L.S. STONE: LENS REGENERATION–CONTRIBUTIONS TO THE ESTABLISHMENT OF AN IN VIVO MODEL OF TRANSDIFFERENTIATION.

The publication of 4 studies between 1880–1895 that described the process of lens regeneration in amphibians introduced an experimental model of tissue transdifferentiation and marked the beginning of an active area of research in experimental embryology on the remarkable events of Wolffian lens regeneration. The next 45 years proved to be a very active period of research on the description of amphibian lens regeneration. This resulted in the publication of many studies that described similar regeneration events in various amphibian species, e.g., Rana, Amblystoma and even the fish, Fundulus. The seminal papers of Stone and his coworkers that contributed to an understanding of the processes of lens regeneration, its initiation and regulation, appeared from the late 1930s to the late 1960s. The topics of these studies focused upon the establishment of the class of amphibians that demonstrate lens regeneration; the polarized localization of cells of the iris that exhibit the potential to regenerate a specific tissue; the inter dependence of activation or inhibition of lens regeneration on adjacent eye tissues, i.e., lens, neural retina, and aqueous humor which introduced the concept that factors from the intact lens inhibit regeneration while factors from the neural retina stimulate regeneration, and that the aqueous humor serves as a medium for the diffusion of these soluble factors. Stone and his coworkers provided a precise description of in vivo transdifferentiation, an area of research that to this day, continues to be active. It was indeed a pleasure to have revisited these very important papers, especially in the context of our current knowledge of the molecular, cellular biology and genetic mechanisms of embryonic development, and specifically with respect to the role these studies played in our understanding of the processes of tissue differentiation and transdifferentiation. In this tribute to L.S. Stone’s contributions to experimental embryology of the lens, I have selected a specific group of papers published in the Journal of Experimental Zoology that dealt with major contributions to analysis and understanding of lens regeneration.