Dorsal, ventral, animal and vegetal half-embryos of Xenopus laevis were isolated at the 8-cell stage, and their synthesis of protein examined during 12 h of culture. The kinetics of the uptake and incorporation of [³⁵S]-methionine did not differ greatly among the four kinds of half-embryos. Two-dimensional gel electrophoreses showed that there were no detectable differences in the pattern of protein synthesis for the four types of half-embryos, at least during the first 6 h of culture which covered the period from the cleavage to late blastula stage. The patterns, however, changed greatly, espe-cially between those of the animal and vegetal half-embryos, during the latter 6 h of culture which covered the period from the early gastrula to early neurula stage.
These results are evidence that equal qualitative and quantitative maternal mRNA-dependent protein synthesis takes place in the four types of embryonic regions, including the vegetal half-embryos, although later in the post-blastular stages, syntheses of region-specific proteins start that are dependent on new genome expression.