Integration of morphological and cytophysiological studies on estrogen receptor

Ultrastructural and immunocytochemical studies of an intra-nuclear particle, the perichromatin granule (PCG), demonstrated the presence of processed mRNA in this structure. Ovariectomy caused an increase in the number of PCGs in uterine cells and administration of estradiol drastically reduced the nuclear pool of PCGs in 15 min. In vitro studies demonstrated that this depletion was accompanied by an increase of the export of previously synthesized RNA. Similar quantitative changes of the abundance of PCG and of the rate of the export of RNA were found in ventral prostate after orchiectomy and testosterone restitution, as well as in the target cells of FSH, LH, TSH, and ACTH. These results taken together led us to conclude that PCGs constitute an intra-nuclear compartment of a few processed mRNA in equilibrium with transcription and export. This mRNA is rapidly transferred to the cytoplasm by specific hormone signals.