Intranuclear localization of hormone-occupied and -unoccupied estrogen receptors in the mouse uterus: application of 1 nm immunogold-silver enhancement procedure to ultrathin frozen sections.

Employing immunoelectron microscopy with ultrathin frozen sections, intranuclear localization of hormone-occupied and -unoccupied estrogen receptors (ER) was examined in the uterine epithelium; after 1 h of 17 beta-estradiol (E2, 20 micrograms/kg b.w.) or saline intraperitoneal injection, adult ovariectomized mice were sacrificed. ER were localized with both anti-ER monoclonal antibody and polyclonal antibody (AS 409) and 1 nm immunogold followed by silver enhancement. No significant differences in ultrastructure were recognized in either the nuclei or the cytoplasm of the uterine epithelium in E2-treated and control animals. E2-occupied and -unoccupied ER showed the same distribution pattern in the nuclei of both luminal and glandular epithelium. ER were exclusively localized in the dispersed and slightly condensed chromatin; the margins of the condensed chromatin also showed strong immunoreaction. Little immunolabeling was observed in the highly condensed chromatin associated with nuclear membranes. The reaction was negative in the nucleoli. Both antibodies provided the same ER intranuclear localization. It is suggested that marked change in the distribution of steroid receptors, i.e. rapid translocation from condensed chromatin to dispersed chromatin or the margins of condensed chromatin as described in some previous reports, probably takes place as a consequence of conformational changes in the chromatin-binding receptors.