Conservation of gene expression during embryonic lens formation and cornea-lens transdifferentiation in Xenopus laevis

Few molecular comparisons have been made between the processes of embryo-genesis and regeneration or transdifferentiation that lead to the formation of the same structures. In the amphibian, Xenopus laevis, the cornea can undergo transdifferentiation to form a lens when the original lens is removed during tadpole larval stages. Unlike the process of embryonic lens induction, cornea-lens transdifferentiation is elicited via a single inductive interaction involving factors produced by the neural retina. In this study, we compared the expression of a number of genes known to be activated during various phases of embryonic lens formation, during the process of cornea-lens transdifferentiation. mRNA expression was monitored via in situ hybridization using digoxigenin-labeled riboprobes of pax-6, Xotx2, xSOX3, XProx1, and γ6-cry. We found that all of the genes studied are expressed during both embryogenesis and cornea-lens transdifferentiation, though in some cases their relative temporal sequences are not maintained. The reiterated expression of these genes suggests that a large suite of genes activated during embryonic lens formation are also involved in cornea-lens transdifferentiation. Ultimately functional tests will be required to determine whether they actually play similar roles in these processes. It is significant that the single inductive event responsible for initiating cornea-lens transdifferentiation triggers the expression of genes activated during both the early and late phases of embryonic lens induction. These findings have significant implications in terms of our current understanding of the 'multistep' process of lens induction.