Polarizing power of touch

When one epithelial cell meets another, it immediately begins to polarize its membrane, as Nejsum and Nelson report on page 323. The researchers describe the mechanism that helps create distinct membrane domains by delivering characteristic proteins.

As an epithelial cell polarizes, the basolateral portion of the cell membrane—the sides and bottom—accumulates one set of proteins, whereas another set takes up residence in the apical, or upper, surface. Researchers know more about how cells keep these two regions unique than about how the difference arises. Studies suggest that, as fresh proteins emerge from the Golgi apparatus, they carry an address that directs them toward a specialized patch on the membrane. Nejsum and Nelson wanted to determine how and when this patch assembles and when cell polarity appears.

The...