Studies on cell damage, healing and regeneration mechanism in insects using heavy-ion microbeams

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Previously we have developed the specific heavy-ion irradiation system for eggs, 4th and 5th instar larvae of the silkworm, Bomby mori. using heavy-ion microbeams with desired beam size and dose. In this study, we established a new irradiation method optimized for the first instar larvae. Now, we have completed heavy-ion irradiation methods available for all developmental stages of the insect, except for adult. Next, we studied the process and mechanism of degradation and regeneration of heavy-ion irradiated hemopoietic organs. As we previously demonstrated, locally-targeted irradiation of the larval hemopoietic organs of B. mori with heavy-ions causes serious cell damage, but subsequently these organs regenerate with high frequency. In this study we clarified that the circulating hemocytes could invade into the irradiated hemopoietic organs and eliminate the injured cells by phagocytosis. We also indicated that the stem cells responsible for regeneration might originate from the hemocytes (possibly prohemocytes) in circulation by implantation experiment of irradiated organs into the transgenic silkworms expressing GFP. On the other hand, we investigated the effects of heavy-ions on the differentiation of epidermal cells of the silkworm. Local targeted heavy-ion irradiation resulted in no marked morphological changes during larval stages, but the resultant moth loosed their scales in the irradiated site in a dose dependent manner. Moreover, it was shown that heavy-ion irradiation could suppress abnormal proliferation of epidermal cells in a mutant strain "Knobbed" (K). From these results it is suggested that epidermal cells are considerably resistant to heavy-ions and that epidermal differentiation is suppressed by inhibition of cell division after irradiation.