Abstract

We report a novel method to profile intrcellular oxygen concentration (icO2) during in vitro mammalian oocyte and preimplantation embryo development using a commercially available multimodal phosphorescent nanosensor (MM2). Abattoir-derived bovine oocytes and embryos were incubated with MM2 in vitro. A series of inhibitors were applied during live-cell multiphoton imaging to record changes in icO2 associated with mitochondrial processes. The uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) uncouples mitochondrial oxygen consumption to its maximum, while antimycin inhibits complex III to ablate mitochondrial oxygen consumption. Increasing oxygen consumption was expected to reduce icO2 and decreasing oxygen consumption to increase icO2. Use of these inhibitors quantifies how much oxygen is consumed at basal in comparison to the upper and lower limits of mitochondrial function. icO2 measurements were compared to mitochondrial DNA copy number analysed by qPCR. Antimycin treatment increased icO2 for all stages tested, suggesting significant mitochondrial oxygen consumption at basal. icO2 of oocytes and preimplantation embryos were unaffected by FCCP treatment. Inner cell mass icO2 was lower than trophectoderm, perhaps reflecting limitations of diffusion. Mitochondrial DNA copy numbers were similar between stages in the range 0.9–4 × 106 copies and did not correlate with icO2. These results validate the MM2 probe as a sensitive, non-toxic probe of intracellular oxygen concentration in mammalian oocytes and preimplantation embryos.

Highlights

  • We report a novel method to profile intrcellular oxygen concentration ­(icO2) during in vitro mammalian oocyte and preimplantation embryo development using a commercially available multimodal phosphorescent nanosensor (MM2)

  • The primary function of mitochondria is to provide energy in the form of Adenosine Triphosphate (ATP) which is coupled to the consumption of oxygen by oxidative phosphorylation (OXPHOS)[10]

  • We present a novel method to visualise and quantitatively assess ­icO2 during oocyte maturation and preimplantation embryo development

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Summary

Introduction

We report a novel method to profile intrcellular oxygen concentration ­(icO2) during in vitro mammalian oocyte and preimplantation embryo development using a commercially available multimodal phosphorescent nanosensor (MM2). Mitochondrial DNA copy numbers were similar between stages in the range 0.9–4 × 1­ 06 copies and did not correlate with ­icO2 These results validate the MM2 probe as a sensitive, non-toxic probe of intracellular oxygen concentration in mammalian oocytes and preimplantation embryos. IVP In vitro production COC Cumulus-oocyte complex MEM Minimum essential medium M199 Medium 199 TALP Tyrode’s albumin lactate pyruvate medium HM Holding medium SOF Synthetic oviduct fluid LSM Laser scanning microscope FCCP Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone mtDNA Mitochondrial deoxyribonucleic acid PCR Polymerase chain reaction qPCR Quantitative real-time polymerase chain reaction COI Cytochrome c oxidase subunit 1 ICM Inner cell mass TE Trophectoderm PI Propidium iodide ANOVA Analysis of variance ATP Adenosine triphosphate OXPHOS Oxidative phosphorylation AA Antimycin A. There is currently no established method to measure TE vs ICM metabolism without biopsy

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