研究のタイプ: 医学/生物学の研究 (experimental study)

[低周波電磁界に対するキイロショウジョウバエの日周リズム上の反応に関する遺伝子解析] med./bio.

Genetic analysis of circadian responses to low frequency electromagnetic fields in Drosophila melanogaster.

掲載誌: PLoS Genet 2014; 10 (12): e1004804

この研究は、μメタル製の磁気遮蔽箱で環境磁界を排除して、超低周波磁界(3または50Hz;90または300μT)ばく露キイロショウジョウバエ行動上の表現型(日周性周期、活動レベル)に与える影響を遺伝子解析により検討した。青色光受容タンパク質クリプトクロム(CRY)は日周行動に関与するが、その一方、磁界感受性への関与(外部磁界に感受性をもつ分子の構造が変化する)について、ラジカル対形成モデル(RPM)などいくつかのモデルが提唱されている。結果として、磁界による行動表現型誘導には、CRYおよび青色光への依存性がみられ、CRY安定性上昇との相関性があった;CRY変異体を用いた実験で、従来のRPMを支持しない結果が示された;遺伝子改変によりショウジョウバエに導入した哺乳類のCRYは磁界に反応した;CRYの磁界/青色光のセンサとしての働きには細胞内環境の関与が示唆された、などを報告している。

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研究目的(著者による)

The effects of exposure of different strains of Drosophila melanogaster to static and different extremely low frequency magnetic fields and to visible light on the circadian and general locomotor activity should be examined. Additionally, the bioluminescence as a response to 50 Hz magnetic fields was examined in brain slices from the suprachiasmatic nucleus (brain region which is responsible for controlling circadian rhythms) of mice.

詳細情報

The mechanism of magnetoreception in animals cannot be explained by now. A hypothesis suggests that cryptochrome (a photoreceptor, activated by light and as a consequence becomes susceptible to magnetic fields) may act as a magnetoreceptor through a radical pair mechanism involving tryptophans and the flavin cofactor (FAD)). This hypothesis should be investigated by using wild type Drosophila melanogaster, different genetically modified cryptochrome mutants of Drosophila melanogaster, and mammalian cryptochrome both in transgenic Drosophila as well as in its "mammalian environment" (brain slices).
While Drosophila melanogaster contains CRY as a photoreceptor, in non-drosophilid insects there can be type 1 CRY and type 2 CRY and in mammalian species there are two similar type 2 CRYs.

The wild type flies were exposed to different conditions: 1) static magnetic field (300 µT), 2) 50 Hz magnetic field (300 µT), 3) 3 Hz magnetic field (300 µT), 4) 3 Hz magnetic field (90 µT), and 5) 3 Hz magnetic field (1000 µT). The genetically modified strains were exposed to a 3 Hz magnetic field (300 µT). The suprachiasmatic nuclei slices were exposed to a 50 Hz magnetic field with different magnetic flux densities of 50 µT (number of slices =10), 150 µT (n=5), 300 µT (n=10), or 500 µT (n=10).
The experimental design was as follows for the experiments with the flies: Two groups of flies of the same genotype were studied for seven days under constant dim blue light followed by eight days under the same illumination but exposed either to a magnetic field or a sham exposure. The tissue slices were magnetic field exposed for five days and afterwards 5 days sham exposed or vice versa. Different illumination conditions (wavelength) were used.

影響評価項目

ばく露

ばく露 パラメータ
ばく露1:
  • DC/static
ばく露時間: continuous for 8 days
wild type flies
ばく露2: 50 Hz
ばく露時間: continuous for 8 days
wild type flies
ばく露3: 3 Hz
ばく露時間: continuous for 8 days
wild type flies
ばく露4: 3 Hz
ばく露時間: continuous for 8 days
wild type flies
ばく露5: 3 Hz
ばく露時間: continuous for 8 days
wild type flies
ばく露6: 3 Hz
ばく露時間: continuous for 8 days
genetically modified flies
ばく露7: 50 Hz
ばく露時間: continuous for 5 days
brain slices
ばく露8: 50 Hz
ばく露時間: continuous for 5 days
brain slices
ばく露9: 50 Hz
ばく露時間: continuous for 5 days
brain slices
ばく露10: 50 Hz
ばく露時間: continuous for 5 days
brain slices

