Rainbow trout follicular maturational competence acquisition is associated with an increased expression of follicle stimulating hormone receptor and insulin-like growth factor 2 messenger RNAs.

Post-vitellogenic female rainbow trout (Oncorhynchus mykiss) were assayed in vitro for follicular maturational competence (FMC). Ovarian follicles were stimulated with a range of concentrations of partially purified gonadotropin. The efficient concentration for 50% germinal vesicle breakdown (GVBD) was calculated and used as an indicator of FMC. Before in vitro assay, ovarian tissue was sampled in order to quantify mRNA abundance of specific genes in the ovarian follicle by real-time PCR. In addition, maturation-inducing steroid (MIS, 17, 20 beta-dihydroxy-4-pregnen-3-one) and estradiol (E2) plasma levels were measured by radioimmunoassay. The mRNA expression of several genes such as luteinizing hormone receptor (LH-r), follicular stimulating hormone receptor (FSH-r), insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), insulin-like growth factor receptor 1a (IGF-r1a), and 20 beta-hydroxysteroid dehydrogenase (20 beta-HSD) that are putatively expressed in the preovulatory ovary, was studied in females of varying FMC using real-time PCR. FMC acquisition is characterized by an increase of MIS circulating levels and a concomitant drop of E2 levels. At the ovarian level, no significant variation of LH-r, 20 beta-HSD, IGF1, and IGF-r1a mRNA abundance was observed among females of varying FMC. In contrast, FSH-r and IGF2 mRNA levels were significantly higher in females exhibiting high FMC. In addition, correlation analyses showed that IGF2 and FSH-r, mRNA levels were positively correlated with FMC. These results indicate that FMC acquisition is associated with an increased expression of these gene products that may be useful markers of FMC. Copyright 2003 Wiley-Liss, Inc.