%0 Journal Article
%T Biochemical characterization of the Arctic char (Salvelinus alpinus) ovarian progestin membrane receptor
%A A H£¿kan Berg
%A Peter Thomas
%A Per-Erik Olsson
%J Reproductive Biology and Endocrinology
%D 2005
%I BioMed Central
%R 10.1186/1477-7827-3-64
%X Meiosis is arrested at prophase 1 in vertebrate oocytes during their growth phase and a surge in gonadotropin secretion is required to induce the resumption of meiosis and oocyte maturation (OM). It has been demonstrated that gonadotropin (luteinizing hormone, LH) initiates oocyte maturation and ovulation in teleost fish and amphibians by stimulating the production of a maturation inducing substance (MIS) by the ovarian follicles [1]. The MISs have been identified as progesterone in a variety of amphibians and as hydroxylated progestins in teleost fishes [2,3]. Two C21 steroids, 17, 20¦Â-dihydroxy-4-pregnen-3-one (17,20¦Â-P) [4] and 17, 20¦Â, 21-trihydroxy-4-pregnen-3-one (20¦Â-S) [5,6], have been positively identified as the MISs in amago salmon and Atlantic croaker, respectively. While 17,20¦Â-P is the major MIS for salmonids and cyprinids [2], 20¦Â-S has been shown to be the predominant MIS in sciaenids and some other perciform fishes [3].MIS does not induce OM in amphibians and teleosts by the classical mechanism of steroid action, instead it acts at the cell surface by binding to receptors located on the oocyte plasma membrane [3,7]. Activation of the MIS receptor results in induction of OM via a non-genomic mechanism [8] mediated by G-proteins and second messengers such as cAMP [9,10]. Progestin membrane receptors (mPRs) have been identified and characterized in several amphibian and teleost species [11-15]. Moreover, membrane progestin receptor (mPR) upregulation by gonadotropins during OM has been demonstrated in several teleost species [14,16] and has been associated with development of the ability of oocytes to become responsive to the MIS (oocyte maturational competence, OMC) and complete OM [17]. A two-stage model of the gonadotropic control of OM in teleosts has been proposed based on the results with several teleost species showing that priming of fully grown follicle-enclosed oocytes by gonadotropin is required to induce OMC [18]. Early studies in rainbow t
%U http://www.rbej.com/content/3/1/64