Data from: Cilia-driven epithelial folding and unfolding in an early-diverging animal

Multicellular organisms utilize epithelial folding to achieve remarkable
three-dimensional forms. During embryonic development, stereotypical
epithelial folds emerge from underlying active cellular and molecular
processes including cell shape change and differential cell growth.
However, the origin of epithelial folding in early animals and how folding
may be harnessed in synthetic systems remain open questions. Here we
discover a novel modality of behavior-induced epithelial folding and
unfolding arising from cilia-substrate adhesion and ciliary walking in the
basal animal Trichoplax adhaerens (phylum Placozoa). We show that T.
adhaerens is capable of exhibiting dynamic non-stereotyped folding states,
providing a novel 3D perspective to an organism previously only
characterized in its 2D state. We correlate these folding states to local
substrate geometry, revealing that the animal conforms to available
substrate surface area, promoting the maintenance of a folded state. Using
4D fluorescence light sheet microscopy, we characterize fold geometry,
curvature evolution during unfolding, and the non-stereotypy of unfolding
behavior. Through repeated unfolding trials, we reveal the robustness and
timescales associated with unfolding behavior and employ scaling analysis
and toy model simulations to establish how collective ciliary activity can
robustly drive unfolding. In this way, despite lacking any
folding-unfolding "pathway," transitions between folding and
unfolding states emerge as a function of the animal’s environment and
motility. Our work reveals a remarkable behavior exhibited by a brainless,
nerveless animal, and demonstrates the capacity for 3D-2D transitions in
folding epithelial sheets using ciliary activity.