Using acid to find direction

For a cell with signaling receptors distributed uniformly on its plasma membrane, deciding which direction to move in response to a stimulus is a serious problem. Earlier work traced this polarity decision to the amplification of phosphoinositide signaling at the cell's leading edge. But on page 1087, Denker and Barber follow the signal back one step further, to the highly conserved ion exchange protein NHE1. The exchanger appears to be necessary not only for defining the front and rear of the cell, but also for coordinating events at the two ends.

The authors previously found that NHE1 is not only a sodium proton exchanger, but also a plasma membrane anchor for the cytoskeleton. Both functions are needed for PI-3 kinase activation and localization...