Abstract
The ric (Radiation Induced Curly tailed malformation) mutation is isolated by ENU mutagenesis screening in the Medaka. We reported that the ric1 phenotype is associated with defective rapid repair of DNA double-strand breaks induced by ionizing radiation (IR) in embryos (Aizawa et al 2004). We examined radiation effects on testis and intesitine histologically. At 24 hours after 2.5Gy γ-irradiation, a lot of apoptosis in spermatogonial stem cells (SSCs) were detected in the wild-type CAB strain, but in the ric1 testis, few pycnotic SSCs and spermatocytes were detected and filled with differentiating spermatogonia, and almost all spermatocyte disappeared. At 3days after irradiation, there was no pycnotic SSC in CAB but many were observed in ric1. Within 5days after irradiation almost all SSCs disappeared in ric1 and within 30days after irradiation they became sterile. These results show that the different pathways for DNA repair and apoptosis induction are employed during spermatogenesis and the ric1 gene product has an important role in triggering the early apoptosis in the SSCs and differentiating spermatogonia. The intestine of ric1 showed similar radiosensitivity to that of CAB, which means the ric1 is not involved intestinal stem cells. The ric1 locus was mapped in LG9, and about 400kb genomic region containing ric1 gene was determined. Now, we are examining the radiation effects on primordial germ cells (PGCs) in ric1 using olvas-ric1 strain obtained by the crossing of ric1 with olvas-GFP with germ cell specific expression of GFP.
