Institutional Repository of Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences
|Place of Conferral||中国科学院海洋研究所|
|Keyword||许氏平鲉 卵生鱼 滤泡胎盘 激素 基因表达模式|
Viviparous is a reproductive method that exists widely in nature. it occurrs in most vertebrates, including most cartilaginous fishes, several clades of bony fishes, amphibians, reptiles and most mammals. Viviparous reproduction provides stable nutrition, protection and other development conditions for embryos, reduces the adverse effects of external conditions on embryonic development, and greatly improves the survival rate of offspring. An important feature of viviparous birth is that the egg is fertilized in the female's body and the fertilized egg completes development in the female's body. In mammals, the placenta completes the exchange of nutrients and gas between the mother and the embryo. Therefore, for the viviparous bony fish, the morphological and physiological adaptations of the ovaries have great significance. In Scorpaenidae, four genera (Sebastes, Sebasticus, Helicolenus and Hozukius) also belong to the marine viviparity. Black rockfish (Sebastes schlegelii) belongs to viviparous fish and farmed as an important marine economic fish in China. It is widely inhabits in the waters of China, Japan and South Korea, and its special reproductive method has been widely concerned by scholars. In this paper, by analyzing the differences in follicular structure, hormone secretion and related gene expression patterns around oocytes during the oocyte maturation and embryonic development of black rockfish, the identification of the follicular placenta structure and the occurrence process of black rockfish were studied. The main results are as follows
1. The most obvious feature of the egg maturation process of black rockfish is the formation of many independent follicles. Follicles are formed by reproductive epithelium surrounding oocytes, and they first appear in stage III. After mate, the sperm are scattered in the ovarian cavity of the female fish. The independent follicles are connected to the ovarian stroma through the stem-like structure, so that each follicle can be in contact with sperm, and the follicle can directly obtain nutrition through the follicular stem and the blood vessels surrounding the follicular layer, reducing the competition of eggs to ensure the efficiency of fertilization and nutrient absorption. Independent follicles may be the basis of follicular placenta formation. During fertilization, the blood vessels and connective tissues in the interstitium of the ovary proliferate rapidly, the follicular layer structure of the oocytes is broken, the basement membrane and granular layer disappear, and the theca cell layer rapidly proliferates and invades the surrounding interstitium, forming a follicular placenta-like structure. The structure is extremely developed, the surface is widely folded to form large folds and is highly vascularized. It is further enlarged and denser during the development from fertilization to the blastocyst stage; in the subsequent pregnancy process, as the embryo develops, it gradually becomes loose.
2. Among the genes closely related to ovarian development and pregnancy, cyp17-I is a marker gene of the theca cell layer, and it has a strong expression signal on the follicular placenta during pregnancy. Before fertilization, cyp17-I was expressed in the theca cell layer of the oocyte, and at stage V, the stroma cells around the oocyte also showed expression signals, indicating that the formation of the follicular placenta of blackrock fish may be related to the theca cells and the expansion trend begins before fertilization. In mammals, HLA-E and lama4 play an important role in reducing the mother’s immune rejection of embryos and promoting trophoblast invasion. The signal be detected on the follicular placenta during pregnancy and the theca cell layer of oocytes before fertilization. The strong expression signal indicates that the follicular placenta may originate from the theca cell layer and perform similar functions to the mammalian placenta. cyp19a1a and fshr are genes specifically expressed in granulosa cells. Signals are only detected on the granulosa cell layer of oocytes before fertilization. No signal can be detected on the follicular placenta during pregnancy, indicating that granulosa cells may not be involved in the formation of follicular placenta. These results prove that the follicular placenta of black rockfish may be formed by the proliferation, migration, and expansion of the theca cell layer, and may perform similar functions to the mammalian placenta.
3. In black rockfish, the 11-ketotestosterone has been at a low level during the process of oogenesis, and gradually increased after fertilization, reaching a peak in the blastula stage, and maintaining a high level throughout the pregnancy. The level of 17-βestradiol increases significantly during egg maturation, peaks at stage IV, and then drops sharply from stage V to blastula stage, but 17-βestradiol also maintains a high level in the middle and late stages of pregnancy, and reaches its peak again in the gastrula stage . During the process of oogenesis, the level of progesterone is low, but the level of progesterone rises rapidly after fertilization and remains high during pregnancy. Compared with turbot, the level of 11-ketotestosterone in black rockfish increases from stage V to the blastula stage, and the level of 17-βestradiol decreases, resulting in a gradual decrease in the ratio of 17-βestradiol to 11-ketotestosterone in the body, reaching a minimum in the blastocyst stage. This may be due to the driving factor that promotes the outward expansion of the theca cell layer and follicular placenta. And during pregnancy, 11-ketotestosterone, 17-βestradiol and progesterone are all at high levels, which may help maintaining pregnancy.
|MOST Discipline Catalogue||理学|
|徐小杰. 许氏平鲉滤泡胎盘发生过程解析[D]. 中国科学院海洋研究所. 中国科学院大学,2021.|
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