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Fig. 2. In situ expression patterns of Xenopus pax-6 (A–G) and Xotx2 (H–K) mRNA. (A) Left lateral view of the head of a stage-32 embryo. pax-6 expression is seen in the fore- and mid-brain, retina and lens epithelium (expression appears to be absent from the central lens fiber cells). (B–G) Lateral views of lentectomized and unoperated larval eyes. (B) Expression of pax-6 can be seen in about half of the 4-day transdifferentiating cornea overlying the pupillary space. (C) After 5 days expression expands and fills the entire area over the pupillary space. (D) By 8 days corneal expression becomes focused to a tight spot, which in this case is located at the edge of the pupillary space, indicated by the white arrow head. Even though we examined albino frogs, dark brown pigment is normally present in the eye (pigmented epithelium). Condensa- tions of natural brown pigment lying just outside the collapsed pupillary space are indicated by black arrowheads. This pigmentation can be readily distinguished from hybridized probe. (E) A typical unoperated right eye exhibits no hybridization of the anti-sense RNA probe. (F) Example of a 5-day transdifferentiating cornea hybridized with sense-control probe also exhibits no hybridization. (G) Example of a younger, 2 day transdiffer- entiating cornea hybridized with anti-sense probe, which exhibits no expression of pax-6. (H) Left lateral view of the head of a stage-32 embryo. Expression of Xotx-2 is seen in the lens placode, optic vesicle and the developing brain. (I–K) Left lateral views of lentectomized larval eyes. (I) Example of an eye exhibiting positive expression in a 6-day transdifferentiating cornea. Expression appears as a solitary spot overly- ing the pupillary space, indicated by the white arrowhead. (J) Example of a 6-day transdifferentiating cornea exhibiting no hybridization of the sense-control probe. (K) Example of a younger, 2-day transdifferentiating cornea hybridized with anti-sense probe, which exhibits no expression of xOtx2. Partial dotted lines in B–G, and I–K are included to help demarcate the perimeter of the pupillary space. Abbreviations: rt, retina; le, lens; ps, pupillary space; lp, lens placode. Scale bar: 200 μm (the scale bars in G and K apply to A–G; and H–K, respectively). |
