How is it that endodermal cells of the vegetal hemisphere exhibit a blastocoel-directed migration, such that a tissue-level rotation is generated? The mechanisms of vegetal rotation are only starting to be elucidated. Wen and Winklbauer (2017) recently employed a live explant and embryo analysis of cell behaviors exhibited in the vegetal hemisphere during Xenopus gastrulation. They detailed a regionally diverse series of cell rearrangements and migratory velocities over the course of a cell’s rotating displacement across the vegetal hemisphere (Figure 1). Endodermal cells appear to use an amoeboid-like behavior of cell migration, during which a wide leading edge forms new junctions with adjacent cells while a narrowing and retracting trailing edge advances the cell forward. In the most vegetal regions, this migration resembles true ingression behaviors as a cell crawls from one cell to the next toward the blastocoel (see Figure 1B). Interestingly, as the cell nears the blastocoel floor, its velocity progressively increases until the cell undergoes a reorientation of its leading and trailing edges toward the dorsal and ventral sides of the explant tissue (creating the fountain-like behavior). Similarly, in the embryo, cells will also reorient toward both the ventral and dorsal sides. Although several factors, among them C-cadherin, fibronectin, and ephrin B1, have all been suggested as being necessary for these migratory events, more information is needed about the guidance and locomotor mechanisms before they are well understood.
Wen, J. W. and R. Winklbauer. 2017. Ingression-type cell migration drives vegetal endoderm internalisation in the Xenopus gastrula. Elife 6.
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