Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 47 (2014)

Development of the mutant isolation system in fruit flies
K. Tsuneizumi,*1 and T. Abe,*1
Heavy-ion beam mutagenesis is an effective mutation
breeding method 1, 2). Although this method has been highly
successful with plants, its use for animals has been limited.
To extend its application to animals, we plan to acquire
more basic data to determine optimal conditions forheavy-ion-beamirradiation
usingDrosophilamelanogaster (fruit fly) as a useful model system.
Over the past century, several unique genetics tools havebeen developed using the fruit fly. A balancer chromosome
is one such popular tool and is known to prevent
homologous recombination during meiosis. A single
balancer line was previously found to be more suitable forstabilizing the mutant isolation system than a double
balancer line3). Therefore, we focused only on thirdchromosome events and re-established a third chromosome
balancer line before starting the irradiation experiment.
To overcome the instability problem of a graphic record
at previous data3), we decided to use commercial cuvettes
with a plane surface [Fig. 1a]. Because most of the vials
commonly used for fly maintenance have a curved surface,
heavy-ion-beam irradiation condition is uneven in the vials
depending on the thickness of curved plastic. To decrease
the opportunity of the energy loss in heavy-ion beam byflies overlapping, only two flies were put into each cuvette.
Then, six cuvettes were arranged in a commercial container
in order to use a uniform irradiation range with anautomatic sample changer [Fig. 1b]. To evaluate thestability of the improved mutant isolation system, wesubjected the fruit flies to a carbon-ion beam with linear
energy transfer (LET) values of [80keV/µm] at several doselevels (1.0, 3.0, 10.0, 30.0, and 60.0 Gy).
To estimate the effect of heavy-ion-beam irradiation, we
measured the number of F1 progeny as a biological effect.
In this study, males and females were immediately
separated after eclosion and were bred for 3 days. Thenevery two males were put into each cuvette for irradiation[Fig. 1b]. It was performed in the females equally. Afterirradiation with different heavy-ion-beam doses, the males
were provided fresh harems of virgin females every 2–3days. The females were provided with males and themedium was replaced every 2–3 days. The oviposited eggs
were bred, and the number of progeny that survived to theadult stage was determined.
Decrease in the reproductive ability of males was found tobe caused by aging and not irradiation. In contrast, thereproductive ability of females did not change during theobservation period [Fig.2]. The results for the males showeda linear correlation between the number of progeny andirradiation dose. In contrast, a non-linear curve wasobserved for the females [Fig. 2]. These data suggest that aradiosensitivity is different between males and females.
We have developed a stable mutant isolation system using＊1

RIKEN Nishina Center- 285 -

fruit flies by using heavy-ion-beam irradiation. Currently,
we are establishing various mutants and will be analyzing
DNA damage in homozygotes. These data will be helpful
for optimizing the irradiation system in the future.

Fig. 1. a) A photograph of a cuvette and a breeding vial.
b) A photograph of sample cuvettes for irradiation using anautomatic sample changer.

Fig. 2. Upper panels show the correlation between thenumber of F1 progeny and the days after heavy-ion-beamirradiation. Lower panels show the correlation between thenumber of F1 progeny and the irradiation dose. F: filialgeneration.
References

1) T. Abe et al.: Gamma Field Symp. 39, 45 (2000).
2) A. Tanaka et al.: J. Radiat. Res. 51, 223 (2010).
3) K. Tsuneizumi et al.: RIKEN Accel. Prog. Rep. 46, 255 (2013).