Worm Breeder's Gazette 10(3): 95
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.
Neutrons from the Argonne National Laboratory's JANUS reactor were used to irradiate worms in order to identify any enhanced effectiveness that they might have over gamma rays in inducing several classes of lesions. The neutrons were of a fission spectrum with a mean energy of 0.8 MeV. Two preliminary results are presented here. Using the eT1 balancer method reported previously, induction of autosomal recessive lethals in a 400 essential gene region was measured and yielded a linear dose vs response rate of about 0.6% mutants/rad/balanced region. This compares with a rate of 0.38% for [60cobalt] gammas and yields an RBE (relative biological effectiveness) of approximately 1.6 which is a bit lower than predicted. This result was obtained using adult worms having meiotic oocytes and mature spermatozoa. However, when dauer larvae are used as the target, the rate is dramatically reduced for gammas and neutrons. Perhaps the dauer gonia are: 1) killed outright, 2) selectively sampled, or 3) repaired as efficiently as gamma irradiated cells. The latter seems likely because heavy ion-irradiated dauers yield mutants at 1/2 to 1/6 the adult rate. This is surprising as neutrons are known to interact with tissue by generating recoil protons which are themselves ionized particles. The results are shown in the upper panel. Stable karyoplasmic bridges were induced in L1 intestinal syncytial nuclei which divide at the first larval molt and are visualized by DAPI staining of adults. We believe these to be caused by chromosome breaks leading to polycentric or ring chromosome formation. Non- ionizing UV irradiation is ineffective. Neutrons were about 1.7 fold more effective than cobalt gammas for this endpoint and two of the radiation hypersensitive mutants (rad-2 and rad-7) were hypersensitive to neutrons. rad-2 is also sensitive to heavy ions for nuclear bridge formation but rad-7 is not. rad mutant results are still incomplete for gammas. All of the rads tested: 1, 2, 3, 4 & 7 are sensitive for embryo inactivation by UV while rads 1, 3, & 7 also respond to gammas and X-rays. rad-3 is hypermutable to UV while rads 1, 3 & 7 are hypomutable to gammas. In this light, the selective pattern of rad-7 sensitivity to neutrons is surprising as neutrons and ions are expected to induce similar types of lesions both of which are distinct from the gamma-induced variety. The lower panel illustrates the results. [See Figures 1 & 2]