Figure 3: Retroviral expression of NeuroD1 in dividing glial cells further demonstrates in vivo glia-to-neuron conversion. (A–B) Representative images illustrating retrovirus-infected cells at early stage (6 days post viral injection, 6 dpi) showing typical astrocytic morphology with numerous fine processes and immunostained with glial fibrillary acidic protein (GFAP) signal. A few NeuroD1-GFP infected cells also showed weak neuronal nuclei (NeuN) signal (arrowhead). Scale bars: 20 μm. (C, D) By 14 dpi, some of the NeuroD1-GFP infected cells were still going through a transitional stage with co-localized signal of GFAP and NeuN together (C), whereas other NeuroD1-GFP infected cells had converted into NeuN+ neurons with typical neuronal morphology (D). Scale bar: 20 mm. Retroviruses were CAG::NeuroD1-GFP (1 × 107 TU/mL, 1 µL).