Mouse L-cells have proven to be an extremely useful model system for investigating the properties of cadherins because they do not normally express any cadherins. If different population of L-cells are transfected with vectors expressing one or the other of two different cadherins, and are the dissociated and mixed together, they segregate into two separate balls of cells, each held together by a different cadherin. If two populations of cells expressing different levels of the same cadherin are mixed, they segregate into a single ball of cells, with the low-expressing population on the outside.

A. Why do you suppose populations of cells expressing different levels of the same cadherin segregate with this characteristic layered structure? Why don't they segregate into two separate balls? Or a ball with the low-expressing population on the inside?

B. What sort of final architecture might you expect if you were to mix together two populations of cells that expressed P-cadherin in common, but, in addition, one population expressed E-cadherin and the other expressed N-cadherin??