Neurulation: coming to closure.

Neurulation is a morphogenetic event par excellence. During this highly choreographed four-dimensional process, a flat sheet of ectoderm is transformed into an elongated tubular rudiment, the neural tube, which exhibits rostro-caudal and mediolateral regionalization. Many tissues interact during neurulation to induce and regionalize the neuroectoderm and to produce the morphogenetic forces that drive neurulation. Such forces are generated by fundamental cell behaviors such as changes in cell shape, position and number. In addition, morphoregulatory molecules expressed during neurulation underlie induction and patterning of the forming neuraxis. Despite recent advances in our understanding of neurulation, neural tube defects continue to be a major health care concern. Further research, utilizing a panoply of approaches, is necessary to resolve this issue. Thus, although we are beginning to come to closure in terms of understanding the cellular and molecular mechanisms responsible for normal neural tube formation, 'coming to closure' is exactly the problem that requires resolution to prevent these devastating birth defects.