Abstract
DNA double strand-breaks (DSBs) caused by ionizing radiation and some chemical agents can induce great damage to genetic material. All cells maintain repair systems for such breaks, however, these activities are fluctuated in a tissue specific and/or age dependent manners. We have studied the effects of radiation on meiosis and reproductive development using an experimental model organism, the nematode Caenorhabditis elegans. In the adult C. elegans hermaphrodite, germ line nuclei in the tip of the gonad arm divide mitotically and thereafter enter meiotic prophase I, progressing from the leptotene/zygotene stages to diakinesis stage in maturing oocyte. The linear array of the developmental phases of oogeneisis makes the adult hermaphrodite a convenient model system to study these effects.
We found that meiotic pachytene nuclei of C. elegans are hyper-resistant to X-rays, gamma rays and heavy ion particle irradiations, whereas early (post-fertilization) embryonic cells and diakinesis stage oocytes are not. The high level of expression of enzymes involved in meiotic homologous recombination accounts for these differences in resistance. In addition, we would like to discuss the radiation response of the pachytene checkpoint system including apoptosis and to introduce the construction of bystander effects in germ line cells using micro-beam system.
