Upregulation of XXXX in the skin of Xenopus laevis during thyroid hormone-induced metamorphosis.

@entity73155 @entity73156 @entity21987 @entity1954
During amphibian metamorphosis dramatic changes occur in the morphogenesis and differentiation of the epidermis. Concurrently with these changes, the 63 kDa @entity73155 gene is upregulated from low basal levels to high levels. What makes these processes unique is that they are controlled by @entity1954 (T3) and can be duplicated in cultures of purified epidermal cells. Since there is a 2 day lag period between the addition of T3 and the upregulation of @entity73155 gene expression and terminal differentiation, recent studies have focused on identifying the genes activated during the lag period. We assume that the transcription factors required for upregulation of the @entity73155 gene are induced by T3 during the lag period, and therefore we have cloned the @entity73155 gene so that promoter analyses can be conducted. S1 mapping assays have shown that the same transcription start sites are used during premetamorphosis when the @entity73155 gene is basally expressed, during metamorphosis when it is T3-upregulated, and in the adult epidermis where it is expressed independently of T3. During the early part of the lag period @entity21987 and @entity73156 mRNA levels are upregulated in the epidermis by T3. The transcription factor @entity73156 is expressed at high levels in the skin of premetamorphic larvae and induced about fivefold by T3 but is not induced in an epithelial cell line (XL-177). Since the @entity73155 mRNA, @entity73156 mRNA, and other genes induced during the lag period are expressed in premetamorphic larvae it appears that T3 functions by upregulating the expression of genes previously activated by a T3-independent process. This preprogramming may account for the tissue specificity of T3 action during metamorphosis.
