D4 and E4 represent a high magnification of framed areas in panels D2 and E2, respectively. Scale bars: 50 mm (A1–D3 and E1–3). Found at: doi:10.1371/journal.pone.0004779.s005 (4.26 MB TIF) Figure S6 NeuroD1 overexpression induces neuronal granule neuron maturation in vivo. (A–B6) Indirect immunofluorescence performed on hippocampal coronal sections of two weeks old rats that were injected with NeuroD1 retrovirus at the embryonic age of E15.5. (A) The overexpression of NeuroD1 results in the generation of hippocampal DG granule neurons. These neurons (NeuroD1/GFP -positive) express the mature neuronal marker NeuN and are very often localized in the external granule layer (first layers generated during the DG development). (B1–B6) A few cells transduced with NeuroD1 retrovirus (GFP-positive) have a glial-like shape. These cells still express NeuroD1. 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