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Harmful environmental factors - namely ionizing radiation - will continue to influence future manned space missions. The Cellular Biodiagnostic group at the German Aerospace Center (DLR) develops cellular monitoring systems, which include bacterial and mammalian cell systems capable of recognizing DNA damage as a consequence of the presence of genotoxic conditions. Such bioassay or biosensor systems will complement the physical detector systems used in space, insofar as they yield intrinsically biologically weighted measures of cellular responses. Furthermore, synergistic mutagenic and cancerogenic impacts of the radiation environment together with other potentially genotoxic constituents of the space habitat can be quantified using such systems, whose signals are especially relevant for the molecular damage to the DNA or the chromosomes. The experiment Cellular Responses to Radiation in Space (CERASP) has been selected by NASA to be performed on the International Space Station. It will supply basic information on the cellular response to radiation applied in microgravity. One of the biological end-points under investigation will be survival reflected by radiation-dependent reduction of constitutive expression of the enhanced variant of green fluorescent protein (EGFP), originally isolated from the bioluminescent jellyfish Aequorea victoria. A second end-point will be gene activation by space flight conditions in mammalian cells, based on fluorescent promoter reporter systems using the destabilized EGFP variant (d2EGFP). The promoter element to be investigated will reflect the activity of the NF-kappaB stress response pathway as an anti-apoptotic radiation response. DNA damage will be measured by fluorescent analysis of DNA unwinding (FADU). The systems have worked properly for terrestrial applications during the first experiments. Experiments using accelerated particles produced at the French heavy ion accelerator GANIL have given insights into cellular mechanisms relevant for the exceptional radiation field in space.
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