Developmental toxicity and apoptosis in zebrafish embryos induced by low-dose γ-ray irradiation

In this paper, the developmental toxicity and apoptosis in zebrafish (Danio rerio) embryos induced by 0.01, 0.05, and 0.10-Gy γ-ray irradiation were investigated and verified by single cell gel electrophoresis, acridine orange staining, flow cytometry, transmission electron microscopy, digital gene expression sequencing, and Western blot analysis. DNA damage, deformity rates, and apoptosis of zebrafish embryos were found to increase significantly with the increase of irradiation dose, and survival and hatching rates significantly decreased when the irradiation dose exceeds 0.10 and 0.05 Gy, respectively. Exposure to 0.10-Gy γ-ray irradiation resulted in the swelling of cell mitochondria of zebrafish embryos and changes in their intracellular vacuoles. mRNA and protein expression levels of Shh (sonic hedgehog 19 KDa) and Smo (smoothened 86 KDa) of Hh signaling pathway associated with the development of early embryos significantly increased with the increase of irradiation dose. Expression of the AKT (56 KDa) and PiK3r3 (55 KDa) genes, which are anti-apoptotic and involved with the PI3K/Akt signaling pathway, significantly decreased, while expression of the bada gene, which is pro-apoptotic, significantly increased. The results show that γ-ray irradiations of 0.01 and 0.05 Gy can induce developmental toxicity and apoptosis in zebrafish embryos via Hh and PI3K/Akt signaling pathways, respectively.