Freezing fruit flies for future function

In a new study published in Communications Biology, researchers from the University of Tsukuba identify a method to preserve Drosophila primordial germ cells (PGCs), which give rise to reproductive cells and may be used to produce Drosophila offspring when implanted into a host.

Drosophila are useful as a scientific model because their genome may be easily manipulated, and such genetic alterations may facilitate our understanding of how particular genes function. However, when Drosophila populations are maintained by living culture over extended periods of time, unwanted genetic mutations may be inadvertently introduced into the genome. Until now, Drosophila strains have been preserved by freezing embryos or eggs, but these processes may be labor intensive and difficult to reproduce. Therefore, the researchers sought to develop a new technique for the preservation of Drosophila strains that is simple and reproducible.

"We treated PGCs from donor flies with a cryopreservation agent and stored them in liquid nitrogen, which maintains samples at an extremely low temperature," explains senior author of the study Professor Satoru Kobayashi. "We found that cryopreserved PGCs that were thawed and transplanted into host flies were able to produce offspring with the same genetic characteristics as the donor flies."

The researchers tested this technique using frozen PGCs from several Drosophila strains with different genetic backgrounds and found that offspring could be effectively produced from frozen PGCs regardless of strain. The cryopreserved PGCs were still effective after up to 400 days of long-term storage.

The researchers also transplanted frozen PGCs into a Drosophila strain that is normally unable to reproduce and found that the frozen cells were capable of inducing offspring from these hosts.

"We are very pleased with the results, and in fact, our protocol has already been implemented at KYOTO Stock Center in the Kyoto Institute of Technology (KIT)," says Professor Toshiyuki Takano-Shimizu in KIT. "We hope that this technique may be used broadly for the preservation of Drosophila strains."

The researchers are currently preparing a video report demonstrating their protocol to help further communicate this technique to other research teams. This method represents a simple and effective way to preserve Drosophila populations for future use and minimize the risk of unwanted genetic mutations.