miR-21 is expressed during embryonic development. In situ hybridization with a digoxigenin-labeled probe, showing differential expression of miR-21 in normal E18 (A), newborn (P1) (B) and P7 (C) Gtv a wild type mouse brain. miR-21 could be seen in hippocampus as well as areas close to the ventricle. A digoxigenin miR-29b was used as an independent miRNA control. Scale bar is indicated in the figure and represents 50 μm.