An autoradiographic study of tritiated uridine incorporation into the larval ovary of Xenopus laevis.

Abstract

The in vitro incorporation of 3H-5-uridine into the germinal and somatic cells of the larval ovary of Xenopus laevis has been studied using both light and electron microscope autoradiography. Incubation for only one hour in the presence of precursor revealed that the follicle cells are highly active in rRNA synthesis, whereas substantial oogonial nucleolar labeling was not detected for several hours. Semi-quantitative analysis of high-resolution autoradiograms indicated that the density of silver grains associated with "nuage" in oogonia was almost 4-fold greater than the surrounding cytoplasm. This strongly suggests that a significant amount of RNA is associated with "nuage" at this stage of Xenopus oogenesis, in addition to its well documented protein composition. "Pulse-chase" experiments further suggest that the nuage-associated RNA is stable for at least 24 hours. These results are discussed (within the limitations imposed by the methodology) both in relation to other studies on the composition of nuage in a wide variety of germinal cell types and in the light of growing speculation that nuage and germinal granules are synonymous.