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      Differential Regulation of Luteinizing Hormone and Follicle-Stimulating Hormone Expression during Ovarian Development and under Sexual Steroid Feedback in the European Eel

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          Pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are, in teleosts as in mammals, under the control of hypothalamic factors and steroid feedbacks. In teleosts, feedback regulations largely vary depending on species and physiological stage. In the present study the regulation of FSH and LH expression was investigated in the European eel, a fish of biological and phylogenetical interest as a representative of an early group of teleosts. The eel FSHβ subunit was cloned, sequenced and together with earlier isolated eel LHβ and glycoprotein hormone α (GPα) subunits used to study the differential regulation of LH and FSH. In situ hybridization indicated that FSHβ and LHβ are expressed by separate cells of the proximal pars distalis of the adenohypophysis, differently from the situation in mammals. The profiles of LHβ and FSHβ subunit expression were compared during experimental ovarian maturation, using dot-blot assays. Expression levels for LHβ and GPα increased throughout ovarian development with a positive correlation between these two subunits. Conversely, FSHβ mRNA levels decreased. To understand the role of sex steroids in these opposite variations, immature eels were treated with estradiol (E<sub>2</sub>)and testosterone (T), both steroids being produced in eel ovaries during gonadal development. E<sub>2</sub> treatment induced increases in both LHβ and GPα mRNA levels, without any significant effect on FSHβ. In contrast, T treatment induced a decrease in FSHβ mRNA levels, without any significant effect on the other subunits. These data demonstrate that steroids exert a differential feedback on eel gonadotropin expression, with an E<sub>2</sub>-specific positive feedback on LH and a T-specific negative feedback on FSH, leading to an opposite regulation of LH and FSH during ovarian development.

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          Most cited references 43

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          Molecular biology of the pituitary gonadotropins.

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            The brain-pituitary-gonad axis in male teleosts, with special emphasis on flatfish (Pleuronectiformes).

            The key component regulating vertebrate puberty and sexual maturation is the endocrine system primarily effectuated along the brain-pituitary-gonad (BPG) axis. By far most investigations on the teleost BPG axis have been performed on salmonids, carps, catfish and eels. Accordingly, earlier reviews on the BPG axis in teleosts have focused on these species, and mainly on females (e.g. 'Fish Physiology, vol. IXA. Reproduction (1983) pp. 97'; 'Proceedings of the Fourth International Symposium on the Reproductive Physiology of Fish. FishSymp91, Sheffield, UK, 1991, pp. 2'; 'Curr. Top. Dev. Biol. 30 (1995) pp. 103'; 'Rev. Fish Biol. Fish. 7 (1997) pp. 173'; 'Proceedings of the Sixth International Symposium on the Reproductive Physiology of Fish. John Grieg A/S, Bergen, Norway, 2000, pp. 211'). However, in recent years new data have emerged on the BPG axis in flatfish, especially at the level of the brain and pituitary. The evolutionarily advanced flatfishes are important model species both from an evolutionary point of view and also because many are candidates for aquaculture. The scope of this paper is to review the present status on the male teleost BPG axis, with an emphasis on flatfish. In doing so, we will first discuss the present understanding of the individual constituents of the axis in the best studied teleost models, and thereafter discuss available data on flatfish. Of the three constituents of the BPG axis, we will focus especially on the pituitary and gonadotropins. In addition to reviewing recent information on flatfish, we present some entirely new information on the phylogeny and molecular structure of teleost gonadotropins.
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              The first production of glass eel in captivity: fish reproductive physiology facilitates great progress in aquaculture

               H Tanaka,  H Kagawa,  H Ohta (2003)

                Author and article information

                S. Karger AG
                July 2005
                06 July 2005
                : 81
                : 2
                : 107-119
                aDepartment of Aquaculture, Swedish University of Agricultural Sciences, Umea, Sweden; bBiologie des Organismes Marins et Ecosystèmes, DMPA, Museum National d’Histoire Naturelle, Paris, and cCemagref, Unité RAC, Cestas, France
                86404 Neuroendocrinology 2005;81:107–119
                © 2005 S. Karger AG, Basel

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                Figures: 6, Tables: 1, References: 62, Pages: 13
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