145 EXTRA LIGHT EXPOSURE DECREASES DEVELOPMENT AND QUALITY OF PORCINE PARTHENOTE EMBRYOS

Abstract

During in-vitro handling, oocytes and embryos are always exposed to light. This has been shown to affect embryonic development and quality in different species, i.e. hamster and mouse (Takenaka et al. 2007 PNAS, 104, 14 289–14 293) and human (Tatsuo et al. 2010 J. Assist. Reprod. Genet. 27, 93–96). However, similar experiments have not been made on porcine embryos, so our aim was to test effects of different types of light on the development and quality of porcine parthenote embryos. Cumulus–oocyte complexes from slaughterhouse-derived sow ovaries were aspirated and matured (38.5°C, 5% CO₂, maximum humidity, 42 h). Parthenogenetic activation was made (Day 0) first by an electric pulse (1.26 kV cm^–1, 80 µs) and then by incubation with 5 µg mL^–1 cytochalasin B and 10 µg mL^–1 cycloheximide in porcine zygote medium-3 (PZM-3) for 4 h. During these processes, the oocytes would be exposed to ~30 min of light. After activation, the oocytes were either directly cultured in incubator (0 h), or experimentally exposed to two types of light (DAY: near window, no direct sunlight; LAB: app. 40 cm from warm white lamps (12 V, 40 W) in PZM-3 while placed on a heating plate (38.5°C) with the culture dish covered by a crystal plastic foil filled with the appropriate gas (5% O₂, 5% CO₂) for different periods (1 h, 4 h, 24 h), and then cultured in PZM-3 in incubator. On Day 6, total and good blastocysts were counted. Good blastocysts were defined as blastocysts having expanded to 1.5 times the oocytes’ size, having cells of uniform color and distribution, and having formed a regular blastocyst cavity. The total number of cells and the apoptotic cells were detected on Day 6 blastocysts with TUNEL assay to evaluate embryonic quality. All statistics analysis were performed by ANOVA test (R). The results are summarized in Table 1. The developmental rates were decreased with both types of light: the decrease appeared earlier for good blastocyst rates, only after 1 h exposure; however, a clear adverse effect was also found on total blastocyst rates after 24 h exposure. The total cell number decreased after 4 h light exposure for both types of light. The rate of apoptotic cells tended to increase with both types of light (from approximately 7 to 9.5%) when embryos were exposed during 24 h, but no significant difference was found between groups. We conclude that the blastocyst morphology would be altered already after 1 h extra exposure to both light types, and their quality would further decrease after 4 h exposure. However, under normal working conditions, this should not represent a real problem.

Table 1.  Effect of light exposure on development of porcine parthenote embryos