Cryopreservation of Drosophila melanogaster embryonic nuclei in a Dimethyl sulfoxide (ME2SO)-free solution

Drosophila melanogaster is a well-known organism for biological research. With more than 150,000 live stocks maintained, there is an urgent need for cryopreservation of Drosophila stocks to limit maintenance costs and genetic drift. Two methods have been described for freezing Drosophila stocks: vitrification of embryos and of primordial germ cells. These methods show success in cryopreserving stocks, but the robustness and the applicability of these approaches in preserving a wide range of mutant stocks has not been established. Here, we describe a method for cryopreserving isolated embryonic nuclei using a slow-cooling method. Using a differential evolution algorithm, we identified five different formulations that show >80% recovery and used Raman spectroscopy to image nuclei at low temperatures. Finally, we demonstrate that cryopreserved nuclei retain biological function through an induced hsp70 transcriptional response. This work represents steps towards cryopreserving nuclei with the ultimate goal of regenerating stocks by embryonic nuclear transplantation.