PERSISTENCE DURING G(1) OF GAMMA RAY-INDUCED OR MITOMYCIN C-INDUCED LESIONS ELICITING SCE IN MURINE SALIVARY-GLAND CELLS IN-VIVO

The efficiency of mitomycin C or gamma rays to induce SCE in early or late G(1) was determined in synchronized murine salivary gland cells in vivo, as a measure of the capacity of this tissue to repair the lesions involved in SCE formation before S. The SCE frequencies induced by MMC in the first division (before BrdU incorporation) were significantly lower in the early G(1) compared to the late G(1) indicating some repair of SCE-inducing lesions. In the second division (after BrdU incorporation), there was no difference between SCE induced in early and late G(1), indicating that MMC-induced lesions in such conditions are very persistent and not repairable during G(1). The radio induced SCE frequency at early G(1) was significantly lower than that observed in late G(1), in cells irradiated after BrdU incorporation, suggesting that half of gamma ray-induced DNA lesions that elicit SCEs were repaired.