PARENT SESSION

(T668) APOPTOSIS IN MOUSE PREIMPLANTATION EMBRYOS PRODUCED IN THE DIFFERENT SYSTEMS.

Bing, Yin Zhong ¹, Chian, Ri Cheng¹, Tan, Seang Lin¹, Zhao, Xin¹, ¹ McGill University, Montreal, QC, Canada

ABSTRACT- Apoptosis occurs in mammalian embryos and its occurrence is affected by many factors during preimplantation development. The present study aims to track and compare the incidence of apoptotic cells in mouse preimplantation embryos produced in vivo or in vitro at different developmental stages. Outbred CD1 mice were superovulated by exogenous ovarian stimulation (eCG and hCG). Embryos at the stages of 2-cell, 4-8-cell, 9-16-cell, morula and blastocyst were collected in vivo (group A) or produced in vitro using in vivo fertilized oocytes collected at 22-24 hrs after hCG injection (group B), matured oocytes collected at 13.5 hrs after hCG injection and fertilized in vitro (group C), or immatured oocytes collected at 46-47 hrs after eCG injection and matured and fertilized in vitro (group D). The DNA fragmentation in the embryos at different stages was detected by the TUNEL assay. Apoptotic cells were detected in 87-100% of blastocysts produced either in vivo or in vitro. The earliest appearance of apoptotic cells in groups A, B, C, D were at 22-, 14-, 14- and 8-cell embryos, respectively. The highest rate of apoptotic cells in the blastocyst was observed in the group D, which was significantly different from other groups (P<0.05). Group A had the lowest percentage of apoptotic cells. Results from groups B and C indicated that the condition of fertilization did not significantly affect the degree and pattern of apoptosis. Our results demonstrate that the incidences of apoptosis are affected by the embryonic production systems and in vitro production is associated with a higher degree of apoptosis in mouse preimplantation embryos.

KEY WORDS: apoptosis, mouse preimplantation embryo, embryonic production system