Studies On Hypoxanthine Control Of Meiosis Of Oocytes Of Kunming Mice

Embryo technology needs large quantities of high quality oocytes. However, the quality of in vitro matured oocytes is generally lower than that of the in vivo matured. The poor quality of in vitro matured oocytes was thought to be due to the lack of capacitation during dominancy of follicular development in vivo. Therefore, people attempted to improve the quality of IVM oocytes by inhibiting nuclear maturation. Hypoxanthine, a biological inhibitors in the follicular fluid, was used to control meiosis of mouse oocytes, and influencing factors and the reversibility of HX inhibition, were investigated in tfrs study. The results are summarized as follows:1. The total number of oocytes and the number of type A COCs recovered from mice of 18-23 days of age were higher than those from mice 7-10 weeks of age, but the ability of maturation and parthenogenetic activation of oocytes was not different between the two age groups of mice.2. HX, at the concentration of 4 mmol/L, inhibited the meiotic maturation of mouse oocytes efficiently, but inhibition rates decreased with time, and thus the percentage of oocytes with GV was significantly lower at 18h than Oh of inhibition.3. The percentage of SN oocytes was significantly lower in mice of 19-21 days old than in mice of 7-10 weeks of age. The percentage of SN oocytes in mice of 19-21 days increased from 38.1 % before HX inhibition to 93 %(P<0.05)after 6 h of inhibition. These results indicated that HX inhibition facilitated the transition from NSN to SN. At 3h of normal in vivo or in vitro maturation, the percentage of SN oocytes decreased to 27.5% and 15.5%, respectively (P<0.05), indicating that the meiotic progression of SN was faster than that of NSN.4. Maturating of oocytes was not affected when the HX exposure time was less than 24h, but maturation rate decreased significantly after 24h of HX inhibition. This result indicated that the inhibitory effect of HX was reversible, but long exposure to HX may cause damage to oocytes.5.The cumulus did not expand in medium containing HX, but the ability of cumulus expansion was recovered when returned to normal culture, if exposure time to HX was less than 6h.6. Meiotic progression of oocytes was accelerated after treated with HX for 6 h, and thus the time for GVBD and polar body extrusion was shortened from 2-4h and 9-12h to l-3h and 6-9h, respectively. This indicated that meiosis was synchronized after HX treatment.7. Rates of activation (86 %) and morulae/blastocysts (64 %) were significantly higher in the in vivo maturated oocytes than those in the in vitro maturated (20 and 17%). The activation rate increased significantly after treatment with HX for 6 h (42 vs. 20%), but no embryo developed to morulae stage.8. Rates of fertilization and morulae/blastocysts were significantly higher in the in vivo maturated oocytes than those of the in vitro maturated. The fertilization rate decreased significantly after oocytes were treated with HX for 6 h (35 vs. 16%) and the ratio of morulae/blastocysts was also lower (22 % vs. 12%,P=0.19).9. After 24 h of HX inhibition, the percentage of oocyte with GV intact was not different significantly between the denuded and type A oocytes. However, the maturation rate of DO was significantly lower than that of COC when returned to normal culture after HX treatment. This indicated that the inhibitory effect of HX was not mediated by cumulus cells, but cumulus cells could alleviate the deleterious effects of HX.