The cover image from our recent study in the March 3 issue of Biophysical Journal captures a glimpse into the nanoscale world of cell-cell adhesion. Using DNA/peptide-PAINT super-resolution microscopy, we visualized E-cadherin (magenta) and F-actin (cyan) at adherens junctions in the Drosophila embryonic epidermis. This high-resolution view allows us to resolve the two sides of the cell-cell interface, revealing new insights into how cells organize and communicate during development.

The image was created by using DNA/peptide-PAINT, a single-molecule localization microscopy technique. GFP was knocked into the endogenous shotgun locus, resulting in E-cadherin expressed at native levels with a C-terminal GFP tag. E-cadherin–GFP was labeled by using a GFP-specific nanobody conjugated to a single-stranded DNA docking strand, which transiently bound fluorophore-labeled complementary imager strands via DNA hybridization, producing stochastic blinking events for super-resolution imaging. F-actin was visualized by using a fluorophore-labeled Lifeact peptide, which similarly generated blinking fluorescence signals simultaneously. A spinning disc microscope enabled optical sectioning several micrometers deep into the tissue, and salvaged fluorescence microscopy allowed simultaneous imaging of both proteins in the same detection channel, eliminating the need for post-processing alignment. The result is a detailed map of E-cadherin and F-actin organization at the nanoscale.

This cover image reflects our scientific research by highlighting the complex, and somewhat unexpected, architecture of adherens junctions. First, although these junctions are often viewed as continuous belts of adhesion, our super-resolution view reveals a more nuanced reality. E-cadherin forms distinct clusters on opposite sides of the junction (paired) and isolated clusters (unpaired). This suggests that not all E-cadherin molecules engage in trans-homodimeric interactions. Secondly, the image captures the relationship of these clusters to the cortical F-actin, providing a visual foundation for our quantitative analysis of how these two components interact. F-actin cortices on neighboring cells show strong spatial correlation, even in the absence of E-cadherin. This indicates that F-actin organization is not solely dictated by E-cadherin, opening new avenues for understanding mechanical coordination between cells.

These observations were made possible by analyzing the image by using advanced statistical tools, including entropy analysis, cross-correlation functions, and patch comparison methods. The image thus serves as a visual cornerstone for our broader investigation into the molecular architecture of adherens junctions.

Our findings have implications beyond developmental biology. E-cadherin dysfunction is linked to tumor metastasis. Basic research on understanding its nanoscale dynamics could translate into therapies targeting cancer cell invasion down the line. Moreover, insights into how cells form and maintain junctions could improve strategies for engineering functional tissues in the lab. Nonetheless, we see the most direct implications in the field of mechanobiology. The interplay between E-cadherin and F-actin is critical for tissue mechanics. Our work provides a framework for studying how mechanical forces influence cell behavior in health and disease.

Although our research focuses on Drosophila embryos, the principles governing cell adhesion and tissue organization are universal. E-cadherin is a central and evolutionarily conserved component of epithelial cell adhesion, forming the core of cadherin–catenin complexes that link cell–cell junctions to the contractile actomyosin cytoskeleton. Through these connections, E-cadherin influences the mechanics of cell–cell interactions and coordinates homeostatic responses to mechanical changes. By uncovering the nanoscale rules that govern these molecular architectures, our work advances a deeper understanding of how complex tissues are built and maintained. This knowledge provides a foundation for addressing disease mechanisms and informing regenerative medicine. Our cover image is therefore more than a snapshot; it is a window into the intricate organization of molecules that shape multicellular life on a fundamental level. You can find more information about our research at the following sites: Göttingen CIDBN, https://uni-goettingen.de/de/608362.html; Developmental Genetics, Philipps-Universität Marburg, https://www.uni-marburg.de/en/fb17/disciplines/developmental-genetics-and-animal-cell-biology/grosshans; Laboratory of Cell & Tissue Dynamics, OUC China, https://iemb.ouc.edu.cn/xbyzzdlxsys/list.htm; St Johnston Lab, University of Cambridge, https://www2.gurdon.cam.ac.uk/~stjohnstonlab/alumni.html

  —Matthias Häring, Yuanshu Zhang, Na Zhang, Edward S. Allgeyer, Jennifer H. Richens, George Sirinakis, Zhiyi Lv, Daniel St Johnston, Fred Wolf, Jörg Großhans, and Deqing Kong