Invagination and Evagination: The Making and Shaping of Folds and Tubes - Mechanisms of Morphogenesis - page 211

FIGURE 18.9 Neural tube formation in a generalized vertebrate. A flat epithelium folds to create a trough, the
lips of which then fuse to form a tube. In chicks, mice and salamanders the epithelium is a monolayer as depicted
here but in some species, such as the frog Xenopus laevis, it has more layers.
plate, curvature is convex (from the point of view of the outside of the embryo) while at the
middle of the plate it is concave ( Figure 18.10 ). A key feature of the hinge points is that cells
within them acquire a distinct wedge shape, constriction being apical in the case of the
median hinge point but basal in the case of the dorsolateral hinge points.
Cells in the region of the presumptive concave hinge points, orange in Figure 18.10 ,
express Shroom, just before and during neural tube folding, and their means of folding is
assumed to be similar or identical to that depicted in Figure 18.4 . 24,25 Neural folding fails
in Xenopus tropicalis embryos that express a dominant-negative version of Shroom, or in
embryos treated with morpholino antisense oligonucleotides that target the endogenous
Shroom message. 24 Actin filaments are required for neural tube formation in a variety of
species including amphibians, chicks and rats, and inhibition of actin filament formation
using cytochalasins prevents neural tube formation. 26,27 Careful studies of the events