Fig. 3. Wnt2b suppresses premature neurogenesis induced by an inactivation of Notch signaling. (A-L) Effects of DAPT and Wnt2b on progenitor cell differentiation. The retinal explants were prepared from E5 retina electroporated with control (A,B,E,F,I,J) or Wnt2b-expressing (C,D,G,H,K,L) provirus vectors, and were cultured for 2 days in the absence (A,E,I,C,G,K) or presence (B,F,J,D,H,L) of DAPT, a -secretase inhibitor that blocks Notch signaling. The sections were stained for visinin (green), and Hu (purple) in A-D, for Pax6 (green) and Chx10 (purple) in E-H, and for BrdU (green) and phosphorylated histone H3 (purple) in I-L. In the control explants, the DAPT treatment induced premature neuronal differentiation, as revealed by the increase of neuronal markers (B) and a decrease of retinal progenitor cell markers (F). In the Wnt2b-expressing retinal explants, however, a large population of the cells still co-expressed the progenitor markers (H) and incorporated BrdU (L). (M-P) Effects of a dominant negative Delta1 and Wnt2b on retinal progenitor cell differentiation. The optic vesicles were electroporated with provirus vectors encoding control RCASBP (A,B) in M, RCASBP (A) encoding a dominant-negative form of Delta1 and RCASBP (B) in N, RCASBP (A) and RCASBP (B) encoding Wnt2b in O, or RCASBP (A) encoding a dominant-negative form of Delta1 and RCASBP (B) encoding Wnt-2b in P. The retinas were fixed at E5, and sections were stained for visinin (green) and Hu (purple). Note that Wnt2b completely suppressed the effect of the dominant-negative Delta in promoting the neurogenesis. (Q-T) Effect of Delta1 and Wnt2b on Müller cell differentiation. Note that Wnt2b suppressed the effect of Delta1 in inducing Müller glia differentiation when co-expressed in the same explants. (U) Percentage of BrdU+ cells in the explants expressing each construct (n=4). Scale bars: 30 µm.