Cryopreservation of Drosophila melanogaster embryonic nuclei

Drosophila melanogaster is a well-known organism for biological research. With over 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 of 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 demonstrated that cryopreserved nuclei retain biological function through an induced hsp70 transcriptional response. This work represents steps toward cryopreserving nuclei with the ultimate aim of regenerating stocks by embryonic nuclear transplantation.