DIFFERENCE IN TYPES OF RADIATION-INDUCED STRUCTURAL CHROMOSOME-ABERRATIONS AND THEIR INCIDENCES BETWEEN CHINESE AND SYRIAN-HAMSTER SPERMATOZOA

The effects of ionizing radiations on sperm chromosomes were studied i n the Chinese hamster (Crisetulus griseus) and the Syrian (golden) ham ster (Mesocrisetus auratus). Testes of mature male Chinese hamsters (C H) were irradiated with X-rays (0.91, 1.82 and 3.63 Gy) and gamma-rays (1.10, 2.15, 2.95 and 4.01 Gy) at a single acute dosage, whereas the irradiation was done with lower doses of X-rays (0.45, 0.91 and 1.82 G y) and gamma-rays (0.49, 0.99 and 1.98 Gy) in mature male Syrian hamst ers (SH), taking the higher radiosensitivity of this species into cons ideration. They were mated with normal females within 6 days of exposu re. Sperm-derived chromosomes were analyzed in 1125 and 1966 fertilize d ova of the CH and the SH, respectively. In both species, there was n o great difference in the induction of structural chromosome aberratio ns between X-irradiated and gamma-irradiated spermatozoa. Chromosome-t ype aberrations were predominantly induced. The incidence of breakage- type aberrations increased linearly, and that of exchange-type aberrat ions lineal-quadratically with increase of dosage. A species-specific difference in chromosomal radiosensitivity of spermatozoa was clear. I n spite of the same radiation dosage, the incidence of chromosomally a bnormal spermatozoa in the SH was about twice as high as that in the C H (e.g., 27.0% vs. 14.7% at 0.91 Gy of X-rays). The incidences of brea kage-type aberrations (69-89%) were far higher than those of exchange- type aberrations (11-31%) in the SH, while the disparity of the two in cidences was much smaller in the CH (46-65% vs. 35-54%). Exchange-type aberrations consisted of both chromosome-type and chromatid-type in t he SH, while almost all of them were of the chromosome-type in the CH. These results suggest that the DNA-repairing capacity of oocytes is m uch higher in the CH than in the SH. Moreover, it seems likely that ra diation-induced sperm DNA damage is repaired with both pre-replication repair (excision repair) and pest-replication repair systems in SH oo cytes, whereas the excision repair system operate most exclusively in CH oocytes.