Cryopreservation, or the long-term storage of biomaterials at ultra-low temperatures, has been used in all cell types and species. However, until now, practical cryopreservation of the fruit fly (Drosophila melanogaster) – which is crucial for genetic research and essential for scientific breakthroughs beneficial to human health – has not been available.
“To keep alive the ever-increasing number of fruit flies with the unique genotypes that are contributing to these breakthroughs, some 160,000 different flies, laboratories and storage facilities are engaged in costly and frequent transfers from adults to fresh food, potentially contaminating and deriving genetics, “said Li Zhan, associate postdoctoral fellow at the College of Science and Engineering at the University of Minnesota and the Center for Advanced Technologies for the Preservation of Biological Systems (ATP-Bio).
In new research published in Nature Communications, a team from the University of Minnesota has developed a unique method that cryopreserves fruit fly embryos so that they can be successfully recovered and turned into adult insects. This method optimizes the permeabilization and age of the embryo, the composition of the cryoprotective agent, the different nitrogen phases (liquid vs slush) and the methods of post-cryopreservation embryo culture.
The researchers were able to:
show that the method is widely applicable and easily adopted by non-specialists, since it has been successfully implemented in 25 different strains of fruit flies from different sources (eg laboratories);
demonstrate that for most strains, more than 50% of the embryos hatch and more than 25% of the resulting larvae transform into adults after cryopreservation; and
show that flies retain a normal sex ratio, fertility and original mutation after successive cryopreservation through generations and long-term storage in liquid nitrogen.
“Our multidisciplinary team is pleased to contribute to an accessible protocol to cryopreserve numerous strains of Drosophila, an important biomedical model, while also hopefully informing the preservation of embryos of other insects and related species,” said the study co-author John Bischof, director of the Institute for Engineering in Medicine and professor in the Faculty of Science and Engineering and the Faculty of Medicine.
As humans share more than half of their genes with the fruit fly, research on Drosophila and its implications for human health is important.
“By studying the mutants in the Drosophila model system, he can reveal how these genes function in human development and disease,” said Tom Hays, head of the Department of Genetics, Cell Biology and Development at the School of Medicine and at the College of Biological Sciences. “Studies on flies have provided crucial information on human diseases from Alzheimer’s disease to Zika and have revealed genetic pathways and mechanisms underlying embryonic development, olfaction and innate immunity.
Beyond training individuals in this method, the University of Minnesota team is seeking to adapt it to other applications.
“It will be important to understand the genetics that influence cryopreservation in Drosophila and other insects,” said study co-author Mingang Li, associate researcher in the Department of Genetics, Cell Biology and Development. “This method could support research aimed at controlling pests of Drosophila suzukii, a fruit fly that infests ripening fruits and has become a pest in the Americas and Europe, as well as for research on malaria in Anopheles mosquitoes. “
Research funding was provided by the United States National Institutes of Health, the National Science Foundation, the ATP-Bio of the Institute for Engineering in Medicine, and the University Doctoral Fellowship.
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