Identification of plakoglobin in oocytes and early embryos of Xenopus laevis: maternal expression of a gene encoding a junctional plaque protein

We have isolated a cDNA encoding the junctional plaque protein plakoglobin of Xenopus laevis and determined its amino acid sequence. Comparisons with sequences of related proteins of the same and other species revealed that in Xenopus plakoglobin and beta-catenin are two different proteins, encoded by separate genes, that both genes are expressed in embryogenesis, and that the amphibian plakoglobin is more closely related to the human plakoglobin than to beta-catenin of the same species. Using this cDNA as a probe, we also show that plakoglobin mRNA is produced and stored in Xenopus oocytes and eggs. We discuss the possibility that the maternal pool of this junctional protein contributes to the junctional structures connecting the oocyte with the follicle epithelium and to the rapid formation of desmosomes and other plaque-bearing junctions in pregastrulation embryogenesis.     

Production of transforming growth factor (TGF) β by fetal lung cells

Summary— TGF β is supposed to play an important role in the process of epithelial maturation in the developing fetal lung. Using an immunofluorescence approach, we showed that fetal rat lung fibroblasts elaborate the three TGF β isoforms known in mammals (TGF β1, β2 and β3) whereas epithelial cells appear to synthesize only TGF β1 and β3. Isolated fibroblasts secrete the three isoforms. Biological assay of TGF β activity in fibroblast-conditioned media did not reveal significant changes according to the stage when fibroblasts were isolated.