Cell surface proteins of wholeXenopus embryos identified by radioiodination

We have examined the proteins ofXenopus whole oocytes and embryos that are accessible to surface iodination. These cell surface proteins appear to undergo stagespecific modulation during development. The most pronounced changes were observed between oocytes and the 32-cell stage when the number of labelled proteins doubled, and between early and late gastrula when the complexity declined by two thirds. The simplification of the pattern during gastrulation may reflect changes in cell position as endodermal cells move inside leaving ectodermal cells at the external surface. The lectin binding patterns for NP-40 solubilized proteins extracted from oocytes and embryos also changed in a stage-dependent manner. Con A and WGA recognized a complex pattern of glycoproteins containing glucose and mannose residues. In contrast, SAB and RCA binding to galactose residues recognized far fewer glycoproteins. Many of the observed changes occurred during cleavage stages before embryonic gene transcription is initiated and may be due to post-translational modifications.