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YSL nuclei on dorsal side of a zebrafish gastrula, undergoing epiboly, convergence and extension. Converging YSL nuclei form an axial morphogenetic domain near the embryonic midline. Nuclei are vitally labeled with Sytox Green.
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Epiboly of YSL cytoplasm and epiboly of YSL nuclei can be experimentally decoupled. When the animal cap is mechanically removed, the EVL/YSL margin undergoes accelerated epiboly. In contrast, YSL nuclei undergo doming, but do not undergo epiboly.
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Ventral Side of Zebrafish Gastrula. YSL nuclei undergo epiboly, and undergo directed migration toward the dorsal side of the embryo, during gastrulation. The constricting circumblastoporal ring of YSL nuclei (a distinctive morphogenetic domain) involved is clearly seen near the vegetal pole of the yolk cell.
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Dorsal Side of Zebrafish Gastrula. YSL nuclei in marginal zone join different morphogenetic domains as epiboly proceeds. Convergence and extension of nuclei toward the dorsal midline.
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Doming of the yolk cell occurs autonomously, after removal of the blastoderm. YSL cytoplasm undergoes epiboly toward the vegetal pole.
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YSL nuclei and hypoblast cells follow similar trajectories. Several morphogenetic domains in the hypoblast are co-incident with similar morphogenetic domains in the YSL. (YSL nuclei labeled with Alexa 488-histone, deep cells labeled with Alexa 488)
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YSL nuclei undergo sustained convergence and extension movements toward the doral midline. Hypoblast deep cells undergo directed, but meandering, migrations in the same directions as YSL nuclei.
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