Lineage tracing in a Xenopus laevis embryo.
Lineage tracing of three dorsal blastomeres of 32-cell Xenopus laevis embryos injected with Molecular Probes fluorescent dextran conjugates. The tier 1 dorsal (A1) blastomere was injected with lysine-fixable 10,000 MW fluorescein dextran (Cat. No. D1820), the tier 2 dorsal (B1) blastomere with lysine-fixable 10,000 MW Texas Red dextran (Cat. No. D1863), and the tier 3 dorsal (C3) blastomere with lysine-fixable 10,000 MW Cascade Blue dextran (Cat. No. D1976). Embryos were fixed in formaldehyde, embedded and sectioned. The image on the left shows a 13 µm–thick section of a stage 6 (32-cell) embryo fixed right after injection; this section exhibits significant autofluorescence due to the presence of residual yolk. The image on the right is a stage 10 (early gastrula) embryo. Triple-exposure photographs of the sectioned embryos were taken on a Zeiss Axiophot with a 10× objective. Images contributed by Marie Vodicka, University of California, Berkeley.