The pattern of DNA replication during the initial stages of Wolffian lens regeneration has been examined by an autoradiographic study of tritiated thymidine uptake in zero to five-day regenerates (Triturus viridescens). Scanning of complete sets of serial sections for each iris revealed the absence of labeled cells in normal, one-, and two-day iris epithelia, and a very infrequent occurrence of labeled iris epithelial cells in some three-day regenerates. After this stage, cell labeling is seen in all iris epithelia. Cell labeling frequency increases markedly by four days, and is at a very high level in five-day regenerates.
Further data indicate that labeling begins in the dorsal sector of the iris epithelium.
By five days after lens removal, however, it reaches siinilar levels in dorsal, lateral, and ventral sectors. Thus, DNA replication is induced throughout the iris epithelium after lens removal, even though the lateral and ventral sectors of the iris epithelium do not participate in actual lens formation.
Comparison between the outer and inner laminae of the iris epithelium shows that during all stages studied the great majority of labeled cells are in the inner lamina.
1 Research sponsored by the. U. S . Atomic Energy Commission under contract with the Union Carbide Corporation.