Autoregulation and crossregulation of nuclear receptor genes.

Whereas crossregulation of nuclear receptors has been known for some time, recently several examples of autoregulation have been described, especially during development and specific gene expression. In this review, I discuss both these phenomena, based on some studies from our laboratory on amphibian metamorphosis and egg protein gene expression. These include autoinduction of estrogen receptor (ER) accompanying egg protein gene expression in adult and larval Xenopus; autoinduction of thyroid hormone receptor (TR) during metamorphosis and in adult Xenopus; crossregulation by triiodothyronine (T(3)) and dexamethasone of autoinduction of ER; and inhibition by PRL of autoinduction and crossinduction of TR and ER genes. A dual receptor threshold model to explain the interplay between T(3), estrogen and PRL is presented and its significance to the general question of nuclear receptor autoregulation and crossregulation during development is also discussed.