title: Insulin-like growth factor 3 regulates expression of genes encoding steroidogenic enzymes and key transcription factors in the Nile tilapia gonad.
abstract: Insulin-like growth factors (Igfs) are implicated in a wide variety of physiological roles in teleost gonadal development and reproduction. In the present study, igf3 mRNA expression in the tilapia ovary was found to be higher than in the testis from 5 to 40 days after hatching (dah) but was lower than that in testis from 50 to 70 dah. Consistently, Igf3 protein signal was detected in the somatic cells of XX and XY gonads from 10 dah until adulthood by immunohistochemistry, using a specific Igf3 polyclonal antibody. Incubation of ovarian and testicular cells in primary culture with recombinant Igf3 significantly increased nr5a1, foxl2, dmrt1, cyp19a1a, cyp11a1, cyp11b2, hsd3b2 , and cyp17a1 expression in a time- and dose-dependent manner. Promoter analysis using luciferase assays in HEK293 cells revealed that igf3 promoter activity was directly activated by Nr5a1 (Sf1) and further enhanced by Foxl2, Nr0b1a (Dax1), and Nr0b1b (Dax2) but repressed by Dmrt1 and estrogen receptor (Esr1, Esr2a, or Esr2b) along with 17beta-estradiol treatment. In addition, igf3 promoter activity was increased slightly by forskolin treatment alone but synergistically up-regulated by transfection with nr5a1. These in vitro results correlated well with the expression profile of igf3 during early gonad differentiation. Our results indicated that igf3 is involved in fish gonad steroidogenesis because of its ability to regulate the expression of foxl2, dmrt1, and nr5a1 and steroidogenic enzymes. The expression of igf3 is in turn regulated by transcription factors Foxl2, Dmrt1, and Nr5a1, as well as by 17beta-estradiol treatment.
authors.affiliation: Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, School of Life Science, Southwest University, Chongqing, China.
authors.forename: Minghui
authors.initials: M
authors.lastname: Li
authors.forename: Fengrui
authors.initials: F
authors.lastname: Wu
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gu
authors.forename: Tingru
authors.initials: T
authors.lastname: Wang
authors.forename: Hai
authors.initials: H
authors.lastname: Wang
authors.forename: Shijie
authors.initials: S
authors.lastname: Yang
authors.forename: Yunlv
authors.initials: Y
authors.lastname: Sun
authors.forename: Linyan
authors.initials: L
authors.lastname: Zhou
authors.forename: Xigui
authors.initials: X
authors.lastname: Huang
authors.forename: Baowei
authors.initials: B
authors.lastname: Jiao
authors.forename: Christopher H K
authors.initials: CH
authors.lastname: Cheng
authors.forename: Deshou
authors.initials: D
authors.lastname: Wang
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D023681:Cichlids / Q000235:genetics*; D005576:Colforsin / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D010053:Ovary / Q000187:drug effects / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D011960:Receptors, Estrogen / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013002:Somatomedins / Q000235:genetics / Q000378:metabolism*; D013256:Steroids / Q000096:biosynthesis*; D013737:Testis / Q000187:drug effects / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D011960:Receptors, Estrogen; D013002:Somatomedins; D013256:Steroids; D014157:Transcription Factors; D005576:Colforsin; D004958:Estradiol