OLIG2 and Stroke: Indeed, H3 lysine 9 trimethylation (H3K9me3), a post-translational histone modification marker for OPC differentiation40, was concurrently elevated in these Olig2+ cells in the cKO brains at 3-day post-stroke (1.4-fold, p = 0.030), further evidence of accelerated OPC differentiation in the cKO brains (Fig. 7d).