Meiotic Progression And Its Control By Hypoxanthine In Goat Oocytes

Techniques in embryo technology (such as in vitro production of embryos and animal cloning) need large quantities of high quality oocytes. But the quality of in vitro matured oocytes from slaughtered animals is generally lower than that of the in vivo matured oocytes. It is usually thought that the reason for this poor quality in in vitro matured oocytes is the lack of capacitation during the dominancy of follicular development in vivo. Therefore,people begin to attempt to inhibit nuclear maturation of oocytes,to improve oocyte quality. Few studies have been conducted so far on meiotic progression and none was carried out on its control via hypoxanthine in goat oocytes. In this study,the meiotic progression and its control by hypoxanthine were studied in the goat oocytes aspirated from slaughtered ovaries. The result are summarized as follows:1 .The surface diameter and the dissected diameter (measured after the follicles were dissected from the ovary) of follicles larger than 1.5-2.5mm in diameter were closely correlated (r= 0.72),and therefore we can classify follicles in accordance with the surface diameter.2.Oocytes from follicles larger than 1.5-2.5mm in diameter had achieved the maximal diameter (about 130 u m),the maximal volume of zona pellucida (ZP),and stopped growth. In the smaller antral follicles,oocyte diameter and ZP volume increased with follicular growth.3. Oocytes from different sized follicles showed different meiotic competence. Oocytes from 0.5mm diameter follicles were unable to resume meiosis;Oocytes from 0.8-1.2mm diameter follicles resumed meiosis but developed only to MI (metaphase-I) stage;Oocytes from 1.5-2.5mm and 3-5mm diameter follicles resumed meiosis and developed to Mil (metaphase-II) stage at a rate of 93% and 91%,respectively,after 24 h culture.4.The meiotic progression of oocytes from 1.5-2.5mm follicles were calculated as follows:germinal vesicle (GV) stage lasted from 0 to 4.2h,;prometaphase-I (PROM),4.2-9.0h;metaphase I (MI),9.0-15.6h;anaphase-I and telophase-I (Ana I /Tel I),15.6-18.4h;and metaphase-II (Mil),18.4-24h.5.The HX concentration in goat follicular fluid is 0.45-1.19 mmol/L,and it is decreasing with the increase of follicle diameter.6. HX inhibited GVBD of goat oocytes in a dose-dependent manner,with 4mmol/L being the most effective (the rate of GV was 55% at 6h). But this inhibition lasted only for 6h,and GV rate decreased to 32% by 8h. Oocytes resumed meiosis and developed to Mil stage after HX removal.7. By renewing medium,we showed that the decreased inhibition of HX was not due to degradation of HX,and the inhibiting effect of HX might be produced by cAMP,which wassecreted by oocytes metabolizing HX. The competence of oocytes to utilize HX and producethis meiosis-inhibiting substance lasted only a limited period (4h in this case),and after this time oocytes became incompetent8. HX showed a multiple effect on oocyte maturation. In the presence of HX,oocyte maturation to Mil and the extrusion of polar body were highly synchronized,the oocytes matured to Mil stage were activated in higher rates than oocytes matured without HX,and those oocytes matured exposed to HX for all the 24h showed a high rate (55%) of spontaneous activation.Ma Suofeng,Animal Histology and Embryology Advisor:Pro. Tan Jinghe...