Abstract
The purpose of this study is to reveal the surveillance mechanisms to DNA damage in male germ cells using Medaka, Oryzias latipes, because of the ease with which the differentiation stages of its spermatogenic cells can be identified. In our laboratory, the three radiation sensitive Medaka mutants (RIC; Radiation Induced Curly tailed malformation) were isolated by ENU mutagenesis screening in the Medaka. We reported that RIC1 mutant has a defect of DNA double strand breaks repair during early embryogenesis. We examined the effect of DNA double-strand breaks (DSBs) in the mutant testis. We investigated the testis by histological analysis in wild type (CAB strain) and RIC1 after 2.5Gy gamma-irradiation. At day 30 after irradiation, there were no spermatogonial stem cells (SSCs) and histological recovery like in the CAB was not observed in the RIC1 testis. RIC2 is sensitive at morula stage than RIC1. In the RIC2 testis, there were SSCs and partial recovery was observed at day 30 after 2.5Gy gamma-irradiation. These results suggest that SSCs in RIC1 testis are very sensitive compared to those in CAB, and that there are differences in the responses (e.g. DNA repair system and apoptosis) of SSCs to DSBs after gamma-irradiation between RIC1 and RIC2.
