Convergent expansion is a cell rearrangement in a multicellular organism in which the cells rearrange themselves in such a way that the cell layer both narrows and elongates. This is achieved by a reorganization of the cytoskeleton, whereby arrangements of microfilaments contract the apical end of each cell so that the cells become wedge-shaped and can then push (converge) into each other. When many cells converge in this way, it can cause a considerable increase in the size of a tissue layer.
This process is probably triggered and controlled by the extracellular matrix, a network of secreted glycoproteins that plays an important role in the morphogenetic migration of cells.
Convergent extension is relevant in the early stages of embryonic development; it occurs, for example, in the invagination of the gastrula and in the extension of the primordial intestine (archenteron).
Neil A. Campbell, Jane B. Reece, Jürgen Markl (eds.): Biology. 6. updated edition, Pearson, 2006, ISBN 978-3-8273-7180-5, p. 1212.