Gonadotropin regulation of NGFI-B messenger ribonucleic acid expression during ovarian follicle development in the rat

NGFI-B is an immediate-early gene that encodes an orphan nuclear receptor. The present study was designed to examine the localization and gonadotropin regulation of NGFI-B expression in the rat ovary. Northern blot analysis o f ovaries obtained from prepubertal rats revealed the increased expression of NGFI-B during prepubertal development. Treatment of immature rats with P MSG, however, decreased ovarian NGFI-B expression. The major cell types exp ressing NGFI-B messenger RNA were thecal cells of follicles in different si zes. In contrast, treatment of PMSG-primed rats with human (h) CG resulted in the rapid and transient stimulation of ovarian NGFI-B messenger RNA, rea ching a peak within 1 h. In situ hybridization analysis revealed that hCG t reatment induced the expression of NGFI-B in granulosa cells of preovulator y follicles. Treatment of cultured preovulatory follicles in vitro with LH further confirmed the time- and dose-dependent stimulation of NGFI-B messen ger RNA and protein. LH-stimulated NGFI-B expression in preovulatory follic les was abolished by a-amanitin, but was superinduced by cycloheximide. Fur thermore, treatment of adult cycling rats with pentobarbital abolished NGFI -B expression on proestrus, and exogenous administration of hCG restored it , indicating the role of the preovulatory surge of LH in the stimulation of NGFI-B expression. These results demonstrate the cell type-specific expres sion and gonadotropin induction of NGFI-B in granulosa cells of preovulator y follicles and suggest a role for NGFI-B in the ovulatory process.