Cell sorting: some things to think about
Consider these three videos:
The debate about the cause of cell sorting includes whether crawling cells are pulled by forces of cell-cell adhesion ("reversible work of adhesion"), or whether the cells crawl actively by each mesenchymal cell being pulled by actin "treadmilling" in different directions, so that each cell continually undergoes a "tug of war" between different sides of itself. The net result of these tug-of-war counter-balances of each cell is to pull them preferentially onto more adhesive surfaces (which appear gray in these videos).
- Are the two cell aggregates being pulled together to become a single sphere by forces of cell-cell adhesion ("passive locomotion"), or by active contractility of the cells, with cells at the aggregate surfaces pulling more strongly than cells in the interior?
- By watching these videos, see whether you can find specific reasons to distinguish whether cells are actively crawling in opposing directions, as if playing "tug-of-war", or whether they are being pulled by adhesive forces.
- The gray areas and small gray squares were created by vacuum evaporation of heated atoms of the inert metal palladium. Blurred boundaries of these gray areas are adhesion gradients.