Fig. 2. Six3 is required for retina and forebrain development. (A-E) Dorsal views of embryos (A,B) at six-somite stage (21) and (C-E) late gastrula stage (16), anterior is towards the left. (B) Injection of high MoSix3 concentrations results in loss of anterior structures (severe) compared with MoGFP control injected embryos (A). Arrow indicates region of forming mid-hindbrain boundary. (C,D) Ectopic cell death (TUNEL) in response to MoSix3 overlapping with (E) Six3 expression. Broken yellow line outlines forming embryonic axis. (F,G) Lateral views and (H) Rx2 (red) and Vax1 (purple) in situ analysis of (F) GFP control and (G,H) mouse Six3-injected embryos at somitogenesis stage (23); (F-H) transverse section (dorsal is upwards) at the midbrain level of another embryo. Six3 overexpression results in ectopic formation of proximal (Vax1) and distal (Rx2) eye structures in the midbrain (22%; n=37). (I-K) Dorsal views of organogenesis stage embryos (30). (J,K) MoSix3-injected embryos exhibit a small eye (mild) and a cyclopic (intermediate) phenotype. Arrow indicates proximal retinal structures lost, arrowhead indicates forebrain structures lost (K). ey, eye; gt, gut; hb, hindbrain; inj., injected; ot, optic tectum.