Integrative Science Center of Germplasm Creation in Western China (CHONGQING) Science City & College of Fisheries, Key Laboratory of Freshwater Fish Reproduction and Development Ministry of Education, Key Laboratory of Aquatic Sciences of Chongqing, Southwest University, Chongqing 402460, China.
Int J Mol Sci. 2024 Aug 21;25(16):9063. doi: 10.3390/ijms25169063.
In mammals, 17-beta hydroxysteroid dehydrogenase 2 (Hsd17b2) enzyme specifically catalyzes the oxidation of the C17 hydroxyl group and efficiently regulates the activities of estrogens and androgens to prevent diseases induced by hormone disorders. However, the functions of the gene involved in animal sex differentiation are still largely unclear. The ricefield eel (), a protogynous hermaphroditic fish with a small genome size (2 = 24), is usually used as an ideal model to study the mechanism of sex differentiation in vertebrates. Therefore, in this study, gene cDNA was cloned and its mRNA expression profiles were determined in the ricefield eel. The cloned cDNA fragment of was 1230 bp, including an open reading frame of 1107 bp, encoding 368 amino acid residues with conserved catalytic subunits. Moreover, real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis showed that mRNA expressed strongly in the ovaries at early developmental stages, weakly in liver and intestine, and barely in testis and other tissues. In particular, mRNA expression was found to peak in ovaries of young fish and ovotestis at the early stage, and eventually declined in gonads from the late ovotestis to testis. Likewise, chemical in situ hybridization results indicated that the mRNA signals were primarily detected in the cytoplasm of oogonia and oocytes at stage I-II, subsequently concentrated in the granulosa cells around the oocytes at stage Ⅲ-Ⅳ, but undetectable in mature oocytes and male germ cells. Intriguingly, in ricefield eel ovaries, mRNA expression could be significantly reduced by 17β-estradiol (E2) or tamoxifen (17β-estradiol inhibitor, E2I) induction at a low concentration (10 ng/mL) and increased by E2I induction at a high concentration (100 ng/mL). On the other hand, both the melatonin (MT) and flutamide (androgen inhibitor, AI) induction could significantly decrease mRNA expression in the ovary of ricefield eel. This study provides a clue for demonstrating the mechanism of sexual differentiation in fish. The findings of our study imply that the gene could be a key regulator in sexual differentiation and modulate sex reversal in the ricefield eel and other hermaphroditic fishes.
在哺乳动物中，17-β羟甾类脱氢酶 2（Hsd17b2）酶特异性催化 C17 羟基的氧化，并有效地调节雌激素和雄激素的活性，以防止由激素紊乱引起的疾病。然而，涉及动物性别分化的基因的功能在很大程度上仍然不清楚。稻鳗（）是一种具有小基因组大小（2=24）的雌雄同体的鱼类，通常被用作研究脊椎动物性别分化机制的理想模型。因此，在本研究中，克隆了基因的 cDNA，并确定了其在稻鳗中的 mRNA 表达谱。克隆的 cDNA 片段长 1230bp，包含一个 1107bp 的开放阅读框，编码 368 个氨基酸残基，具有保守的催化亚基。此外，实时定量逆转录聚合酶链反应（RT-qPCR）分析显示，mRNA 在早期发育阶段的卵巢中强烈表达，在肝脏和肠道中弱表达，在睾丸和其他组织中几乎不表达。特别是，mRNA 表达在幼鱼和早期卵巢中发现峰值，最终在卵巢从晚期卵巢到睾丸中下降。同样，化学原位杂交结果表明，在 I-II 期的卵母细胞和卵母细胞中，主要检测到 mRNA 信号，随后在 III-IV 期集中在卵母细胞周围的颗粒细胞中，但在成熟卵母细胞和雄性生殖细胞中检测不到。有趣的是，在稻鳗卵巢中，低浓度（10ng/mL）的 17β-雌二醇（E2）或他莫昔芬（17β-雌二醇抑制剂，E2I）诱导和高浓度（100ng/mL）的 E2I 诱导均可显著降低 mRNA 的表达。另一方面，褪黑素（MT）和氟他胺（雄激素抑制剂，AI）的诱导均可显著降低稻鳗卵巢中 mRNA 的表达。本研究为阐明鱼类性分化机制提供了线索。我们的研究结果表明，基因可能是性分化的关键调节因子，并调节稻鳗和其他雌雄同体鱼类的性反转。
