New geometric shape discovered from the way cells pack together

Epithelial cells are the foundation of tissues which band into three-dimensional shapes during embryonic development, ultimately giving rise to organs such as the outer layer of skin. It has been previously assumed that epithelial cells form into column-like or bottle-like shapes as they pack tightly together to accommodate the transformation of the embryo.

But now, an international research team led by Lehigh University has found that epithelial cells take on a specific geometric shape during tissue bending that was previously unknown. The shape is very efficient, enabling the cells to maximize packing stability while minimizing energy use.

“We have unlocked nature’s solution to achieving efficient epithelial bending,” said study lead author Javier Buceta.

The research team first made the discovery while modeling with a tool known as Voronoi diagramming, which is used in a number of fields to understand geometrical organization.

“During the modeling process, the results we saw were weird,” said Buceta. “Our model predicted that as the curvature of the tissue increases, columns and bottle-shapes were not the only shapes that cells may developed. To our surprise the additional shape didn’t even have a name in math! One does not normally have the opportunity to name a new shape.”

To confirm this finding, the team analyzed the three-dimensional packing of various tissues found in animals. The data showed that epithelial cells did, in fact, form three-dimensional shapes similar to the ones predicted by the computational model.

The results of this research could help experts understand the three-dimensional organization of epithelial organs and may ultimately lead to advancements in tissue engineering.

“In addition to this fundamental aspect of morphogenesis, the ability to engineer tissues and organs in the future critically relies on the ability to understand, and then control, the 3D organization of cells,” wrote the study authors.

“For example, if you are looking to grow artificial organs, this discovery could help you build a scaffold to encourage this kind of cell packing, accurately mimicking nature’s way to efficiently develop tissues,” said Buceta.

The new geometric shape identified in the study has been named “scutoid” because it resembles the posterior part of an insect thorax or midsection known as a scutellum.

The research is published in the journal Nature Communications.

a) Scheme representing planar columnar/cubic monolayer epithelia. Cells are simplified as prisms. b) Scheme illustrating a fold in a columnar/cubic monolayer epithelium. Cells adopt the called “bottle 23 shape” that would be simplified as frusta. c) Mathematical model for an epithelial tube. d) Modelling clay figures illustrating two scutoids participating in a transition and two schemes for scutoids solids. Scutoids are characterized by having at least a vertex in a different plane to the two bases and present curved surfaces. e) A dorsal view of a Protaetia speciose beetle of the Cetoniidae family. The white lines highlight the resemblance of its scutum, scutellum and wings with the shape of the scutoids. Illustration from Dr. Nicolas Gompel, with permission. f) Three-dimensional reconstruction of the cells forming a tube. The four-cell motif (green, yellow, blue and red cells) shows an apico-basal cell intercalation. g) Detail of the apico-basal transition, showing how the blue and yellow cells contact in the apical part, but not in the basal part. The figure also shows that scutoids present concave surfaces.

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By Chrissy Sexton, Earth.com Staff Writer

Image Credit: Luis M. Escudero (Seville University, Spain), Javier Buceta (Lehigh University, USA), Pedro Gomez-Galvez, Pablo Vicente-Munuera and scientists from Andalucian Center of Developmental Biology, and the Severo Ocha Center of Molecular Biology, among others.