There are so many images that are in our collective memory…images that mark historic and significant events. There are the photos of Tiananmen Square, the “Migrant Mother” from the Great Depression, Abbey Road, etc. Well, cell biologists have our own images that stick in our collective memory. One of those more recent images is the “Svitkina image” of actin filaments, which I’ve mentioned before. So, when I saw that the Svitkina lab published a paper recently, I knew I had to share!
Cell-cell junctions are crucial for development, tissue structure, and cell-cell communication. One type of cell-cell junction is the adherens junction (AJ), which is a cadherin-based junction that links to the actin cytoskeleton within the cell. Although AJs are well-studied structures, how they assemble is still not completely known. A recent paper looks at the underlying actin filaments in developing AJs. According to Hoelzle and Svitkina, a junction is formed first by neighboring cells’ lamellipodia, sheet-like membrane extensions. Next, the two cells are connected by cadherin on thin bridges that look similar to filopodia, which are finger-like actin projections. Interestingly, these bridges form by actin filament growth from the rear-side of the lamellipodia towards the cell periphery. The images above are transmission electron micrographs of actin filaments in a bridge that connects two different cells (each cell labeled a different color in middle image). Gold beads (yellow, right image) found at the far ends of each cell’s bridge label VASP proteins, which are markers for filopodia.
Hoelzle, M., & Svitkina, T. (2011). The cytoskeletal mechanisms of cell-cell junction formation in endothelial cells Molecular Biology of the Cell, 23 (2), 310-323 DOI: 10.1091/mbc.E11-08-0719