Protein synthesis and messenger RNA levels along the animal–vegetal axis during early Xenopus development

The patterns of proteins synthesized in animal and vegetal regions of Xenopus oocytes, eggs and embryos were examined by 2D gel electrophoresis. In oocytes and eggs, the only proteins synthesized asymmetrically along the animal-vegetal axis were a small number of proteins synthesized predominantly in the vegetal hemisphere. At the cleavage stage there were a total of four proteins synthesized unevenly in animal and vegetal regions: three synthesized predominantly in the vegetal hemisphere and one synthesized predominantly in the animal hemisphere. By the gastrula stage, when maternal messages have largely been replaced by embryonic transcripts, the number of differences in proteins synthesized in the animal-derived ectoderm and mesoderm, and the vegetal-derived endoderm started to increase rapidly with time of development with many more animal-characteristic proteins than vegetal-characteristic proteins appearing. Comparison of protein synthesis patterns with those obtained when extracted RNA was translated in vitro and run on 2D gels, showed that the asymmetry in protein synthesis along the animal-vegetal axis in the oocyte and early embryo reflected directly the distribution of their mRNAs along the axis. There was no evidence for localized ‘masked’ abundant messages along the animal-vegetal axis of oocytes and cleavage embryos.