X-ray- and chemically induced germ-line mutation causing phenotypical anomalies in mice

Abstract

A large and significant increase of phenotypical anomalies was observed in the progeny of ICR parent mice treated before mating with X-rays, urethane, 7,12-dimethylbenz[ a]anthracene, ethylnitrosourea (ENU), and 4-nitroquinoline 1-oxide, but the increase was not significant with furylfuramide. Major types of induced anomalies were cleft palate, dwarf, open eyelid, tail anomalies, and exencephalus. Dwarf, open eyelid and tail anomalies were predominant types of viable anomalies and were inherited as if they were dominant mutations with varying expressivity or penetrance. Incidence of prenatal anomalies increased with treated doses of X-rays, urethane, or ENU for both spermatozoa and spermatogonia. Spermatogonia were less sensitive to X-rays and urethane than spermatozoa, while ENU induced a very high incidence of prenatal anomalies by the spermatogonial treatment. In contrast to the previous works with X-rays, there was a clear, almost linear increase of anomalies in the dose range from 0 to 216 rad after spermatogonial exposure. For treatment of oocytes, there was also a clear increase with doses of X-rays and urethane. Doubling doses of X-rays for prenatal anomalies were 12 rad for spermatozoa, 27 rad for spermatogonia, and 19 rad for mature oocytes. These values are similar to those for ordinary mouse mutations. However, the mean rate of prenatal anomalies per rad (1.2 × 10 −4, 6.6 × 10 −5 and 9.1 × 10 −5 for spermatozoa, spermatogonia and mature oocytes, respectively) and that for 1 μg/g of ENU (3.4 × 10 −4 for spermatogonia) were 4–40 times higher than that of ordinary mutation in mice, because overall phenotypical abnormalities were scored in this study. Information obtained from the work on phenotypical anomalies is valuable to assess gentic risk of radiation and chemicals, because a majority of human genetic diseases show this kind of irregular and uncertain inheritance and most of the induced anomalies are similar to those found in humans.