To culture preimplantation embryos in vitro, water-jacketed CO2 incubators are used widely for maintaining an optimal culture environment in terms of gas phase, temperature and humidity. We investigated the possibility of mouse embryo culture in a plastic bag kept at 37°C. Zygotes derived from in vitro fertilization or collected from naturally mated B6D2F1 female mice were put in a drop of medium on a plastic culture dish and then placed in a commercially available plastic bag. When these were placed in an oven under air at 37°C for 96 h, the rate of blastocyst development and the cell numbers of embryos decreased. However, when the concentration of O2 was reduced to 5% using a deoxidizing agent and a small oxygen meter, most zygotes developed into blastocysts. These blastocysts were judged normal according to their cell number, Oct3/4 and Cdx2 gene expression levels, the apoptosis rate and the potential for full-term development after embryo transfer to pseudopregnant recipients. Furthermore, using this system, normal offspring were obtained simply by keeping the bag on a warming plate. This culture method was applied successfully to both hybrid and inbred strains. In addition, because the developing embryos could be observed through the transparent wall of the bag, it was possible to capture time-lapse images of live embryos until the blastocyst stage without needing an expensive microscope-based incubation chamber. These results suggest that mouse zygotes are more resilient to their environment than generally believed. This method might prove useful in economical culture systems or for the international shipment of embryos.
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