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 quantitati ve autoradiography. Normal or hypophysectomized rats as well as hypoph ysectomized animals treated with the follicle-stimulating hormone (FSH ), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), or adr enocorticotropic hormone (ACTH), were used and the corresponding targe t 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 correla ted with the changes of the nuclear and cytoplasmic RNA labeling. Hypo physectomy causes a decrease of nuclear and cytoplasmic labeling and a large increase of the number of perichromatin granules in the four ce ll types studied. The administration of any of the four hormones bring s about an increase in the rate of RNA transport to the cytoplasm in t he target cells, within short periods (15 to 135 min). This augmentati on of the RNA export takes place before any significant increase of th e transcription rate, suggesting that the exiting RNA was previously s tored in the nucleus. This is in agreement with a decrease of the numb er of perichromatin granules detected as early as 30 min after the adm inistration of the hormones. Previous work demonstrated that steroid h ormones such as estradiol and testosterone have similar effects on the ir target cells. All these observations indicate that the regulation o f the RNA transport to the cytoplasm is an important means of rapid po sttranscriptional modulation of the expression of genetic information that can mediate the early action of various regulatory factors. (C) 1 997 Academic Press.