Session 1: DNA repair

The first plenary session of the meeting was dedicated to DNA repair. Investigators from six outstanding groups in the field were invited to present their latest findings. Speakers in the order of appearance included Dr Takashi Morita from Osaka City University in Japan, Dr Erica Werner from the group of Dr Paul Doetsch at Emory University in the USA, Dr Akinari Yokoya from the Japan Atomic Energy Agency, Dr Susan Bailey from Colorado State University in the USA, Dr Sandro Conrad from the group of Dr Marcus Lobrich at Darmstadt University of Technology in Germany, and Dr Aroumougame Asaithamby of the University of Texas Southwestern Medical Center in the USA. Overall the talks focused on aspects of cellular responses to DNA damage as they relate to space radiation biology for missions to the International Space Station (ISS), the moon or Mars, as well as to ion radiotherapy. The presentation of Dr Morita focused on the detection of chromosome aberrations in γ-H2AX-proficient and -deficient mouse embryonic stem (ES) cells in the space environment of the Japanese experimental module ‘KIBO’ at the ISS [1]. It is planned that cells will be flown to KIBO and stored there for up to 3 years in a frozen state (at − 95°C) and will be periodically returned to Earth (overall five times), where analysis for chromosome aberration formation from space radiation will be carried out. Notably, radiation-exposed and control ES cells can also be microinjected into unirradiated embryos, and surviving embryos can be implanted into pseudo-pregnant mice to analyze for developmental defects induced by space radiation. The authors provided evidence that all related assays required for this set of experiments are already developed in their laboratories. The first experiments were therefore designed to validate the potential of the system. For this purpose, the investigators characterized the selected mouse ES cells using γ-rays or Fe-ions and measured chromosome aberrations by fluorescence in situ hybridization (FISH). The results obtained in these validating experiments demonstrated increased radiosensitivity compared with wildtype H2AXdeficient cells, and this was confirmed by analyzing certain forms of chromosomal aberrations. This validated system of ES cells can now be used for the quantitative estimation of the biological consequences of space radiation. The actual space radiation experiment started in March 2013 by flying wildtype and histone H2AX-deficient ES cells to ISS. This is the first experiment of its type designed to directly examine the effect of the space radiation environment at different endpoints. Although the ISS is not receiving the spectrum of particles expected in deep space, and cells in a frozen state sustain a different spectrum of lesions in their DNA than non-frozen cells, the results are awaited with great interest. The presentation of Dr Erica Werner focused on the role of Reactive Oxygen Species (ROS) in the resolution of persistent genomic instability following exposure to radiation [2]. This work is based on the hypothesis that ROS generated as a consequence of a radiation exposure can amplify the initially induced radiation damage sustained by macromolecules. It is further considered that ROS can amplify downstream responses to DNA damage that determine DNA repair and cell death. ROS are even thought to amplify delayed radiation responses leading to tissue damage and/or tumorigenesis. Results were presented showing that in immortalized normal human bronchial epithelial cells (HBEC-3KT) exposed to X-rays or Fe-ions, increased ROS levels can persist in surviving cells for up to eight population doublings (2 weeks). It was observed that this increased ROS production overlapped temporally with the persistence of reporters for genomic instability, proliferation and senescence, and was associated with increased frequency of micronucleus formation and the presence of γH2AX-53BP1 foci. Although low-LET radiation Journal of Radiation Research, 2014, 55, i9–i11 Supplement doi: 10.1093/jrr/rrt206