115 APOPTOSIS EVENT OF PREIMPLANTATION DEVELOPMENT STAGES IN PORCINE IN VITRO-FERTILIZED EMBRYOS

Abstract

Little is known about apoptosis events in porcine preimplantation embryos. In this study, we aimed to determine whether the evaluated markers of cell death could be found at particular developmental stages of normal porcine in vitro-fertilized (IVF) embryos. We investigated the characteristics of spontaneous and induced apoptosis during preimplantation development stages of porcine IVF embryos. In experiment 1, to induce apoptosis of porcine IVF embryos, porcine IVF embryos at 22 h postinsemination were treated at different concentrations of actinomycin D (0, 5, 50 and 500 ng mL^–1 in NCSU medium). Four groups were incubated at 37°C in 5% CO₂, 5%O₂ for 8 h, and then washed to NCSU medium and incubated until blastocyst (BL) stage. We examined cleavage rate at 2 days and BL development rate at 7 days after in vitro culture (IVC). A significantly less rate of cleavage was found in the 500 ng mL^–1 group compared with others (500 ng mL^–1 v. 0, 5, 50 ng mL^–1; 15.4% v. 48.6%, 40%, 32%). In the results of BL formation rate, there was a significantly less BL formation rate in 500 ng mL^–1 compared with others (500 ng mL^–1 v. 0, 5, 50 ng mL^–1; 0% v. 10%, 8.8%, 9%). In experiment 2, to evaluate apoptotic cells at different stage (2-cell, 4-cell, 8-cell and BL stage) of all groups, we conducted TUNEL assay based on morphological assessment of nuclei and on detection of specific DNA degradation under fluorescence microscope. This result showed that apoptosis is a normal event during preimplantation development in control group (0 ng mL^–1 actinomycin D). A high number of the BL derived control group contained at least one apoptotic cell. Actinomycin D treated BL responded to the presence of apoptotic inductor by a significant decrease in the average number of blastomeres and a significant increase in the incidence of apoptotic cell death. In the 500 ng mL^–1 group, the incidence of apoptosis increased at the 4-cell stage and later. This result suggested that apoptosis is a process of normal embryonic development and actinomycin D is a useful tool for the apoptosis study of porcine preimplantation embryos.

This work was supported by a grant (#20070301034040) from BioGreen 21 program, Rural Development Administration, Republic of Korea.