RADIOBIOLOGY DIVISION

13.RADIOBIOLOGY DIVISION

Spore Dosimetry of Solar-UV Radiation

    Solar UV radiation is one of the most ubiquitous and powerful genotoxic agents on earth. The genotoxicity is due mainly to the induction of UV-specific photoproducts in DNA in exposed cells. Those photoproducts, when not correctly repaired, can produce cellular lethality and mutagenesis. Hence, in human skin, solar-UV exposure is the major cause of tumorigenesis and various diseases. However, the intensity of genotoxic UV-radiation received by organisms is difficult to determine. This is because solar radiation is polychromatic and each wavelength component exerts different biological effects with varying efficacy. Genotoxic effects generally exhibit a steep rise in effectiveness at the shortest end of the UV wavelength spectrum reaching the earth. Physical irradiation data obtained from spectral photometers must be converted to biologically relevant values ("biologically-effective dose"). It was thought to be necessary to introduce biological dosimeters for assessment of risks to the biosphere.
    Spore dosimetry, using Bacillus subtilis UV-hypersensitive mutant spores spotted and dried on a membrane filter, was developed and applied under various environmental conditions.⁽¹⁷⁷⁾ Several comparative investigations have been carried out to pursue side-by-side comparisons with spectral photometry in order to evaluate the validity of effectiveness spectra for the dosimetry.⁽¹⁷⁸⁾
    Reduction of the transmission using combinations of two types of filter sheets made it possible to measure weekly and monthly doses anywhere on earth. Continual monthly measurements started at three sites (Tokyo, Jakarta, and Denpasar) in late 1998, and the initial results have been presented.⁽¹⁷⁹⁾ This is the first quantification of UV doses in tropical Asia, which includes densely-populated areas and diverse ecosystems.
Test for Fused-cell Origin of Tumors

    An interesting hypothesis is that a tumor is a clone arising from a fused-cell origin. A test system for examining the fused-cell origin of tumors was developed by application of Mus caroli carrying the X-chromosome inactivation cellular mosaicism for G6PD. The G6PD heterodimer pattern of the tumor from a fused-cell was not found. Although the results obtained were not conclusive, this system is thought to be useful for detecting a possible fused-cell origin of tumors.⁽¹⁸⁰⁾




13.RADIOBIOLOGY DIVISION



	Spore Dosimetry of Solar-UV Radiation Solar UV radiation is one of the most ubiquitous and powerful genotoxic agents on earth. The genotoxicity is due mainly to the induction of UV-specific photoproducts in DNA in exposed cells. Those photoproducts, when not correctly repaired, can produce cellular lethality and mutagenesis. Hence, in human skin, solar-UV exposure is the major cause of tumorigenesis and various diseases. However, the intensity of genotoxic UV-radiation received by organisms is difficult to determine. This is because solar radiation is polychromatic and each wavelength component exerts different biological effects with varying efficacy. Genotoxic effects generally exhibit a steep rise in effectiveness at the shortest end of the UV wavelength spectrum reaching the earth. Physical irradiation data obtained from spectral photometers must be converted to biologically relevant values ("biologically-effective dose"). It was thought to be necessary to introduce biological dosimeters for assessment of risks to the biosphere. Spore dosimetry, using Bacillus subtilis UV-hypersensitive mutant spores spotted and dried on a membrane filter, was developed and applied under various environmental conditions.⁽¹⁷⁷⁾ Several comparative investigations have been carried out to pursue side-by-side comparisons with spectral photometry in order to evaluate the validity of effectiveness spectra for the dosimetry.⁽¹⁷⁸⁾ Reduction of the transmission using combinations of two types of filter sheets made it possible to measure weekly and monthly doses anywhere on earth. Continual monthly measurements started at three sites (Tokyo, Jakarta, and Denpasar) in late 1998, and the initial results have been presented.⁽¹⁷⁹⁾ This is the first quantification of UV doses in tropical Asia, which includes densely-populated areas and diverse ecosystems. Test for Fused-cell Origin of Tumors An interesting hypothesis is that a tumor is a clone arising from a fused-cell origin. A test system for examining the fused-cell origin of tumors was developed by application of Mus caroli carrying the X-chromosome inactivation cellular mosaicism for G6PD. The G6PD heterodimer pattern of the tumor from a fused-cell was not found. Although the results obtained were not conclusive, this system is thought to be useful for detecting a possible fused-cell origin of tumors.⁽¹⁸⁰⁾