Increased levels of miR-21 in mouse glioma cell lines and glioma. A) Compared to normal mouse brain the different mouse primary glioma cultures had an increased expression of miR-21 as measured by Northern blot. U6 was used as a loading control. In B) in situ hybridization of miR-21 in the tumor area of a Gtv-a p16Ink4a−/−/p19Arf−/− mouse brain is presented, using a digoxigenin-labeled miR-29b probe as an independent miRNA control. In C) a Gtv-a p16Ink4a−/−/p19Arf−/− mouse brain could be seen, showing miR-21 expression specifically to the tumor area adjacent to the ventricle and the choroid plexus. T = tumor, and N = normal. Scale bar is indicated in the figure and represents 50 μm.