CELL-DEATH - ARE NEW PROTEINS SYNTHESIZED DURING HORMONE-INDUCED TADPOLE TAIL REGRESSION

The possibility that tadpole tail regression might be initiated by thyroid hormone-induced synthesis of new proteins was investigated. Changes in the newly-synthesized proteins of cultured Xenopus laevis tadpole tails treated with 1.5 .times. 10-7 M tri-iodothyronine (T3) were studied, using polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate for protein separation. After initial studies of unfractionated tail proteins, fractionated mixtures of [3H]methionine and [35S]methionine labeled proteins derived from control and hormone-treated tails respectively were examined for hormone-induced changes. Using a new procedure developed to allow effective analysis of small differences in distribution of 2 isotopes within gel slices, no significant changes in synthesis of fractionated tail proteins are induced by the hormone during the first 3-4 days in culture. The average detection limit was approximately 0.02% of total tail protein synthesis. Although no changes in the synthesis of the tissue structural or enzymic proteins are induced by the hormone this study still leaves open the possibility of changes in the synthesis of regulatory proteins. Based on the known method of activation of the tadpole tail collagenase (which is shown directly for the first time to be involved in T3-induced tail regression), many of the initial hormone-induced changes might result from T3-induced activation of proteolytic cascades.