notochord formation, oriented cell divisions at the level of the floorplate, view of the otic placode
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Movie#flrp. Zebrafish Embryo, from tailbud to 16-hour stage, stained with 100 micromolar Bodipy-Ceramide.
Bodipy-Ceramide permeates the enveloping layer epithelium of the embryo, accumulating in the interstitial spaces of the segmentation cavity.
The sequence begins at the level of the hypoblast. Chorda mesoderm cells intercalate in a mediolateral fasion. This cellular convergence causes the chorda mesoderm to extend in an axial direction. During cell intercalation, the notochord develops a transient bilateral symmetry.
As the sequence progresses, the notochord is depressed ventrally by mediolateral convergence of cells in the neural plate (this begins neural keel formation). The floorplate comes into view. Cells at the level of the floorplate along the embryonic midline begin to round up in preparation for mitosis. At one point at least four cells are undergoing synchronous division. The daughter cells of these divisions segregate to either side of the embryonic midline.
The embryo undergoes a torsional rotation. The rotation brings into view the edge of the neural keel at the level of the hindbrain. The ridges along the edge of the neural keel delineate neuromeres of the hindbrain.
The sequence ends with a view of the otic placode.
The time-lapse sequence compresses approximately 11 hours of development.