Guchhait Rajkumar, Chatterjee Ankit, Mukherjee Dilip, Pramanick Kousik
Integrative Biology Research Unit, Department of Life Sciences, Presidency University, 86/1, College Street, Kolkata 700073, India.
Endocrinology Laboratory, Department of Zoology, University of Kalyani, Kalyani 741235, India.
Gen Comp Endocrinol. 2018 Nov 1;268:40-49. doi: 10.1016/j.ygcen.2018.07.014. Epub 2018 Jul 25.
The endocrine regulation of gonadal development and annual variation of key sex steroids is the basic knowledge to understand the reproductive cycle of teleost fish. Present study was aimed to investigate the levels of gonadotropins in relation to the follicular development and plasma steroids during the reproductive cycle of female Trichogaster fasciata. Female fish were sampled and ovarian development is described histologically throughout the year in relation to the seasonal variations of gonadosomatic index (GSI); follicle stimulating hormone (FSH) and luteinizing hormone (LH); three key steroids for folliculogenesis and maturation i.e. testosterone (T), 17β-estradiol (E) and 17α20βdihydroxy4pregnen3one (17,20β-P). Relatively higher level of FSH was observed till the ovary reaches in late vitellogenic stage confirms that FSH regulates the early folliculogenesis of the ovary, whereas LH peak was observed in the postvitellogenic stage, which indicates that maturation and ovulation were controlled by LH. Seasonal steroid profiles show that both T and E reach its maximum level prior to the 17,20β-P which attain its peak value in the month of August. Thus, single peak values of LH and 17,20β-P coinciding with GSI peak, clearly indicates that T. fasciata breeds only once in a year. Furthermore, to elucidate the molecular basis of the reproductive cycle, this study analyzes the other key factors of ovarian function such as cyp19a1a gene expression, aromatase activity and SF-1 localization throughout the year. cyp19a1a gene expression and the aromatase activity were highest in vitellogenic stages indicate that relatively higher E production in this stage is regulated by FSH. Immunohistochemical localizations of aromatase and SF-1 in the cellular layer of oocytes demonstrated that aromatase is FSH-dependent and SF-1 could be regulated by both FSH and LH as relatively higher amount of aromatase was localized in the vitellogenic stage oocytes than the postvitellogenic and post germinal vesicle breakdown (post-GVBD) stages; whereas, high amount of SF-1 was observed in vitellogenic, postvitellogenic and post-GVBD stages. These data regarding the reproductive endocrinology of T. fasciata may be useful to understand the interaction between gonadotropins, steroids, aromatase and SF-1 in teleost fishes and may contribute to restoration of the ecologically important fish through artificial reproduction.
性腺发育的内分泌调节以及关键性类固醇的年度变化是理解硬骨鱼繁殖周期的基础知识。本研究旨在调查雌性条纹毛足鲈繁殖周期中促性腺激素水平与卵泡发育及血浆类固醇的关系。对雌鱼进行采样，并根据性腺体指数（GSI）的季节性变化，从组织学角度描述全年的卵巢发育情况；同时检测促卵泡激素（FSH）和促黄体生成素（LH）；以及卵泡发生和成熟的三种关键类固醇，即睾酮（T）、17β-雌二醇（E）和17α20β-二羟基-4-孕烯-3-酮（17,20β-P）。在卵巢达到卵黄生成后期之前，观察到FSH水平相对较高，这证实FSH调节卵巢的早期卵泡发生，而在卵黄生成后期观察到LH峰值，这表明成熟和排卵受LH控制。季节性类固醇谱显示，T和E在17,20β-P之前达到最高水平，17,20β-P在8月份达到峰值。因此，LH和17,20β-P的单峰值与GSI峰值一致，清楚地表明条纹毛足鲈一年只繁殖一次。此外，为了阐明繁殖周期的分子基础，本研究分析了全年卵巢功能的其他关键因素，如cyp19a1a基因表达、芳香化酶活性和SF-1定位。cyp19a1a基因表达和芳香化酶活性在卵黄生成阶段最高，表明该阶段相对较高的E产生受FSH调节。芳香化酶和SF-1在卵母细胞细胞层的免疫组织化学定位表明，芳香化酶依赖于FSH，SF-1可能受FSH和LH两者调节，因为在卵黄生成阶段的卵母细胞中定位的芳香化酶量比卵黄生成后期和生发泡破裂后期（GVBD后）阶段的多；而在卵黄生成、卵黄生成后期和GVBD后阶段观察到大量的SF-1。这些关于条纹毛足鲈生殖内分泌学的数据可能有助于理解硬骨鱼中促性腺激素、类固醇、芳香化酶和SF-1之间的相互作用，并可能通过人工繁殖有助于恢复具有生态重要性的鱼类。
