Pax-6 and Prox 1 expression during lens regeneration from Cynops iris and Xenopus cornea: evidence for a genetic program common to embryonic lens development.

Lens regeneration from non-lens ocular tissues has been well documented in amphibians, from the dorsal iris in the newt and from the outer cornea in Xenopus. To understand the early molecular events which govern lens regeneration, we examined the expression of two early marker genes of normal lens development, Pax-6 and Prox 1. In both Cynops (newt) iris and Xenopus cornea, Pax-6 is expressed soon after lentectomy in a region broader than that giving rise to the regenerating lens, indicative of an important role for Pax-6 in determination of the regeneration potential. Then Prox 1 expression begins within the Pax-6-expressing tissue, and these Prox 1-expressing cells give rise to the regenerating lens. This sequence of events also takes place in the lens placode of the embryo, indicating that the presence of the same genetic program operates in both embryonic lens development and lens regeneration, at least partly. In the Cynops iris, Pax-6 expression occurs initially in the entire marginal region of the iris after lentectomy but then becomes restricted to the dorsal region. Further studies are expected to elucidate the mechanism of this long-standing problem of the dorsal-restriction of lens regeneration from the newt iris.