Somatic-cell mutation induced by UVA and monochromatic UV radiation in repair-proficient and -deficient Drosophila melanogaster¶

Abstract

Near-ultraviolet light (UVA: 320-400 nm) constitutes a major part of sunlight UV. It is important to know the effect of UVA on the biological activities of organisms on the earth. We have previously reported that black light induces somatic-cell mutation in Drosophila larvae. To investigate which wavelength of the UVA is responsible for the mutation we have now carried out a series of monochromatic irradiations (310, 320, 330, 340, 360, 380 and 400 nm) on Drosophila larvae, using the large spectrograph of the National Institute for Basic Biology (Okazaki National Research Institutes, Okazaki, Japan). Mutagenic activity was examined by the Drosophila wing-spot test in which we observe mutant wing hair colonies (spots) on the wings of adult flies obtained from the treated larvae. The induction of mutation was highest by irradiation at 310 nm and decreased as the wavelength became longer. Neither the 380 nor the 400 nm light was mutagenic. Excision repair is known to protect cells from UV damage. In the excision-repair-deficient Drosophila, the mutagenic response induced by 310 nm irradiation was 24-fold higher than that of the wild-type (7.2 +/- 1.5 spots/wing/kJ vs 0.3 +/- 0.08 spots/wing/kJ), and at 320 nm the difference of the response was 14-fold (0.21 vs 0.015 +/- 0.005). In the case of irradiation at 330 and 340 nm the difference of the response was only two-fold (at 330 nm, 6.9 +/- 2.9 x 10(-3) vs 3.1 +/- 1.1 x 10(-3) spots/wing/kJ; at 340 nm, 3.5 +/- 0.9 x 10(-3) vs 2.0 +/- 0.7 x 10(-3). These results suggest that the lesion caused in the larvae by 320 nm irradiation may be similar to the damage induced by 310 nm and that the lights of 330 and 340 nm may induce damage different from the lesions induced by shorter-wavelength lights.

Increased Levels of 8-Hydroxy-2′-Deoxyguanosine in Drosophila Larval DNA after Irradiation with 364-nm Laser Light but not with X-rays

“…We reported previously that somatic cell mutations could be induced by 320–360 nm spectroscopic UVA light when larvae were irradiated for a long time ( i.e. 6 h) using an OLS separating a consecutive beam from a xenon lamp spectroscopically (7). In the present study, we examined the mutagenicity of a 364‐nm laser light that uses a homogeneous monochromatic beam.…”

“…Sunlight reaching the surface of the earth includes both mid‐ultraviolet (UVB: 290–320 nm) and near‐ultraviolet (UVA: 320–400 nm) light, and both are etiologically relevant to the development of human skin cancer (1–3). Evidence is accumulating that UVA plays an important role in photo‐aging and photo‐carcinogenesis of the skin, and various studies have investigated UVA‐induced mutations and oxidative stress (4–10). However, nearly all investigations have been performed using a broad‐band UVA light source and photosensitizer.…”

“…An area of 5.4 × 5.4 cm was homogeneously irradiated with a vertical beam at 316 ± 37 W m −2 . Irradiation with 310‐ or 364‐nm spectroscopic light was performed using the Okazaki Large Spectrograph (OLS) as described previously (7,8). X‐ray irradiation was carried out at a dose of 0.5 Gy min −1 with a 1‐mm aluminum filter using a Hitachi X‐ray generator (140 kV, 40 mA).…”

“…Somatic cell mutation was detected using the wing spot test as described previously (7). Third instar larvae were prepared by mating virgin y; mwh j v females to y; Dp(1;3)sc J4 , y + flr/TM1, Mè ri sbd 2 males .…”

Development of a Test System for Mutagenicity of Photosensitizers Using Drosophila melanogaster¶

“…As mentioned before, the amount of UV‐A and UV‐B produced by the light source used in the experiments was measured. The amounts of UV‐A and UV‐B were such that no mutagenic effects in Drosophila were to be expected (19, 20; M. J. M. Nivard, unpublished). Moreover, the experimental setup is such that the sample spot is situated beneath glass.…”