We investigated the induction of morphological transformation in Syrian/golden hamster embryo cells irradiated with X-rays. While the frequency of morphological transformation increased steeply at lower dosey (0-2 Gy), its increment became smaller with doses above 2 Gy. Compared with morphological transformation, the expression of mutation required an expression time more than 5 days and the induction curves for both phenotypes were different.
A large fraction of morphologically transformed colonies (about 80%) could be cloned with the use of feeder layer cells. Only the progeny of these clones expressed malignant phenotypes, such as an anchorage-independence and tumorigenicity under the skin of nude mice.
These results suggested that different mechanisms might be responsible for the induction of morphological transformation and mutation and that morphologically transformed cells suspected to have the predisposition to malignant transformation.