Ontogeny of follicle-stimulating hormone and luteinizing hormone gene expression during pubertal development in the female striped bass, Morone saxatilis (Teleostei)

Pubertal development in teleost fish is characterized by gonadal growth that is directly stimulated by the pituitary gonadotropins, FSH and LH. We used a quantitative ribonuclease protection assay to provide, for the first time, the developmental profiles of the alpha-, beta FSH-, and beta LH-subunit gene expression in a seasonal breeding fish, the female striped bass (3-yr study, n = 207). Two-year-old females were sexually immature, although a transient rise in all gonadotropin subunit mRNAs was measured in the pituitary. Pubertal ovarian development occurred in 65% of S-yr-old females, characterized by the appearance of lipid droplets within the oocytes. This reproductive phase, termed pubertal development, was associated with a 34-fold increase in the mRNA levels of beta FSH and a rise in the pituitary concentration of LH. The first sexual maturation took place in 4-yr-old females and coincided with a 218-fold increase in the mRNA levels of beta FSH. During this time period, the mRNA levels of the alpha and beta LH subunits increased by 11- and 8-fold, respectively. At the final stages of vitellogenic growth, mRNA levels of beta FSH declined to basal levels, whereas the mRNA levels of the alpha and beta LH subunits remained elevated. Throughout the study, pituitary LH concentration was positively correlated to the mRNA levels of beta LH, but plasma levels of LH remained low and unchanged (0.4-0.8 ng/ml) despite increasing levels of pituitary LH concentration, suggesting a regulated secretion pathway. Taken together, the data show that the profiles of beta FSH and beta LH mRNAs appear to follow an annual rhythm that is associated with developmental events in the growing oocytes. In particular, increasing levels of beta FSH mRNA appear to underlie the first sexual maturity in the female striped bass.