Gene and teratogen induced defects of early central nervous system development.

The events involved in the histogenesis of the primitive nervous system involve precise control over cell shape changes, cellular migrations, cell-cell and cell-extracellular matrix interactions. The coordinated procession of these events results in the elevation of the neural folds, and their apposition and fusion in the dorsal midline, forming the primary neural tube. This is followed by a second series of cellular migrations and rearrangements (collectively called secondary neurulation) which result in lengthening of the caudal neural tube. After a brief consideration of the mechanisms involved in neurulation, the effects of gene or teratogen induced perturbations of these events are presented and reviewed. New data are presented on neurulation in the delayed Splotch mutant embryo and on the effects of altering mesenchymal or neuroepithelial basal lamina constituents on primary and secondary neurulation.