title: Dual role of IGF-II in oocyte maturation in southern flounder Paralichthys lethostigma: up-regulation of mPRα and resumption of meiosis.
abstract: Increasing evidence suggests a regulatory role for the IGF system in teleost oocyte maturation (OM). Our objectives were to determine if IGF-I and IGF-II regulate different stages of OM in southern flounder (Paralichthys lethostigma) and to identify the likely maturation-inducing steroid (MIS) in this species. The most abundant final product of ovarian steroidogenesis assays eluted at the position of 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S). 20β-S was also more potent in inducing germinal vesicle breakdown (GVBD) of maturationally-competent oocytes than other teleost MISs. IGF-II (100 nM) induced maturational competence (OMC), as greater GVBD was induced after incubation with IGF-II+20β-S compared to that of the 20β-S+20β-S or IGF-II+no treatment group. Incubation with IGF-II (100 nM) for 4-8 h significantly increased ovarian membrane progestin receptor alpha (mPRα or Paqr7b) mRNA levels 12-15% and mPRα protein levels 75-101%. Further, the IGF-II-induced increase in mPRα protein concentrations was partially blocked by pretreatment with Wortmannin, a Pik3 inhibitor, and PD 098,059, a Mapk inhibitor. Both IGF-I and -II (100 nM) induced GVBD of maturationally-competent oocytes was blocked by incubation with cycloheximide. Incubation with D,L-Aminoglutethimide decreased IGF-II-induced GVBD but had no effect on IGF-I-induced GVBD. IGF-I and -II were also able to induce GVBD of maturationally-incompetent oocytes, and elicited 75% and 135% greater GVBD, respectively, than hCG+20β-S at 100 nM. In conclusion, we show that 20β-S is the likely MIS in this species and that IGF-I and -II are also able to induce GVBD. Further, IGF-II not only induces OMC but also up-regulates ovarian mPRα mRNA and protein through Pik3- and Mapk-dependent pathways. This is the first demonstration of mPRα regulation by an IGF in any vertebrate species.
authors.affiliation: University of Texas at Austin Marine Science Institute, Port Aransas, TX 78373, USA.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Picha
authors.forename: Bao
authors.initials: B
authors.lastname: Shi
authors.forename: Peter
authors.initials: P
authors.lastname: Thomas
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D003001:Cloning, Molecular; D005260:Female; D005432:Flounder / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D008540:Meiosis / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009866:Oogenesis / Q000187:drug effects / Q000235:genetics; D010053:Ovary / Q000737:chemistry / Q000378:metabolism; D011980:Receptors, Progesterone / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D011980:Receptors, Progesterone; C101118:progesterone receptor A; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II