Solo polarization

Single epithelial cells can polarize when given a healthy dose of activated LKB1, a human homologue of the Par-4 polarity protein characterized in worms and flies, according to Annette Baas, Hans Clevers (Center for Biomedical Genetics, Utrecht, The Netherlands), and colleagues.

The experiment overturns the dogma of epithelial polarity research, which holds that contact between adjacent cells defines boundaries and junctional complexes needed to divide one surface domain from another. By contrast, activated LKB1 creates a polarization triumvirate: cells form an apical brush border; position junctional proteins around the border; and sort membrane proteins to the respective apical and basolateral domains.

The direct consequence of activated LKB1 is probably the activation of Cdc42, a Rho family small GTPase. Cdc42's reorganization of actin should form the brush border, perhaps creating binding...