Figure 2. Expression of typical optic vesicle markers is missing or defective in Six3 conditional–mutant embryos.
(A) At the 13-somite stage, Fzd5 expression is normally seen in the optic vesicles (arrow) and ventral forebrain of control embryos. (B) This expression was absent in the Six3-mutant littermates. (C) At the 15-somite stage, normal Rax expression is seen in the optic vesicles (arrow). (D) In the mutant littermates, Rax expression is missing from the dorsal optic vesicles and does not separate properly in the ventral midline region of the forebrain (arrowhead). (E and G) At this same stage, Six6 expression is seen in presumptive NR progenitors in the optic vesicles (arrows) and ventral forebrain (arrowhead). (F and H) In Six3 conditional–mutant littermates, Six6 expression was almost completely absent from those territories (arrow and arrowhead). At the 21-somite stage, expression of the ventral (Vax2; I and J) and dorsal (Tbx5; K and L) optic vesicle markers was also undetectable in Six3-mutant embryos. (M–P) At this stage, expression of Mitf remained in the mutant optic vesicles. Scale bar: 100 μm.