Steroidogenic and maturation-inducing potency of native gonadotropic hormones in female chub mackerel, Scomber japonicus
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RESEARCH
Open Access
Steroidogenic and maturation-inducing potency of native gonadotropic hormones in female chub mackerel, Scomber japonicus Hirofumi Ohga1, Kensuke Kaneko1, Akio Shimizu2, Hajime Kitano1, Sethu Selvaraj1, Mitsuo Nyuji1, Hayato Adachi1, Akihiko Yamaguchi1 and Michiya Matsuyama1*
Abstract Background: The gonadotropins (GtHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are produced in the pituitary gland and regulates gametogenesis through production of gonadal steroids. However, respective roles of two GtHs in the teleosts are still incompletely characterized due to technical difficulties in the purification of native GtHs. Methods: Native FSH and LH were purified from the pituitaries of adult chub mackerel, Scomber japonicus by anion-exchange chromatography and immunoblotting using specific antisera. The steroidogenic potency of the intact chub mackerel FSH (cmFSH) and LH (cmLH) were evaluated in mid- and late-vitellogenic stage follicles by measuring the level of gonadal steroids, estradiol-17beta (Ε2) and 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P). In addition, we evaluated the maturation-inducing potency of the GtHs on same stage follicles. Results: Both cmFSH and cmLH significantly stimulated E2 production in mid-vitellogenic stage follicles. In contrast, only LH significantly stimulated the production of 17,20beta-P in late-vitellogenic stage follicles. Similarly, cmLH induced final oocyte maturation (FOM) in late-vitellogenic stage follicles. Conclusions: Present results indicate that both FSH and LH may regulate vitellogenic processes, whereas only LH initiates FOM in chub mackerel. Keywords: Chub mackerel, Perciform, Asynchronous, FSH, LH, Steroidogenesis, Oocyte maturation
Background In teleosts and other vertebrates, reproductive processes are regulated by a network of endocrine hormones on the brain–pituitary–gonad (BPG) axis. Pituitary gonadotropins (GtHs), follicle-stimulating hormone (FSH), and luteinizing hormone (LH), are key central signaling molecules on the BPG axis. GtHs regulate different stages of ovarian development by stimulating gonadal steroid production in the somatic cells surrounding the germ cells [1,2]. In mammalian vertebrates, the physiological roles of GtHs are well established; FSH regulates ovarian follicular development and LH promotes follicular maturation [3]. However, the role of GtHs in teleosts * Correspondence: [email protected] 1 Laboratory of Marine Biology, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan Full list of author information is available at the end of the article
reproduction is still incompletely characterized, mainly due to diverse reproductive strategies and technical difficulties in the purification of native GtHs. Specific roles for teleost GtHs have been revealed mainly in salmonids, which exhibit synchronous or group-synchronous ovarian development and spawn single batch of eggs. These features enable an easy correlation between changes in endocrine hormones and ovarian devel
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