Abstract
The effects of low-dose heavy ions on the prenatal development of animals as well as of cells are not well elucidated. The neural crest-derived melanocyte is a good model to study the effects of heavy ions on the proliferation and differentiation of cells, since it possesses a higher proliferation rate in the embryonic stage and visible pigment melanin as a differentiation marker. In 18-day-old murine skin, the accumulation of melanoblast, precursors of melanocyte, and the initiation of differentiation of melanocyte are observed in the epidermis, in addition, hair bulb melanocytes are already colonized with the initiation and progression of the development of hair follicles. Therefore, in this study, 18-day-old murine skin was selected to study the effects of low-dose heavy ions. Pregnant females of C57BL/10J mice at 9 days of gestation were whole-body irradiated with a single acute dose of heavy ions (0.1, 0.25, 0.5, and 0.75 Gy). The effects were studied by scoring changes in the prenatal development of mice as well as of epidermal melanoblasts/melanocytes and hair bulb melanocytes. Although the frequency of developmental anomalies such as bent tails, short tails, microphthalmia and anophthalmia is increased as dose and LET increased, the frequency of developmental anomalies such as cacomelia and hemorrhage showed no change by dose and LET. The number of epidermal melanoblasts/melanocytes and hair bulb melanocytes in the dorsal and ventral skins significantly decreased even at 0.1 Gy-treated embryos, and gradually decreased as dose increased. The effects in the ventral skin were greater than those in the dorsal skin. The effects of heavy ions on the number of hair bulb melanocytes were increased as LET of heavy ion species increased, whereas the number of epidermal melanoblasts/melanocuytes showed no difference between heavy ions and gamma-rays. These results suggest that heavy ions cause cell death or inhibition of the differentiation of melanoblasts/melanocytes and other cells even at the low dose in a tissue-specific manner. Their effects in the ventral skin appear to be greater than those in the dorsal skin.
