Zhao Chunyan, Xu Shihong, Liu Yifan, Wang Yanfeng, Liu Qinghua, Li Jun
Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
Fish Physiol Biochem. 2017 Feb;43(1):265-278. doi: 10.1007/s10695-016-0284-5. Epub 2016 Sep 8.
As a flatfish, the turbot (Scophthalmus maximus) is one of the most important farmed fish species with great commercial value, which has a strong sexual dimorphism on growth rate and sexual maturity. In this study, using histology, the basic information on proliferation and migration of germ cells and early gonadal development during sex differentiation in turbot were described in detail. There were six to nine individual primordial germ cells (PGCs) with large nuclei until 15 days post-hatching (dph). The PGCs located under the mesonephric ducts undergo migration along the dorsal mesentery toward the region of the genital ridge from 0 to 15 dph. During migration, the number of PGCs was constant, and the expression of vasa had no significant changes. At 20 dph, the aggregation of somatic cells at genital ridge indicated the formation of primary gonad. Furthermore, the number of PGCs was increased to 60 and the expression of vasa was upregulated for the first time. The undifferentiated gonads with no morphological indications of sex differentiation grew larger with the increase in germ cells and somatic cells number/size from 20 to 35 dph. During 36-52 dph, cytological gonadal differentiation was observed. In presumptive testes of type I gonadal tissue (with a lance shape), the number of germ cells increased steadily and the germ cells had the same characteristics as before. Meanwhile, in presumptive ovaries of type II gonadal tissue (with a club-like shape), the germ cells proliferated and induced in two different populations of germ cells. One type had the morphological characteristics as undifferentiated germ cells, while the other type of germ cells underwent mitosis exhibiting smaller size and mottled nuclei. At 60 dph, ovarian cavity was present in the gonad of type II, which would develop into ovaries. However, spermatogonial cysts were not noticed in the gonad of type I until 90 dph, which indicated the formation of the testes.
作为一种比目鱼，大菱鲆（Scophthalmus maximus）是具有重要商业价值的重要养殖鱼类之一，其在生长速度和性成熟方面具有强烈的性别二态性。在本研究中，利用组织学方法，详细描述了大菱鲆性别分化过程中生殖细胞增殖和迁移以及早期性腺发育的基本信息。孵化后15天（dph）之前，有6至9个单个的原始生殖细胞（PGC），其细胞核较大。从0至15 dph，位于中肾管下方的PGC沿着背系膜向生殖嵴区域迁移。在迁移过程中，PGC的数量保持恒定，vasa的表达没有显著变化。在20 dph时，生殖嵴处体细胞的聚集表明初级性腺形成。此外，PGC的数量增加到60个，vasa的表达首次上调。从20至35 dph，未分化的性腺没有性别分化的形态学迹象，随着生殖细胞和体细胞数量/大小的增加而变大。在36 - 52 dph期间，观察到性腺的细胞学分化。在I型性腺组织（长矛状）的假定睾丸中，生殖细胞数量稳步增加，且生殖细胞具有与之前相同的特征。同时，在II型性腺组织（棒状）的假定卵巢中，生殖细胞增殖并诱导出两种不同的生殖细胞群体。一种类型具有未分化生殖细胞的形态特征，而另一种类型的生殖细胞进行有丝分裂，表现出较小的尺寸和斑驳的细胞核。在60 dph时，II型性腺中出现卵巢腔，其将发育为卵巢。然而，直到90 dph才在I型性腺中注意到精原细胞囊肿，这表明睾丸形成。
