Cell specificity of nuclear protein antigens in the development of Xenopus species

Protein antigens accumulated in the oocyte nucleus of Xenopus spp. are found later in all nuclei of the embryo. During and after organogenesis, the fate of different nuclear antigens diverges: Some are permanently expressed in all nuclei, some are no longer detectable in any nuclei, and some show a high degree of specificity relative to cell type. Of the class of antigens permanently expressed in all cells, a nucleolar antigen has been studied that is relatively enriched in the gonia of both sexes. A possible correlations of its occurrence with ribosomal DNA amplification and transcription is examined. The cell-specific expression of 4 antigens has been analyzed in detail, using indirect immunofluorescent staining methods as well as conventional histology. The tissue-specificity of 2 of these antigens does not change during metamorphosis, whereas the pattern of others is dynamic until after metamorphosis. We conclude that the observed tissue-specificity does not correlate with descendence from one of the 3 primary germ layers: Some antigens appear to accumulate in the nucleus when a cell takes up its specific function.