Chemotaxis: navigating by multiple signaling pathways.

During chemotaxis, phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) accumulates at the leading edge of a eukaryotic cell, where it induces the formation of pseudopodia. PIP(3) has been suggested to be the compass of cells navigating in gradients of signaling molecules. Recent observations suggest that chemotaxis is more complex than previously anticipated. Complete inhibition of all PIP(3) signaling has little effect, and alternative pathways have been identified. In addition, selective pseudopod growth and retraction are more important in directing cell movement than is the place where new pseudopodia are formed.