Dynamics of Cellular and Syncytial Endoderm. An ectopic embryonic axis was induced by injecting a marginal blastomere of a 32-cell stage embryo with TARAM-A (Tar*, a receptor for Nodal-like ligands) RNA and GFP-RNA (tracer) (Peyrieras et al., 1998). Yolk syncytial layer (YSL) nuclei (yellow) were labeled by injecting the YSL with Sytox Green. Tailbud stage: GFP-labeled endodermal cells are distributed as over the YSL surface. As the posterior YSL contracts to form the yolk extension, endodermal cells on the YSL surface move coherently with underlying YSL nuclei toward the contraction center. Images made available through Mark Cooper and Zebrafish - The Living Laboratory.