DIFFERENTIAL EXPRESSION OF SECRETOGRANIN-II AND CHROMOGRANIN-A GENES IN THE FEMALE RAT PITUITARY THROUGH SEXUAL-MATURATION AND ESTROUS-CYCLE

Secretogranin II (SgII) is a protein of pituitary secretory granules released by LHRH-stimulated gonadotrope cells. Estrogens and androgens are modulators of SgII release. Experiments were performed to determine the regulation of expression of the SgII gene in the female rat pituitary, during sexual maturation and according to the estrous cycle. Age- and cycle-related changes in SgII mRNA content were estimated through cytoplasmic slot blot; SgII content was determined by western blotting; maturation of the protein was controlled through [S-35]sulfate labeling. Variations in chromogranin A (CgA), another protein of secretory granules, were analyzed in the same experimental conditions to assess the specificity of SgII regulation. The pituitary SgII concentration increased between days 7 and 21 (2.2-fold) and then declined to the initial 7-day-old value. Simultaneously, the CgA concentration went through a maximum between days 14 and 21 and then strongly dropped to barely detectable levels in the adult pituitary. The SgII mRNA concentration followed roughly the same pattern as the protein. Moreover, the sulfation level remained constant between days 14 and 60. These results demonstrated a regulatory mechanism operating, during sexual maturation, on the SgII gene and not on the protein processing or on storage/release steps. In the 4-day cycling females, the pituitary SgII mRNA and protein contents were the lowest during estrus. They then increased to their highest values in diestrus II. Moreover, the sulfation level of SgII was significantly higher during estrus than during any other stage. Due to its low content level, variations in pituitary CgA could not be demonstrated during the cycle.