title: Testosterone regulates FGF-2 expression during testis maturation by an IRES-dependent translational mechanism.
abstract: Spermatogenesis is a complex process involving cell proliferation, differentiation, and apoptosis. Fibroblast growth factor 2 (FGF-2) is involved in testicular function, but its role in spermatogenesis has not been fully documented. The control of FGF-2 expression particularly occurs at the translational level, by an internal ribosome entry site (IRES)-dependent mechanism driving the use of alternative initiation codons. To study IRES activity regulation in vivo, we have developed transgenic mice expressing a bicistronic construct coding for two luciferase genes. Here, we show that the FGF-2 IRES is age-dependently activated in mouse testis, whereas EMCV and c-myc IRESs are not. Real-time PCR confirms that this regulation is translational. By using immunohistological techniques, we demonstrate that FGF-2 IRES stimulation occurs in adult, but not in immature, type-A spermatogonias. This is correlated with activation of endogenous FGF-2 expression in spermatogonia; whereas FGF-2 mRNA transcription is known to decrease in adult testis. Interestingly, the FGF-2 IRES activation is triggered by testosterone and is partially inhibited by siRNA directed against the androgen receptor. Two-dimensional analysis of proteins bound to the FGF-2 mRNA 5'UTR after UV cross-linking reveals that testosterone treatment correlates with the binding of several proteins. These data suggest a paracrine loop where IRES-dependent FGF-2 expression, stimulated by Sertoli cells in response to testosterone produced by Leydig cells, would in turn activate Leydig function and testosterone production. In addition, nuclear FGF-2 isoforms could be involved in an intracrine function of FGF-2 in the start of spermatogenesis, mitosis, or meiosis initiation. This report demonstrates that mRNA translation regulation by an IRES-dependent mechanism participates in a physiological process.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U589, Toulouse, France.
authors.forename: Irma G
authors.initials: IG
authors.lastname: Gonzalez-Herrera
authors.forename: Leonel
authors.initials: L
authors.lastname: Prado-Lourenco
authors.forename: Frédéric
authors.initials: F
authors.lastname: Pileur
authors.forename: Caroline
authors.initials: C
authors.lastname: Conte
authors.forename: Aurélie
authors.initials: A
authors.lastname: Morin
authors.forename: Florence
authors.initials: F
authors.lastname: Cabon
authors.forename: Hervé
authors.initials: H
authors.lastname: Prats
authors.forename: Stephan
authors.initials: S
authors.lastname: Vagner
authors.forename: Francis
authors.initials: F
authors.lastname: Bayard
authors.forename: Sylvie
authors.initials: S
authors.lastname: Audigier
authors.forename: Anne-Catherine
authors.initials: AC
authors.lastname: Prats
mesh_terms: D020121:5' Untranslated Regions; D000367:Age Factors; D059002:Androgen Receptor Antagonists; D000818:Animals; D003062:Codon; D016222:Fibroblast Growth Factor 2 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D017930:Genes, Reporter; D005813:Genes, Synthetic; D007985:Leydig Cells / Q000502:physiology*; D049410:Luciferases, Renilla / Q000235:genetics; D008297:Male; D008540:Meiosis; D051379:Mice; D008822:Mice, Transgenic; D008938:Mitosis; D019899:Paracrine Communication; D010442:Peptide Chain Initiation, Translational / Q000502:physiology; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics* / Q000528:radiation effects; D034741:RNA, Small Interfering / Q000494:pharmacology; D011944:Receptors, Androgen / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid; D012270:Ribosomes / Q000378:metabolism; D012708:Sertoli Cells / Q000502:physiology*; D013091:Spermatogenesis / Q000502:physiology*; D013737:Testis / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D013739:Testosterone / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D014466:Ultraviolet Rays
chemical_list: D020121:5' Untranslated Regions; D059002:Androgen Receptor Antagonists; D003062:Codon; D020033:Protein Isoforms; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011944:Receptors, Androgen; D011993:Recombinant Fusion Proteins; D016222:Fibroblast Growth Factor 2; D013739:Testosterone; D049410:Luciferases, Renilla