Studies On The PGCs’ Origin Migration And Differentiation Of Gobiocypris Rarus And Its Ovarian Development And Oogenesis

Rare minnow (Gobiocypris rarus) which belongs to order of Cypriniformes, family of Cyprinidae, genus Gobiocypris, is a small freshwater fish endemic to China. It has become an important experimental fish because of its strong adaptability, Short maturation cycle, anniversary breeding, high spawning frequency and sensitive to pollutants and so on.The rare minnow that we used this study were obtained from the Key laboratory of Aquatic Organism Reproduction and Development (Southwest University). We choose1-140days of Gobiocypris rarus and mainly using histological method to research the PGCs,(primordial germ cells, PGCs) origin, migration and differentiation of Gobiocypris rarus and its ovarian development and oogenesis. The results are as follows:1. The PGCs’origin, migration of Gobiocypris rarus:The PGCs migrate from the mesonephric duct above the yolk sac to mesentery along the body cavity back wall, this migration patterns belongs to.the back of endoderm through splanchnic mesoderm reach to the mesentery, and then migrate to the genital ridge, and thus deduce the PGCs of Gobiocypris rarus originated from endoderm.2. The differentiation of Gobiocypris rarus:The results show that the ovarian differentiation occurred much earlier than the testicular differentiation. The anatomical indication of ovarian differentiation was the formation of ovarian cavity and clusters of oogonia which appeared about21dah; the cytological indication of ovarian differentiation was the formation of primary oocyte which appeared about35dah. While the anatomical indication of testicular differentiation was the formation of sperm duct primordium and seminiferous lobule which appeared about50dah and60dah, respectively; the cytological indication of testicular differentiation was the formation of primary permatocyte which appeared about60dah.3. The ovarian development of Gobiocypris rarus:According to the characteristics of ovarian shape, color, and vascular distribution, combined with the staging method of osteichthyes gonadal development, the ovarian development of Gobiocypris rarus can be divided into five stages:Ovary in stage Ⅰ is small and transparent, and can not see the outline of oocytes and capillaries, indistinguishable to the testis and ovary in eyes. Histological observation, ovarian mainly composed of the type Ⅰ oogonium and type Ⅱ oogonium; Ovary in stage Ⅱ becomes big, transparent or white and the outline of oocytes is not very obvious, but we can see the capillaries; Histological observation, ovarian mainly composed of the phase of Ⅱ oocytes, and a small amount of phase of Ⅰ oogonium and III oocytes; Ovary in stage Ⅲ is flatter ribbon-like, we can see the prototype of oocytes and the blood vessels is thicker and the amount of blood vessels increased apparently. Histological observation, ovarian mainly composed of the phase of Ⅲ oocytes, and a small amount of phase of Ⅰ、Ⅱ and IV oocytes; Ovary in stage IV is round cystic, pale yellow, the eggs are sticking together, but the shape or size or color is different from each other. The surface of the ovary is covered many blood vessels; Histological observation, ovarian mainly composed of the phase of IV oocytes, and a small amount of phase of Ⅱ、Ⅲ and V oocytes; Ovary in stage IV is fluffy, the eggs have fallen from the drape of ovarian into the ovarian cavity and become the matured oocytes.Gently press its abdomen, a large number of eggs can be squeezed out. Histological observation, ovarian mainly composed of the phase of V oocytes, and a small amount of phase of Ⅱ、 Ⅲ and IV oocytes;According to the changes of yolk accumulating and development of follicle cells, the oogenesis of Gobiocypris rarus can be divided into five phases①The phase of oogonium:There are two types of oogonium—The type I oogonium is no in the mitosis stage, the type II oogonium is in the mitosis stage, and form of clusters development oogonium group.②The phase of single-layer follicular cells:The yolk nucleus and spawning plate appeared in the oocytes, and the number of oocytes increased significantly, the basophilic of cytoplasm enhanced, the number and size of nucleolus is different in different oocytes.③The phase of yolk vesicle:Yolk vesicle into multi-layer assignment, yolk granules began to accumulated; nuclear membrane is corrugated and zone radiate appeared in oocytes.④The phrase of yolk filled:cortical alveoli appeared in oocytes, yolk granules accumulated rapidly and its number and volume increased, nuclear membrane disappeared gradually, the number of nucleolus increased but its volume is reduced and so on.⑤The phase of marure oocyte:Yolk granules filled with cytoplasm and nucleus moved to the animal pole, the nuclear membrane disappeared, the follicular membrane degradated, the zone radiate became thin, but the microvilli became thick.