Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Eﬀects of heavy-ion beam irradiation on non-model fruit ﬂy,
Drosophila miranda
M. Ogawa,∗1 K. Tsuneizumi,∗2 T. Abe,∗2 and M. Nozawa∗1,∗3
Irradiation has been a useful tool for making deletion mutants and establishing strains with balancer
chromosomes in Drosophila melanogaster.1) These ﬂies
have been fundamental resources in the ﬁelds of genetics, development, evolutionary biology, and so on.
However, irradiation has so far been applied primarily only to this model species of Drosophila. If thesame resources become available for other Drosophila
species, researchers working on other ﬂy species canutilize these resources for a variety of studies. For example, D. miranda acquired the so-called neo-sex chromosomes by fusing an autosome with the ordinary Y
chromosome approximately a million years ago, and it
has a high potential for elucidating the early evolutionary phase of sex chromosomes.2,3) The purpose of thisstudy is, therefore, to examine the eﬀects of heavy-ion
beam irradiation on the fertility and the genome of
D. miranda.
We irradiated the iron (Fe)-ion beam (806 keV/µm;0.5, 1, or 2 Gy) to the ﬂies with 3–4 days after eclosion.
For irradiation, 15-mL tubes were used, in which 3 mLof the medium consisting of 1% agar and 50% grape
juice was poured at an angle of 30◦ . Five males with
the irradiation of the Fe-ion beam were then crossedwith ﬁve virgin females on the same (zeroth) day of theirradiation in a vial containing a normal corn medium(Fig. 1). On the 1st, 4th, and 7th days after irradiation, only the males were transferred to a new vial
and crossed with another ﬁve virgin females. After 3
days of crossing, all the females were discarded fromeach vial. All the males were also discarded with fe-males on the 10th day. The number of F1 ﬂies eclosed
in each vial was counted. To consider variations, weprepared four vials (that is, 5 males × 4 vials) for each
irradiation condition as replicates. Among the F1 individuals (Fig. 2), we extracted genomic DNA fromeach of the ﬁve males from the 1–3 days vials derived
from the males with irradiation of 2 Gy indicating alower fertility, and resequenced the genomes using Illumina HiSeq X. Following sequencing, the regions withmapping depth of zero in the F1 individual but of atleast 1 in the wildtype individuals were regarded as
the candidate regions of deletions. The same experiments were also conducted for the argon-ion beam(Ar, 189 keV/µm; 1 Gy) and the carbon-ion beam (C,30 keV/µm; 5 Gy) and the genomes of two F1 males
were sequenced for each ion beam.

Fig. 2. Transition of male fertility after Fe-ion irradiation.

Using the strategy described, we successfully detected a number of genes containing the candidate regions of deletions on the Y/neo-Y chromosomes (Table 1). However, deletions were also detected on theX/neo-X chromosomes, which was not expected because the X/neo-X chromosomes were inherited only
Table 1. Number of genes in which deletions were detected.

Fig. 1. Crossing experiments following irradiation.
∗1
∗2
∗3

Department of Biological Sciences, Tokyo Metropolitan University
RIKEN Nishina Center
Research Center for Genomics and Bioinformatics, TokyoMetropolitan University- 200 -* The average number of genes with deletions per individual is shown. Only the genes in which deletions weredetected within the exons were counted.

Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 56 (2023)

from the non-irradiated females. We speculate thatsequence polymorphism between each F1 male and reference genomes caused such erroneous identiﬁcations.
We would like to optimize the conditions for making
mutants with large deletions in future studies by repeating the irradiations under various conditions.
This research was supported by the KAKENHI(21H02539), granted to MN.
References
1) R. F. Grell et al., DIS 30, 71 (1956).
2) D. Bachtrog et al., Nature 416, 323 (2002).
3) M. Nozawa et al., Nat. Commun. 7, 13659 (2016).

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