Effects of ionizing radiation on meiotic maturation of frog oocytes. II. In vitro studies.

In an attempt to examine genomic function of the oocyte nucleus during meiotic maturation, the effects of X-irradiation on the oocyte of the frog (Rana pipiens) were studied. When oocytes were irradiated with 6000-36000 R before initiation of maturation, the ovulated eggs frequently failed to be fertilized and the jelly surrounding the unfertilizable eggs was always damaged. However, the egg itself proved to retain the capability of cleaving when a nucleus was transplanted from a blastula. Also, X-irradiated eggs when invested with the jelly from unirradiated frogs recovered their capacity for fertilization. The eggs thus fertilized developed and exhibited abnormalities characteristic of X-irradiation such as arrest of gastrulation and neurulation as well as production of haploidy. Irradiation of oocytes after completion of maturation brought about developmental abnormalities more frequently than irradiation before initiation of maturation. The Hertwig effect was found only when oocytes were irradiated after completion of maturation. However, no qualitative differences were found in the developmental abnormalities produced by irradiation before maturation and those produced by irradiation after maturation.