Biochemical characterization of the Arctic char (Salvelinus alpinus) ovarian progestin membrane receptor

• Published in: Reproductive Biology and Endocrinology
• Main Authors: Berg, A Håkan, Thomas, Peter, Olsson, Per-Erik
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2005
• Subjects: Developmental Biology; Endocrinology; Reproductive Medicine; Obstetrics and Gynecology; Arctic; Salvelinus alpinus
• Online Access: http://dx.doi.org/10.1186/1477-7827-3-64; https://link.springer.com/content/pdf/10.1186/1477-7827-3-64.pdf

Abstract Membrane progestin receptors are involved in oocyte maturation in teleosts. However, the maturation-inducing steroid (MIS) does not appear to be conserved among species and several progestins may fulfill this function. So far, complete biochemical characterization has only been performed on a few species. In the present study we have characterized the membrane progestin receptor in Arctic char (Salvelinus alpinu s ) and show that the 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) receptor also binds several xenobiotics, thus rendering oocyte maturation sensitive to environmental pollutants. We identified a single class of high affinity (K d , 13.8 ± 1.1 nM), low capacity (B max , 1.6 ± 0.6 pmol/g ovary) binding sites by saturation and Scatchard analyses. Receptor binding displayed rapid association and dissociation kinetics typical of steroid membrane receptors, with t 1/2 s of less than 1 minute. The 17,20beta-P binding also displayed tissue specificity with high, saturable, and specific 17,20beta-P binding detected in ovaries, heart and gills while no specific binding was observed in muscle, brain or liver. Changes in 17,20beta-P binding during oocyte maturation were consistent with its identity as the oocyte MIS membrane receptor. Incubation of fully-grown ovarian follicles with gonadotropin induced oocyte maturation, which was accompanied by a five-fold increase in 17,20beta-P receptor binding. In addition, competition studies with a variety of steroids revealed that receptor binding is highly specific for 17,20beta-P, the likely maturation-inducing steroid (MIS) in Arctic char. The relative-binding affinities of all the other progestogens and steroids tested were less than 5% of that of 17,20beta-P for the receptor. Several ortho, para derivatives of DDT also showed weak binding affinity for the 17,20beta-P receptor supporting the hypothesis that xenobiotics may bind steroid receptors on the oocyte's surface and might thereby interfere with oocyte growth and maturation.