title: Expression and functional characterization of intrafollicular GH-IGF system in the zebrafish ovary.
abstract: The somatotrophic axis plays important roles in influencing reproduction. All key members of this axis including growth hormone (GH, gh), GH receptors (ghra and ghrb), insulin-like growth factors (IGFs, igf1, igf2 and igf3) and IGF receptors (igf1ra and igf1rb) were detected in the zebrafish ovary. GH was exclusively expressed in the full-grown oocytes, while its receptors were detectable in both the follicle cells and oocytes. The IGFs and their receptors were all expressed in both compartments except igf3, which was expressed in the follicle cells only. During folliculogenesis, there was a sharp decrease of gh expression at follicle activation; however, the expression of its receptors increased significantly. The expression profiles of igf1, igf2a, and igf2b were similar to that of fshr, whereas igf3 expression was close to lhcgr, suggesting differential roles for different forms of IGFs in follicle development. To examine if the ovarian GH-IGF system is regulated by gonadotropins (e.g., hCG) and GH, we performed in vitro experiments using cultured zebrafish follicle cells. The expression of igf1 and igf1ra, but not others, was down-regulated by hCG (LH analog), whereas recombinant zebrafish GH stimulated igf1 expression. In addition, GH also increased the expression of activin βA subunit (inhbaa). In agreement with this, the stimulatory effect of GH but not IGF-I on oocyte maturation could be abolished by follistatin. In conclusion, the present study revealed an intrafollicular network involving GH-IGF mini-axis in the zebrafish ovary; however, it might not work in the same way as that of the systemic somatotrophic axis.
authors.affiliation: School of Life Sciences and Centre for Cell and Developmental Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhou
authors.affiliation: School of Life Sciences and Centre for Cell and Developmental Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Susana Man Ying
authors.initials: SM
authors.lastname: Yu
authors.affiliation: Centre of Reproduction, Development and Aging, Faculty of Health Sciences, University of Macau, Taipa, Macau, China; School of Life Sciences and Centre for Cell and Developmental Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China. Electronic address: weige@umac.mo.
authors.forename: Wei
authors.initials: W
authors.lastname: Ge
mesh_terms: D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D006080:Ovarian Follicle / Q000378:metabolism; D010053:Ovary / Q000502:physiology*; D015027:Zebrafish / Q000502:physiology*
chemical_list: D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone
keywords: Follicles; Growth hormone (GH); Insulin-like growth factors (IGFs); Ovary; Zebrafish