Differential Sensitivity of Preimplantation Mouse Embryos to UV Irradiation in Vitro and Evidence for Postreplication Repair

Abstract

The sensitivity of various stages of preimplantation mouse embryos to UV irradiation in vitro was determined by 2 criteria of development during in vitro culture after UV irradiation: development throughout the following 24 h and the ability to form a blastocyst. The UV sensitivity was the highest in 1-cell embryos and it decreased with development towards the morula stage as indicated by the ED50 values of the rate of blastulation following UV irradiation: 2-cell embryos 90 erg/mm2, 4- and 8-cell embryos 100 erg/mm2 and morulae 140 erg/mm2. After UV irradiation the in vitro development of the embryos was further impaired by the presence of caffeine in the culture medium at concentration levels which did not interfere with the development of nonirradiated embryos. In 2-cell embryos caffeine treatment was only effective during the first 24 h after irradiation. Early mammalian embryos were able to repair UV-induced DNA lesions by the postreplication repair mechanism.