3D reconstructed brain images reveal the possibility of the ogg1 gene to suppress the irradiation-induced apoptosis in embryonic brain in medaka

The accumulation of oxidative DNA lesions in neurons is associated with neurodegenerative disorders and diseases. Oggl (8-oxoG DNA glycosylase-l) is a primary repair enzyme to excise 7,8-dihydro-8-oxoguanine (8-oxoG), the most frequent mutagenic base lesion produced by oxidative DNA damage. We have developed oggl-deficient medaka by screening with a high resolution melting (HRM) assay in Targeting-Induced Local Lesions In Genomes (TILLING) library. In this study, we identified that oggl-deficient embryos have smaller brains than wild-type during the period of embryogenesis and larvae under normal conditions. To reveal the function of oggl when brain injury occurs during embryogenesis, we examined the induction of apoptosis in brains after exposure to gamma-rays with 10 Gy(l37Cs, 7.3Gy/ min.) at 24h post-irradiation both in wild-type and oggl-deficient embryos. By acridine orange (AO) assay, clustered apoptosis in irradiated oggl-deficient embryonic brains were distributed in a similar manner to those of irradiated wild-type embryos. To evaluate possible differences of gamma-ray induced apoptosis in both types of embryonic brains, we constructed 3D images of the whole brain based on serial histological sections. This analysis identified that the clustered apoptotic volume was about 3 times higher in brain of irradiated oggl-deficient embryos (n = 3) compared to wild-type embryos (n = 3) (P = 0.04), suggesting that irradiation-induced apoptosis in medaka embryonic brain can be suppressed in the presence of functional oggl. Collectively, reconstruction of 3D images can be a powerful approach to reveal slight differences in apoptosis induction post-irradiation. Keywords: oggl; apoptosis; medaka; irradiation; 3D reconstruction; embryonic brain