Quantification of ionizing radiation-induced cell death in situ in a vertebrate embryo.
Quantitative studies of radiation cytotoxicity have been performed mostly in cells in culture. For a variety of reasons, however, the response of cells in culture may not reflect the response for cells in situ in a whole organism. We describe here an approach for quantification of radiation-induced cell death in vivo using the transparent embryo of the zebrafish, Danio rerio, as a model vertebrate system. Using this system, we show that the number of TUNEL-positive cells within a defined region increases approximately linearly with radiation dose up to 1 Gy. The results are consistent with predictions of a linear-quadratic model. The use of alternative models, accommodating a response threshold or low-dose hypersensitivity, did not significantly improve the fit to the observed data. Attenuation of the expression of the 80-kDa subunit of Ku, an essential protein for the nonhomologous end-joining pathway of repair, led to a dose reduction of 30- to 34-fold, possibly approaching the limit where each double-strand break causes a lethal hit. In both the Ku80-attenuated and the control embryos, apoptotic cells were distributed uniformly, consistent with a cell-autonomous mechanism of cell death. Together, these results illustrate the potential of the zebrafish for quantitative studies of radiation-induced cell death during embryogenesis and in vivo.
Bladen
Catherine L
CL
Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912, USA.
Flowers
Melody A
MA
Miyake
Katsuya
K
Podolsky
Robert H
RH
Barrett
John T
JT
Kozlowski
David J
DJ
Dynan
William S
WS
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004625:Embryo, Nonmammalian / Q000528:radiation effects*; D020287:In Situ Nick-End Labeling; D011836:Radiation Tolerance; D015027:Zebrafish