title: Neuroendocrine gene expression reveals a decrease in dopamine D2B receptor with no changes in GnRH system during prepubertal metamorphosis of silvering in wild Japanese eel.
abstract: Silvering is a prepubertal metamorphosis preparing the eel to the oceanic reproductive migration. A moderate gonad development occurs during this metamorphosis from the sedentary yellow stage to the migratory silver stage. The aim of this study was to elucidate the molecular aspects of various endocrine parameters of BPG axis at different ovarian developmental stages in wild yellow and silver female Japanese eels. The GSI of the sampled female eels ranged between 0.18 and 2.3%, corresponding to yellow, pre-silver and silver stages. Gonad histology showed changes from previtellogenic oocytes in yellow eels to early vitellogenic oocytes in silver eels. Both serum E2 and T concentrations significantly increased with ovarian development indicating a significant activation of steroidogenesis during silvering. In agreement with previous studies, significant increases in pituitary gonadotropin beta subunits FSH-β and LH-β transcripts were also measured by qPCR, supporting that the activation of pituitary gonadotropin expression is likely responsible for the significant ovarian development observed during silvering. We investigated for the first time the possible brain neuroendocrine mechanisms involved in the activation of the pituitary gonadotropic function during silvering. By analyzing the expression of genes representative of the stimulatory GnRH control and the inhibitory dopaminergic control. The transcript levels of mGnRH and the three GnRH receptors did not change in the brain and pituitary between yellow and silver stages, suggesting that gene expression of the GnRH system is not significantly activated during silvering. The brain transcript levels of tyrosine hydroxylase, limiting enzyme of DA synthesis did not change during silvering, indicating that the DA synthesis activity was maintained. In contrast, a significant decrease in DA-D2B receptor expression in the forebrain and pituitary was observed, with no changes in DA-D2A receptor. The decrease in the pituitary expression of DA-D2BR during silvering would allow a reduced inhibitory effect of DA. We may raise the hypothesis that this regulation of D2BR gene expression is one of the neuroendocrine mechanisms involved in the slight activation of the pituitary gonadotropin and gonadal activity that occur at silvering.
authors.affiliation: Department of Aquaculture, National Kaohsiung Marine University, Kaohsiung 811, Taiwan. Electronic address: srjeng@webmail.nkmu.edu.tw.
authors.forename: Shan-Ru
authors.initials: SR
authors.lastname: Jeng
authors.affiliation: Department of Aquaculture, National Kaohsiung Marine University, Kaohsiung 811, Taiwan.
authors.forename: Wen-Shiun
authors.initials: WS
authors.lastname: Yueh
authors.affiliation: Department of Aquaculture, National Kaohsiung Marine University, Kaohsiung 811, Taiwan.
authors.forename: Yi-Ting
authors.initials: YT
authors.lastname: Pen
authors.affiliation: Tungkang Biotechnology Research Center, Fisheries Research Institute, Council of Agriculture, Tungkang 928, Taiwan.
authors.forename: Yan-Horn
authors.initials: YH
authors.lastname: Lee
authors.affiliation: Freshwater Aquaculture Research Center, Fisheries Research Institute, Council of Agriculture, Lukang 505, Taiwan.
authors.forename: Guan-Ru
authors.initials: GR
authors.lastname: Chen
authors.affiliation: Muséum National d'Histoire Naturelle, Sorbonne Universités, Research Unit BOREA, Biology of Aquatic Organisms and Ecosystems, CNRS 7208 - IRD207 - UPMC - UCBN, 75231 Paris Cedex 05, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Dufour
authors.affiliation: Department of Aquaculture, National Taiwan Ocean University, Keelung 202, Taiwan; Center of Excellence for the Oceans, National Taiwan Ocean University, Keelung 202, Taiwan. Electronic address: b0044@mail.ntou.edu.tw.
authors.forename: Ching-Fong
authors.initials: CF
authors.lastname: Chang
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004298:Dopamine / Q000378:metabolism*; D004524:Eels / Q000254:growth & development* / Q000378:metabolism; D005260:Female; D037201:Follicle Stimulating Hormone, beta Subunit / Q000378:metabolism; D005786:Gene Expression Regulation; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D015151:Immunoblotting; D007124:Immunoenzyme Techniques; D037101:Luteinizing Hormone, beta Subunit / Q000378:metabolism; D008675:Metamorphosis, Biological / Q000502:physiology*; D009490:Neurosecretory Systems / Q000502:physiology*; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D010053:Ovary / Q000166:cytology / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D012098:Reproduction / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012741:Sexual Maturation; D012880:Skin Pigmentation / Q000502:physiology*
chemical_list: D037201:Follicle Stimulating Hormone, beta Subunit; D037101:Luteinizing Hormone, beta Subunit; D012333:RNA, Messenger; D017448:Receptors, Dopamine D2; D007987:Gonadotropin-Releasing Hormone; D004298:Dopamine
keywords: Dopamine; Dopamine D2 receptor; GnRH; Gonadotropins; Silvering