Unimpaired fertilization with thymidine-3H-labelled spermatozoa in the mouse

Thymidine-3H-labelled spermatozoa were obtained in the sixth week after injection of males with a single or repeated doses of thymidine-3H, in amounts of 3.5 to 50 muCi per gramme body weight. Mouse ova were fertilized in vivo or in vitro by such labelled spermatozoa. It was found by means of autoradiography that heavily labelled spermatozoa compete successfully with non-labelled ones in performing fertilization. The distribution of relative levels of activity in fertilizing spermatozoa was similar to that in the population of inseminated spermatozoa. The early development of ova fertilized by generally labelled spermatozoa (followed up to the first cleavage) was not impaired. It is concluded that spermatozoa labelled with thymidine-3H in their DNA to a level sufficient for autoradiographic detection may be probably used in the studies of the cytology of fertilization without greater precautions regarding possible radiation-induced artefacts.