Sticky polarity

Cell adhesion can instruct cell polarity, according to new results from Chung-hui Yang, Jeff Axelrod, and Michael Simon (Stanford University, Stanford, CA). They found that polarity across an epithelial surface—perpendicular to apical–basal polarity—involves interactions between cadherins.

This form of planar cell polarity (PCP) achieves a remarkable feat. In the fly eye, for example, two nearby cells can somehow tell which one is closer to the equator (middle) of the eye, and specify the R3 (equatorial) and R4 (polar) fates, accordingly. “This is one of the great puzzles of PCP,” says Simon. “The cells are reading the gradient rather than the absolute values, and sensing the smallest differences.”For that process to have any fidelity, polarity researchers believe that communication between the neighboring cells is essential. “The process is not merely one of cells...