Without cell–cell connections our bodies would fall apart. McGill et al. have now delved into the dynamics of connection construction.
The connections are called adherens junctions. Within each cell these junctions are built, not by assembling proteins at single sites, but by bringing two different protein complexes together, the team now shows. One of the complexes, Bazooka clusters, remains steadfast at the cell cortex and catches the other complex, the cadherin–catenin clusters, as they flow along in the membrane.
To determine these dynamics, the team followed fluorescently tagged versions of the complexes in fly embryos at a stage called cellularization—when one giant multinucleated cell becomes an epithelial layer of mononucleated cells.
Bazooka clusters formed at the contacts between these cells. Meanwhile, cadherin–catenin clusters first formed between microvilli structures on the apical surface. They then moved down to the cell–cell contacts, where the Bazooka clusters were waiting.
In between microvilli might seem like a strange place to form complexes involved in cell–cell contact, but senior author Tony Harris suggests that the movement of the microvilli membranes might help accumulate the cadherin and catenin into clusters. Also, at the transition region between apical and lateral (cell–cell contact) membranes, microvilli can interlock. This could then produce clusters between neighboring cells enabling the cells to grab hold of each other.