Genetic and Molecular Dosimetry of HZE Radiation (RADIAT)

Radiation biology

Caenorhabditis elegans (nematode larvae)
Flight: ~ 7 million Male/Hermaphrodite

Delayed synchronous

Biorack US1 Experiment Hardware

One of the major features of the space environment is the presence of cosmic rays or HZE (high energy and charge) particles. Understanding the biological effects of the complex radiation environment in space is crucial to the safety of space flight crews. Of greatest importance are changes to chromosomes that lead to the conversion of normal cells to cancer cells. The objective of this study was to isolate genetic changes in animal cells caused by cosmic rays in space so that their likelihood of occurrence and structural features could be evaluated.

Two strategies were used for the selection of mutations induced by space radiation. The first method used a large genetic target of 1500 genes and the second used a single large gene, unc-22, as a target. Four tests (growth, mating, segregation, and recombination) were carried out to assess development and the behavior of chromosomes during meiosis. Each test was performed with two different genotypes to control for specific gene effects. Worms from selected cultures were fixed and stained using the fluorescent DNA- binding dye DAPI to reveal cell nuclei. Some embryos recovered at landing were also fixed and stained with antibodies specific for cytoplasmic determinants that localize to different cell lineages. Several hundred animals were analyzed for their anatomy based on cell number and distribution, nuclear morphology, karyotype, and symmetry relationship.

No obvious differences were seen in the development, behavior, and chromosome mechanics of C. elegans as a function of microgravity. Both self-fertilization and mating of males with hermaphrodites were successful. Gross anatomy, symmetry, and gametogenesis were normal based on light microscope observations. No defective karyotypes or cell distributions were observed. The pairing, disjoining, and recombination of chromosomes showed no differences correlated with gravity levels. A variety of mutants were isolated in the unc-22 gene and in essential genes balanced by the eT1 translocation. Phenotypic assessment of mutants suggests that mutants isolated from regions of identified high linear energy transfer (LET) particles are more severe than those isolated by random screening. Large deletions have been identified amongst the unc-22 mutants. The rates of mutagenesis were significantly above those in ground controls.

Johnson, T.E. and G.A Nelson: Caenorhabditis elegans: a Model System for Space Biology Studies. Experimental Gerontology, vol. 26(2–3), 1991, pp. 299–309.†

Nelson, G.A.: Genetic and Molecular Dosimetry of HZE radiation (7-IML-1). First International Microgravity Laboratory Experiment Descriptions, T.Y. Miller, ed., NASA TM-4353, 1992, pp. 25–31.

Nelson, G.A.: Radiation in Microgravity. Handbook of Physiology, M.J. Fregly and C.M. Blatteis, eds., Section 4, vol. 2, 1996. New York: Oxford University Press, pp. 785–798.

Nelson, G.A. et al: Development and Chromosome Mechanics in Nematodes: Results from IML-1. Advances in Space Research, vol. 14(8), 1994, pp. 209–214.

Nelson, G.A. et al. Genetic and Molecular Dosimetry of HZE Radiation. In: BIORACK on Spacelab IML-1, C. Mattock, ed. Noordwijk, The Netherlands: European Space Agency SP-1162, 1995, pp. 41–50.

Nelson, G.A. et al.: Nematode Radiobiology and Development in Space. Results from IML-1. Fifth European Symposium on Life Sciences Research in Space, European Space Agency SP- 366, 1994, pp. 187–191.

Nelson, G.A. et al.: Radiation Effects in Nematodes: Results from IML-1 Experiments. Advances in Space Research, vol. 14(10), Oct 1994, pp. 87–91.