Normal neurulation in amphibians.

How does cell behaviour accomplish neurulation in amphibian embryos? During neurulation, the neural plate (while preserving the same volume) doubles its length, triples its thickness, narrows 10-fold, greatly decreases its surface and rolls into a tube. Cells that compose the neural plate produce these changes in three ways. They change shape, change neighbours and attempt to crawl beneath the contiguous epidermis. Plate width, length and area are decreased and the plate thickens when apical surfaces of plate cells contract radially, but plate length increases and width is further decreased when cells reposition themselves and collect along plate boundaries. Contraction of the apical surfaces of plate cells also helps roll the plate into a tube. Poisson buckling resulting from elongation of plate borders may contribute bending forces that help tube formation. The main folding force in tube formation is a rolling moment toward the midline produced by neural plate cells attempting to crawl beneath the contiguous epidermis. Experiments, observations and computer simulations support these assertions, reveal the organization of cell behaviour and implicate contraction of actin filaments as the main source of the necessary forces.