87 EVALUATION OF MITOCHONDRIAL FUNCTION IN SINGLE CLONED MINIATURE PIG EMBRYOS BY MEASURING OXYGEN CONSUMPTION

Abstract

Mitochondria are organelles that produce energy for embryogensis. Their function [oxidative phosphorylation (OXPHOS) and electron transport] is regulated by intercommunication with the nucleus. In somatic cell nuclear transfer (SCNT) embryos, incomplete reprogramming may lead to dysfunction of the intercommunication before or after embryonic activation, or both, although it is unknown whether reprogramming for energy synthesis is required. In the previous report (Abe et al. 2004 J. Mamm. Ova Rec. 21, 22), we developed a noninvasive method using a scanning electrochemical microscopy (SECM) for measurement of oxygen consumption that provides more direct information about mitochondrial function (Trimarch et al. 2000 Biol. Reprod. 62, 1866–1874). In the present study to evaluate mitochondrial function in individual miniature pig SCNT embryos, we measured oxygen consumption by SECM. Oocytes in pig ovaries collected from the local slaughterhouse were matured for 44 h in NCSU23 and used as recipient. After SCNT with fetal miniature pig fibroblasts, reconstructed embryos were cultured in vitro in NCSU23 or PZM-3. Oxygen consumption in single 2- and 4-cell-stage embryos, morulae, and blastocysts were measured, and the values were compared with those derived from IVF. All data were analyzed by ANOVA. In IVF embryos, oxygen consumption was lowest at the 2- and 4-cell stages, and reached a peak at the blastocyst stage on Day 5. However, there were significant differences (P < 0.05) in blastocysts between NCSU23 and PZM-3: 0.61 � 0.14 vs. 0.83 � 0.18 at Day 5, 0.53 � 0.14 vs. 0.70 � 0.24 at Day 6, 0.47 � 0.11 vs. 0.73 � 0.20 � 10-14 mol s-1 at Day 7, respectively. In contrast, SCNT embryos showed no increase in oxygen consumption during pre-implantation stages in the 2 media, but there was a significant difference (P < 0.05) at the 2-cell stage between NCSU23 and PZM-3 (0.35 � 0.09 vs. 0.43 � 0.10, respectively). Comparison of the Day 5 IVF and SCNT blastocysts cultured in PZM-3 showed no difference in total cell numbers but significantly (P < 0.05) lower oxygen consumption in SCNT (0.83 � 0.18 vs. 0.40 � 0.13 � 10-14 mol s-1, respectively). After treatment with 1 �M CCCP (mitochondrial uncoupler) or 1 mM NaCN (mitochondrial electron transporter inhibitor), oxygen consumption in IVF and SCNT blastocysts at Day 5 increased (112 � 18 and 51 � 44%, respectively) or decreased (50 � 20 and 21 � 32%, respectively) compared with those of nontreated embryos. Sensitivity to these reagents differed significantly (P < 0.05) between IVF and SCNT, indicating that the SCNT blastocysts had a lower OXPHOS capacity than those from IVF. These results suggest that reprogramming for sustaining mitochondrial function during pre-implantation development may be required in miniature pig SCNT embryos.