The cortex of Xenopus laevis embryos: regional differences in composition and biological activity.

The cortex of fertilized Xenopus laevis eggs undergoes regional changes in its composition and morphogenetic activity during the first three divisions. Gray crescent and animal pole cortex of stage 1 (1-cell) and stage 4 (8-cell) embryos each contain a characteristic array of proteins. Implantation of pieces of cortex into the blastocoel of midblastula embryos was used to assay their inductive capacity. The gray crescent cortex was shown to be the only region that had significant axis-inducing activity. This activity increased from stage 1 to stage 4.