Oxidative Phosphorylation-Dependent and -Independent Oxygen Consumption by Individual Preimplantation Mouse Embryos1

Abstract

The self-referencing electrode technique was employed to noninvasively measure gradients of dissolved oxygen in the medium immediately surrounding developing mouse embryos and, thereby, characterized changes in oxygen consumption and utilization during development. A gradient of depleted oxygen surrounded each embryo and could be detected >50 μm from the embryo. Blastocysts depleted the surrounding medium of 0.6 ± 0.1 μM of oxygen, whereas early cleavage stage embryos depleted the medium of only 0.3 ± 0.1 μM of oxygen, suggesting a twofold increase in oxygen consumption at the blastocyst stage. Mitochondrial oxidative phosphorylation (OXPHOS) accounted for 60–70% of the oxygen consumed by blastocysts, while it accounted for only 30% of the total oxygen consumed by cleavage-stage embryos. The amount of oxygen consumed by non-OXPHOS mechanisms remained relatively constant throughout preimplantation development. By contrast, the amount of oxygen consumed by OXPHOS in blastocysts is greater than that consumed by OXPHOS in cleavage-stage embryos. The amount of oxygen consumed by one-cell embryos was modulated by the absence of pyruvate from the culture medium. Treatment of one-cell embryos and blastocysts with diamide, an agent known to induce cell death in embryos, resulted in a decline in oxygen consumption, such that the medium surrounding dying embryos was not as depleted of oxygen as that surrounding untreated control embryos. Together these results validate the self-referencing electrode technique for analyzing oxygen consumption and utilization by preimplantation embryos and demonstrate that changes in oxygen consumption accompany important physiological events, such as development, response to medium metabolites, or cell death.