Convergence and extension movements during vertebrate gastrulation.

During vertebrate gastrulation, coordinated cell movements shape the basic body plan. Key components of gastrulation are convergence and extension (C&E) movements, which narrow and lengthen the embryonic tissues, respectively. The rates of C&E movements differ significantly according to the position and the stage of gastrulation. Here, we review the distinct cellular behaviors that define the spatial and temporal patterns of C&E movements, with the special emphasis on zebrafish. We also summarize the molecular regulation of these cellular behaviors and the interplay between different signaling pathways that drive C&E. Finally, to ensure efficient C&E movements, cells must achieve mediolaterally-elongated cell morphology and polarize motile protrusions. We discuss the recent discoveries on the molecular and cellular mechanisms by which the mediolateral cell polarity is established.