A study of DNA synthesis during the transformation of the Iris into lens in the lentectomized newt

An autoradiographic study of the pattern of DNA synthesis in Wolffian lens regeneration of adult newt Triturus viridescens was carried out. Animals were injected with thymidine‐H 3 at different stages of lens regeneration, and killed after different time intervals ranging between 2 hours to 15 days. The temporal pattern of incorporation and localization of labeled cells was studied with autoradiograms. DNA synthesis, which is not detectable in the normal iris, is activated in the dorsal as well as in the ventral iris within five days after lens removal when the cells are still heavily pigmented. When the dorsal iris cells become depigmented, all depigmented cells show a high labeling frequency. Cessation of DNA synthesis is indicated immediately before the depigmented cells start to elongate and differentiate into fibers. At later stages of regeneration, when the regenerate is composed of fibers, lens epithelium, and stalk, DNA synthesis is limited to the latter two. It has been pointed out that cells synthesizing a detectable amount of gamma crystallins never synthesize DNA. The data suggest that all the cells which form the new lens pass through a period of DNA synthesis, which starts approximately five days following lens removal. However, not all cells which are activated to DNA synthesis participate in lens formation. Thus, DNA synthesis is a necessary but not sufficient condition for transformation of iris cells into the lens cells.