Fig. 1. Four-dimensional confocal analysis of Xl-ß-catenin-GFP expression. (A-E) Frames from a time-lapse sequence following injection of Xl-wt-ß-catenin-GFP mRNA at the 1-cell stage. Times after the start of recording (hours:minutes) are shown in the bottom left corner of each panel and cell number is shown in the bottom right corner. GFP-tagged ß-catenin was initially localized in the nuclei, cytoplasm and junctional complexes of all blastomeres (A). GFP-tagged ß-catenin disappeared from the animal region of the embryo over a period of approximately two cell cycles (B-E). GFP-tagged ß-catenin eventually became restricted to a small territory of cells surrounding the vegetal pole (asterisk). (F-I) Frames from a time-lapse sequence following injection of Xl-pt-ß-catenin-GFP at the 1-cell stage. Mutation of residues phosphorylated by GSK3ß and a priming kinase at the N-terminus of ß-catenin blocked the disappearance of GFP-tagged protein from animal blastomeres. The vegetal pole is marked by an asterisk. (J) Co-injection of mRNAs encoding Xl-wt-ß-catenin-GFP and a kinase-dead, dominant negative form of GSK3ß (Xl-dnGSK3ß) at the 1-cell stage. Expression of dnGSK3ß stabilized GFP-tagged ß-catenin in animal blastomeres.