Cytochemical analysis of neural dysraphism in the vl mutant mouse.

Closure of the posterior neuropore was analyzed by means of ultrastructural cytochemistry in ten-day dysraphic mouse embryos homozygous for the mutant gene vl, and comparisons were made with normal embryos in terms of convergence, apposition and fusion of the apices of the neural folds. In abnormal embryos, regional differences in the distribution of the surface coat were comparable to those in normal embryos. However, there was an abnormally acute medial bending of the neural folds, as well as a delay in closure of the posterior neuropore. In closed areas of the abnormal embryos the dorsum also showed an erratic knot of disorganized cells. Thus, the pathogenetic mechanism in this mutant appears to involve not only a failure in apposition in open areas, as well as an inappropriate association of cells in areas which do fuse, but possibly also a failure of proper alignment of neural fold apices prior to apposition and fusion.