Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Yokohama, 236-8648, Japan.
Hakatajima Field Station, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Kinoura, Imabari, Ehime, 794-2305, Japan.
BMC Genomics. 2020 Sep 29;21(1):668. doi: 10.1186/s12864-020-07080-1.
The clupeoid fishes are ecologically and commercially important fish species worldwide that exhibit a high level of population fluctuation, accompanied by alteration of reproductive traits. However, knowledge about their reproductive physiology in order to understand mechanisms underlying such population dynamics is limited. The endocrine system along with the brain-pituitary-gonadal (BPG) axis is critical for regulating reproduction. The aims of this study were to provide transcript data and genes related to the BPG axis, and to characterize the expression profiles of ovarian steroidogenesis-related genes in the Japanese sardine (Sardinops melanostictus, Clupeidae).
RNA sequencing was performed using the sardine brain, pituitary, and gonad in both sexes. A total of 290,119 contigs were obtained and 115,173 non-redundant ORFs were annotated. The genes differentially expressed between ovary and testis were strongly associated with GO terms related to gamete production. The tissue-specific profile of the abundance of transcripts was characterized for the major regulators in the BPG axis, such as gonadotropin-releasing hormone, gonadotropin, and steroidogenic enzyme. By comparing between ovary and testis, out of eight different 17β-hydroxysteroid dehydrogenase (Hsd17b) genes identified, higher hsd17b7 expression was found in testis, whereas higher expression of hsd17b8, hsd17b10, hsd17b12a, and hsd17b12b was found in ovary. The cDNAs encoding key endocrine factors in the ovarian steroidogenic pathway were cloned, sequenced, and quantitatively assayed. In the pituitary, follicle-stimulating hormone beta peaked during vitellogenesis, while luteinizing hormone beta peaked at the completion of vitellogenesis. In the ovary, follicle-stimulating hormone receptor and luteinizing hormone receptor were upregulated from mid- to late phase of vitellogenesis. Furthermore, three steroidogenic enzyme genes (cyp11a1, cyp17a1, and cyp19a1a) gradually increased their expression during ovarian development, accompanying a rise in serum estradiol-17β, while 3β-hydroxysteroid dehydrogenase and steroidogenic acute regulatory protein did not change significantly.
This is the first report of deep RNA sequencing analysis of Japanese sardine, in which many key genes involved in the BPG axis were identified. Expression profiles of ovarian steroidogenesis-related genes provide a molecular basis of the physiological processes underlying ovarian development in the sardine. Our study will be a valuable resource for clarifying the molecular biology of clupeoid fishes.
鲱形目鱼类是全球具有重要生态和商业价值的鱼类，其种群波动较大，生殖特征也随之改变。然而，人们对于这些鱼类生殖生理学的了解，还不足以解释其种群动态的机制。内分泌系统与脑垂体性腺（BPG）轴对于调节生殖功能至关重要。本研究旨在提供与 BPG 轴相关的转录数据和基因，并对日本沙丁鱼（Sardinops melanostictus，鲱科）卵巢甾体生成相关基因的表达谱进行特征描述。
对雌雄沙丁鱼的脑、垂体和性腺进行了 RNA 测序。共获得 290119 个连续序列，注释了 115173 个非冗余 ORF。卵巢和精巢中差异表达的基因与配子生成相关的 GO 术语密切相关。BPG 轴主要调控因子的组织特异性丰度谱特征明显，如促性腺激素释放激素、促性腺激素和甾体生成酶。通过比较卵巢和精巢，在所鉴定的 8 种不同的 17β-羟类固醇脱氢酶（Hsd17b）基因中，hsd17b7 在精巢中的表达水平较高，而 hsd17b8、hsd17b10、hsd17b12a 和 hsd17b12b 在卵巢中的表达水平较高。克隆、测序并定量检测了卵巢甾体生成途径中关键内分泌因子的 cDNA。在垂体中，β-促卵泡激素在卵黄发生期达到峰值，而β-促黄体激素在卵黄发生完成时达到峰值。在卵巢中，促卵泡激素受体和黄体生成素受体在卵黄发生的中晚期上调。此外，三种甾体生成酶基因（cyp11a1、cyp17a1 和 cyp19a1a）在卵巢发育过程中逐渐表达增加，同时血清雌二醇-17β水平升高，而 3β-羟类固醇脱氢酶和甾体急性调节蛋白的表达没有显著变化。
这是首次对日本沙丁鱼进行深度 RNA 测序分析，其中鉴定了许多参与 BPG 轴的关键基因。卵巢甾体生成相关基因的表达谱为沙丁鱼卵巢发育的生理过程提供了分子基础。本研究将为阐明鲱形目鱼类的分子生物学提供有价值的资源。
