Novel aspects of estrogen action.

The discovery of a second estrogen receptor, ER beta, in 1996 introduced a new paradigm in our understanding of estrogen action. ER alpha predominates in the uterus and mammary gland, whereas ER beta has significant roles in the central nervous, cardiovascular, and immune systems, urogenital tract, bone, kidney, and lung. ER beta appears to be the only from expressed in the embryonal central nervous system. Photoestrogens may be good candidates for physiologic ligands of ER beta. Coactivator proteins play critical roles in regulating estrogen. Female ER beta-deleted mice (beta ERKO) develop follicular arrest and anovulation.