Effects of hypophyseal hormones on transcription and RNA export to the cytoplasm

The effects of hypophyseal hormones on RNA transcription and export to the cytoplasm were evaluated by means of light microscopic quantitative autoradiography. Normal or hypophysectomized rats as well as hypophysectomized animals treated with the follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), or adrenocorticotropic hormone (ACTH), were used and the corresponding target cells (Sertoli cells, Leydig cells, epithelial thyroid gland cells, or adrenal cortical cells, respectively) were analyzed. Moreover, the variations of the concentration of perichromatin granules were correlated with the changes of the nuclear and cytoplasmic RNA labeling. Hypophysectomy causes a decrease of nuclear and cytoplasmic labeling and a large increase of the number of perichromatin granules in the four cell types studied. The administration of any of the four hormones brings about an increase in the rate of RNA transport to the cytoplasm in the target cells, within short periods (15 to 135 min). This augmentation of the RNA export takes place before any significant increase of the transcription rate, suggesting that the exiting RNA was previously stored in the nucleus. This is in agreement with a decrease of the number of perichromatin granules detected as early as 30 min after the administration of the hormones. Previous work demonstrated that steroid hormones such as estradiol and testosterone have similar effects on their target cells. All these observations indicate that the regulation of the RNA transport to the cytoplasm is an important means of rapid posttranscriptional modulation of the expression of genetic information that can mediate the early action of various regulatory factors.