Tissue interactions and lens-forming competence in the outer cornea of larval Xenopus laevis.

After lentectomy through the pupillary hole, the outer cornea of larval Xenopus laevis can undergo transdifferentiation to regenerate a new lens. This process is elicited by inductive factor(s) produced by the neural retina and accumulated into the vitreous chamber. During embryogenesis, the outer cornea develops from the outer layer of the presumptive lens ectoderm (PLE) under the influence of the eye cup and the lens. In this study, we investigated whether the capacity of the outer cornea to regenerate a lens is the result of early inductive signals causing lens-forming bias and lens specification of the PLE, or late inductive signals causing cornea formation or both signals. Fragments of larval epidermis or cornea developed from ectoderm that had undergone only one kind of inductive signals, or both kinds of signals, or none of them, were implanted into the vitreous chamber of host larvae. The regeneration potential and the lens-forming transformations of the implants were tested using an antisense probe for pax6 as an earlier marker of lens formation and a monoclonal antibody anti-lens as a definitive indicator of lens cell differentiation. Results demonstrated that the capacity of the larval outer cornea to regenerate a lens is the result of both early and late inductive signals and that either early inductive signals alone or late inductive signals alone can elicit this capacity.