Sex steroid hormones play important roles in fish sex differentiation, gonadal development and secondary sexual characteristics. Olive flounder Paralichthys olivaceus is a valuable commercial marine fish species and has marked sexual dimorphism. However, the mechanisms of action of sex hormones in flounder sex are still unclear. In this study, a total of ten Hsd17b family genes, including Hsd17b3, -4, -7, -8, -9, -10, -12a, -12b, -14 and -15, were identified in the flounder, which encoded critical enzymes acting on sex steroid synthesis and metabolism. Hsd17b genes were distributed on eight chromosomes. Hsd17b12a and -12b were located on chromosomes 19 and 7, respectively. It was speculated that these two genes were just highly similar rather than different transcripts derived from the same gene. According to the results of domain and motif analyses, they all belonged to the SDR superfamily and contained conserved Hsd17b motifs TGxxxGxG, PGxxxT, NNAG and YxxxK. Analysis of amino acid sequences predicted that Hsd17b1, -4, -7, -12a and -14 were hydrophilic proteins. The stability of Hsd17b1, -3 and -12b proteins was predicted to be low. The various Hsd17b family genes differed in tissue expression pattern, and Hsd17b10, -12a and -12b were highly expressed in the flounder ovary. Moreover, throughout gonadal development, Hsd17b3 was highly expressed in the testis, and Hsd17b1, -12a and -12b were highly expressed in the ovary, suggesting that they might play an important role in testosterone synthesis in the testis or estrogen synthesis in the ovary. Activities of Hsd17b3 at stages I-V were all significantly higher in the testis than in the ovary (P < 0.05, P < 0.01). Transfection analysis in HEK293T cells showed that Hsd17b1 and -3 were located in both the cytoplasm and nucleus. Additionally, after challenging fish with tamoxifen, Hsd17b3 expression level in the testis decreased significantly (P < 0.01), and in the ovary no significant change was observed. Moreover, the expression of Hsd17b1 in the ovary was significantly upregulated after injection with flutamide (P < 0.05). These findings introduce the characteristics of the flounder Hsd17b in subfamily, which contribute to our understanding of the regulation of sex steroid hormone synthesis in fish gonadal development.

中文翻译：

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橄榄比目鱼Paralichthys olivaceus中17β-羟类固醇脱氢酶家族基因的特征和性别二态性。

性类固醇激素在鱼类性别分化，性腺发育和第二性征中起着重要作用。橄榄比目鱼Paralichthys olivaceus是一种有价值的商业海水鱼类，具有明显的性二态性。然而，性激素在比目鱼性生活中的作用机理仍不清楚。在这项研究中，在比目鱼中鉴定了总共十个Hsd17b家族基因，包括Hsd17b3，-4，-7，-8，-9，-10，-12a，-12b，-14和-15，它们编码作用于类固醇合成和代谢的关键酶。Hsd17b基因分布在八个染色体上。Hsd17b12a和-12b分别位于19号和7号染色体上。推测这两个基因是高度相似的，而不是源自相同基因的不同转录本。根据域和基序分析的结果，它们都属于SDR超家族，并包含保守的Hsd17b基序TGxxxGxG，PGxxxT，NNAG和YxxxK。氨基酸序列分析预测Hsd17b1，-4，-7，-12a和-14是亲水蛋白。Hsd17b1，-3和-12b蛋白的稳定性预计较低。各种Hsd17b家族基因的组织表达方式不同，并且Hsd17b10，-12a和-12b在比目鱼卵巢中高表达。此外，在整个性腺发育过程中，Hsd17b3在睾丸中高表达，Hsd17b1，-12a和-12b在卵巢中高表达，表明它们可能在睾丸中睾丸激素合成或卵巢中雌激素合成中发挥重要作用。在IV期，Hsd17b3的活性在睾丸中均显着高于卵巢（P <0.05，P <0.01）。HEK293T细胞的转染分析表明，Hsd17b1和-3位于细胞质和细胞核中。此外，用他莫昔芬攻击鱼后，睾丸中Hsd17b3的表达水平显着降低（P <0.01），而卵巢中则没有观察到显着变化。此外，注射氟他胺后，Hsd17b1在卵巢中的表达显着上调（P <0.05）。这些发现介绍了比目鱼Hsd17b在亚科中的特征，有助于我们了解鱼性腺发育中性类固醇激素合成的调控。HEK293T细胞的转染分析表明，Hsd17b1和-3位于细胞质和细胞核中。此外，用他莫昔芬攻击鱼后，睾丸中Hsd17b3的表达水平显着降低（P <0.01），而卵巢中则没有观察到显着变化。此外，注射氟他胺后，Hsd17b1在卵巢中的表达显着上调（P <0.05）。这些发现介绍了比目鱼Hsd17b在亚科中的特征，有助于我们了解鱼性腺发育中性类固醇激素合成的调控。HEK293T细胞的转染分析表明，Hsd17b1和-3位于细胞质和细胞核中。此外，用他莫昔芬攻击鱼后，睾丸中Hsd17b3的表达水平显着降低（P <0.01），而卵巢中则没有观察到显着变化。此外，注射氟他胺后，Hsd17b1在卵巢中的表达显着上调（P <0.05）。这些发现介绍了比目鱼Hsd17b在亚科中的特征，有助于我们了解鱼性腺发育中性类固醇激素合成的调控。注射氟他胺后，Hsd17b1在卵巢中的表达明显上调（P <0.05）。这些发现介绍了比目鱼Hsd17b在亚科中的特征，有助于我们了解鱼性腺发育中性类固醇激素合成的调控。注射氟他胺后，Hsd17b1在卵巢中的表达明显上调（P <0.05）。这些发现介绍了比目鱼Hsd17b在亚科中的特征，有助于我们了解鱼性腺发育中性类固醇激素合成的调控。