Study of the gonocyte cell cycle in irradiated TP53 knockout mouse foetuses and newborns

PURPOSE: To investigate the role of p53 in gonocyte cell-cycle arrest in rodents with or without radiation exposure. MATERIALS AND METHODS: Pregnant p53 (+/-) mice, mated with p53 (-/-) males, were exposed to (137)Cs gamma-rays at day 18 postcoitum (p.c.) at doses ranging from 1.5 Gy to 3 Gy. The gonocyte cell cycle was studied in p53 (-/-) male foetuses and newborns after BrdU incorporation and DAPI staining, and compared with those of p53 wild-type animals. RESULTS: The proliferation of gonocytes in wild-type mice is normally arrested between day 16 p.c. and birth, a period when p53 is strongly expressed in gonocytes; p53 high expression is prolonged in all gonocytes after 3 Gy irradiation. In p53 (-/-) mice, this period of gonocyte cell-cycle arrest is not modified, compared with wild-type mice. It is also prolonged after a 3 Gy exposure. CONCLUSION: Two hypotheses are proposed. Either p53 is not involved in the control of gonocyte cell-cycle arrest in control and irradiated mice, or its role is redundant in this process.