DNA synthesis and turnover in the bullfrog tadpole during metamorphosis.

125I-labeled deoxyuridine (IdUrd) has been used to estimate the turnover of DNA in liver, tail, and hind limb during spontaneous and triiodothyronine-induced metamorphosis. It was found that the total amount of liver DNA remained constant and there was no significant loss of the label from the liver DNA, which would be expected if there was an increase in DNA turnover during metamorphosis. Also, the change in specific activity of liver DNA parallels that of tail DNA during spontaneous metamorphosis. These data suggest that metamorphic transitions in the tadpole liver do not involve significant changes in DNA turnover. It was observed that the incorporation of label into hind limb DNA showed a high variability among individual animals as compared to liver and tail tissue. The data presented suggest that the observed variability is not a random phenomenon but related directly to the rate at which animals will metamorphose.