title: Rat ovarian insulin-like growth factor I (IGF-I) gene expression is granulosa cell-selective: 5'-untranslated mRNA variant representation and hormonal regulation.
abstract: We, and others, have recently reported that the ovary is a site of insulin-like growth factor (IGF)I gene expression. It was the objective of the present studies to assess the relative ovarian abundance of IGF-I transcripts with alternative 5'-untranslated (UT) regions, their cellular localization, and hormonal regulation. To this end, a solution hybridization/RNase protection assay was employed wherein total rat ovarian RNA was hybridized with a 404-base 32P-labelled rat IGF-I riboprobe corresponding to the Class A 5'UT variant. As in liver, three protected bands [322 (Class A), 297 (Class B), and 242 (Class C) bases long] were noted, in keeping with established alternative 5' UT transcripts. The ovarian (as the hepatic) Class C variant proved the most abundant. The ovarian Class B variant was barely detectable. Cellular localization studies revealed these ovarian IGF-I transcripts to be primarily, if not exclusively, of granulosa but not theca-interstitial cell origin. Treatment of immature (21-23 days old) hypophysectomized rats with a diethylstilbestrol (DES)-containing subcutaneous silastic implant for a total of 5 days resulted in a 2-fold increase in the (densitometrically quantified) abundance of ovarian IGF-I transcripts, a diametrically-opposed effect (2.6-fold decrease) being noted at the level of the liver. Whereas treatment of hypophysectomized rats with oGH by itself (150 micrograms, qd, sc x5 days) resulted in a 5-fold increase in hepatic IGF-I gene expression, a limited, albeit distinct inhibitory effect was observed on the steady-state levels of ovarian IGF-I mRNA. In contrast, combined treatment with oGH and DES yielded a 3-fold increase in the abundance of ovarian IGF-I transcripts, there being no net alteration in hepatic IGF-I gene expression. Taken together, these findings reveal ovarian expression of the 3 known 5'-UT IGF-I mRNA variants, document the granulosa cell as the main somatic ovarian cell of IGF-I mRNA generation, and indicate that hepatic and ovarian IGF-I gene expression are differentially regulated in diametrically opposed directions.
authors.affiliation: Department of Obstetrics/Gynecology, University of Maryland School of Medicine, Baltimore 21201.
authors.forename: E R
authors.initials: ER
authors.lastname: Hernandez
authors.forename: C T
authors.initials: CT
authors.lastname: Roberts
authors.forename: D
authors.initials: D
authors.lastname: LeRoith
authors.forename: E Y
authors.initials: EY
authors.lastname: Adashi
mesh_terms: D000818:Animals; D005260:Female; D005786:Gene Expression Regulation; D014644:Genetic Variation; D006107:Granulosa Cells / Q000502:physiology*; D013006:Growth Hormone / Q000494:pharmacology; D006728:Hormones / Q000502:physiology*; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D013002:Somatomedins / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D006728:Hormones; D012333:RNA, Messenger; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone