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Figure 2. Spatial and temporal distribution of β-catenin (catenin beta 1) during early development of the Xenopus embryo. Embryos were bisected along the dorso-ventral axis after immunolabeling so that each half contained dorsal and ventral blastomeres. Each half was imaged from the bisected surface in the confocal microscope. Embryos are oriented with dorsal on the right, ventral on the left, animal hemisphere at the top, and vegetal hemisphere at the bottom, in A–F. Immunocytochemistry reveals an increase in cytoplasmic β-catenin (orange) on the dorsal side of the embryo from the two-cell (A), to four-cell (B), to eight-cell (C) stages. At the 16-cell stage, intense β-catenin is observed in the cytoplasm (D, arrow denotes nucleus) as well as in the nucleus (G, arrow) of the dorsal vegetal blastomeres. At the 32-cell stage, β-catenin is enriched in the cytoplasm (E, arrows denote nuclei) and nuclei (I, arrow) of all dorsal blastomeres, while ventral blastomeres have lower cytoplasmic staining (E) but neglible nuclear staining (H, arrow). Overall, 93% of the embryos analyzed (n = 120) from the 2–32-cell stages displayed this dorsal enrichment of β-catenin. At the blastula stage, β-catenin is detected in the cytoplasm of both dorsal and ventral cells (F), as well as in ventral (J) and dorsal (L) nuclei, though the dorsal signal was stronger in both cellular compartments. Primarily the outer layers of blastomeres demonstrate intense cytoplasmic β-catenin staining, even when blastula were bisected before immunolabeling to assure access of the antibodies to the inner blastomeres. Specific β-catenin staining is detectable in these inner vegetal blastomeres (K) when fluorescence sensitivity is increased to the point where the dorsal signal becomes saturated. |
