AUTOREGULATION AND CROSSREGULATION OF NUCLEAR RECEPTOR GENES

Whereas crossregulation of nuclear receptors has been known for some t ime, recently several examples of autoregulation have been described, especially during development and specific gene expression. In this re view, I discuss both these phenomena, based on some studies from our l aboratory 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 Xenop us; crossregulation by triiodothyronine (T-3) and dexamethasone of aut oinduction of ER; and inhibition by PRL of autoinduction and crossindu ction of TR and ER genes. A dual receptor threshold model to explain t he interplay between T-3, estrogen and PRL is presented and its signif icance to the general question of nuclear receptor autoregulation and crossregulation during development is also discussed.