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

Abstract

ABSTRACT To investigate genomic activities in ovarian follicle cells and oocytes during meiotic maturation, ovarian pieces isolated from adult frogs (Rana pipiens) were irradiated with doses of X-ray ranging from 12000 to 96000 R and then treated with a pituitary extract and/or progesterone. When the ovarian tissue was treated with the pituitary extract alone or the pituitary extract plus a low dose of progesterone, irradiation with 12000 or 24000 R brought about an enhancement of ovulation, while irradiation with X-ray doses higher than 36000 R suppressed ovulation. On the contary, when the tissue was treated with high doses of progesterone, X-irradiation always suppressed ovulation. X-Irradiation at high dosages suppressed pituitary-induced maturation of oocytes with follicles, but not progesterone-induced maturation. When oocytes irradiated with 48000 R or less were transferred into unirradiated female frogs, they proved to be fertilizable, but those irradiated with 72000 R or more were un-fertilizable. Nuclear transplantation experiments revealed that X-irradiation did not deprive the oocytes of their capability to cleave, although it did retard the emergence of this capability in maturing oocytes. The embryos from oocytes irradiated with 48000 R or less developed into tadpoles, but no embryos developed beyond the gastrula stage if the oocytes were irradiated with 72000 R or more.