Freezing fruit flies for future function

Freezing fruit flies for future function
Fig. 1: F-PGCs can migrate into the gonads and give rise to GSCs. a Representative images of PGCs in the gonads of EGFP-vas donor embryos (Donor), y w host embryos (Host), and y w embryos transplanted with PGCs without both CPA-treatment and freeze-thawing (Naive-PGCs) or treated with CPA and freeze-thawed (F-PGCs). Stage 15 embryos were double-stained for a germline-marker, Vasa (magenta), and for GFP (green). Yellow and white arrows indicate GFP-positive donor PGCs and GFP-negative host PGCs in y w host embryos, respectively. b Donor-derived PGCs in the gonads of y w host embryos transplanted with Naive-PGCs, PGCs treated with CPA but not subject to freeze-thawing (CPA-PGCs), and F-PGCs were counted. Each dot represents the number of GFP-positive PGCs per gonad. c Representative images of ovariole and testis with F-PGC–derived germline. Ovaries and testes were dissected from adult y w hosts 10 days after eclosion (Supplementary Fig. 2), and stained for GFP (green), Vasa, Hts (a spectrosome/fusome marker), FasIII, and nuclei (DAPI). FasIII stains pre-follicle cells in ovaries, and hub cells in testes. DIC image merged with GFP signal is shown (top left). Images for Vasa (bottom left), DAPI (top right), and Hts and FasIII signals (bottom right) are also shown. Yellow and white arrows indicate F-PGC–derived GSCs and host GSCs, respectively. GSC niche cells, cap cells in the ovary, and hub cells in the testis are outlined in red. d Donor-derived GSCs were counted in adult y w hosts producing F1 progeny derived from Naive-PGCs, CPA-PGCs, or F-PGCs. Each dot represents the number of GFP-positive GSCs per adult host. See Supplementary Fig. 2. for details. e Percentage of female y w hosts carrying GSCs derived from Naive-PGCs (gray), CPA-PGCs (orange), or F-PGCs (red) producing donor-derived F1 progeny on days 1–3 (d1–3), 4–6 (d4–6), and 7–9 (d7–9) after mating. f Donor-derived F1 progeny produced from y w female host carrying GSCs derived from Naive-PGCs, CPA-PGCs, and F-PGCs were counted. Each dot represents the number of donor-derived progeny produced from each female host on days 1–9 after mating. “N” represents the number of gonads (b) and adults (d–f) examined. “ns” indicates not significant (P > 0.1, Wilcoxon test) in b, d, and f. In b, d, and f, red bars represent median values. The upper and lower borders of the box show the 75% and 25% quartiles, respectively. Scale bars, 10 µm (a) and 20 µm (c). Credit: DOI: 10.1038/s42003-021-02692-z

The fruit fly Drosophila melanogaster has long been an important experimental model for biological research. While you may be eager to rid your kitchen of this unwanted pest, researchers in Japan have developed a new technique to keep Drosophila in the laboratory even longer.

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.



More information:
Miho Asaoka et al, Offspring production from cryopreserved primordial germ cells in Drosophila, Communications Biology (2021). DOI: 10.1038/s42003-021-02692-z

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Freezing fruit flies for future function (2021, October 13)
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