Figure 9.

Identification of the neuronal progenitors in the Tg(olig2:egfp)^vu12 transgenic line. Retinal sections from the Tg(olig2:egfp)^vu12 transgenic line were labeled with an anti-EGFP (green) and anti-PCNA (red) antibodies. A, Control section from a retina injected with 0.65% saline possessed very few PCNA-labeled cells (red; arrowheads), and EGFP expression was only detected in the GCL nerve fiber (green). B, At 3 dpi, the majority of the PCNA-labeled cells were located in the INL, and EGFP expression was limited to the interface of the degenerated retina and the vitreous. C, At 5 dpi, the number of PCNA-labeled cells increased, and they were present in distinct clusters that coexpressed EGFP. D, At 7 dpi, PCNA-labeled cells were present throughout the inner retina. However, the majority of the PCNA-labeled cells did not colabel with EGFP. E, At 14 dpi, PCNA expression persisted, although at a reduced level relative to 7 dpi. Furthermore, EGFP expression was dramatically reduced, with very little coexpression with the PCNA. Although some EGFP-positive, PCNA-negative cells exist (arrowhead), they are in the minority compared with the random clusters of EGFP-positive, PCNA-positive cells (arrows) and the even greater number of PCNA-positive, EGFP-negative cells. This suggests that olig2–EGFP expression is limited to a distinct phase of proliferating neuronal progenitor cells during retinal regeneration, which occurs immediately or shortly after the Müller glia terminate PCNA expression. Scale bar, 75 μm.