Figure 7.

Xvax1 expression is positively regulated by X-bhh. Xenopus embryos were injected into one cell (c–g) or into both cells (h) at the two-cell stage with synthetic mRNA encoding X-bhh. (a) Control embryos (stage 34) express Xvax1 in the optic stalk and disc, as well as in the ventral forebrain. (b) Transverse section from a stage 34 control embryo at the level of the eye define differentially regulated Xvax1 (purple) and Xpax6 (red) expression domains. Xvax1 is expressed in the ventral hypothalamus and in the eye disc, whereas Xpax6 is strongly expressed in the neural retina and in the lens, as well as in the dorsal midbrain. (c–h) Injection of X-bhh leads to a strong induction of Xvax1 (purple) expression (d,e,g,h) and to a severe inhibition of Xpax6 (red) expression (g,h) in the optic primordium. (c) Uninjected side of the embryo shown in d. (e) Transverse section of the embryo in c and d. Xvax1 (purple) is ectopically expressed in the whole remaining eye vesicle. (f) The uninjected side of the same embryo in g reveals almost normal Xpax6 expression (red) in the eye. (h) Transverse section of an embryo injected into both cells at the two-cell stage. Xvax1 is strongly expressed in both eye vesicles. (le) Lens; (od) optic disc; (os) optic stalk; (ov) optic vesicle; (vh) ventral hypothalamus.