Fig. 1. Wnt2b induces prolonged proliferation of retinal progenitor cells. (A,B) Exogenous gene expression by replication-competent retroviruses. The optic vesicles were electroporated with a GFP-expressing RCASBP provirus vector and fixed after 24 hours (A) or 72 hours (B). Transverse sections of neural retinas were observed using confocal microscopy. Nuclei were counterstained with propidium iodide and pseudocolored in purple. (C) Whole-mount view of E5 retina. The purple box shows the region from which retinal explants were prepared. (D-F) Whole-mount view of the retinal explants taken from control (D,G), Wnt2b-expressing (E,H), and Delta1-expressing (F,I) E6 retina immediately after the dissection (D-F) or after 7 days in culture (G-I). The small insets in G-I show the explants after the dissection at the same magnification. Note that Wnt2b-expressing explants increased in size enormously, making folded sheets (H), whereas control or Delta1-expressing explants made a much smaller sphere (G,I). (J) The change in cell number in the explants during the culture period (shown on the x axis). The cell number is shown in a logarithmic vertical scale. Note the exponential growth in the Wnt2b-expressing explants. Scale bars: 20 µm (A,B); 250 µm (D-I).