenotypically heterogeneous.