Radioadaptive response in primary mouse spermatocytes revealed by analysis of synaptonemal complexes

This study was aimed at estimating the damage to the synaptonemal complex (SC) of male mice caused by radiation exposure at the ultimate pre-meiotic interphase. Four experimental groups were formed: group 1 was an untreated control, group 2 received a low dose (50 mGy) of radiation, group 3 a high dose (4 Gy) of radiation, group 4 was first treated with a low dose (50 mGy) and 4 h later with a high dose (4 Gy). Mice were killed 4 days after the treatment. Early pachytene cells were selected for the electron microscopic analysis of SCs. These cells were supposed to be at pre-meiotic interphase at the time of irradiation. Treatment with a low dose of radiation did not produce any substantial increase in the frequency of SC aberrations, while exposure to the high dose resulted in various types of damage. Group 4 demonstrated significantly lower frequencies of axial breaks/fragments and multiaxial configurations than group 3. At the same time, these two groups did not differ in the frequencies of inter- and intrachromosomal exchanges such as translocations, inversions, and deletions. We suppose that the number of breaks produced by a high dose of radiation was the same in the both groups. However, a proportion of the breaks that remained unrepaired until pachytene and were expressed as gaps, fragments, and multiaxial configurations was reduced by pretreatment with the low dose of radiation.