65 cisional lesions that slice the exposed amnioserosa from canthus to canthus, and then
measuring the consequential gaping of the leading-edge epithelium. This epithelium twangs
back at a rate about 80 times the rate of its previous forward motion, until it reaches a new
equilibrium where the applied tissue forces are again in balance. The quantitative data
gathered from these “mechanical-jump experiments” revealed that the amnioserosa and the
force-generating mechanisms in the adjacent epithelium make comparable contributions to …

Can this kind of mathematical modeling be done for other morphogenetic events, and will it
be as revealing? Dorsal closure is the morphogenetic episode about which we have the
most genetic clues, partly because it takes place late, after the maternal pools of mRNA and
protein are diminished. Also, because it occurs superficially (unlike the epithelial
invagination events of fly gastrulation) and essentially in one plane, it is particularly
amenable to imaging and to experimental manipulations such as laser ablation. But, with …