부산대학교 도서관

The occurrence of cell death by apoptosis was examined in blastocyst and pre-blastocyst stage bovine embryos. Zygotes were obtained by in vitromaturation and in vitrofertilization of oocytes from abattoir derived ovaries. Two-cell to hatched blastocyst stage embryos were stained with propidium iodide to label all nuclei and by terminal deoxynucleotidyl transferase (TdT)-mediated d-UTP nick end-labelling (TUNEL) to label apoptotic nuclei, and were analysed by epifluorescent and confocal microscopy. Apoptosis was first observed at the 9–16-cell stage of development, decreasing at the morula stage before increasing at the blastocyst stage. Apoptotic dead cell index in day 7 blastocysts was negatively correlated with the total number of cells; the percentage of dead cells ranged from approximately 1 to 10% and occurred predominantly within the inner cell mass. In addition, apoptotic dead cell index was significantly higher (P< 0.05) in blastocysts cultured (from the two-cell stage) in the presence of 10% fetal bovine serum compared with those developed in serum-free medium. Embryos selected for early cleavage at < 29 h after fertilization and cultured together until the blastocyst stage showed a significantly lower rate of apoptosis (P< 0.01) compared with slower cleaving embryos.