Epithelial architecture

How does epithelial shape arise?

Epithelial tissues are the most abundant tissue type in the animal body. They form structural and protective barriers between body compartments in animals. Epithelia are composed of mostly identical cells that share an apical-basal polarity and are mechanically linked via lateral cell–cell junctions to form confluent sheets. Some cells in culture can form epithelial layers that are similar to those found in bodies. To investigate how single cells in culture assemble into cultured epithelial sheets we plated individual cells and watched how they assemble, and performed a quantitative analysis of the shapes that they make.

The problem we encountered

Epithelial tissues are commonly considered to be ‘pseudo-two-dimensional,’ meaning that architecture is primarily considered with respect to the tissue plane/surface. We found that this perspective is not always predictive of architecture with respect to tissue depth (see Figure, right). We also found that cultured epithelial architecture can vary drastically between experiments, and this can be the case even across a single 1 x 1 mm culture well (Dawney & Cammarota, MBoC 2023).

Confocal light microscopy image showing a Madin-Darby canine kidney (MDCK) cell monolayer cultured on a collagen-coated glass well. DNA (nuclei) is shown in cyan, F-Actin in shown in magenta.

This image shows 2 regions of tissue that exhibit different architectures with respect to their apical-basal axis (top images), despite looking morphologically similar in the plane of the tissue (bottom images).

A tool for the unbiased, automated analysis of epithelial architecture

Because we are interested in the mechanical and biological parameters that contribute to epithelial layer architecture we decided that we needed to develop a tool to quantify architecture development over time. Our goal was to accurately and quantitatively assess the effect of genetic and mechanical perturbations on epithelial shape. Due to the variability in the shape of layers and the complexity of attempting to perform 3D analysis manually, it was important to us to develop an unbiased and automated tool which required as little user input as possible.

We developed a python-based tool for the unbiased analysis of layer architecture (Automated Layer Analysis or ALAn). A detailed protocol for the use of this tool can be found here. As a consequence of developing ALAn, we identified a developmental series of layer architectures that progress through the process of 'epithelialization', whereby individual cells form a tissue layer (Dawney & Cammarota et al., 2023 MBoC, Cammarota et al., 2023 bioRxiv). Our quantifications of cell height, cell density, and circularity show distinct morphological regimes for each architecture.