Knock down of HIF-1α reduces invasion of murine glioma cells in vivo . Representative tumors derived from GFP-tagged GL261 shHIF-1 and control cells showing tumor sections stained for GFP, H&E and HIF-1α. (A) The bar graph represents the average depth of invasion (μm) at the edge of tumors derived from GL261 control and GL261 shHIF cells (N = 7/group) (asterisk denotes p = 0.03). (B) As shown by GFP staining and confirmed by H&E, control tumors derived from cells expressing HIF-1α displayed an invasive edge compared with tumors derived from GL261 shHIF-1 cells with marginal invasion. HIF-1α immunohistochemistry confirms lack of HIF-1 expression in HIF-1α knockdown tumors and its expression in the controls. Open arrowheads point to HIF-1α expressing cells at the infiltrative margin in the control tumors. Scale bar represents 50 μm.