UV effect on germ cell determinant and a proposed scheme for germ cell formation process in embryos of Xenopus laevis.

Abstract

Ultraviolet light (UV) irradiation of vegetal hemispheres of many anuran eggs results in an elimination of primordial germ cells in the tadpoles. Quantitative studies were performed on this phenomenon. In this report, UV irradiation experiments were performed on the eggs just before the first cleavage division, and a dose-response curve was obtained at the stage. The results supported the probabilistic model for germ cell determination process, previously presented by the authors. Cell diameter analysis suggested that the germinal plasm-containing cells (i. e. presumptive primordial germ cells) divide at the same rate as ordinary endodermal cells during stage 10-33. This led to a calculation of the doubling time of presumptive primordial germ cells, odtaining its value as about 30 hrs at 20°C. Finally, a scheme for the proliferation kinetics of germ cells in Xenopus laevis embryos was presented. Several UV experiments on the vegetal hemisphere of anuran eggs have presented favorable evidence that histologically identifiable germinal plasm contains the UV-labile germ cell determinant. Their significance was also discussed.