An Analysis of Hereditary Increase in Frequency of Cell Mortality Induced by External Factors (Experiments on Nuclear Transplantation in Amoebae)

Abstract

By using nuclear transplantations in Amoeba proteus a study was made of a peculiar heritable effect, a stable increase in the frequency of cell mortality induced by comparatively low doses of x-ray radiation (5 kr) or slight heating (29 °C during 6 to 7 h). This effect differs qualitatively from the known radiation effects (reproductive death, lethal sectoring) by its being non-specific for radiation. In addition, the effect is saltatory appearing in 100% of the treated cells and the extent of its expression is not dependent on the dose of an inducing factor (at supra-threshold doses) and the period of time after treatment. It was found that (1) the hereditary changes in amoebae, unlike those resulting in reproductive death, are transmitted during intercellular transplantations both by the nucleus and cytoplasm of an altered cell; (2) Transfer of the character under test is accomplished by means of a certain factor capable of shuttling between the nucleus and cytoplasm, (3) The effect is not necessarily a consequence of primary injury of nuclear structures and it may be induced by treatment of the cytoplasm, of an enucleated cell renucleated then by the nucleus of a normal amoeba. In this respect, the effect under test differs also from the known types of hereditary post-radiation lethal effects which are commonly suggested to involve primary injury of the nucleus. Possible mechanisms of genetic control over the character tested are discussed.