Establishment of a novel method for the production of chimeric mouse embryos using oil droplets.

The production of chimeric animals is frequently necessary for the constructing genetically modified animals, and has gained popularity in regenerative medicine in the recent years for the reconstruction of xenogeneic organs. The aggregation method and the injection method are generally used for producing chimeric mice. In the aggregation method, the chimeras are produced by co-culturing embryos and stem cells, and keeping them physically adhered. In the injection method, the chimeras are produced by injecting stem cells into the zona pellucida using microcapillaries. These methods only focus on the generation of chimeric animals, and are not expected to produce reproducible results or allow quantitative evaluation. This study aimed to establish a novel method for producing chimeric embryos via droplets for improving on the conventional methods that are used for producing chimeric embryos. In this study, the embryonic stem cells and embryos were successfully isolated in the droplets, and the emergence of chimeric embryos was confirmed by co-culture for 6 hours. By this method, the control and operability of stem cell numbers can be regulated, and the method allows better reproducibility and quantification during the production of chimeric embryos. In addition to the conventional methods for producing chimeric embryo, the novel method described herein could be employed for the efficient production of chimeric animals.