Remote Control of Apical Epithelial Sheet Contraction by Laser Ablation or Nano-Perfusion: Acute Stimulus Triggers Rapid Remodeling of F-Actin Network in Apical Cortex

Apical contraction is the major tissue movement during remodeling of epithelial sheets in development. During apical contraction, groups of cells narrow their apices to form bottle-shaped structures, driving events such as sea-urchin gastrulation [1], Drosophila ventral-furrow formation, vertebrate neurulation and wound healing [2]. Tissue-folding events such as invagination, ingression and involution involve this tissue movement in which cells actively build “rifts” and “tubes”. Epithelial cells integrate genetic information, mechanical signals, and biochemical gradients to build these structures, but how they do so is unknown [3]. Theoretical models [4] provide some mechanical explanation for these events. Here we experimentally induce apical contractions controllably for the first time in amphibian embryos. Two independent methods, namely, laser ablation of cell membranes and nano-perfusion with cell lysate induce cell contraction in tissue isolates and in whole embryos. We demonstrate a biochemical pathway that stimulates rapid actin-reorganization/ polymerization accompanied by increases in α-actinin. The F-actin remodeling correlates with increased levels of Ca⁺⁺. Cell contraction begins within few seconds of laser ablation or nano-perfusion, peaks within a minute and is followed by a similar relaxation. Acute control of epithelial mechanics will allow us to better understand how molecular genetic processes drive shape change in tissues and will help future bioengineers build complex 3D epithelial organs.