EFFECTS OF GAMMA-IRRADIATION ON THE YIELD OF MID-VENTRAL WHITE SPOTS IN MICE IN DIFFERENT GENETIC BACKGROUNDS AND AT DIFFERENT TIMES DURING DEVELOPMENT

Pregnant females C57BL/10JHir-p/p mice crossed with C57BL/10JHir males were whole-body irradiated with a single acute dose of Co-60-gamma-rays to investigate the effect of gamma-radiation on embryonic melanoblasts. The effect was studied by scoring changes in the cutaneous coats of F-1 offspring 25 days after birth. White spots were found in mid-ventrum of the animals. Melanoblasts and melanocytes were not observed in the spotted skin. The frequency of the spots increased in a dose-dependent manner. White spots were found in mid-ventrum of (C57BL/6J female X C3H/HeJmsHir male) F-1 exposed to gamma-rays. However, the frequency of the spots in (C57BL/6J female X C3H/HeJmsHir male) F-1 were extremely lower than that in (C57BL/10JHir-p/p female X C57BL/10JHirs)male) F-1, suggesting the possibility that the frequency of mid-ventral white spots are genetically controlled. Moreover, the highest frequency was found in (C57BL/10JHir-p/p female X C57BL/10JHir male F-1 irradiated at 8.5 days of gestation. This stage corresponds to the stage of initiation of neural-crest cell migration. These results indicate that gamma-radiation affects the differentiation of melanocytes in the skin both with genetical control and with greater effects seen at the stage of initiation of neural-crest cell migration.