ばく露1

主たる特性
周波数
  • DC/static
タイプ
  • magnetic field
偏波
  • linear
ばく露時間 continuous for 8 days
Additional information wild type flies
ばく露装置
ばく露の発生源/構造
ばく露装置の詳細 flies were exposed in a modified Schuderer apparatus (Schuderer et al., 2004); field was generated by two independent double-wrapped coils placed inside two µ-metal boxes within a commercial incubator; four quadratic Helmholtz coil systems produced a homogenous magnetic field (static or oscillating) with perpendicular orientation to the horizontal plane of the Trikinetics monitors, each coil was formed with a pair of wires with the current passing in the same direction through both wires for EMF exposure but in opposite directions to provide a sham exposure condition
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 300 µT - - - -

ばく露2

主たる特性
周波数 50 Hz
タイプ
  • magnetic field
偏波
  • linear
ばく露時間 continuous for 8 days
Additional information wild type flies
ばく露装置
ばく露の発生源/構造
  • E1と同じ装置
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 300 µT - - - -

ばく露3

主たる特性
周波数 3 Hz
タイプ
  • magnetic field
偏波
  • linear
ばく露時間 continuous for 8 days
Additional information wild type flies
ばく露装置
ばく露の発生源/構造
  • E1と同じ装置
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 300 µT - - - -

ばく露4

主たる特性
周波数 3 Hz
タイプ
  • magnetic field
偏波
  • linear
ばく露時間 continuous for 8 days
Additional information wild type flies
ばく露装置
ばく露の発生源/構造
  • E1と同じ装置
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 90 µT - - - -

ばく露5

主たる特性
周波数 3 Hz
タイプ
  • magnetic field
偏波
  • linear
ばく露時間 continuous for 8 days
Additional information wild type flies
ばく露装置
ばく露の発生源/構造
  • E1と同じ装置
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 1,000 µT - - - -

ばく露6

主たる特性
周波数 3 Hz
タイプ
  • magnetic field
偏波
  • linear
ばく露時間 continuous for 8 days
Additional information genetically modified flies
ばく露装置
ばく露の発生源/構造
  • E1と同じ装置
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 300 µT - - - -

ばく露7

主たる特性
周波数 50 Hz
タイプ
  • magnetic field
ばく露時間 continuous for 5 days
Additional information brain slices
ばく露装置
ばく露の発生源/構造
ばく露装置の詳細 slices were exposed through coils in a system based on the Schuderer apparatus (µ-metal shielded chamber, see Schuderer et al., 2004) within an incubator at 37°C
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 50 µT - - - -

ばく露8

主たる特性
周波数 50 Hz
タイプ
  • magnetic field
ばく露時間 continuous for 5 days
Additional information brain slices
ばく露装置
ばく露の発生源/構造
  • same setup as in Exposure 7
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 150 µT - - - -

ばく露9

主たる特性
周波数 50 Hz
タイプ
  • magnetic field
ばく露時間 continuous for 5 days
Additional information brain slices
ばく露装置
ばく露の発生源/構造
  • same setup as in Exposure 7
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 300 µT - - - -

ばく露10

主たる特性
周波数 50 Hz
タイプ
  • magnetic field
ばく露時間 continuous for 5 days
Additional information brain slices
ばく露装置
ばく露の発生源/構造
  • same setup as in Exposure 7
Sham exposure A sham exposure was conducted.
パラメータ
測定量 種別 Method Mass 備考
磁束密度 500 µT - - - -

Reference articles

ばく露を受けた生物:

方法 影響評価項目/測定パラメータ/方法

研究対象とした生物試料:
調査の時期:
  • ばく露前
  • ばく露中
  • ばく露後

研究の主なアウトカム(著者による)

In wild type flies (CRY), exposure to magnetic fields (field 1-5) significantly shortened the circadian periods and significantly increased locomotor activity levels compared to sham exposure. Furthermore, the Western blot analysis showed that the magnetic field exposure significantly increased the stability of cryptochrome compared to the sham exposure.
In genetically modified flies which did not express cryptochrome, no response to the magnetic field was observed. Further experiments with cryptochrome mutant flies showed that the tryptophan hypothesized to be essential to the electron transfer in the radical pair mechanism is not necessary for magnetic field responses. Transformants bearing an hCRY1 were not able to detect the magnetic fields.
The mammalian cryptochrome (hCRY2) responded to the magnetic field when cloned into flies but not in its "mammalian environment" i.e. in the brain slices of mice.
The authors suggest that cryptochromes act as blue-light/magnetic field sensors depending on factors that are present in particular cellular environments.

研究の種別:

研究助成

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