Understanding thyroid hormone receptor function in controlling developmental timing and rate in Xenopus: A journey...

Anuran metamorphosis has long been used as a model to study thyroid hormone (T3) function during vertebrate development. The cloning of T3 receptor (TR) in the late 1980 s opened a door for using anuran metamorphosis to address some fundamental questions on T3 action in development that were difficult to ask or address in mammalian models. Here, I will review some of the studies ranging from biochemical and molecular investigations to more recent genetic studies that have not only uncovered novel and critical roles of TR in regulating adult organ development and larval tissue resorption/remodeling but also revealed in vivo mechanisms of T3 action. I will focus mainly on the work involving two highly related species, the allotetraploid Xenopus laevis and diploid Xenopus tropicalis, which offer many unique but complementary advantages for in vivo studies of TR function.