X-ray Inactivation of Nuclei as a Method for Studying their Function in the Early Development of Fishes

Abstract

ABSTRACT The effect of high radiation doses (20-60 kr.) on different stages of the early development of the loach (Misgurnus fossilis L.) was studied. Analysis of dose dependence shows that a radio-sensitive component (presumed to be the nuclei) is affected maximally by such doses, whereas a radio-resistant component (presumed to be the cytoplasm) is not affected significantly. The use of such radiation doses is, therefore, a means of investigating the role of nuclei in development. Irradiation with these doses at any time from fertilization to early blastula leads to the arrest of development at one stage—the late blastula—and to death some hours later. Irradiation at any time during the period from late blastula to mid-gastrula similarly leads to arrest of development at one stage—the end of gastrulation. Irradiation during the period from early to late blastula results in the arrest of development at different stages of gastrulation depending on the moment of irradiation. Irradiation after the mid-gastrula results in the arrest of development at different stages of organogenesis, depending also on the moment of irradiation. The results cannot be explained by changes of nuclear sensitivity, nor by non-specific critical periods in development. They can be explained by changes in the role of nuclei in development, by periods of specific dependence on the function of nuclei. The independence of the stage of developmental arrest on the stage of irradiation, when irradiating from fertilization up to early blastula and from late blastula up to mid-gastrula, shows the relative inactivity of nuclei during these periods of normal development. The strong dependence of the stage of development reached at arrest on the stage of irradiation, when irradiating the early to late blastula and after the mid-gastrula stages, demonstrates the activity of nuclei in development during these periods. The conclusion may be drawn that in the early development of the loach the nuclei function periodically, each period of activity ensuring a subsequent episode of development. Nuclear activity during ovogenesis ensures the development of the egg up to the stage of the late blastula; nuclear activity during the early and mid-blastula stages ensures gastrulation. Development of axial organs and further organogenesis is ensured by nuclear function beginning from the mid-gastrula stage.