Interaction of the ectomesenchyme and optic vesicle in mice.

We investigated eye development in embryos at the 17, 24, and 31 somite-pair stages homozygous for the two genes white (Mi-wh) and fidget (fi) (Mi-wh/Mi-whfi/fi), single homozygotes (fi/fi and Mi-wh/Mi-wh), and normal mice (the inbred C57 BL/Mib strain). The fi gene retards optic-vesicle growth, while the Mi-wh gene inhibits ectomesenchyme migration. It was shown that the mitotic index of the optic-vesicle wall and the retinal rudiment was considerably higher in Mi-wh/Mi-whfi/fi embryos than in fi/fi embryos and lower than in Mi-wh/Mi-wh and +/+ embryos. Ectomesenchyme affected by the white gene stimulated optic-vesicle growth, to some extent suppressing the effect of the fidget gene. The stimulation of optic-vesicle growth in the double homozygotes led to intensified induction of the lens placode. This indicates that the ectomesenchyme affects the optic rudiment at the optic-vesicle stage.