The number of nuclei in compacted embryos assessed by optical coherence microscopy is a non-invasive and robust marker of mouse embryo quality

摘要

Optical coherence microscopy (OCM) visualizes nuclei in live, unlabeled cells. As most cells are uninucleated, the number of nuclei in embryos may serve as a proxy of the cell number, providing important information on developmental status of the embryo. Importantly, no other non-invasive method currently allows for the cell number count in compacted embryos. We addressed the question of whether OCM, by providing the number of nuclei in compacted mouse embryos, may help evaluate embryo quality. We subjected compacted embryonic Day 3 (E3.0: 72 h after onset of insemination) mouse embryos to OCM scanning and correlated nuclei number and developmental potential. Implantation was assessed using an outgrowth assay (in vitro model meant to reflect embryonic ability to implant in vivo). Embryos with more cells at E3.0 (>18 cells) were more likely to reach the blastocyst stage by E4.0 and E5.0 (P ≪ 0.001) and initiate hatching by E5.0 (P 18 cells) were also more likely to implant in vitro than their counterparts with fewer cells (<12 cells; P ≪ 0.001). Finally, we tested the safety of OCM imaging, demonstrating that OCM scanning affected neither the amount of reactive oxygen species nor mitochondrial activity in the embryos. OCM also did not hinder their preimplantation development, ability to implant in vitro, or to develop to term after transfer to recipient females. Our data indicate that OCM imaging provides important information on embryo quality. As the method seems to be safe for embryos, it could be a valuable addition to the current repertoire of embryo evaluation methods. However, our study was conducted only on mouse embryos, so the proposed protocol would require optimization in order to be applied in other species.