Mechanisms of elongation in embryogenesis.

Here, I discuss selected examples of elongation in embryogenesis to identify common and unique mechanisms, useful questions for further work, and new systems that offer opportunities for answering these questions. Fiber-wound, hydraulic mechanisms of elongation highlight the importance of biomechanical linkages of otherwise unrelated cellular behaviors during elongation. Little-studied examples of elongation by cell intercalation offer opportunities to study new aspects of this mode of elongation. Elongation by oriented cell division highlights the problem of mitotic spindle orientation and the maintenance of cell-packing patterns in anisotropic force environments. The balance of internal cell-adhesion and external traction forces emerges as a key issue in the formation of elongate structures from compact ones by directed migration.