Changes In Germinal Vesicle (GV) Chromatin Configurations During Growth And Maturation Of Rat Oocyte

The oocyte nucleus or germinal vesicle (GV) exhibits a unique chromatin configuration that is subject to dynamic modifications during oogenesis. A common feature in the configuration of GV chromatin in most species studied is that the diffuse chromatin condenses into a perinucleolar ring with oocyte development. Studies have shown that this modification occurs coincidently with the acquisition of meiotic competence, and that it reflects a greater potential for normal embryo development. In this experiment we studied the dynamic modifications of rat oocyte chromatin during oocyte growth and the maturation competence of oocytes with different chromatin configuration in vitro culture.The results are as follows:1. The GV chromatin configuration of rat oocytes was classified into four configurations based on the degree of condensation and distribution.1): the diffuse configuration which had diffuse chromatin in the whole nuclear area and no ring around the nucleolus (GV1); 2) the partly surrounded configuration which had an intermittent ring around the nucleolus (GV2); 3): the surrounded and diffuse configuration which had a ring around the nucleolus and much diffuse chromatin in the whole nuclear area (GV3); 4): the surrounded configuration which had a ring around the nucleolus only and little diffuse chromatin in the whole nuclear area (GV4).2. The appearance of the surrounded configuration (GV4) oocytes was firstly observed in 17-day-old rat, and the percentage of GV4 oocytes rat increased at the age from 17 to 22 days.3. All oocytes less than 40μm in diameter were GV1 chromatin configuration. When the diameter reached more than 60μm, GV3 and GV4 chromatin configuration oocyte began to appear and the percentages of GV3 and GV4 oocytes increased with an increase in oocyte diameter. No diffuse configuration was found in oocytes more than 80μm in diamter.4. The rate of GV4 oocytes significantly increased in COCs+/+ derived from PMSG stimulated 27-day or 28-day rats.5. The rate of GV4 oocytes was significantly lower in estrus when compared with the other three periods; on the contrary, the rate of GV3 oocytes was the highest in estrus. The rate of GV4 oocytes was significantly higher in proestrus than in the other three periods. 6. The percentage of GV4 oocytes in COCs+/+ increased in interval from 18h to 66h after hCG stimulated in 3-4 months old rats.7. All GV4 oocytes were competent to undergo maturation and maturation rate was significantly higher in GV4 oocytes than in GV3 oocytes.8. The percentage of GV4 oocytes significantly increased after 18h, 36h and 48h in vitro culture inα-MEM supplement with HX.