Convergence and extension in vertebrate gastrulae: cell movements according to or in search of identity?

During vertebrate gastrulation, convergence and extension cell movements both narrow and lengthen the forming embryonic axis. Concurrently, positional information established principally by the ventral-to-dorsal gradient of bone morphogenetic protein activity specifies cell fates within the gastrula. New data, primarily from zebrafish, have identified domains of distinct convergence and extension movements, and have established a role for the noncanonical Wnt signaling pathway in promoting the mediolateral cell polarization that underlies this morphogenetic process. Other observations suggest the intriguing possibility that positional information regulates convergence and extension movements in parallel with cell-fate specification.