Amphibian Metamorphosis: A Complex Program of Gene Expression Changes Controlled by the Thyroid Hormone

Abstract

Publisher Summary Thyroid hormone (TH) is the inducer or causal agent of the phenomenon of metamorphosis in amphibians. This chapter discusses the three phases to the general approach that treats metamorphosis as a series of changes in gene expression: (1) isolate TH-induced up and down-regulated genes, (2) identify the genes by similarity to known genes in the data base, and (3) ascertain their role in metamorphosis by a functional assay. The up-regulation of genes by TH is clearly a much more important event than the down-regulation judged by the number of responding genes and the extent and reproducibility of the regulation. In a study described in the chapter, each of the screens of tail, intestine, and cultured cells found multiple cDNA fragments that mapped to the same gene, demonstrating that the number of up-regulated genes is limited in these tissues. There are two correlations to which each regulated gene is subjected to assess its role in metamorphosis: (1) the gene should not be regulatable until the tadpole becomes competent to respond to the hormone, and (2) the gene should be regulated during spontaneous metamorphosis.