Worm Breeder's Gazette 10(3): 157
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Synchronous populations of young embryos were exposed to various fluences of 254 radiation and incubated in the presence of tritiated thymidine. At selected times, samples were processed to determine the effects of irradiation on DNA synthesis (measured as the incorporation of tritium into TCA precipitable material) and cell division [measured by counting nuclei a la Gossett and Hecht (1980. J. Histochem. Cytochem. 28, 507-510)]. Despite the fact that over 50% of embryos failed to develop into adults after fluences of 25 Jm-2 or greater, they displayed control (unirradiated) levels of both cell division and replication at fluences of up to 250 Jm-2. This resistance was not due to UV light attenuation, since both parameters were strongly inhibited in two UV radiation hypersensitive mutants (rad-1 and rad-3) by fluences of 10 Jm-2 and greater. Other systems (e.g., bacteria, mammalian cells, yeast) are much more sensitive to the effects of UV radiation on DNA replication. Analysis of the sizes of newly synthesized DNA in irradiated and unirradiated embryos may provide an explanation for this extreme radiation resistance. Synchronous embryos were irradiated, pulse labeled with tritiated thymidine, and chased for various time intervals. After lysis with proteinase K and SDS, samples were subjected to centrifugation through alkaline sucrose gradients. Inclusion of [14C]-labeled T4 and T7 DNA's allowed determination of molecular weights. Fluences of up to 270 Jm-2 failed to reduce the molecular weight of newly synthesized DNA relative to unirradiated controls. This was unexpected, since damage to the parental strand in other organisms suppresses the size of nascent molecules by preventing elongation of DNA polymerase. It can be calculated, based upon the induction frequency of cyclobutane dimers as well as the size of the newly synthesized DNA, that greater than ten cyclobutane dimers were induced in the template opposite each nascent fragment. This leads to the provocative possibility that a DNA polymerase from C. elegans is capable of trans-lesion synthesis through radiation-induced DNA damage. These data are in keeping with the observation, described in the preceding paragraph, that DNA synthesis and cell division during embryogenesis are refractory to super-lethal doses of UV radiation.