342 — Scutoids are a geometrical solution to three-dimensional packing of epithelia

Conventional models of simple columnar epithelial growth represent the cells as polygonal prisms — like an ice-cube tray (I’ll come back to that in a second). That is, the top surface is the same polygon as the bottom surface, and it’s all the same shape all the way through.

But much of this information is the result of work that looked only at the apical and basal surfaces. To be clear, I don’t imagine many biologists actually believe that a prism is a realistic shape for epithelial cells. It’s just a useful model. But the thing about models is that they’re all wrong. These researchers looked at the ratio of surface area of basal and apical surfaces of the cells and asked if it is feasible for the curvature required of cells along a columnar epithelial surface to be explained by cells of a prismic or frustrum-like geometry.

The geometry simulation evidence suggests that another shape — unnamed thus far — is the most likely candidate for the highest level of contact between an epithelial cell and its neighbors. Unlike a regular hexagon, the new geometrical solid, dubbed a “scutoid,” allows a cell to contact different sets of neighbors on its apical and basal surfaces. When compared to biological observations, this shape appears to closely replicate the behavior of epithelial cells along complex curves, which has serious implications for what we can now learn or simulate about developmental biology.